Thermocouple:

Thermocouple:

A Thermocouple is a sensor used to measure temperature. Thermocouples consist of two wire legs made from different metals. The wires legs are welded together at one end, creating a junction. This junction is where the temperature is measured. When the junction experiences a change in temperature, a voltage is created. The voltage can then be interpreted using thermocouple reference tables to calculate the temperature.

The working principle of thermocouple is based on three effects, discovered by Seebeck, Peltier and Thomson. They are as follows:

1.      Seebeck effect: The Seebeck effect states that when two different or unlike metals are joined together at two junctions, an electromotive force (emf) is generated at the two junctions. The amount of emf generated is different for different combinations of the metals.

2.      Peltier effect: As per the Peltier effect, when two dissimilar metals are joined together to form two junctions, emf is generated within the circuit due to the different temperatures of the two junctions of the circuit.

3.      Thomson effect: As per the Thomson effect, when two unlike metals are joined together forming two junctions, the potential exists within the circuit due to temperature gradient along the entire length of the conductors within the circuit. In most of the cases the emf suggested by the Thomson effect is very small and it can be neglected by making proper selection of the metals. The Peltier effect plays a prominent role in the working principle of the thermocouple.

Working principle:

Fig 1

The general circuit for the working of thermocouple is shown in the figure 1 above. It comprises of two dissimilar metals, A and B. These are joined together to form two junctions, p and q, which are maintained at the temperatures T₁ and T₂ respectively. Remember that the thermocouple cannot be formed if there are not two junctions. Since the two junctions are maintained at different temperatures the Peltier emf is generated within the circuit and it is the function of the temperatures of two junctions.

If the temperature of both the junctions is same, equal and opposite emf will be generated at both junctions and the net current flowing through the junction is zero. If the junctions are maintained at different temperatures, the emf will not become zero and there will be a net current flowing through the circuit. The total emf flowing through this circuit depends on the metals used within the circuit as well as the temperature of the two junctions. The total emf or the current flowing through the circuit can be measured easily by the suitable device.

The device for measuring the current or emf is connected within the circuit of the thermocouple. It measures the amount of emf flowing through the circuit due to the two junctions of the two dissimilar metals maintained at different temperatures. In figure 2 the two junctions of the thermocouple and the device used for measurement of emf (potentiometer) are shown.

Now, the temperature of the reference junctions is already known, while the temperature of measuring junction is unknown. The output obtained from the thermocouple circuit is calibrated directly against the unknown temperature. Thus the voltage or current output obtained from thermocouple circuit gives the value of unknown temperature directly.

Application:

·         There are many types of thermocouples, each with its own unique characteristics in terms of temperature range, durability, vibration resistance, chemical resistance, and application compatibility. Type J, K, T, & E are “Base Metal” thermocouples, the most common types of thermocouples. Type R, S, and B thermocouples are “Noble Metal” thermocouples, which are used in high temperature applications.

·         Thermocouples are used in many industrial, scientific, and OEM applications.

·         They can be found in nearly all industrial markets: Power Generation, Oil/Gas, Pharmaceutical, Biotech, Cement, Paper & Pulp, etc.

·         Thermocouples are also used in everyday appliances like stoves, furnaces, and toasters. 
Thermocouples are typically selected because of their low cost, high temperature limits, wide temperature ranges, and durable nature.

Signal Generators:

Signal Generator: Electronic test instrument that delivers an accurately calibrated signal at frequencies from the audio to the microwave ranges. The signal generator provides a signal that can be adjusted according to frequency, output voltage, impedance, waveform, and modulation. Signal generators (also known variously as function generators, frequency generators), are electronic devices that generate repeating or non-repeating electronic signals (in either the analog or digital domains). The Function generator is a type of signal generator that is used to generator simple repetitive waveforms. Typically this signal generator type will produce waveforms or functions such as sine waves, saw tooth waveforms, square and triangular waveforms They are generally used in designing, testing, troubleshooting, and repairing electronic or electroacoustic devices; though they often have artistic uses as well.

Types and Application:

1.      Oscillators: It generate sine waves useful in measuring the response of loudspeakers, amplifiers, microphones, transducers, and acoustic systems; 

2.      Standard signal generators: It generate sine waves over a wide range of output power and modulation, used, for example, to test radio receivers and measure gain, bandwidth, and signal-to-noise ratio;

3.       Frequency synthesizers: which generate highly precise output frequencies over wide ranges; pulse generators, which produce pulsed signals at precise duration at precise frequencies; and random-noise generators, which produce a wideband noise for various inputs

4.      Arbitrary waveform generator:   The arbitrary waveform generator is a type of signal generator that creates very sophisticated waveforms that can be specified by the user. These waveforms can be almost any shape and can be entered in a variety of ways, even extending to specifying points on the waveform.RF signal generator:   As the name indicates, this type of signal generator is used to generate RF or radio frequency signals.
An RF signal generator may use a variety of methods to generate the signal. Analogue signal generator types used free running oscillators, although some used frequency locked loop techniques to improve stability. However most RF signal generators use frequency synthesizers to provide the stability and accuracy needed. Both phase locked loop and direct digital synthesis techniques may be used. Read more about the RF signal generator

5.      Vector signal generator:   The vector signal generator is a type of RF signal generator that generates RF signals with complex modulation formats such as QPSK, QAM, etc. Read more about the Vector signal generator

6.      Audio signal generator:   As the name implies this type of signal generator is used for audio applications. Signal generators such as these run over the audio range, typically from about 20 Hz to 20 kHz and more. They are often used in audio measurements of frequency response and for distortion measurements

7.      Pulse generator:   As the name suggests, the pulse generator is a form of signal generator that creates pulses. These signal generators are often into the form of logic pulse generators that can produce pulses with variable delays and some even offer variable rise and fall times.

Strain Guage:

It can be used for measurement of force, strain, stress, pressure, displacement, acceleration etc. It is often easy to measure the parameters like length, displacement, weight etc. that can be felt easily by some senses. However, it is very difficult to measure the dimensions like force, stress and strain that cannot be really sensed directly by any instrument. For such cases special devices called strain gauges are very useful.

There are some materials whose resistance changes when strain is applied to them or when they are stretched and this change in resistance can be measured easily. For applying the strain you need force, thus the change in resistance of the material can be calibrated to measure the applied force. Thus the devices whose resistance changes due to applied strain or applied force are called as the strain gauges.

In order to measure strain with a bonded resistance strain gage, it must be connected to an electric circuit that is capable of measuring the minute changes in resistance corresponding to strain. Strain gage transducers usually employ four strain gage elements electrically connected to form a Wheatstone bridge circuit (Figure 2-6).
  A Wheatstone bridge is a divided bridge circuit used for the measurement of static or dynamic electrical resistance. The output voltage of the Wheatstone bridge is expressed in millivolts output per volt input. The Wheatstone circuit is also well suited for temperature compensation.

Figure 2-6: Wheatstone Bridge Circuit Schematic

  

In Figure 2-6, if R1, R2, R3, and R4 are equal, and a voltage, VIN, is applied between points A and C, then the output between points B and D will show no potential difference. However, if R4 is changed to some value which does not equal R1, R2, and R3, the bridge will become unbalanced and a voltage will exist at the output terminals. In a so-called G-bridge configuration, the variable strain sensor has resistance Rg, while the other arms are fixed value resistors.
  The sensor, however, can occupy one, two, or four arms of the bridge, depending on the application. The total strain, or output voltage of the circuit (VOUT) is equivalent to the difference between the voltage drop across R1 and R4, or Rg. This can also be written as:

For more detail, see Figure 2-6. The bridge is considered balanced when R1/R2 = Rg/R3 and, therefore, VOUT equals zero. 

Any small change in the resistance of the sensing grid will throw the bridge out of balance, making it suitable for the detection of strain. When the bridge is set up so that Rg is the only active strain gage, a small change in Rg will result in an output voltage from the bridge. If the gage factor is GF, the strain measurement is related to the change in Rg as follows:

  The number of active strain gages that should be connected to the bridge depends on the application. For example, it may be useful to connect gages that are on opposite sides of a beam, one in compression and the other in tension. In this arrangement, one can effectively double the bridge output for the same strain.
  In a four-element Wheatstone bridge, usually two gages are wired in compression and two in tension. For example, if R1 and R3 are in tension (positive) and R2 and R4 are in compression (negative), then the output will be proportional to the sum of all the strains measured separately.

Applications of the Strain Gauges

·         Measurement of strain: Whenever any material is subjected to high loads, they come under strain, which can be measured easily with the strain gauges. The strain can also be used to carry out stress analysis of the member.

·         Measurement of other quantities: The principle of change in resistance due to applied force can also be calibrated to measure a number of other quantities like force, pressure, displacement, acceleration etc. since all these parameters are related to each other. The strain gauges can sense the displacements as small as 5 µm. They are usually connected to the mechanical transducers like bellows for measuring pressure and displacement and other quantities.

Tachometer

A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine..A tachometer usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common. Essentially the words tachometer and speedometer have identical meaning: a device that measures speed. It is by arbitrary convention that in the automotive world one is used for engine and the other for vehicle speed.

The first mechanical tachometers were based on measuring the centrifugal force, similar to the operation of a centrifugal governor. Tachometers or revolution counters on cars, aircraft, and other vehicles show the rate of rotation of the engine's crankshaft, and typically have markings indicating a safe range of rotation speeds. This can assist the driver in selecting appropriate throttle and gear settings for the driving conditions. This is more applicable to manual transmissions than to automatics. On analogue tachometers, speeds above maximum safe operating speed are typically indicated by an area of the gauge marked in red, giving rise to the expression of "redlining" an engine — revving the engine up to the maximum safe limit. The red zone is superfluous on most modern cars, since their engines typically have a revolution limiter which electronically limits engine speed to prevent damage. 

Application:

·         Tractors fitted with a power take off (PTO) system have tachometers showing the engine speed needed to rotate the PTO at the standardized speed required by most PTO-driven implements

·         In older vehicles, the tachometer is driven by the RMS voltage waves from the low tension (LT) side of the ignition coil, while on others (and nearly all diesel engines, which have no ignition system) engine speed is determined by the frequency from the alternator tachometer output.

·         Traffic engineering: Tachometers are used to estimate traffic speed and volume (flow). A vehicle is equipped with the sensor and conducts "tach runs" which record the traffic data. These data are a substitute or complement to loop detector data.

·         In trains and light rail vehicles as Wheel speed Sensor

·         Speed sensing devices, termed variously "wheel impulse generators" (WIG), speed probes, or tachometers are used extensively in rail vehicles. Common types include opto-isolator slotted disk sensors and Hall Effect sensors.

·         For recording in synchronization with a movie camera. For such purposes, special recorders that record pilot tone must be used.

·         Tachometer signals can be used to synchronize several tape machines together, but only if in addition to the tach signal, a directional signal is transmitted, to tell slave machines in which direction the master is moving.

Impedance bridges

 This bridge is used to find out the self-inductor and the quality factor of the circuit. As it is based on the bridge method (i.e. works on the principle of null deflection method), it gives very accurate results. Maxwell Bridge is an AC bridge so before going in further detail let us know more about the Ac Bridge.

AC Bridges

AC Bridges consist of a source, balance detector and four arms. In AC bridges, all the four arms consists of impedance. The AC bridges are formed by replacing the DC battery with an AC source and galvanometer by detector of bridge. They are highly useful to find out inductance, capacitance, storage factor, dissipation factor etc.

Now let us derive general expression for an AC bridge balance

Figure given below shows AC bridge network:

Here Z₁, Z₂, Z₃ and Z₄ are the arms of the bridge.

Now at the balance condition, the potential difference between b and d must be zero. From this, when the voltage drop from from a to d equals to drop from a to b both in magnitude and phase.

Thus, we have from figure e₁ = e₂

From equation 1, 2 and 3 we have Z₁.Z₄ = Z₂.Z₃ and when impedance are replaced by admittance, we have Y₁.Y₄ = Y₂.Y₃.

Now consider the basic form of an AC bridge. Suppose we have bridge circuit as shown below,

In this circuit R₃ and R₄ are pure electrical resistances. Putting the value of Z₁, Z₂, Z₃ and Z₄ in the equation that we have derived above for AC Bridge.

Now equating the real and imaginary parts we get

Following are the important conclusions that can be drawn from the above equations:

(a) We get two balanced equations that are obtained by equating real and imaginary parts this means that for an ac bridge both the relation (i.e. Magnitude and phase) must be satisfied at the same time. Both the equations are said to be independent if and only if both equation contain single variable element. This variable can be inductor or resistor.

(b) The above equations are independent of frequency that means we do not require exact frequency of the source voltage and also the applied source voltage waveform need not to be perfectly sinusoidal.

Maxwell's Bridge

Under this we going to study about the following (a) Maxwell's inductor bridge (b) Maxwell's inductor capacitance bridge

Maxwell's Inductance Bridge

Let us now discuss Maxwell's inductor bridge. The figure shows the circuit diagram of Maxwell's inductor bridge.

In this bridge the arms bc and cd are purely resistive while the phase balance depends on the arms ab and ad.

Here l₁ = unknown inductor of r₁. l₂ = variable inductor of resistance R₂. r₂ = variable electrical resistance. As we have discussed in ac bridge according to balance condition, we have at balance point

We can vary R₃ and R₄ from 10 ohms to 10,000 ohms with the help of resistance box.

Maxwell's Inductance Capacitance Bridge

In this Maxwell Bridge, the unknown inductor is measured by the standard variable capacitor. Circuit of this bridge is given below,

Here, l₁ is unknown inductance, C₄ is standard capacitor. Now under balance conditions we have from ac bridge that Z₁.Z₄ = Z₂.Z₃

Let us separate the real and imaginary parts, the we have,

Now the quality factor is given by,

Advantages of Maxwell's Bridge

(1) The frequency does not appear in the final expression of both equations, hence it is independent of frequency.

(2) Maxwell's inductor capacitance bridge is very useful for the wide range of measurement of inductor at audio frequencies.

Disadvantages of Maxwell's Bridge

(1) The variable standard capacitor is very expensive.

(2) The bridge is limited to measurement of low quality coils (1 < Q < 10) and it is also unsuitable for low value of Q (i.e. Q < 1) from this we conclude that a Maxwell bridge is used suitable only for medium Q coils.

The above all limitations are overcome by the modified bridge which is known as Hay’s bridge which does not use an electrical resistance in parallel with the capacitor.

Hay's Bridge Applications

Before we introduce Hay's bridge let us recall the limitations of Maxwell bridge, in order to understand what the necessity of Hay’s is bridge applications. Maxwell bridge is only suitable for measuring medium quality factor coils however it is not suitable for measuring high quality factor (Q > 10). In order to to overcome from this limitation we need to do modification in Maxwell bridge so that it will become suitable for measuring Q factor over a wide range. This modified Maxwell bridge is known as Hay's bridge.

Hay's Bridge Theory

As I said earlier that Hay's bridge is modified Maxwell bridge, now question arises here in our mind that where we need to do modification. In order to to understand this, let us consider the connection diagram given below:

In this bridge the electrical resistance is connected in series with the standard capacitor. Here l₁ is unknown inductor connected in series with resistance r₁. C4 is standard capacitor and r₂, r₃, r₄ are pure electrical resistance forming other arms of the bridge.

From the theory of Ac Bridge we can write at balance point,

Substituting the values of z₁, z₂, z₃ and z₄ in equation (1) we get,

Now, Q factor of a coil is given by

The equations (4) and (5) are dependent on the source frequency hence, in order to find the accurate value of l₁ and r₁ we should know the correct value of source frequency. Let us rewrite the expression for l₁, Now if we substitute Q >10 then 1/Q² = 1 / 100 and hence we can neglect this value, thus neglecting 1/Q² we get r₂r₃c₄ which is same as we have obtained in Maxwell bridge hence Hay's bridge circuit is most suitable for high inductor measurement.

Let us know more about Hay's bridge circuit diagram of Hay's bridge that will be very useful in understanding the Hay's bridge phasor diagram. A meter is connected between point’s b and d of the bridge. The arm ab consists of resistance r₁ and inductor, l₁ (total drop across this is e₁) and arm ad consists of pure resistance r₂ (total drop across this is e₂). The arm bc consists of pure resistance making a drop of e₃ while the arm cd consists of resistor r₄ and a capacitor making the total drop of e₄. Now let us draw phasor diagram of Hay's bridge, at null point e₁ must be equal to e₂ and also e₃ must be equal to e₄ as the current flow through bd is zero. Let us take i₁ as the reference axis and thus current i₂ leads by i₁ by some angle (as shown in Hay's bridge phasor diagram below) because a capacitor is connected in branch cd making current i₂ lead by i₁. Let us mark e₁ and e₂ and the resultant of e₁ and e₂ of course equal to e. The phase difference between the voltage drop across the electrical resistance r₄ and capacitor c₄ is 90° (measured in degrees) is clearly shown in the phasor diagram of Hay's Bridge.

 .

In many practical situations bridge circuit that uses ac source, an electron ray indicating is utilized to find out the balance condition by opening and closing the shadow area of the tube. For audible balance headsets are used, but accuracy is reduces due to this method. In order to control the operating power to the bridge and to complete the detector circuit various switches are used. Many times the two switching functions are merge into single key, known bridge key this is to ensure that power applied to the bridge before to the detector circuit, due this sequence the effect of inductor and capacitance is reduced.

Advantages of Hay's Bridge

(1) The bridge gives very simple expression for the calculation of unknown inductor of high value. The Hay's bridge require low value of r₄ while Maxwell Bridge requires high value of r₄. Now let us analyze why should put low value of r₄ in this bridge:

Consider the expression of quality factor,   as r₄ represents in the denominator hence for high quality factor, r₄ must be small.

Disadvantages of Hay's Bridge

Hay's bridge is not suitable for measurement of quality factor (Q<10) for Q<10 we should use Maxwell bridge.

Schering Bridge Theory

This bridge is used to measure to the capacitance of the capacitor, dissipation factor and measurement of relative permittivity. Let us consider the circuit of Schering Bridge as shown below:

Here, c₁ is the unknown capacitance whose value is to be determined with series electrical resistance r₁. C2 is a standard capacitor. C4 is a variable capacitor. R3 is a pure resistor (i.e. non inductive in nature). And r₄ is a variable non inductive resistor connected in parallel with variable capacitor c₄. Now the supply is given to the bridge between the points a and c. The detector is connected between b and d. From the theory of ac bridges we have at balance condition,

Substituting the values of z₁, z₂, z₃ and z₄ in the above equation, we get

Equating the real and imaginary parts and the separating we get,

Let us consider the phasor diagram of the above Shering bridge circuit and mark the voltage drops across ab, bc, cd and ad as e₁, e₃, e4 and e₂ respectively. From the above Schering bridge phasor diagram, we can calculate the value of tanδ which is also called the dissipation factor.

The equation that we have derived above is quite simple and the dissipation factor can be calculated easily. Now we are going to discuss high voltage Schering bride in detail. As we have discussed that simple schering bridge (which uses low voltages) is used for measuring dissipation factor, capacitance and measurement of other properties of insulating materials like insulating oil etc. What is the need of high voltage schering bridge? The answer to this question is very simple, for the measurement of small capacitance we need to apply high voltage and high frequency as compare to low voltage which suffers many disadvantages. Let us discuss more features of this high voltage Schering bridge:

(a) The bridge arms ab and ad consists of only capacitors as shown the bridge given below and impedances of these two arms are quite large as compared to the impedances of bc and cd. The arms bc and cd contains resistor r₃ and parallel combination of capacitor c₄ and resistor r₄ respectively. As impedances of bc and cd are quite small therefore drop across bc and cd is small. The point c is earthed, so that the voltage across bc and dc are few volts above the point c.

(b) The high voltage supply is obtained from a transformer 50 Hz and the detector in this bridge is a vibration galvanometer.

(c) The impedances of arms ab and ad very are large therefore this circuit draws low current hence power loss is low but due to this low current we need a very sensitive detector to detect this low current.

(d) The fixed standard capacitor c₂ has compressed gas which works as dielectric therefore dissipation factor can be taken as zero for compressed air. Earthed screens are placed between high and low arms of the bridge to prevent errors caused due to inter capacitance.
Frequency response:
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system.
It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input. In simplest terms, if a sine wave is injected into a system at a given frequency, a linear system will respond at that same frequency with a certain magnitude and a certain phase angle relative to the input. Also for a linear system, doubling the amplitude of the input will double the amplitude of the output. In addition, if the system is time-invariant (so LTI), then the frequency response also will not vary with time. Thus for LTI systems, the frequency response can be seen as applying the system's transfer function to a purely imaginary number argument representing the frequency of the sinusoidal excitation.
Two applications of frequency response analysis are related but have different objectives. For an audio system, the objective may be to reproduce the input signal with no distortion. For a feedback apparatus used to control a dynamic system, the objective is to give the closed-loop system improved response as compared to the uncompensated system. The feedback generally needs to respond to system dynamics within a very small number of cycles of oscillation (usually less than one full cycle), and with a definite phase angle relative to the commanded control input. For feedback of sufficient amplification, getting the phase angle wrong can lead to instability for an open-loop stable system, or failure to stabilize a system that is open-loop unstable. Digital filters may be used for both audio systems and feedback control systems, but since the objectives are different, generally the phase characteristics of the filters will be significantly different for the two applications.








Transducers
A transducer is an electronic device that converts energy from one form to another. Common examples include microphones, loudspeakers, thermometers, position and pressure sensors, and antenna. Although not generally thought of as transducers, photocells, LEDs (light-emitting diodes), and even common light bulbs are transducers.
Efficiency is an important consideration in any transducer. Transducer efficiency is defined as the ratio of the power output in the desired form to the total power input. Mathematically, if P represents the total power input and Q represents the power output in the desired form, then the efficiency E, as a ratio between 0 and 1, is given by:
E = Q/P
If E% represents the efficiency as a percentage, then:
E% = 100Q/P
No transducer is 100 percent efficient; some power is always lost in the conversion process. Usually this loss is manifested in the form of heat. Some antennas approach 100-percent efficiency. A well-designed antenna supplied with 100 watts of radio frequency (RF) power radiates 80 or 90 watts in the form of an electromagnetic field. A few watts are dissipated as heat in the antenna conductors, the feed line conductors and dielectric, and in objects near the antenna. Among the worst transducers, in terms of efficiency, are incandescent lamps. A 100-watt bulb radiates only a few watts in the form of visible light. Most of the power is dissipated as heat; a small amount is radiated in the UV (ultraviolet) spectrum.
Common Sensors and Transducers
Quantity being
Measured
Input Device
(Sensor)
Output Device
(Actuator)
Light Level
Light Dependent Resistor (LDR)
Photodiode
Photo-transistor
Solar Cell
Lights & Lamps
LED’s & Displays
Fibre Optics
Temperature
Thermocouple
Thermistor
Thermostat
Resistive Temperature Detectors
Heater
Fan
Force/Pressure
Strain Gauge
Pressure Switch
Load Cells
Lifts & Jacks
Electromagnet
Vibration
Position
Potentiometer
Encoders
Reflective/Slotted Opto-switch
LVDT
Motor
Solenoid
Panel Meters
Speed
Tacho-generator
Reflective/Slotted Opto-coupler
Doppler Effect Sensors
AC and DC Motors
Stepper Motor
Brake
Sound
Carbon Microphone
Piezo-electric Crystal
Bell
Buzzer
Loudspeaker

Piezoelectric transducers 
Piezoelectric transducers are a type of electroacoustic transducer that convert the electrical charges produced by some forms of solid materials into energy. A piezoelectric sensor is a device that uses the piezoelectric effect, to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. ezoelectric" literally means electricity caused by pressure.
Applications
Due to its excellent frequency response, it is normally used as an accelerometer, where the output is in the order of (1-30) mV per gravity of acceleration.
The device is usually designed for use as a pre-tensional bolt so that both tensional and compression force measurements can be made.
Can be used for measuring force, pressure and displacement in terms of voltage.
Advantages
Very high frequency response.
Self-generating, so no need of external source.
Simple to use as they have small dimensions and large measuring range.
Barium titan ate and quartz can be made in any desired shape and form. It also has a large dielectric constant. The crystal axis is selectable by orienting the direction of orientation.
Disadvantages
It is not suitable for measurement in static condition.
Since the device operates with the small electric charge, they need high impedance cable for electrical interface.
The output may vary according to the temperature variation of the crystal.
The relative humidity rises above 85% or falls below 35%, its output will be affected. If so, it has to be coated with wax or polymer material.

  Basic computer hardware and software:
ü  Input Devices: devices that input information into the computer such as a keyboard,      mouse, scanner, and digital camera.
ü  Output Devices: devices that output information from the computer such as a printer and monitor.
ü  Central Processing Unit (CPU): also called the Microprocessor or “The Brain” of the Computer
ü  Processor speed: The speed at which a microprocessor executes instructions. This is usually measured in megahertz (MHz)
ü  Central Processing Unit (Computer chip): also called the microprocessor and may contain an entire processing unit. Computer chips contain millions of transistors. They are small pieces of semi- conducting material (silicon).
ü  Data Storage Devices: The hard-drive is a mechanical storage device typically located internally. CD-ROM (compact disk read only memory) contains approximately 600 to 700 megabyte of storage. Floppy diskette is magnetic storage device for small amounts of data (1.44MB).FLASH drive is a compact and portable electronic storage device.
ü  Computer Memory: Computer memory is binary (0 or 1) (on or off).The byte is the standard unit of measurement. A byte is composed of 8 bits (binary digits) RAM (random access memory) stores data that is processing. This type of memory is erased when the computer is turned off. ROM (read only memory) contains special instructions for the computer to operate .Cache memory increases the speed of the processor by recording and anticipating instructions.
ü  GUI (Graphic User Interface): It is a set of images and icons seen on the desktop used to operate a program. The GUI makes the programs loaded on the computer easier to access and use. Windows is a GUI operating system unlike UNIX, which uses text commands.
ü  Video Cards: They are plug into the motherboard and are used to display video. VRAM is video memory that enhances the refreshment rate of the image. Video cards have chipsets that can increase the speed of video display.
ü  Ports and Peripherals: Ports are an interface between the computer and another peripheral device such as a disk drive, mouse, printer, modem, monitor, camera, FLASH drive or keyboard. Examples: Serial Parallel hot-wire USB
ü  Peripherals are devices that plug into a computer and are not housed internally. Examples: Printers Scanners Cameras. Resolution: Resolution refers to the number of pixels (picture elements) in the monitor image. Increased resolution uses more computer resources but increases the visual clarity of the display. Screen resolution is measured in pixel per inch (ppi).printer resolution is measured in dots per inch (dpi).Computer screen resolution is approximately 72 ppi. Width x Height.
ü  LAN and WAN: LAN are networks usually in the same company or building. The Local Area Network is connected via telephone lines or radio waves. Most LANs connect workstations. WAN: are systems of LANs that are connected. (Wide-area network)
ü  Bandwidth and Baud Rate: Bandwidth is how much information can be carried in a given time period (usually a second) over a wired or wireless communications link. Baud rate is the rate at which information is transferred in a communication channel.
ü  Multitasking and Multiprocessing: Multitasking is the ability to execute more than one task (program) at the same time. Only one CPU is used but switches from one program to another. In multiprocessing, more than one CPU is used to complete a task. Example: network rendering.
ü  Multimedia: Multimedia software programs include sound, pictures, video, text, and hypertext to create presentations. Software includes: PowerPoint Macromedia
ü  File Management: Different programs have different file extensions.
·         Saving files - know the difference between “save” and “save as”. “Save” will save the open document over the saved document while “save as” creates a new document if you rename the document. Save often so work will not be lost.
·         Merging files - in 3D graphics, bringing an outside file into an open file (another name for this may be loading or replacing objects in the workspace)
·         Importing files - bringing a converted non-native format file into an open file.

COMPUTER NETWORK

When two humans converse, they may have to use the same language but they generally understand each other without having to adhere to rigid rules of grammar or formal language frameworks. Computers, on the other hand, have to have everything explicitly defined and structured. If computers wish to communicate with one another, they have to know in advance exactly how information is to be exchanged and precisely what the format will be. Therefore, standard methods of transmitting and processing various kinds of information are used and these methods are called "protocols". Protocols are established by international agreement and ensure that computers everywhere can talk to one another. There are a variety of protocols for different kinds of information and functions. This article will discuss some of the common protocols that the average PC user is likely to encounter.
TCP/IP:
TCP (Transmission Control Protocol) and IP (Internet Protocol) are two different procedures that are often linked together. The linking of several protocols is common since the functions of different protocols can be complementary so that together they carry out some complete task. The combination of several protocols to carry out a particular task is often called a "stack" because it has layers of operations. In fact, the term "TCP/IP" is normally used to refer to a whole suite of protocols, each with different functions. This suite of protocols is what carries out the basic operations of the Web. TCP/IP is also used on many local area networks. The details of how the Web works are beyond the scope of this article but I will briefly describe some of the basics of this very important group of protocols. More details can be found in the references in the last section.
When information is sent over the Internet, it is generally broken up into smaller pieces or "packets". The use of packets facilitates speedy transmission since different parts of a message can be sent by different routes and then reassembled at the destination. It is also a safety measure to minimize the chances of losing information in the transmission process. TCP is the means for creating the packets, putting them back together in the correct order at the end, and checking to make sure that no packets got lost in transmission. If necessary, TCP will request that a packet be resent.
Internet Protocol (IP) is the method used to route information to the proper address. Every computer on the Internet has to have its own unique address known as the IP address. Every packet sent will contain an IP address showing where it is supposed to go. A packet may go through a number of computer routers before arriving at its final destination and IP controls the process of getting everything to the designated computer. Note that IP does not make physical connections between computers but relies on TCP for this function. IP is also used in conjunction with other protocols that create connections.
UDP and ICMP:
Another member of the TCP/IP suite is User Datagram Protocol (UDP). (A datagram is almost the same as a packet except that sometimes a packet will contain more than one datagram.) This protocol is used together with IP when small amounts of information are involved. It is simpler than TCP and lacks the flow-control and error-recovery functions of TCP. Thus, it uses fewer system resources.
A different type of protocol is Internet Control Message Protocol (ICMP). It defines a small number of messages used for diagnostic and management purposes. It is also used by Ping and Trace route.
Mail Protocols POP3 and SMTP:
Email requires its own set of protocols and there are a variety, both for sending and for receiving mail. The most common protocol for sending mail is Simple Mail Transfer Protocol (SMTP). When configuring email clients, an Internet address for an SMTP server must be entered. The most common protocol used by PCs for receiving mail is Post Office Protocol (POP). It is now in version 3 so it is called POP3. Email clients require an address for a POP3 server before they can read mail. The SMTP and POP3 servers may or may not be the same address. Both SMTP and POP3 use TCP for managing the transmission and delivery of mail across the Internet.
A more powerful protocol for reading mail is Interactive Mail Access Protocol (IMAP). This protocol allows for the reading of individual mailboxes at a single account and is more common in business environments. IMAP also uses TCP to manage the actual transmission of mail.
Hypertext Transfer Protocol:
Web pages are constructed according to a standard method called Hypertext Markup Language (HTML). An HTML page is transmitted over the Web in a standard way and format known as Hypertext Transfer Protocol (HTTP). This protocol uses TCP/IP to manage the Web transmission.
A related protocol is "Hypertext Transfer Protocol over Secure Socket Layer" (HTTPS), first introduced by Netscape. It provides for the transmission in encrypted form to provide security for sensitive data. A Web page using this protocol will have https: at the front of its URL.
File Transfer Protocol:
File Transfer Protocol (FTP) lives up to its name and provides a method for copying files over a network from one computer to another. More generally, it provides for some simple file management on the contents of a remote computer. It is an old protocol and is used less than it was before the World Wide Web came along. Today, its primary use is uploading files to a Web site. It can also be used for downloading from the Web but, more often than not, downloading is done via HTTP. Sites that have a lot of downloading (software sites, for example) will often have an FTP server to handle the traffic. If FTP is involved, the URL will have ftp: at the front

BASIC COMPUTER ARCHITECTURE:



The main components in a typical computer system are the processor, memory, input/output devices, and the communication channels that connect them.
Processor: It is the workhorse of the system; it is the component that executes a program by performing arithmetic and logical operations on data. It is the only component that creates new information by combining or modifying current information. In a typical system there will be only one processor, known at the central processing unit, or CPU. Modern high performance systems, for example vector processors and parallel processors, often have more than one processor. Systems with only one processor are serial processors, or, especially among computational scientists, scalar processors.
Memory: It is a passive component that simply stores information until it is requested by another part of the system. During normal operations it feeds instructions and data to the processor, and at other times it is the source or destination of data transferred by I/O devices. Information in a memory is accessed by its address.
Input/output (I/O): They are the devices that transfer information without altering it between the external world and one or more internal components. I/O devices can be secondary memories, for example disks and tapes, or devices used to communicate directly with users, such as video displays, keyboards, and mouse.
Communication channels: They tie the system together can either be simple links that connect two devices or more complex switches that interconnect several components and allow any two of them to communicate at a given point in time. When a switch is configured to allow two devices to exchange information, all other devices that rely on the switch are blocked, i.e. they must wait until the switch can be reconfigured.
Advantages of digital system
1 .Ease of programmability
The digital systems can be used for different applications by simply changing the program without additional changes in hardware.
2. Reduction in cost of hardware
The cost of hardware gets reduced by use of digital components and this has been possible due to advances in IC technology. With ICs the number of components that can be placed in a given area of Silicon are increased which helps in cost reduction.
 3. High speed
Digital processing of data ensures high speed of operation which is possible due to advances in Digital Signal Processing.
  4. High Reliability
Digital systems are highly reliable one of the reasons for that is use of error correction codes.
5. Design is easy
The design of digital systems which require use of Boolean algebra and other digital techniques is easier compared to analog designing.
  6. Result can be reproduced easily
Since the output of digital systems unlike analog systems is independent of temperature, noise, humidity and other characteristics of components the reproducibility of results is higher in digital systems than in analog systems.

Multimeter:
A Multimeter an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. It is also known as a VOM (Volt-Ohm meter).
Multimeters may use analog or digital circuits—analog multimeters (AMM) and digital multimeters (often abbreviated DMM or DVOM.)
Analog instruments are usually based on a micrometer whose pointer moves over a scale calibrated for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity being measured.
Digital multimeters:  In a digital multimeter the signal under test is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal. A digital multimeter displays the quantity measured as a number, which eliminates parallax errors.
Analog multimeters: Analog multimeters are common; a quality analog instrument will cost about the same as a DMM. Analog multimeters have the precision and reading accuracy limitations described above, and so are not built to provide the same accuracy as digital instruments.








Application
A multimeter can be a hand-held device useful for fault finding and field service work ,which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.Multimeters can measure many quantities as, Voltage, alternating and direct, in volts.Current, alternating and direct, in amperes. Resistance in ohms. Additionally, some multimeters measure: Capacitance in farads. Conductance in Siemens. Frequency in hertz.Inductance in henrys.Temperature in degrees Celsius or Fahrenheit, with an appropriate temperature test probe, often a thermocouple.


Digital multimeters may also include circuits for: Continuity; beeps when a circuit conducts. Diodes (measuring forward drop of diode junctions, i.e., diodes and transistor junctions) and transistors (measuring current gain and other parameters).Battery checking for simple 1.5 volt and 9 volt batteries. This is a current loaded voltage scale. Battery checking (ignoring internal resistance, which increases as the battery is depleted), is less accurate when using a DC voltage scale. Various sensors can be attached to Multimeters to take measurements such as: Acidity/Alkalinity (pH) Wind speed Relative humidity Light level.

Thermistor
A thermistor is a thermally sensitive resistor whose resistance value changes with changes in operating temperature.
Because of the self-heating effect of current in a thermistor, the device changes resistance with changes in current.
Thermistors exhibit either a positive temperature coefficient (PTC) or a negative temperature coefficient (NTC). If a thermistor has a positive temperature coefficient, its resistance increases as the operating temperature increases. Conversely, if a thermistor has a negative temperature coefficient, its resistance decreases as the operating temperature increases.
The symbol to the right is the schematic symbol of a thermistor. Notice the arrow through the resistor symbol and the letter T within the circle. The arrow indicates that the resistance is variable as the temperature T changes.
Thermistors are frequently used in electronic circuits that handle temperature measurement, temperature control, and temperature compensation. 

Cathode Ray Oscilloscope (CRO):

An oscilloscope, previously called an oscillograph, and informally known as a scope, CRO (for cathode-ray oscilloscope), or DSO(digital storage oscilloscope), is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time.
The cathode ray oscilloscope is an instrument which we use in laboratory to display measure and analyze various waveforms of various electrical and electronic circuits. Actually cathode ray oscilloscope is very fast X-Y plotters that can display an input signal versus time or other signal. Cathode ray oscilloscope uses luminous spot which is produced by striking the beam of electrons and this luminous spot moves in response variation in the input quantity.
Construction of Cathode Ray Oscilloscope

The main part of cathode ray oscilloscope is cathode ray tube which is also known as the heart of cathode ray oscilloscope. Basically the cathode ray tube consists of five main parts and these main parts are written below:

1.      Electron gun.
2.      Deflection plate system.
3.      Fluorescent screen.
4.      Glass envelope.
5.      Base.
Electron Gun: It is the source of accelerated, energized and focused beam of electrons. It consists of six parts namely heater, a cathode, a grid, a pre-accelerating anode, a focusing anode and an accelerating anode. In order to obtain the high emission of electrons the layer of barium oxide (which is deposited on the end of cathode) is indirectly heated at moderate temperature. The electrons after this passes through a small hole called control grid which is made up of nickel Electrostatic focusing.


Oscilloscopes
-          Oscilloscopes are used to observe the change of an electrical signal over time.
-          Oscilloscopes are used in the sciences, medicine, engineering, and telecommunications industry
-          Special-purpose oscilloscopes may be used to display the waveform of the heartbeat as an electrocardiogram(ECG)
·         Types and models
o    Cathode-ray oscilloscope (CRO)
o    Dual-beam oscilloscope
o    Analog storage oscilloscope
o    Digital oscilloscopes
o    Mixed-signal oscilloscopes
o    Mixed-domain oscilloscopes
o    Handheld oscilloscopes
o    PC-based oscilloscopes

1 Fig: Block Diagram of Oscilloscope

Control System:
These two types of control system have contrast with each other. They have dissimilarities some of which are discussed below:
1.      Effect of output
– An open loop control system acts completely on the basis of input and the output has no effect on the control action.
– A closed loop control system considers the current output and alters it to the desired condition. The control action in these systems is based on the output.

2.      Reaction to Internal and External Disturbances
– An open loop control system works on fixed operation conditions and there are no disturbances.
– A closed loop control system doesn’t encounter and react on external disturbances or internal variations.

3.      Stability
– Open loop control systems are mostly stable.
– In closed loop control systems stability is a major issue.

4.      Effect on gain
– There is no effect on gain.
– There is no-linear change in system gain.

5.      Implementation
– The structure of open loop control system is rather easy to construct. These systems can be easily implemented.
– The working principle and structures of closed loop control systems are rather complex and they are often difficult to implement.

6.      Cost
– As an open loop control system is easy to implement, it needs lesser number of components to be constructed. Such systems need good calibration and lesser power rating. The overall cost of these systems is low.
– As the principle is complex, a closed loop control system needs larger number of components than an open loop control systems. These systems comparatively need less calibration and higher power rating. The overall cost of these systems is higher.

7.      Examples
– Stepper motors , Automatic washing machine are one of the major examples of open-loop control systems.
– Television remote, a computer mouse are the most significant example of closed loop control systems.



In three phase circuit, connections can be given in two types:
1.      Star connection
2.      Delta connection
Star Connection

In star connection, there is four wire, three wires are phase wire and fourth is neutral which is taken from the star point. Star connection is preferred for long distance power transmission because it is having the neutral point. In this we need to come to the concept of balanced and unbalanced current in power system.
When equal current will flow through all the three phases, then it is called as balanced current. And when the current will not be equal in any of the phase, then it is unbalanced current. In this case, during balanced condition there will be no current flowing through the neutral line and hence there is no use of the neutral terminal. But when there will be unbalanced current flowing in the three phase circuit, neutral is having a vital role. It will take the unbalanced current through to the ground and protect the transformer. Unbalanced current affects transformer and it may also cause damage to the transformer and for this star connection is preferred for long distance transmission. The star connection is shown below- In star connection, the line voltage is √3 times of phase voltage. Line voltage is the voltage between two phases in three phase circuit and phase voltage is the voltage between one phase to the neutral line. And the current is same for both line and phase. It is shown as expression below
Delta Connection

In delta connection, there is three wires alone and no neutral terminal is taken. Normally delta connection is preferred for short distance due to the problem of unbalanced current in the circuit. The figure is shown below for delta connection. In the load station, ground can be used as neutral path if required. In delta connection, the line voltage is same with that of phase voltaage. And the line current is √3 times of phase current. It is shown as expression below,
In three phase circuit, star and delta connection can be arranged in four different ways-
1.      Star-Star connection
2.      Star-Delta connection
3.      Delta-Star connection
4.      Delta-Delta connection
But the power is independent of the circuit arrangement of the three phase system. The net power in the circuit will be same in both star and delta connection. The power in three phase circuit can be calculated from the equation below,
Since there is three phases, so the multiple of 3 is made in the normal power equation and the PF is power factor. Power factor is a very important factor in three phase system and sometimes due to certain error, it is corrected by using capacitors.

Current
Current is the movement or flow of electrical charge and is measured in Amperes. It is the continuous and uniform flow of electrons (the negative particles of an atom) around a circuit that are being “pushed” by the voltage source. In reality, electrons flow from the negative (-ve) terminal to the positive (+ve) terminal of the supply and for ease of circuit understanding conventional current flow assumes that the current flows from the positive to the negative terminal.
Generally in circuit diagrams the flow of current through the circuit usually has an arrow associated with the symbol, I, or lowercase i to indicate the actual direction of the current flow. However, this arrow usually indicates the direction of conventional current flow and not necessarily the direction of the actual flow.
Conventional Current Flow
Conventionally this is the flow of positive charge around a circuit, being positive to negative. The diagram at the left shows the movement of the positive charge (holes) around a closed circuit flowing from the positive terminal of the battery, through the circuit and returns to the negative terminal of the battery. This flow of current from positive to negative is generally known as conventional current flow.
This was the convention chosen during the discovery of electricity in which the direction of electric current was thought to flow in a circuit. To continue with this line of thought, in all circuit diagrams and schematics, the arrows shown on symbols for components such as diodes and transistors point in the direction of conventional current flow.
Then Conventional Current Flow gives the flow of electrical current from positive to negative and which is the opposite in direction to the actual flow of electrons.
Current that flows in a single direction is called Direct Current, or D.C. and current that alternates back and forth through the circuit is known as Alternating Current, or A.C.. Whether AC or DC current only flows through a circuit when a voltage source is connected to it with its “flow” being limited to both the resistance of the circuit and the voltage source pushing it.
Also, as alternating currents (and voltages) are periodic and vary with time the “effective” or “RMS”, (Root Mean Squared) value given as Irms produces the same average power loss equivalent to a DC current Iaverage . Current sources are the opposite to voltage sources in that they like short or closed circuit conditions but hate open circuit conditions as no current will flow.
.

Electrical Voltage
Voltage (V):It is the potential energy of an electrical supply stored in the form of an electrical charge. Voltage can be thought of as the force that pushes electrons through a conductor and the greater the voltage the greater is its ability to “push” the electrons through a given circuit. As energy has the ability to do work this potential energy can be described as the work required in joules to move electrons in the form of an electrical current around a circuit from one point or node to another.
Then the difference in voltage between any two points, connections or junctions (called nodes) in a circuit is known as the Potential Difference,(p.d.) commonly called the Voltage Drop.
The Potential difference between two points is measured in Volts with the circuit symbol V, or lowercase “v“, although Energy, E lowercase “e” is sometimes used to indicate a generated emf (electromotive force). Then the greater the voltage, the greater is the pressure (or pushing force) and the greater is the capacity to do work.
A constant voltage source is called a DC Voltage with a voltage that varies periodically with time is called an AC voltage. Voltage is measured in volts, with one volt being defined as the electrical pressure required to force an electrical current of one ampere through a resistance of one Ohm.
Voltage Symbols
Voltage is always measured as the difference between any two points in a circuit and the voltage between these two points is generally referred to as the “Voltage drop“. Note that voltage can exist across a circuit without current, but current cannot exist without voltage and as such any voltage source whether DC or AC likes an open or semi-open circuit condition but hates any short circuit condition as this can destroy it.

Resistance
The Resistance(R) of a circuit is its ability to resist or prevent the flow of current (electron flow) through itself making it necessary to apply a greater voltage to the electrical circuit to cause the current to flow again. Resistance is measured in Ohms, Greek symbol ( Ω, Omega ) with prefixes used to denote Kilo-ohms ( kΩ = 103Ω ) and Mega-ohms ( MΩ = 106Ω ). Note that Resistance cannot be negative in value only positive.
Resistor Symbols

The amount of resistance determines whether the circuit is a “good conductor” – low resistance, or a “bad conductor” – high resistance. Low resistance, for example 1Ω or less implies that the circuit is a good conductor made from materials such as copper, aluminum or carbon while a high resistance, 1MΩ or more implies the circuit is a bad conductor made from insulating materials such as glass, porcelain or plastic.
A “semiconductor” on the other hand such as silicon or germanium, is a material whose resistance is half way between that of a good conductor and a good insulator. Semiconductors are used to make Diodes and Transistors etc.
Resistance can be linear in nature or non-linear in nature. Linear resistance obeys Ohm’s Law and controls or limits the amount of current flowing within a circuit in proportion to the voltage supply connected to it and therefore the transfer of power to the load. Non-linear resistance, does not obey Ohm’s Law but has a voltage drop across it that is proportional to some power of the current.
Resistance is pure and is not affected by frequency with the AC impedance of a resistance being equal to its DC resistance and as a result can not be negative. Remember that resistance is always positive, and never negative.
Resistance can also be classed as an attenuator as it has the ability to change the characteristics of a circuit by the effect of loading the circuit or by temperature which changes its resistivity.
For very low values of resistance, for example milli-ohms, ( mΩ´s ) it is sometimes much easier to use the reciprocal of resistance ( 1/R ) rather than resistance ( R ) itself. The reciprocal of resistance is called Conductance, symbol ( G ) and represents the ability of a conductor or device to conduct electricity.
In other words the ease by which current flows. High values of conductance implies a good conductor such as copper while low values of conductance implies a bad conductor such as wood. The standard unit of measurement given for conductance is the Siemen, symbol (S).
Again, using the water relationship, resistance is the diameter or the length of the pipe the water flows through. The smaller the diameter of the pipe the larger the resistance to the flow of water, and therefore the larger the resistance.
The relationship between Voltage, ( v ) and Current, ( i ) in a circuit of constant Resistance, ( R ).

Voltage, Current and Resistance Summary
Hopefully by now you should have some idea of how electrical Voltage, Current and Resistance are closely related together. The relationship between Voltage, Current and Resistance forms the basis of Ohm’s law which in a linear circuit states that if we increase the voltage, the current goes up and if we increase the resistance, the current goes down. Then we can see that current flow around a circuit is directly proportional ( ∝ ) to voltage, ( V↑ causes I↑ ) but inversely proportional ( 1/∝ ) to resistance as, ( R↑ causes I↓ ).
A basic summary of the three units is given below.
·         Voltage or potential difference is the measure of potential energy between two points in a circuit and is commonly referred to as its “ volt drop ”.
·         When a voltage source is connected to a closed loop circuit the voltage will produce a current flowing around the circuit.
·         In DC voltage sources the symbols +ve (positive) and -ve (negative) are used to denote the polarity of the voltage supply.
·         Voltage is measured in “ Volts ” and has the symbol “ V ” for voltage or “ E ” for energy.
·         Current flow is a combination of electron flow and hole flow through a circuit.
·         Current is the continuous and uniform flow of charge around the circuit and is measured in “ Amperes ” or “ Amps ” and has the symbol “ I ”.
·         The effective (rms) value of an alternating current has the same average power loss equivalent to a direct current flowing through a resistive element.
·         Resistance is the opposition to current flowing around a circuit.
·         Low values of resistance implies a conductor and high values of resistance implies an insulator.
·         Resistance is measured in “ Ohms ” and has the Greek symbol “ Ω ” or the letter “ R ”.
Quantity
Symbol
Unit of
Measure
Abbreviation
Voltage
V or E
Volt
V
Current
I
Ampere
A
Resistance
R
Ohms
Ω
In the next tutorial about DC Theory we will look at Ohms Law which is a mathematical equation explaining the relationship between Voltage, Current, and Resistance within electrical circuits and is the foundation of electronics and electrical engineering. Ohm’s Law is defined as: E = I x R.

List of electrical and electronic measuring equipment

Name
Purpose
Ammeter
Measures current
Audio analyzer
Analyzes (analog and digital) systems handling audio signals
Capacitance meter
Measures the capacitance of a component
Cos Phi Meter
Measures the power factor
Distortionmeter
Measures the distortion added to a circuit
Electricity meter
Measures the amount of energy dissipated
ESR meter
Mesures the equivalent series resşstance of capacitors
Frequency counter
Measures the frequency of the current
LCR meter
Measures the inductance, capacitance and resistance of a component
Microwave power meter
Measures power at microwave frequencies
Multimeter
General purpose instrument measures voltage, current and resistance (and sometimes other quantities as well)
Network analyzer
Measures network parameters
Ohmmeter
Measures the resistance of a component
Oscilloscope
Displays waveform of a signal
Psophometer
Measures AF signal level and noise
Q meter
Measures Q factor of the RF circuits
Signal analyzer
Measures both the amplitude and the modulation of a RF signal
Signal generator
Generates signals for testing purposes
Spectrum analyser
Displays frequency spectrum
Sweep generator
Creates constant-amplitude variable frequency sine waves to test frequency response
Transistor tester
Tests transistors
Tube tester
Tests vacuum tubes (triode, tetrode etc.)
Wattmeter
Measures the power
Vectorscope
Displays the phase of the colors in color TV
Video signal generator
Generates video signal for testing purposes
Voltmeter
Measures the potential difference between two points in a circuit.
VU meter
Meaures the level of AF signals in Volume units




Voltage Source and Current Source
Voltage Source:A device which can produce a continuous force to move the electrons (or, continuous voltage) through the wire connected into the two terminals of the device is called a Voltage Source. There are two types of the Voltage Source which are:
1.Direct Voltage Source:
A device which produces a continuous direct voltage output is called a Direct Voltage Source. For example: Cells , Battery , DC Generator.
A direct voltage is the kind of voltage whose polarity remains the same. Direct Voltage causes the current to move only in one direction continuously.
2.Alternating Voltage Source:
A device which produces a alternating direct voltage output is called a Alternating Voltage Source. For example: AC Generator , DC to AC converter etc.
A alternating voltage is the kind of voltage whose polarity is reversed periodically. Alternating Voltage causes the current to move in one direction for a period and then in another direction for another period.
3.Ideal Voltage Source:
An Ideal Voltage source is a kind of Voltage source whose internal resistance is zero! Such that the supplied voltage does not changes even if the external load resistance is changes.
Anatomy of a Virtually Ideal (Constant) Voltage Source:
A Voltage source which have zero internal resistance or impedance is called an Ideal or Constant voltage source!
But practically it is not possible. No matter how much efforts are made the voltage source still have a small internal resistance , But a voltage source can be converted into a Virtually Constant Voltage Source by changing the internal materials used in a cell or voltage source such that the internal resistance of the source is minimized.
A practical virtual constant voltage source haves a very low internal impedance (let it be 0.005 ohm or 5 mili Ohm in this case) and the actual circuit diagram of a voltage source looks like:
constant voltage source

Current Source:
A current source is a device which provides the regular flow or electrons or current on a circuit.
A current source is a type of voltage source which have enough EMF and surplus electrons so as to produce the flow of electrons.
1.Direct Current Source:
The current source made of  a Direct Voltage Source is called Direct Current Source.
2.Alternating Current Source:
The current source made of  a Alternating Voltage Source is called Alternating Current Source.
3.Ideal Current Source:
A current source which provides a constant current without any relation with the voltage supplied to the load is called Ideal Current Source.
Anatomy of a Virtually Ideal (Constant) Current Source:
Practically a Ideal Current source is impossible but a circuit can be configured such that when the voltage across the load is changed the supplied current current varies negligibly. A virtual Constant or Ideal current source can be made by adding a very high internal impedance to a Voltage Source.a shown in the figure below:



Kirchhoff Current Law and Kirchhoff Voltage Law

Kirchhoff's Laws
There are some simple relationships between currents and voltages of different branches of an electrical circuit. These relationships are determined by some basic laws that are known as Kirchhoff laws or more specifically Kirchhoff Current and Voltage laws. These laws are very helpful in determining the equivalent electrical resistance or impedance (in case of AC) of a complex network and the currents flowing in the various branches of the network. These laws are first derived by Guatov Robert Kirchhoff and hence these laws are also referred as Kirchhoff Laws.
Kirchhoff's Current Law
In an electrical circuit, the current flows rationally as electrical quantity. As the flow of current is considered as flow of quantity, at any point in the circuit the total current enters, is exactly equal to the total current leaves the point. The point may be considered anywhere in the circuit.

Suppose the point is on the conductor through which the current is flowing, then the same current crosses the point which can alternatively said that the current enters at the point and same will leave the point. As we said the point may be anywhere on the circuit, so it can also be a junction point in the circuit. So total quantity of current enters at the junction point must be exactly equal to total quantity of current that leaves the junction. This is the very basic thing about flowing of current and fortunately Kirchhoff Current law says the same. The law is also known as Kirchhoff First Law and this law stated that, at any junction point in the electrical circuit, the summation of all the branch currents is zero. If we consider all the currents enter in the junction are considered as positive current, then convention of all the branch currents leaving the junction are negative. Now if we add all these positive and negative signed currents, obviously we will get result of zero. The mathematical form of Kirchhoff's Current Law is as follows,

We have a junction where n number of beaches meet together.

Let's I1, I2, I3, ...................... Im are the current of branches 1, 2, 3, ......m and
Im + 1, Im + 2, Im + 3, ...................... In are the current of branches m + 1, m + 2, m + 3, ......n respectively.
The currents in branches 1, 2, 3 ....m are entering to the junction. Whereas currents in branches m + 1, m + 2, m + 3 ....n are leaving from the junction.
So the currents in the branches 1, 2, 3 ....m may be considered as positive as per general convention and similarly the currents in the branches m + 1, m + 2, m + 3 ....n may be considered as negative.
Hence all the branch currents in respect of the said junction are -
+ I1, + I2, + I3,................+ Im, − Im + 1, − Im + 2, − Im + 3, .................. and − In.
Now, the summation of all currents at the junction is-
I1 + I2 + I3 + ................+ Im − Im + 1 − Im + 2 − Im + 3..................− In.
This is equal to zero according to Kirchhoff Current Law.
Therefore, I1 + I2 + I3 + ................+ Im − Im + 1 − Im + 2 − Im + 3..................− In = 0.
The mathematical form of Kirchhoff First Law is ∑ I = 0 at any junction of electrical network.
Kirchhoff's Voltage Law
This law deals with the voltage drops at various branches in an electrical circuit. Think about one point on a closed loop in an electrical circuit. If someone goes to any other point on the same loop, he or she will find that the potential at that second point may be different from first point. If he or she continues to go to some different point in the loop, he or she may find some different potential at that new location. If he or she goes on further along that closed loop, ultimately he or she reaches the initial point from where the journey was started. That means, he or she comes back to the same potential point after crossing through different voltage levels. It can be alternatively said that net voltage gain and net voltage drops along a closed loop are equal. That is what Kirchhoff Voltage law states. This law is alternatively known as Kirchhoff Second Law.
If we consider a closed loop conventionally, if we consider all the voltage gains along the loop are positive then all the voltage drops along the loop should be considered as negative. The summation of all these voltages in a closed loop is equal to zero. Suppose n numbers of back to back connected elements form a closed loop. Among these circuit elements m number elements are voltage source and n - m number of elements drop voltage such as resistors.
The voltages of sources are V1, V2, V3,................... Vm.
And voltage drops across the resistors respectively, Vm + 1, Vm + 2, Vm + 3,..................... Vn.
As it is said that the voltage gain conventionally considered as positive, and voltage drops are considered as negative, the voltages along the closed loop are -
+ V1, + V2, + V3,................... + Vm, − Vm + 1, − Vm + 2, − Vm + 3,.....................− Vn.
Now according to Kirchhoff Voltage law, the summation of all these voltages results to zero.
That means, V1 + V2 + V3 + ................... + Vm − Vm + 1 − Vm + 2 − Vm + 3 + .....................− Vn = 0.
So accordingly Kirchhoff Second Law, ∑V = 0.
Application of Kirchhoff's Laws to Circuits
The current distribution in various branches of a circuit can easily be found out by applying Kirchhoff Current law at different nodes or junction points in the circuit. After that Kirchhoff Voltage law is applied, each possible loop in the circuit generates algebraic equation for every loop. By solving all these equations, one can easily find out different unknown currents, voltages and resistances in the circuits.
Some Popular Conventions We Generally use During Applying KVL
1) The resistive drops in a loop due to current flowing in clockwise direction must be taken as positive drops.
2) The resistive drops in a loop due to current flowing in anti-clockwise direction must be taken as negative drops.
3) The battery emf causing current to flow in clockwise direction in a loop is considered as positive.
4) The battery emf causing current to flow in anti-clockwise direction is referred as negative.
Inductive Reactance XL
When the current in an Inductor changes, a back emf is created that opposes the change in current, and the faster the initial change in current the greater the back emf. So it is not surprising that, the faster rates of change of current that occur as the frequency of the wave increases, produce a greater back emf effect that in turn, reduces current flow more than it does at lower frequencies.
This variable opposition to current flow in an inductor, is related to the amount of the inductance, because the larger the value of inductance the greater the back emf effect produced. The opposition to current flow through an inductor is proportional to both the amount of inductance and to the frequency of the current in the inductor. This opposition to current flow is called INDUCTIVE REACTANCE (XL). The formula for Inductive Reactance multiplies the angular velocity of the AC wave by the value of Inductance:
Where 2πƒ or ω is the angular velocity and L is the inductance in henries.
Fig 6.1.1 Inductive Reactance
Like resistance, reactance it is measured in ohms, but is separate from the opposition to current caused by any internal resistance within the inductor. Large values of inductance (found in large types of inductors used at low frequencies) have higher values of internal resistance than the much smaller types of inductor used at radio frequencies and above. Inductors are basically coils of wire, and the more coils of wire an inductor has, the longer the wire will be, and the greater its value of resistance. This internal resistance cannot be separated from the inductor and must be accounted for in calculations, especially in low frequency applications that use large inductors. The small amounts of resistance present in the much smaller radio frequency inductors however, can usually be ignored.
Fig 6.1.1 shows a graph of inductive reactance against frequency for a particular value of inductance, with XL increasing with frequency in a linear fashion
Resistance in Inductors
The resistance present in the wire of large inductors has a noticeable effect on current through, and voltage across an inductor. Although the effect of reactance can be calculated, it will not account for the total effect on current and voltage, the resistance must also be taken into account. The internal resistance of an inductor cannot be physically separated from the inductor as shown in Fig 6.1.2
Fig. 6.1.2 How Vr and XL affect VL In a Phasor Diagram.
Fig. 6.1.2 also shows the effect that the internal resistance of an inductor has on its phasor diagram. The voltage across the internal resistance (Vr) may be small in comparison to the voltage across the inductance, but Vr will be in phase with the reference phasor (current I) and so will produce a phase shift causing the phasor for VL to shift towards 0°.
Because VL is the phasor sum of the voltages VXL and Vr (due to both the reactance and the internal resistance of the inductor), it will also be slightly larger than the voltage (VXL) that would be calculated due to the inductance alone. This means that in practical inductor, the voltage phasor is not going to lead the current phasor by exactly +90°, the actual amount of phase shift will also depend on the amount of internal resistance. Whilst this is not a big problem with the small inductors used in high frequency applications, it does need to be considered in large, low frequency inductors where the coil has many more turns an therefore its internal resistance is greater.

Electrical Symbols & Electronic Symbols
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Table of Electrical Symbols
Symbol
Component name
Meaning
Wire Symbols
Electrical Wire
Conductor of electrical current
Connected Wires
Connected crossing
Not Connected Wires
Wires are not connected
Switch Symbols and Relay Symbols
SPST Toggle Switch
Disconnects current when open
SPDT Toggle Switch
Selects between two connections
Pushbutton Switch (N.O)
Momentary switch - normally open
Pushbutton Switch (N.C)
Momentary switch - normally closed
DIP Switch
DIP switch is used for onboard configuration
SPST Relay
Relay open / close connection by an electromagnet
SPDT Relay
Jumper
Close connection by jumper insertion on pins.
Solder Bridge
Solder to close connection
Ground Symbols
Earth Ground
Used for zero potential reference and electrical shock protection.
Chassis Ground
Connected to the chassis of the circuit
Digital / Common Ground
Resistor Symbols
Resistor (IEEE)
Resistor reduces the current flow.
Resistor (IEC)
Potentiometer (IEEE)
Adjustable resistor - has 3 terminals.
Potentiometer (IEC)
Variable Resistor / Rheostat (IEEE)
Adjustable resistor - has 2 terminals.
Variable Resistor / Rheostat (IEC)
Trimmer Resistor
Preset resistor
Thermistor
Thermal resistor - change resistance when temperature changes
Photoresistor / Light dependent resistor (LDR)
Photo-resistor - change resistance with light intensity change
Capacitor Symbols
Capacitor
Capacitor is used to store electric charge. It acts as short circuit with AC and open circuit with DC.
Capacitor
Polarized Capacitor
Electrolytic capacitor
Polarized Capacitor
Electrolytic capacitor
Variable Capacitor
Adjustable capacitance
Inductor / Coil Symbols
Inductor
Coil / solenoid that generates magnetic field
Iron Core Inductor
Includes iron
Variable Inductor
Power Supply Symbols
Voltage Source
Generates constant voltage
Current Source
Generates constant current.
AC Voltage Source
AC voltage source
Generator
Electrical voltage is generated by mechanical rotation of the generator
Battery Cell
Generates constant voltage
Battery
Generates constant voltage
Controlled Voltage Source
Generates voltage as a function of voltage or current of other circuit element.
Controlled Current Source
Generates current as a function of voltage or current of other circuit element.
Meter Symbols
Voltmeter
Measures voltage. Has very high resistance. Connected in parallel.
Ammeter
Measures electric current. Has near zero resistance. Connected serially.
Ohmmeter
Measures resistance
Wattmeter
Measures electric power
Lamp / Light Bulb Symbols
Lamp / light bulb
Generates light when current flows through
Lamp / light bulb
Lamp / light bulb
Diode / LED Symbols
Diode
Diode allows current flow in one direction only - left (anode) to right (cathode).
Zener Diode
Allows current flow in one direction, but also can flow in the reverse direction when above breakdown voltage
Schottky Diode
Schottky diode is a diode with low voltage drop
Varactor / Varicap Diode
Variable capacitance diode
Tunnel Diode
Light Emitting Diode (LED)
LED emits light when current flows through
Photodiode
Photodiode allows current flow when exposed to light
Transistor Symbols
NPN Bipolar Transistor
Allows current flow when high potential at base (middle)
PNP Bipolar Transistor
Allows current flow when low potential at base (middle)
Darlington Transistor
Made from 2 bipolar transistors. Has total gain of the product of each gain.
JFET-N Transistor
N-channel field effect transistor
JFET-P Transistor
P-channel field effect transistor
NMOS Transistor
N-channel MOSFET transistor
PMOS Transistor
P-channel MOSFET transistor
Misc. Symbols
Motor
Electric motor
Transformer
Change AC voltage from high to low or low to high.
Electric bell
Rings when activated
Buzzer
Produce buzzing sound
Fuse
The fuse disconnects when current above threshold. Used to protect circuit from high currents.
Fuse
Bus
Contains several wires. Usually for data / address.
Bus
Bus
Optocoupler / Opto-isolator
Optocoupler isolates connection to other board
Loudspeaker
Converts electrical signal to sound waves
Microphone
Converts sound waves to electrical signal
Operational Amplifier
Amplify input signal
Schmitt Trigger
Operates with hysteresis to reduce noise.
Analog-to-digital converter (ADC)
Converts analog signal to digital numbers
Digital-to-Analog converter (DAC)
Converts digital numbers to analog signal
Crystal Oscillator
Used to generate precise frequency clock signal
Antenna Symbols
Antenna / aerial
Transmits & receives radio waves
Antenna / aerial
Dipole Antenna
Two wires simple antenna
Logic Gates Symbols
NOT Gate (Inverter)
Outputs 1 when input is 0
AND Gate
Outputs 1 when both inputs are 1.
NAND Gate
Outputs 0 when both inputs are 1. (NOT + AND)
OR Gate
Outputs 1 when any input is 1.
NOR Gate
Outputs 0 when any input is 1. (NOT + OR)
XOR Gate
Outputs 1 when inputs are different. (Exclusive OR)
D Flip-Flop
Stores one bit of data
Multiplexer / Mux 2 to 1
Connects the output to  selected input line.
Multiplexer / Mux 4 to 1
Demultiplexer / Demux 1 to 4
Connects selected output to the input line.



There are two different ways to connect two or more electrical devices together in a circuit. They can be connected by means of series connections or by means of parallel connections. When all the devices in a circuit are connected by series connections, then the circuit is referred to as a series circuit. When all the devices in a circuit are connected by  parallel connections, then the circuit is referred to as a parallel circuit. A third type of circuit involves the dual use of series and parallel connections in a circuit; such circuits are referred to as compound circuits or combination circuits
When analyzing combination circuits, it is critically important to have a solid understanding of the concepts that pertain to both series circuits and parallel circuits. Since both types of connections are used in combination circuits, the concepts associated with both types of circuits apply to the respective parts of the circuit. The main concepts associated with series and parallel circuits are organized in the table below.
Series circuits
·         The current is the same in every resistor; this current is equal to that in the battery.
·         The sum of the voltage drops across the individual resistors is equal to the voltage rating of the battery.
·         The overall resistance of the collection of resistors is equal to the sum of the individual resistance values,
Rtot = r1 + r2 + r3 + ...
Parallel circuits
·         The voltage drop is the same across each parallel branch.
·         The sum of the current in each individual branch is equal to the current outside the branches.
·         The equivalent or overall resistance of the collection of resistors is given by the equation
1/req = 1/r1 + 1/r2 + 1/r3 ...
Each of the above concepts has a mathematical expression. Combining the mathematical expressions of the above concepts with the ohm's law equation (δv = i • r) allows one to conduct a complete analysis of a combination circuit.

Analysis of combination circuits
The basic strategy for the analysis of combination circuits involves using the meaning of equivalent resistance for parallel branches to transform the combination circuit into a series circuit. Once transformed into a series circuit, the analysis can be conducted in the usual manner

1 / req = 1 / r1 + 1 / r2 + 1 / r3 + ...
Where r1, r2, and r3 are the resistance values of the individual resistors that are connected in parallel. If the two or more resistors found in the parallel branches do not have equal resistance, then the above formula must be used. An example of this method was presented in a previous section of lesson 4.
By applying one's understanding of the equivalent resistance of parallel branches to a combination circuit, the combination circuit can be transformed into a series circuit. Then an understanding of the equivalent resistance of a series circuit can be used to determine the total resistance of the circuit. Consider the following diagrams below. Diagram a represents a combination circuit with resistors r2 and r3 placed in parallel branches. Two 4-ω resistors in parallel is equivalent to a resistance of 2 ω. Thus, the two branches can be replaced by a single resistor with a resistance of 2 ω. This is shown in diagram b. Now that all resistors are in series, the formula for the total resistance of series resistors can be used to determine the total resistance of this circuit: the formula for series resistance is

Rtot = r1 + r2 + r3 + ...

Ohm's law:
Ohm's law defines a linear relationship between the voltage and the current in an electrical circuit.
The resistor's voltage drop and resistance set the dc current flow through the resistor.
With water flow analogy we can imagine the electric current as water current through pipe, the resistor as a thin pipe that limits the water flow, the voltage as height difference of the water that enables the water flow.
Ohm's law definition
The resistor's current i in amps (a) is equal to the resistor's voltage vr=v in volts (v) divided by the resistance r in ohms (ω):


V is the voltage drop of the resistor, measured in volts (v). In some cases ohm's law uses the lettere to represent voltage. E denotes electromotive force.
I is the electrical current flowing through the resistor, measured in  amperes (a)
R is the resistance of the resistor, measured in ohms (ω)

Voltage calculation
When we know the current and resistance, we can calculate the voltage.
The voltage v in volts (v) is equal to the to the current i in amps (a) times the resistance r in ohms (ω):


Resistance calculation
When we know the voltage and the current, we can calculate the resistance.
The resistance r in ohms (ω) is equal to the voltage v in volts (v) divided by the current i in amps (a):


Since the current is set by the values of the voltage and resistance, the ohm's law formula can show that:
·         If we increase the voltage, the current will increase.
·         If we increase the resistance, the current will reduce.
Ohm's law for ac circuit:
The load's current i in amps (a) is equal to the load's voltage vz=v in volts (v) divided by the impedance z in ohms (ω):

V is the voltage drop on the load, measured in volts (v)
I is the electrical current, measured in amps (a)
Z is the impedance of the load, measured in ohms (ω)






Ohmic resistance:
Resistance is a concept used for dc (direct currents) whereas impedance is the ac (alternating current) equivalent. Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat. Different materials have different resistivities (a property defining how resistive a material of given dimensions will be). 

However, when considering ac you must remember that it oscillates as a sine wave so the sign is always changing. This means that other effects need to be considered - namely inductance and capacitance. So simply resistance and impedance have different fundamental origins even though the calculation for their value is the same: 


Inductance:
It is most obvious in coiled wire. When a current flows through a wire a circular magnetic field is created around it. If you coil the wire into a solenoid the fields around the wire sum up and you get a magnetic field similar to that of a bar magnet on the outside but you get a uniform magnetic field on the inside. With ac since the sign is always changing the direction of the field in the wires is always changing - so the magnetic field of the solenoid is also changing all the time. Now when field lines cut across a conductor an emf is generated in such a way to reduce the effects that created it (this is a combination of lenz's and faraday's laws which state mathematically that e=n*d(thi)/dt , where thi is the magnetic flux linkage). This means that when an ac current flows through a conductor a small back emf or back current is induced reducing the overall          current. 

Capacitance:
It is a property best illustrated by two metal plates separated by an insulator (which we call a capacitor). When current flows electrons build up on the negative plate. An electric field propagates and repels electrons on the opposite plate making it positively charged. Due to the buildup of electrons on the negative plate incoming electrons are also repelled so the total current eventually falls to zero in an exponential decay. The capacitance is defined as the charge stored/displaced across a capacitor divided by the potential difference across it and can also be calculated by the size of the plates and the primitivity of the insulator. 


r=v/i 
answered by: martin archer, physics student, imperial college London, UK

Impedance:
It is a more general term for resistance that also includes reactance. 

In other words, resistance is the opposition to a steady electric current. Pure resistance does not change with frequency, and typically the only time only resistance is considered is with dc (direct current -- not changing) electricity. 

Reactance, however, is a measure of the type of opposition to ac electricity due to capacitance or inductance. This opposition varies with frequency. For example, a capacitor only allows dc current to flow for a short while until it is charged; at that point, current will stop flowing and it will look like an open. However, if a very high frequency is put across that capacitor (a signal that has a voltage which is changing very quickly back and forth), the capacitor will look like a short circuit. The capacitor has a reactance which is inversely proportional to frequency. An inductor has a reactance which is directly proportional to frequency -- dc flows through easily while high-frequency ac is stopped. 

Impedance is the total contribution of both -- resistance and reactance. This is important for ac analysis and design. At dc, reactive elements can be replaced with their steady-state model (capacitor->open, inductor->short) and resistance can be considered. (This isn't true for transient analysis) 

it is important to mention that while energy goes into both, it is only 'burned off' through resistance. Power has to be given in terms of resistive power and reactive power. Resistive power actually burns off energy into heat while reactive power simply stores energy in e-fields and b-fields. 

Often you'll hear about the 'impedance' of transmission lines, like the cables which run between components of your stereo system, and impedance of things like speakers. You'll also hear that it is important to match these or else you'll get reflection. 

This is a much more complicated subject, which a few answers have commented on in recent questions about light and its speed. 

However, what i want to mention is that when you hear about the impedance of a transmission line, like speaker cable or an antenna or coaxial cable or anything else, this does not represent energy which is "burned off" in the cable. This has to do with how energy is stored in the cable as it propagates down it. The cable does not (well, in reality it does, but assume the lossless case for simplicity) get hotter as a signal travels down it. It is not proper to think of a '75-ohm cable' as a 75-ohm 'resistor.' that 75-ohms is purely reactance (ideally, though there really is attenuation in real cables). 

Note that impedance and reactance are both given in units of 'ohms' just like resistance. Capacitance is measured in farads and inductance in henries, and these relate to impedance, but they are not measures of impedance. As i said, the impedance of a capacitor is inversely proportional to its capacitance and the impedance of an inductor directly proportional to its inductance. 

This may sound a little abstract. Impedance really is an abstraction of things that are far more complicated (things like time constants and rise times) that electrical engineers have to constantly consider. The idea of 'impedance' allows for many of these things to be wrapped up into one subject so that they are easier to communicate. 

The short answer is -- impedance includes reactance, and reactance includes effects which vary with frequency due to inductance and capacitance.