electrical and electronics measurement and instrumentation

8/10/2019 electrical and electronics measurement and instrumentation

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Electrical and Electronic measurements & instrumentation 10EE35

Department of EEE, SJBIT Page 1

Question Bank with solution

PART-A

Unit-1

1. Derive the dimensional equation for jan14, july13, jan13 i) EMF in SI unitsii) Magnetizing force in SI unitsiii) Capacitance in SI unitsiv) MMF in LMTIv) Flux density in LMTIvi) Resistivity and conductivity in SI units

Capacitance C = q/v = [M1/2 L3/2 T-1 1/2]/ [M1/2L1/2T-1 -1/2] = [ L]

Resistance R = V/I = [M1/2L1/2 T- 1 -1/2]/[M1/2L3/2T- 21/2] =[L-1T -1]

Where f = frequency, Bm = Max. flux density, d= diameter of wire, resistivityof

material. Find the values a, b,c,and g using L,M,T,I system

P = k fa Bmb dc g

[P] = [I1L-1 ]

[f] = [T-1 ]

[Bm] = [M1T-2I-1 ]

[d] = [L]

[] = [M1 L3 T -3I-2]

[I1L-1 ] = k [T-1 ] a [M1T-2I-1 ] b [L] c [M1 L3 T-3I-2] g


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The length of the lever arm is particularly important; choosing thislength appropriately lies behind the operation of levers ,pulleys, gears, and most other simple machines involving a mechanical advantage. The SI unit for torque is the newton metre (Nm).

3. Derive the balancing equ for Kelvins double bridge jan14, july13, june12,dec11

An interesting variation of the Wheatstone bridge is the Kelvin Double bridge,used for measuring very low resistances (typically less than 1/10 of an ohm). Itsschematic diagram is as such:

The low-value resistors are represented by thick-line symbols, and the wiresconnecting them to the voltage source (carrying high current) are likewise drawnthickly in the schematic. This oddly-configured bridge is perhaps best understood

by beginning with a standard Wheatstone bridge set up for measuring lowresistance, and evolving it step-by-step into its final form in an effort to overcomecertain problems encountered in the standard Wheatstone configuration.
http://en.wikipedia.org/wiki/Leverhttp://en.wikipedia.org/wiki/Pulleyhttp://en.wikipedia.org/wiki/Gearhttp://en.wikipedia.org/wiki/Simple_machinehttp://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/SI_unitshttp://en.wikipedia.org/wiki/Newton_metrehttp://en.wikipedia.org/wiki/Newton_metrehttp://en.wikipedia.org/wiki/SI_unitshttp://en.wikipedia.org/wiki/Mechanical_advantagehttp://en.wikipedia.org/wiki/Simple_machinehttp://en.wikipedia.org/wiki/Gearhttp://en.wikipedia.org/wiki/Pulleyhttp://en.wikipedia.org/wiki/Lever


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If we were to use a standard Wheatstone bridge to measure low resistance, it wouldlook something like this:

When the null detector indicates zero voltage, we know that the bridge is balancedand that the ratios Ra/Rx and RM/RN are mathematically equal to each other.Knowing the values of Ra, RM, and RN therefore provides us with the necessarydata to solve for Rx . . . almost.We have a problem, in that the connections and connecting wires between Ra andRx possess resistance as well, and this stray resistance may be substantialcompared to the low resistances of Ra and Rx. These stray resistances will dropsubstantial voltage, given the high current through them, and thus will affect thenull detector's indication and thus the balance of the bridge:


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Since we don't want to measure these stray wire and connection resistances, butonly measure Rx, we must find some way to connect the null detector so that itwon't be influenced by voltage dropped across them. If we connect the null

detector and RM/RN ratio arms directly across the ends of Ra and Rx, this gets uscloser to a practical solution:


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Now the top two Ewire voltage drops are of no effect to the null detector, and donot influence the accuracy of Rx's resistance measurement. However, the tworemaining Ewire voltage drops will cause problems, as the wire connecting thelower end of Ra with the top end of Rx is now shunting across those two voltagedrops, and will conduct substantial current, introducing stray voltage drops alongits own length as well.Knowing that the left side of the null detector must connect to the two near ends ofRa and Rx in order to avoid introducing those Ewire voltage drops into the nulldetector's loop, and that any direct wire connecting those ends of Ra and Rx willitself carry substantial current and create more stray voltage drops, the only wayout of this predicament is to make the connecting path between the lower end ofRa and the upper end of Rx substantially resistive:


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We can manage the stray voltage drops between Ra and Rx by sizing the two newresistors so that their ratio from upper to lower is the same ratio as the two ratioarms on the other side of the null detector. This is why these resistors were labeledRm and Rn in the original Kelvin Double bridge schematic: to signify their

proportionality with RM and RN:


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With ratio Rm/Rn set equal to ratio RM/RN, rheostat arm resistor Ra is adjusteduntil the null detector indicates balance, and then we can say that Ra/Rx is equal toRM/RN, or simply find Rx by the following equation:

The actual balance equation of the Kelvin Double bridge is as follows (Rwire is theresistance of the thick, connecting wire between the low-resistance standardRa and the test resistance Rx):

5. Obtain wheatstone bridge sensitivity interms of parameters of the bridge jan13, dec11


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The bridge consists of four resistive arms together with a source of e.m.f.and a nulldetector. The galvanometer is used as a null detector.

The arms consisting the resistances R] and R2 are called ratio arms. The armconsisting the standard known resistance R3 is called standard arm. Theresistance R4 is the unknown resistance to be measured. The battery isconnected between A and C while galvanometer is connected between BandD.

6. Explain the neat sketch how megger is used for the measurement of veryhigh resistance. Jan13,

The important construction features of Megger consist of following parts:
http://marineinsight.com/wp-content/uploads/2011/01/h1011v4_101_1.jpg


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1) Control and Deflecting coil : They are normally mounted at right angle toeach other and connected parallel to the generator. The polarities are suchthat the torque produced by them is in opposite direction.

2) Permanent Magnet : Permanent magnet with north and south poles to produce magnetic effect for deflection of pointer.

3) Pointer and scale : A pointer is attached to the coils and end of the pointer floats on a scale which is in the range from zero to infinity. Theunit for this is ohms.

4) D.C generator or battery connection : Testing voltage is supplied by

hand operated D.C generator for manual operated Megger and a battery andelectronic voltage charger for automatic type Megger.

5) Pressure coil and current coil : Provided for preventing damage to theinstrument in case of low external source resistance.

Working : -

The voltage for testing is supplied by a hand generator incorporated in the

instrument or by battery or electronic voltage charger. It is usually 250V or500V and is smaller in size.

- A test volt of 500V D.C is suitable for testing ships equipment operatingat 440V A.C. Test voltage of 1000V to 5000V is used onboard for highvoltage system onboard.

- The current carrying coil (deflecting coil) is connected in series and carries

the current taken by the circuit under test. The pressure coil (control coil) isconnected across the circuit.

- Current limiting resistor CCR and PCR are connected in series with pressureand current coil to prevent damage in case of low resistance in external source.


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- In hand generator, the armature is moving in the field of permanent magnetor vice versa, to generate a test voltage by electromagnetic induction effect.

- With an increase of potential voltage across the external circuit, thedeflection of the pointer increases; and with an increase of current, thedeflection of pointer decrease so the resultant torque on the movement isdirectly proportional to the potential difference and inversely proportional tothe resistance.

- When the external circuit is open, torque due to voltage coil will bemaximum and the pointer will read infinity. When there is short circuit the

pointer will read 0.

Unit-2

1. Explain the sources and detectors used in AC bridges. Jan14, june12

One way to maximize the effectiveness of audio headphones as a nulldetector is to connect them to the signal source through an impedance-matching transformer. Headphone speakers are typically low-impedanceunits (8 ), requiring substantial current to drive, and so a step -downtransformer helps match low -current signals to the impedance of theheadphone speakers. An audio output transformer works well for this

purpose: (Figure below )
http://www.allaboutcircuits.com/vol_2/chpt_12/5.html#02298.pnghttp://www.allaboutcircuits.com/vol_2/chpt_12/5.html#02298.png


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Modern low-Ohm headphones require an impedance matching transformer

for use as a sensitive null detector.

Using a pair of headphones that completely surround the ears (the closed-cup type), I've been able to detect currents of less than 0.1 A with thissimple detector circuit. Roughly equal performance was obtained using twodifferent step-down transformers: a small power transformer (120/6 voltratio), and an audio output transformer (1000:8 ohm impedance ratio). Withthe pushbutton switch in place to interrupt current, this circuit is usable for

detecting signals from DC to over 2 MHz: even if the frequency is far aboveor below the audio range, a click will be he ard from the headphones eachtime the switch is pressed and released.

Connected to a resistive bridge, the whole circuit looks like Figure below.


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Bridge with sensitive AC null detector.

Listening to the headphones as one or more of the resistor arms of the bridge is adjusted, a condition of balance will be realized when theheadphones fail to produce clicks (or tones, if the bridge's power sourcefrequency is within audio range) as the switch is actuated.

When describing general AC bridges, where impedances and not justresistances must be in proper ratio for balance, it is sometimes helpful to

draw the respective bridge legs in the form of box-shaped components, eachone with a certain impedance: (Figure below)


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Generalized AC impedance bridge: Z = nonspecific complex impedance.

For this general form of AC bridge to balance, the impedance ratios of each branch must be equal:

Again, it must be stressed that the impedance quantities in the aboveequation must be complex, accounting for both magnitude and phase angle.It is insufficient that the impedance magnitudes alone be balanced; without

phase angles in balance as well, there will still be voltage across the

terminals of the null detector and the bridge will not be balanced.

Bridge circuits can be constructed to measure just about any device valuedesired, be it capacitance, inductanc e, resistance, or even Q. As always in

bridge measurement circuits, the unknown quantity is always balancedagainst a known standard, obtained from a high-quality, calibratedcomponent that can be adjusted in value until the null detector deviceindicates a condition of balance. Depending on how the bridge is set up, the

unknown component's value may be determined directly from the setting ofthe calibrated standard, or derived from that standard through amathematical formula.

A couple of simple bridge circuits are shown below, one for inductance(Figure below) and one for capacitance: (Figure below)
http://www.allaboutcircuits.com/vol_2/chpt_12/5.html#02242.pnghttp://www.allaboutcircuits.com/vol_2/chpt_12/5.html#02243.pnghttp://www.allaboutcircuits.com/vol_2/chpt_12/5.html#02243.pnghttp://www.allaboutcircuits.com/vol_2/chpt_12/5.html#02242.png


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Symmetrical bridge measures unknown inductor by comparison to astandard inductor.

Symmetrical bridge measures unknown capacitor by comparison to a

standard capacitor.

Simple symmetrical bridges such as these are so named because theyexhibit symmetry (mirror-image similarity) from left to right. The two

bridge circuits shown above are balanced by adjusting the calibrated reactivecomponent (Ls or Cs). They are a bit simplified from their real-life


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counterparts, as practical symmetrical bridge circuits often have a calibrated,variable resistor in series or parallel with the reactive component to balanceout stray resistance in the unknown component. But, in the hypotheticalworld of perfect components, these simple bridge circuits do just fine toillustrate the basic concept.

An example of a little extra complexity added to compensate for real-worldeffects can be found in the so-called Wien bridge, which uses a parallelcapacitor-resistor standard impedance to balance out an unknown seriescapacitor-resistor combination. (Figure below ) All capacitors have someamount of internal resistance, be it literal or equivalent (in the form ofdielectric heating losses) which tend to spoil their otherwise perfectlyreactive natures. This internal resistance may be of interest to measure, andso the Wien bridge attempts to do so by providing a balancing impedancethat isn't pure either:

Wein Bridge measures both capacitive Cx and resistive Rx components ofreal capacitor.


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Being that there are two standard components to be adjusted (a resistor and acapacitor) this bridge will take a little more time to balance than the otherswe've seen so far. The combined effect of Rs and Cs is to alter themagnitude and phase angle until the bridge achieves a condition of balance.Once that balance is achieved, the settings of Rs and Cs can be read fromtheir calibrated knobs, the parallel impedance of the two determinedmathematically, and the unknown capacitance and resistance determinedmathematically from the balance equation (Z1/Z2 = Z3/Z4).

It is assumed in the operation of the Wien bridge that the standard capacitorhas negligible internal resistance, or at least that resistance is already knownso that it can be factored into the balance equation. Wien bridges are usefulfor determining the values of lossy capacitor designs like electrolytics,where the internal resistance is relatively high. They are also used asfrequency meters, because the balance of the bridge is frequency-dependent.When used in this fashion, the capacitors are made fixed (and usually ofequal value) and the top two resistors are made variable and are adjusted bymeans of the same knob.

An interesting variation on this theme is found in the next bridge circuit,used to precisely measure inductances.


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Maxwell-Wein bridge measures an inductor in terms of a capacitor standard.

This ingenious bridge circuit is known as the Maxwell-Wien bridge (sometimes known plainly as the Maxwell bridge), and is used tomeasure unknown inductances in terms of calibrated resistance andcapacitance. (Figure above) Calibration-grade inductors are more difficult tomanufacture than capacitors of similar precision, and so the use of a simplesymmetrical inductance bridge is not always practical. Because the phaseshifts of inductors and capacitors are exactly opposite each other, acapacitive impedance can balance out an inductive impedance if they arelocated in opposite legs of a bridge, as they are here.

Another advantage of using a Maxwell bridge to measure inductance ratherthan a symmetrical inductance bridge is the elimination of measurementerror due to mutual inductance between two inductors. Magnetic fields can

be difficult to shield, and even a small amount of coupling between coils in a bridge can introduce substantial errors in certain conditions. With no secondinductor to react with in the Maxwell bridge, this problem is eliminated.


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For easiest operation, the standard capacitor (Cs) and the resistor in parallelwith it (Rs) are made variable, and both must be adjusted to achieve balance.However, the bridge can be made to work if the capacitor is fixed (non-variable) and more than one resistor made variable (at least the resistor in

parallel with the capacitor, and one of the other two). However, in the latterconfiguration it takes more trial-and-error adjustment to achieve balance, asthe different variable resistors interact in balancing magnitude and phase.

Unlike the plain Wien bridge, the balance of the Maxwell-Wien bridge isindependent of source frequency, and in some cases this bridge can be madeto balance in the presence of mixed frequencies from the AC voltage source,the limiting factor being the inductor's stability over a wide frequency range.

There are more variations beyond these designs, but a full discussion is notwarranted here. General-purpose impedance bridge circuits aremanufactured which can be switched into more than one configuration formaximum flexibility of use.

A potential problem in sensitive AC bridge circuits is that of straycapacitance between either end of the null detector unit and ground (earth)

potential. Because capacitances can conduct alternating current bycharging and discharging, they form stray current paths to the AC voltagesource which may affect bridge balance: (Figure below)


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2. Derive the balance eqn for Anderson bridge jan14, july13, jan13, june12 AC bridges are often used to measure the value of unknown impedance(self/mutual inductance of inductors or capacitance of capacitorsaccurately). A large number of AC bridges are available and Anderson'sBridge is an AC bridge used to measure self inductance of the coil. It is amodification of Wheatstones Bridge. It enables us to measure theinductance of a coil usingcapacitor and resistors anddoes not require repeated

balancing of the bridge. Theconnections are shown inFig: 1.

The bridge is balanced by asteady current by replacing theheadphone H by moving coilgalvanometer and A.C source

by a battery. This is done byadjusting the variable resistance,r. After a steady balance has


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been obtained, inductive balance is obtained by using the A.C source andheadphone.

The condition for balance is that the potentials at the terminals D and Eare same. Then the current flowing through branch AB is I1, through

branch AE and EB is I2. The current flowing through branches AD andDC is I3, while that through branch BC is I1+I2. No current flowsthrough branch DE.

Circuit DetailsConsider the mesh ABCDA

(1)This shows that potential drop along ABC is equal to that along ADC.

Consider the mesh ABEA, there is no e.m.f.

(2)Consider the mesh AEDA,

(3)i.e. potential difference from A to E is equal to that from A to D.From (3) we get,

3. (4) Now substitute the value of I3 from (1) in (4)

(5)Dividing (5) by (2)

4.


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(6)Multiply and divide by R in the L.H.S of (6) and rearrange,

5.

(7)Equating real parts on both sides of (7)

(8)Equation (8) represents the condition for balancing of the bridge.

Equating imaginary parts on both sides of (7)

(9)Substituting :

From (8) and (9) gives us

(10)At this condition of balancing there is minimum sound in the headphone.Further we can make P=Q

(11)

The inductive reactance can be calculated by

(11)

6. Explain how capacitance and dissipation factor is measured using Schering bridge. Jan13

the Schering Bridge is an electrical circuit used for measuring theinsulating properties of electrical cables and equipment .[1] It isan AC bridge circuit, developed by Harald Schering. It has the advantagethat the balance equation is independent of frequency.
http://en.wikipedia.org/wiki/Electrical_circuithttp://en.wikipedia.org/wiki/Schering_Bridge#cite_note-1http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Bridge_circuithttp://en.wikipedia.org/wiki/Harald_Scheringhttp://en.wikipedia.org/wiki/Harald_Scheringhttp://en.wikipedia.org/wiki/Bridge_circuithttp://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Schering_Bridge#cite_note-1http://en.wikipedia.org/wiki/Electrical_circuit


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The connections of the Schering bridge under balance conditions areshown in the figure below.

In this diagram:C1 = capacitor whose capacitance is to be determined,R1 = a series resistance representing the loss in the capacitor C1,C2 = a standard capacitor,R3 = a non-inductive resistance,C4 = a variable capacitor,R4 = a variable non-inductive resistance in parallel with the variable

capacitor C4.

7. Obtain the balance eqn for maxwells inductance , capacitance bridge usedfor measurement of unknown inductance. Dec11.

A Maxwell bridge (in long form, a Maxwell-Wien bridge) is a typeof Wheatstone bridge used to measure an unknown inductance (usually of low Qvalue) in terms of calibrated resistance and capacitance. It is areal product bridge.

It uses the principle that the positive phase angle of an inductive impedance can be

compensated by the negative phase angle of a capacitive impedance when put inthe opposite arm and the circuit is at resonance; i.e., no potential difference acrossthe detector and hence no current flowing through it. The unknown inductance then

becomes known in terms of this capacitance.
http://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Series_resistancehttp://en.wikipedia.org/wiki/Induction_(electricity)http://en.wikipedia.org/wiki/In_parallelhttp://en.wikipedia.org/wiki/Wheatstone_bridgehttp://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Capacitancehttp://en.wikipedia.org/wiki/Real_numberhttp://en.wikipedia.org/wiki/File:Schering_brug.pnghttp://en.wikipedia.org/wiki/Real_numberhttp://en.wikipedia.org/wiki/Capacitancehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Inductancehttp://en.wikipedia.org/wiki/Wheatstone_bridgehttp://en.wikipedia.org/wiki/In_parallelhttp://en.wikipedia.org/wiki/Induction_(electricity)http://en.wikipedia.org/wiki/Series_resistancehttp://en.wikipedia.org/wiki/Capacitor


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With reference to the picture, in a typical application and are known fixedentities, and and are known variable entities. and are adjusted untilthe bridge is balanced.

and can then be calculated based on the values of the other components:

Unit-3

1. Explain clearly how shunts and multipliers are used to extend the rangeof instruments. JAN14, dec11

The theory follows from Ohm's, and Kirchoff''s laws. In the case of the multiplier,the same current flows through the meter and the multiplier resistance. The meterresistance can sometimes be ignored, because it is very small compared to themultiplier.

In the case of the shunt, the same voltage is applied across the shunt and the meterresistance. The meter resistance can not be ignored.

This theory does not work with digital panel meters because the input resistanceis extremely high and is unknown. In addition, they are intrinsically voltmeters -not ammeters or microammeters like a mechanical meter with a d'Arsonvalmovement. To calculate the shunt for a digital meter - just use Ohm's law to seewhat resistor (R) will give you the required V (2Volts or 200mV - depending)for the current (I) to be measured.

Digital meters and valve voltmeters use a potentiometer voltage divider - see potentiometer software next..

FormulaeFor Shunt:

I Rshunt=Rm FSD

whence:

Rshunt= IRm FSD


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For Multiplier:

FSD (Rmult+Rm)=V

and so:

Rmult=(VFSD)Rm

Where:

FSD = Meter Full Scale DeflectionI = Current RangeV = Voltage RangeRshunt = Shunt ResistanceRmult = MultiplierResistance

Rm = Meter Resistance

2. What are the advantages of instrument transformer? Jan14

Advantages:

Single range ammeters and voltmeters can measure a wide range of currentsand voltages, if used in conjunction with suitable Current Transformers(CTs) and Potential Transformers (PTs)

The measuring instruments like ammeter, voltmeter and wattmeters etc areincorporated in the secondary circuit and hence they are totally segregatedfrom the high voltage, thereby ensuring safety for the operator and observer

The meter need not be insulated for high voltages which would be the case ifthey are directly included in a high voltage circuit

Using current transformer with suitable split and hinged core, it easy tomeasure heavy currents in the busbarwithout having to break the conductorcarrying current. The core of the Current Transformer (CT) is opened at thehinge, the current carrying conductor is introduced in the center of the corethrough a opening made and the core is tightly closed again. The conductoritself acts as a single turn primary winding of the current transformer

4. Explain the CT and PT july13, jan13, june12


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Current Transformers (CT) and Potential Transformers (PT) are used to measurethe current and voltage in a circuit of the order of hundreds of amperes and voltsrespectively.

A CT has large number of turns on its secondary winding, but very few turns on its primary winding. The primary winding is connected in series with the load so thatit carries full load current. A low voltage range ammeter (0-5A) is connectedacross the secondary winding terminals. Secondary of the CT is practically shortcircuited since the ammeter resistance is very low. It should be remembered thatsecondary of the CT should not be made open as it draws heavy current anddamages the primary winding of the CTA PT has large number of turns in the primary and fewer turns in the secondaryand hence it steps down the voltage. The primary winding is connected across thesupply voltage and low range voltmeter (0-110V) is connected across thesecondary winding terminalsSome of the main difference between current transformers (CT) and potentialtransformers (PT) are given below:

The secondary of the CT is almost short circuit, whereas the secondary ofthe PT is practically a open circuit

The primary winding of the CT is connected in series with the load so that it

carries the full line current, but there is only a small voltage across it.However the primary winding of the PT has the full supply voltage appliedacross it

In CT the excitation current I0 and flux density vary over a wide rangewhereas in PT, they vary over a limited range only

Unit-41. Explain with a neat figure construction and working of dynamometer

type wattmeter. Jan14, july13, dec11.


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a watt meter is used to measure the electric power of a circuit, or sometime it also measures the

rate of energy transferred from one circuit to another circuit. When a moving coil

(that is free to rotate) is kept under the influence of a current carrying conductor,then automatically a mechanical force will be applied to the moving coil, and thisforce will make a little deflection of the moving coil. If a pointer is connected withthe moving coil, which will move of a scale, then the deflection can be easilymeasured by connecting the moving coil with that pointer. This is the principle ofoperation of all dynamo meter type instruments, and this principle is equallyapplicable for dynamo meter type watt meter also.

This type of watt meter consists of two types of coil, more specifically current coil

and voltage coil. There are two current coils which are kept at constant positionand the measurable current will flow through those current coils. A voltage coil is

placed inside those two current coils, and this voltage coil is totally free to rotate.The current coils are arranged such a way, that they are connected with the circuitin series. And the voltage coil is connected in parallel with the circuit. As simple asother voltmeter and ammeter connection. In fact, a watt meter is a package of anammeter and a voltmeter, because the product of voltage and current is the power,which is the measurable quantity of a watt meter.

When current flows through the current coils, then automatically a magnetic fieldis developed around those coils. Under the influence of the electromagnetic field,voltage coil also carries some amount of current as it is connected with the circuitin parallel. In this way, the deflection of the pointer will proportional to bothcurrent and voltage of the circuit. In this way, Watt = Current Voltage equation issatisfied and the deflection shows the value of power inside the circuit. A dynamo


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meter type watt meter is used in various applications where the power or energytransfer has to be measured.

2. Explain with the help of neat sketch the construction of induction typeenergy meter. Jan14, jan13,june12, dec11.

The principle of working and construction of induction type meter is very simple and easy to

understand that's why these are widely used in measuring energy in domestic aswell as industrial world. In all induction meters we have two fluxes which are

produced by two different alternating currents on a metallic disc. Due to alternatingfluxes there is an induced emf, the emf produced at one point (as shown in thefigure given below) interacts with the alternating current of the other side resultingin the production of torque.

Induction Type Meter


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Similarly, the emf produced at the point two interacts with the alternating currentat point one, resulting in the production of torque again but in opposite direction.Hence due to these two torques which are in different directions, the metallic disc

moves. This is basic principle of working of aninduction type meters. Now let usderive the mathematical expression for deflecting torque. Let us take flux producedat point one be equal to F1and the flux and at point two be equal to F2. Now theinstantaneous values of these two flux can written as:

where Fm1 and Fm2 are respectively the maximum values of fluxes F1 and F2, Bis phase difference between two fluxes.

We can also write the expression for induced emf's at point one be

at point two. Thus we have the expression foreddy currents at point one is

where K is some constant and f is frequency.

3. Write a short note on electronic energy meter. Jan14, july13, juune12,dec11

Electronic meters display the energy used on an LCD or LED display,and some can also transmit readings to remote places. In addition tomeasuring energy used, electronic meters can also record other

parameters of the load and supply such as instantaneous and maximum
http://en.wikipedia.org/wiki/LCDhttp://en.wikipedia.org/wiki/LCD


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rate of usage demands, voltages, power factor andreactive power usedetc. They can also support time-of-day billing, for example, recording theamount of energy used during on-peak and off-peak hours.

4. Explain how 3phase reactive power is measured. Jan13

In a star (wye) connected topology, with rotation sequence L1 - L2 - L3, the time-varying instantaneous voltages can be calculated for each phase A,C,B respectively

by:

where:

is the peak voltage,is the phase angle in radians

is the time in secondsis the frequency in cycles per second and

voltages L1-N, L2-N and L3-N are referenced to the star connection point.

5. Explain the working and operation of LPF wattmeter. June12

with the wattmeter now placed in series and the transmitter off, measure theforward RF power. Here's how:
http://en.wikipedia.org/wiki/Voltagehttp://en.wikipedia.org/wiki/Power_factorhttp://en.wikipedia.org/wiki/Reactive_powerhttp://en.wikipedia.org/wiki/Reactive_powerhttp://en.wikipedia.org/wiki/Power_factorhttp://en.wikipedia.org/wiki/Voltage


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1. Set the meter's FUNCTION switch to the POWER position.2. Set the RANGE switch to the appropriate setting. (For the SX100, use the

30W range; and for the SX200, use the 20W range).3. Verify that the TX and ANT output connections are secure.4. Turn on the transmitter and turn up the output power to 10 watts.5. Set the POWER switch on the wattmeter to FWD (forward) and record the

reading. If you're using the TR6000 transmitter, the power-adjust dial islabeled on the front of the unit. If you have the earlier TR20 (Phase II)transmitter, open the transmitter lid and adjust the blue power potentiometer,located vertically just above the power-switch. (A properly tuned antennashould allow a reading of 10 watts.)

6. Record reflected power by turning the meter's POWER switch to REF. Thisreading should be less than 1, and less than 1/10 the forward power reading.

Unit-5

1. Write a note on true RMS reading voltmeter. Jan14, jan13 A modern digital electronic wattmeter/energy meter samples the voltage

and current thousands of times a second. For each sample, the voltage ismultiplied by the current at the same instant; the average over at least onecycle is the real power. The real power divided by the apparent volt-amperes (VA) is the power factor. A computer circuit uses the sampledvalues to calculate RMS voltage, RMS current, VA, power (watts),

power factor, and kilowatt-hours. The readings may be displayed on thedevice, retained to provide a log and calculate averages, or transmitted toother equipment for further use. Wattmeters vary considerably incorrectly calculating energy consumption, especially when real power ismuch lower than VA (highly reactiveloads, e.g. electric motors) . Simple

meters may be calibrated to meet specified accuracy onlyfor sinusoidal waveforms. Waveforms for switched-mode powersupplies as used for much electronic equipment may be very far fromsinusoidal, leading to unknown and possibly large errors at any power.This may not be specified in the meter's manual .
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3. Explain with the neat sketch the working of Electronic multimeter. July13

A multimeter or a multitester, also known as a VOM (Volt-Ohm meter), is

an electronic measuring instrument that combines several measurement functionsin one unit. A typical multimeter would include basic features such as the ability tomeasure voltage, current, and resistance. Analog multimeters usea microammeter whose pointer moves over a scale calibrated for all the differentmeasurements that can be made. Digital multimeters (DMM, DVOM) display themeasured value in numerals, and may also display a bar of a length proportional tothe quantity being measured. Digital multimeters are now far more common thananalog ones, but analog multimeters are still preferable in some cases, for examplewhen monitoring a rapidly varying value.

A multimeter can be a hand-held device useful for basic fault finding and fieldservice work, or a bench instrument which can measure to a very high degree ofaccuracy. They can be used to troubleshoot electrical problems in a wide array ofindustrial and household devices such as electronic equipment, motorcontrols, domestic appliances, power supplies, and wiring systems.

A multimeter is a combination of a multirange DC voltmeter, multirange ACvoltmeter, multirange ammeter, and multirange ohmmeter. An un-amplified analogmultimeter combines a meter movement, range resistors and switches.

For an analog meter movement, DC voltage is measured with a series resistorconnected between the meter movement and the circuit under test. A set ofswitches allows greater resistance to be inserted for higher voltage ranges. The

product of the basic full-scale deflection current of the movement, and the sum ofthe series resistance and the movement's own resistance, gives the full-scalevoltage of the range. As an example, a meter movement that required1 milliampere for full scale deflection, with an internal resistance of 500 ohms,would, on a 10-volt range of the multimeter, have 9,500 ohms of seriesresistance .[3]

For analog current ranges, low-resistance shunts are connected in parallel with themeter movement to divert most of the current around the coil. Again for the case ofa hypothetical 1-mA, 500-ohm movement on a 1-Ampere range, the shuntresistance would be just over 0.5 ohms.

Moving coil instruments respond only to the average value of the current throughthem. To measure alternating current, a rectifier diode is inserted in the circuit so
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that the average value of current is non-zero. Since the rectified average value andthe root-mean-square value of a waveform need not be the same, simple rectifier-type circuits may only be accurate for sinusoidal waveforms. Other wave shapesrequire a different calibration factor to relate RMS and average value. Since

practical rectifiers have non-zero voltage drop, accuracy and sensitivity is poor atlow values.

To measure resistance, a small battery within the instrument passes a currentthrough the device under test and the meter coil. Since the current availabledepends on the state of charge of the battery, a multimeter usually has anadjustment for the ohms scale to zero it. In the usual circuit found in analogmultimeters, the meter deflection is inversely proportional to the resistance; so full-scale is 0 ohms, and high resistance corresponds to smaller deflections. The ohmsscale is compressed, so resolution is better at lower resistance values.

Amplified instruments simplify the design of the series and shunt resistornetworks. The internal resistance of the coil is decoupled from the selection of theseries and shunt range resistors; the series network becomes a voltage divider. Where AC measurements are required, the rectifier can be placed after theamplifier stage, improving precision at low range.

Digital instruments, which necessarily incorporate amplifiers, use the same principles as analog instruments for range resistors. For resistance measurements,usually a small constant current is passed through the device under test and the

digital multimeter reads the resultant voltage drop; this eliminates the scalecompression found in analog meters, but requires a source of significant current.An autoranging digital multimeter can automatically adjust the scaling network sothat the measurement uses the full precision of the A/D converter.

In all types of multimeters, the quality of the switching elements is critical to stableand accurate measurements. Stability of the resistors is a limiting factor in thelong-term accuracy and precision of the instrument.

4. With a neat sketch explain the construction and operating principal ofsingle phase power factor meter. Jan13, june12
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AC power flow has the three components: real power (also known as active power) (P), measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power (Q), measured in reactive volt-amperes( var) .[6]

The power factor is defined as:

In the case of a perfectly sinusoidal waveform, P, Q and S can be expressed asvectors that form a vectort riangle such that:

If is the phase angle between the current and voltage, then the powerfactor is equal to the cosine of the angle, , and:

Since the units are consistent, the power factor is by definitiona dimensionless number between 1 and 1. When power factor is equalto 0, the energy flow is entirely reactive, and stored energy in the loadreturns to the source on each cycle. When the power factor is 1, all theenergy supplied by the source is consumed by the load. Power factors

are usually stated as "leading" or "lagging" to show the sign of the phaseangle. Capacitive loads are leading (current leads voltage), and inductiveloads are lagging (current lags voltage).

5. Explain the two types of phase sequence indicators. June12
http://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Volt-ampere_reactivehttp://en.wikipedia.org/wiki/Power_factor#cite_note-6http://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Vector_(geometry)http://en.wikipedia.org/wiki/Phase_anglehttp://en.wikipedia.org/wiki/Trigonometric_functionshttp://en.wikipedia.org/wiki/Dimensionless_numberhttp://en.wikipedia.org/wiki/Dimensionless_numberhttp://en.wikipedia.org/wiki/Trigonometric_functionshttp://en.wikipedia.org/wiki/Phase_anglehttp://en.wikipedia.org/wiki/Vector_(geometry)http://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Power_factor#cite_note-6http://en.wikipedia.org/wiki/Volt-ampere_reactivehttp://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Volt-amperehttp://en.wikipedia.org/wiki/Watt


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Phase sequence indicator are the indicator that determines the phasesequence of the three phase supply system.

When we give conventional three phase supply (i.e. RYB) to

the induction motor, we see that the direction of the rotation of the rotoris in clockwise direction.

Now what will happen to direction of rotation of rotor if the phasesequence is reversed, the answer to this question is that the rotor willrotate in the anticlockwise direction. Thus we see that the direction ofrotation of rotor depends on the phase sequence. Let us study how these

phase instruments works and on what principle they work.

Now there are two types of phase sequence indicators and they are:

(a) Rotating type(b) Static type.

Let us discuss one by one each type.

Rotating Type Phase Sequence Indicators

It works on the principle of induction motors. In this coils are connected

in star form and the supply is given from three terminal marked as RYBas shown in the figure. When supply is given the coils produces therotating magnetic field and these rotating magnetic fields produces eddy
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emf in the movable aluminium disc as shown in the diagram.

These eddy emf produces eddy current on the aluminium disc, eddycurrents interact with the rotating magnetic field due this a torque is

produced which causes the light aluminium disc to move. If the discmoves in the clockwise direction then chosen sequence is RYB and if thedirection of rotation is in anticlockwise the sequence is reversed.

Static Type Phase Sequence Indicators

Given below is the arrangement of static type indicator:


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Unit-6

1. Explain with the help of block diagram working of digital storageoscilloscope. jan14, june12

the basic oscilloscope, as shown in the illustration, is typically divided into foursections: the display, vertical controls, horizontal controls and trigger controls. Thedisplay is usually a CRT or LCD panel which is laid out with both horizontal andvertical reference lines referred to as the graticule. In addition to the screen, mostdisplay sections are equipped with three basic controls: a focus knob, an intensityknob and a beam finder button.

The vertical section controls the amplitude of the displayed signal. This sectioncarries a Volts-per-Division (Volts/Div) selector knob, an AC/DC/Ground selector

switch and the vertical (primary) input for the instrument. Additionally, this sectionis typically equipped with the vertical beam position knob.

The horizontal section controls the time base or "sweep" of the instrument. The primary control is the Seconds-per-Division (Sec/Div) selector switch. Alsoincluded is a horizontal input for plotting dual X-Y axis signals. The horizontal

beam position knob is generally located in this section.

The trigger section controls the start event of the sweep. The trigger can be set toautomatically restart after each sweep or it can be configured to respond to aninternal or external event. The principal controls of this section will be the sourceand coupling selector switches. An external trigger input (EXT Input) and leveladjustment will also be included.

In addition to the basic instrument, most oscilloscopes are supplied with a probe asshown. The probe will connect to any input on the instrument and typically has aresistor of ten times the oscilloscope's input impedance. This results in a .1 (-10X)attenuation factor, but helps to isolate the capacitive load presented by the probe


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cable from the signal being measured. Some probes have a switch allowing theoperator to bypass the resistor when appropriate

2. Explain with the help of block diagram working of dual traceoscilloscope. Jan14, july13,dec11

A digital storage oscilloscope is an oscilloscope which stores and analyses thesignal digitally rather than using analoguet echniques. It is now the most commontype of oscilloscope in use because of the advanced trigger, storage, display andmeasurement features which it typically provides

The input analogue signal is sampled and then converted into a digital record of theamplitude of the signal at each sample time. The sampling frequency should be notless than the Nyquist rate to avoid aliasing. These digital values are then turned

back into an analogue signal for display on a cathode ray tube (CRT), ortransformed as needed for the various possible types of output liquid crystaldisplay, chart recorder, plotter or network interface.

Digital storage oscilloscope costs vary widely; bench-top self-containedinstruments (complete with displays) start at US$300or even less, with high-

performance models selling for tens of thousands of dollars. Small, pocket-sizemodels.

3. Explain the measurement of phase and frequency using lissajous patterns. Jan14

In mathematics, a Lissajous curve /lsu /, also known as Lissajousfigure or Bowditch curve / badt /, is the graph of a system of parametricequations

which describe complex harmonic motion. This family of curves was

investigated by Nathaniel Bowditch in 1815, and later in more detail by JulesAntoine Lissajous in 1857.

The appearance of the figure is highly sensitive to the ratio a/b. For a ratio of 1,the figure is an ellipse, with special casesincluding circles (A = B, = /2 radians) and lines ( = 0). Another simpleLissajous figure is the parabola (a/b = 2, = /4). Other ratios produce morecomplicated curves, which are closed only if a/b i srational. The visual form of
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these curves is often suggestive of a three-dimensional knot, and indeed manykinds of knots, including those known as Lissajous knots, project to the planeas Lissajous figures.

Visually, the ratio a/b determines the number of "lobes" of the figure. Forexample, a ratio of 3/1 or 1/3 produces a figure with three major lobes (seeimage). Similarly, a ratio of 5/4 produces a figure with 5 horizontal lobes and 4vertical lobes. Rational ratios produce closed (connected) or "still" figures,while irrational ratios produce figures that appear to rotate. Theratio A/B determines the relative width-to-height ratio of the curve. Forexample, a ratio of 2/1 produces a figure that is twice as wide as it is high.Finally, the value of determines the apparent "rotation" angle of the figure,viewed as if it were actually a three-dimensional curve. For example, =0

produces x and y components that are exactly in phase, so the resulting figureappears as an apparent three-dimensional figure viewed from straight on (0).In contrast, any non-zero produces a figure that appears to be rotated, eitheras a left/right or an up/down rotation (depending on the ratio a/b).

Lissajous figure on an oscilloscope, displaying a 1:3 relationship between thefrequencies of the vertical and horizontal sinusoidal inputs, respectively.

Lissajous figures where a = 1, b = N (N is a natural number) and

are Chebyshev polynomials of the first kind of degree N. This property isexploited to produce a set of points, called Padua points, at which a functionmay be sampled in order to compute either a bivariate interpolation orquadrature of the function over the domain [-1,1][-1,1].
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4. Classify transducers with an example each. Jan13

Transducer Classification Some of the common methods of classifying transducers are given below. Based on their application.

Based on the method of converting the non-electric signal into electricsignal.

Based on the output electrical quantity to be produced.

Based on the electrical phenomenon or parameter that may be changed dueto the whole process. Some of the most commonly electrical quantities in a

transducer are resistance, capacitance, voltage, current or inductance. Thus,during transduction, there may be changes in resistance, capacitance andinduction, which in turn change the output voltage or current.

Based on whether the transducer is active or passive.

5. Explain the construction and operating principal of LVDT withnecessary sketches, jan13, dec11, jan14, june12, july13

The linear variable differential transformer (LVDT) (also called just

a differential transformer linear variable displacementtransformer, or linear variable displacement transducer is a type ofelectrical transformer used for measuring linear displacement (position).A counterpart to this device that is used for measuring rotarydisplacement is called a rotary variable differential transformer (RVDT ).
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6. List out the temperature detectors. Explain resistance temperaturedetector. Jan13.

Thermistor- Thermistors are thermally sensitive resistors whose prime function

is to exhibit a large, predictable and precise change in electrical resistance whensubjected to a corresponding change in body temperature. NegativeTemperature Coefficient (NTC) thermistors exhibit a decrease in electricalresistance when subjected to an increase in body temperature and PositiveTemperature Coefficient (PTC) thermistors exhibit an increase in electricalresistance when subjected to an increase in body temperature.

Thermocouple Resistance thermometer Silicon bandgap temperature sensor

Unit-7& 8

1. Explain the photoconductive and photovoltaic cell. Jan14, july13, june12.

PHOTO- VOLTAIC IN SEMICONDUCTORS:

The height of the potential barrier is an open circuited dark (non-illuminated) P-N junction adjusts itself such that resultant current is zero. Under this condition, theelectric field at the junction is in such a diretion so as to repel the majority carriers.When light is incident on diode surface, minority carriers get injected & hence theminority current increases. But since the diode is open circuited, the resultantcurrent must remain zero. Therefore majority current should increase by the sameamount as the minority carrier current. This increase in majority current is possibleif the retarding electric field at the junction is reduced resulting in the lowering ofthe barrier height. Therefore across the diode terminals there appears voltagewhich is equal the decrease in the barrier potential. This constitutes the

photovoltaic e.m.f. & is of the order of 0.1 volts for the Ge cell & 0.5 volt for Sicell.

DERIVATION OF EXPRESSION:We have seen that the photovoltaic e.m.f. Vp appears across the diode when the netcurrent I in the diode is zero.Substituting I= 0. In the volt ampere characteristics of a photo diode given by
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I = Is + I0 ( 1- eVe/ kT )We get Is + I0 ( 1- eVe/ kT ) = 0

1+ ( Is/I0) = e Vpe/ kT

log ( 1+ ( Is/I0) ) = Vpe/kT .Therefore photo-voltaic e.m.f.Vp =(kT/e) log ( 1+ ( Is/I0) )

But Is/I0 >> 1, except for extremely small light intensities.

Vp = (kT/e) log ( 1+ ( Is/I0) )

This equation shows that the photovoltaic e.m.f Vp increases algorithmically withIs and hence with illumination it has been shown diagrammatically.PHOTOVOLTAIC CELLS:When a pair of electrodes is immersed in an electrolyte & light is allowed toincident on one of them, a potential difference is created between the electrodesthis phenomenon is called photovoltaic effect. Devices based on this effect areknown as photovoltaic cells. In a photovoltaic cells light energy is used to create a

potential difference the potential difference so developed is directly proportionalto the frequency & intensity of incident light.CONSTRUCTION & WORKING:A basic photovoltaic cells consist of peace of semi conducting materials bonded toa metal plate. Materials like selenium & silicon are mostly used for preparing

photovoltaic cells.When light is made to fall on semi conducting material, valence electron holes areliberated from its crystal structures the electrons so liberated move towards themetal plate where as holes flow in opposite directions thus a potential difference iscreated between the semi conducting materials and the metal plate. Consequently aconventional current flows in the external circuit through a load resistor R .In actual form of photovoltaic cells a thin metallic film of silver,gold or platinum isdeposited on a semi conducting layer like cuprous oxide (Cu2O) or iron selenide.The whole arrangement is than attached to a metal based plate (copper) as shownin the figure.When external light is allowed to fall on metallic film F, it penetrates easily and atthe barrier layer between the metallic film and the semiconductor, photo-electricemission occurs. The photoelectrons so emitted from the layer, move towards themetallic film. Consequently the metallic film F becomes negatively charged andthe copper based plate positively charged. Hence a potential difference isdeveloped between two and a current flows in the external circuit.The strength is


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proportional to the intensity of light and flows without any bias i.e. without anyexternal source of e.m.f.USES:These cells are used in devices like

1. Photographic exposure metre.

2. Direct reading illuminations metre.

3. Operation of relays.

SOLAR CELLS:A solar cells or solar battery is basically a P N junction diode which converts solarenergy into electrical energy. It is also called a solar energy converter and is simplya photo diode operated zero bias voltage.

CONSTRUCTION:A solar cell consists of a P N junction diode generally made of Ge or Si. It mayalso be constructed with many other semi conducting materials like GaAs, indiumarsenide and cadmium arsenide. The P N diode so formed is packed in a can withglass windows on top so that light may fall upon P & N type materials. Thethickness of P region of is kept very small so that electrons generated in this regioncan deffuse to the junction before the recombination takes place. Thickness of Nregion is also kept small to allow holes generated near the surface to diffuse to the

junctions before they recombine. A heavy doping of P and N regions isrecommended to obtain a large photo voltage. A nickel plated ring is providedaround the P layer which acts as the positive output terminal. A metal contact atthe bottom serves as the negative output terminal.

WORKING:The working of solar cells may be understood with reference of figure When lightis allowed to fall on a P-N junction diode, photons collide with valence electrons

and impart them sufficient energy enabling them to leave there parent atoms. Thuselectrons hole pairs are generated in both the P and the N sides of the junctions .These electrons and holes reach the depletion region W by diffusion and are thenseparated by a strong barrier field existing between there. However the minority

carriers, electrons in the p-side , slide down the barrier potential to reach the Insideand the holes in the N-side move to P-side. Their flow constitutes the minority


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current which is directly proportional to the illumination and also depends on thesurface area being exposed light.

The accumulation of electrons and holes on the two sides of the jnction givesrise to an open circuit voltage Voc which is a function of illumination. The open

circuit voltage produced for a silicon solar cells is typically 0.6 volt & the shortcircuit current is about 40 m A / cm2 in bright noon day sun light powerconversion efficiency of about 15% are obtained with a thin N diffused layer intoa P wafer. Many such cells are interconnected to provide large quantities ofelectrical power. Solar panels providing 5watt at 12 volt have been built to operate24 hrs a day by recharging the batteries during day light hrs.

Characteristic s:Typical V- I characteristics of a solar cell corresponding to different levels ofilluminations are shown in the figure. It may be seen that for 100 mW/cm2 illuminations the open circuit voltage is about 0.57 volt while the shortcircuit current is 50 m A. maximum power output is however obtained when thecell is operated at the knee of the curve.

4. What do you mean by DIC explain with a help of block diagram.Jan13, june12, dec11, jan14, july13.


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5. With the help of neat sketch the working of XY recorder . jan14, jan13, june12, dec11.

x-y recorder is an instrument which gives a graphic record of therelationship between two variables. In x-y recorder's emf is plotted as afunction of another emf. This is done by one self balancing potentiometer

which controls the position of paper or chart roll while another self balancing potentiometer controls the position of the recording pen. The emfused for the operation of x-y recorders not necessarily measure only voltage.the measure emf may be the output of the transducer which may be measureof displacement ,force,pressure,strain or any other physical quantities.


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6. With the help of neat diagram explain the working of function generator.Jan14, july13.

A function generator is usually a piece of electronic test

equipment or software used to generate different types ofelectrical waveforms over a wide range of frequencies. Some of the most commonwaveforms produced by the function generator are the sine, square, triangular andsawtooth shapes. These waveforms can be either repetitive or single-shot (whichrequires an internal or external trigger source) .[1] Integrated circuits used togenerate waveforms may also be described as function generator ICs.

Although function generators cover both audio and RF frequencies, they areusually not suitable for applications that need low distortion or stable frequencysignals. When those traits are required, other signal generators would be more

appropriate.Working

Simple function generators usually generate triangular waveform whose frequencycan be controlled smoothly as well as in steps .[3] This triangular wave is used asthe basis for all of its other outputs. The triangular wave is generated by repeatedlycharging and discharging a capacitor from a constant current source. This producesa linearly ascending or descending voltage ramp. As the output voltage reachesupper and lower limits, the charging and discharging is reversed usinga comparator, producing the linear triangle wave. By varying the current and thesize of the capacitor, different frequencies may be obtained. Sawtooth waves can

be produced by charging the capacitor slowly, using a current, but using a diodeover the current source to discharge quickly - the polarity of the diode changes the

polarity of the resulting sawtooth, i.e. slow rise and fast fall, or fast rise and slowfall.

A 50% duty cycle square wave is easily obtained by noting whether the capacitoris being charged or discharged, which is reflected in the current switchingcomparator output. Other duty cycles (theoretically from 0% to 100%) can be

obtained by using a comparator and the sawtooth or triangle signal. Most functiongenerators also contain a non-linear diode shaping circuit that can convert thetriangle wave into a reasonably accurate sine wave by rounding off the corners ofthe triangle wave in a process similar to clipping in audio systems.
http://en.wikipedia.org/wiki/Electronic_test_equipmenthttp://en.wikipedia.org/wiki/Electronic_test_equipmenthttp://en.wikipedia.org/wiki/Softwarehttp://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Function_generator#cite_note-cnx.org-1http://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Signal_generatorhttp://en.wikipedia.org/wiki/Function_generator#cite_note-Introduction_to_System_Design_Using_Integrated_Circuits-3http://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Current_sourcehttp://en.wikipedia.org/wiki/Linearhttp://en.wikipedia.org/wiki/Comparatorhttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Sawtooth_wavehttp://en.wikipedia.org/wiki/Duty_cyclehttp://en.wikipedia.org/wiki/Square_wavehttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Waveform_shapinghttp://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Clipping_(audio)http://en.wikipedia.org/wiki/Clipping_(audio)http://en.wikipedia.org/wiki/Sine_wavehttp://en.wikipedia.org/wiki/Waveform_shapinghttp://en.wikipedia.org/wiki/Diodehttp://en.wikipedia.org/wiki/Square_wavehttp://en.wikipedia.org/wiki/Duty_cyclehttp://en.wikipedia.org/wiki/Sawtooth_wavehttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Current_(electricity)http://en.wikipedia.org/wiki/Comparatorhttp://en.wikipedia.org/wiki/Linearhttp://en.wikipedia.org/wiki/Current_sourcehttp://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Function_generator#cite_note-Introduction_to_System_Design_Using_Integrated_Circuits-3http://en.wikipedia.org/wiki/Signal_generatorhttp://en.wikipedia.org/wiki/Integrated_circuithttp://en.wikipedia.org/wiki/Function_generator#cite_note-cnx.org-1http://en.wikipedia.org/wiki/Waveformhttp://en.wikipedia.org/wiki/Softwarehttp://en.wikipedia.org/wiki/Electronic_test_equipmenthttp://en.wikipedia.org/wiki/Electronic_test_equipment


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A typical function generator can provide frequencies up to 20 MHz. RF generatorsfor higher frequencies are not function generators in the strict sense since theytypically produce pure or modulated sine signals only.

Function generators, like most signal generators, may also contain an attenuator, various means of modulating the output waveform, and often the ability toautomatically and repetitively "sweep" the frequency of the output waveform (bymeans of a voltage-controlled oscillator ) between two operator-determined limits.This capability makes it very easy to evaluate the frequency response of agiven electronic circuit.

Some function generators can also generate white or pink noise. [citation needed]

More advanced function generators are called arbitrary waveformgenerators (AWG). They use direct digital synthesis (DDS) techniques to generate

any waveform that can be described by a table of amplitudes.

7. Write a note on display devices. July13.A display device is an output device for presentation

of information in visual or tactile form (the latter used for examplein tactile electronic displays for blind people). When the input informationis supplied as an electrical signal, the display is called an electronic

displayApplications

Full-area 2-dimensional displays are used in, for example:

Television sets Computer monitors Head-mounted display Broadcast reference monitor

Medical monitors

8. Write short notes on LED and LCD display. June12, jan13.

LCD stands for liquid crystal display and technical ly, both LED and LCDTVs are liquid crystal displays. The basic technology is the same in that both
http://en.wikipedia.org/wiki/Signal_generatorhttp://en.wikipedia.org/wiki/Attenuator_(electronics)http://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Voltage-controlled_oscillatorhttp://en.wikipedia.org/wiki/Frequency_responsehttp://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/White_noisehttp://en.wikipedia.org/wiki/Pink_noisehttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Arbitrary_waveform_generatorhttp://en.wikipedia.org/wiki/Arbitrary_waveform_generatorhttp://en.wikipedia.org/wiki/Direct_digital_synthesizerhttp://en.wikipedia.org/wiki/Output_devicehttp://en.wikipedia.org/wiki/Informationhttp://en.wikipedia.org/wiki/Visualhttp://en.wikipedia.org/wiki/Tactilehttp://en.wikipedia.org/wiki/Refreshable_Braille_displayhttp://en.wikipedia.org/wiki/Television_sethttp://en.wikipedia.org/wiki/Computer_monitorhttp://en.wikipedia.org/wiki/Head-mounted_displayhttp://en.wikipedia.org/wiki/Broadcast_reference_monitorhttp://en.wikipedia.org/wiki/Medical_monitorhttp://electronics.howstuffworks.com/lcd.htmhttp://electronics.howstuffworks.com/difference-between-lcd-tv-and-dlp-tv.htmhttp://electronics.howstuffworks.com/difference-between-lcd-tv-and-dlp-tv.htmhttp://electronics.howstuffworks.com/difference-between-lcd-tv-and-dlp-tv.htmhttp://electronics.howstuffworks.com/difference-between-lcd-tv-and-dlp-tv.htmhttp://electronics.howstuffworks.com/lcd.htmhttp://en.wikipedia.org/wiki/Medical_monitorhttp://en.wikipedia.org/wiki/Broadcast_reference_monitorhttp://en.wikipedia.org/wiki/Head-mounted_displayhttp://en.wikipedia.org/wiki/Computer_monitorhttp://en.wikipedia.org/wiki/Television_sethttp://en.wikipedia.org/wiki/Refreshable_Braille_displayhttp://en.wikipedia.org/wiki/Tactilehttp://en.wikipedia.org/wiki/Visualhttp://en.wikipedia.org/wiki/Informationhttp://en.wikipedia.org/wiki/Output_devicehttp://en.wikipedia.org/wiki/Direct_digital_synthesizerhttp://en.wikipedia.org/wiki/Arbitrary_waveform_generatorhttp://en.wikipedia.org/wiki/Arbitrary_waveform_generatorhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Pink_noisehttp://en.wikipedia.org/wiki/White_noisehttp://en.wikipedia.org/wiki/Electronic_circuithttp://en.wikipedia.org/wiki/Frequency_responsehttp://en.wikipedia.org/wiki/Voltage-controlled_oscillatorhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Attenuator_(electronics)http://en.wikipedia.org/wiki/Signal_generator


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television types have two layers of polarized glass through which the liquidcrystals both block and pass light. So really, LED TVs are a subset of LCD TVs.

LED , which stands for light emitting diodes, differs from general LCD TVs inthat LCDs use fluorescent lights while LEDs use those light emitting diodes. Also,the placement of the lights on an LED TV can differ. The fluorescent lights in anLCD TV are always behind the screen. On an LED TV, the light emitting diodescan be placed either behind the screen or around its edges. The difference in lightsand in lighting placement has generally meant that LED TVs can be thinner thanLCDs, although this is starting to change. It has also meant that LED TVs run withgreater energy efficiency and can provide a clearer, better picture than the generalLCD TVs.

LED TVs provide a better picture for two basic reasons. First, LED TVs work witha color wheel or distinct RGB-colored lights (red, green, blue) to produce morerealistic and sharper colors. Second, light emitting diodes can be dimmed. Thedimming capability on the back lighting in an LED TV allows the picture todisplay with a truer black by darkening the lights and blocking more light from

passing through the panel. This capability is not present on edge-lit LED TVs;however, edge-lit LED TVs can display a truer white than the fluorescent LEDTVs.

Because all these LCD TVs are thin-screen, each has particular angle-viewing andanti-glare issues. The backlit TVs provide better, cleaner angle viewing than the

edge-lit LED TV. However, the backlit LED TV will usually have better angleviewing than the standard LCD TV. Both LED and LCD TVs have goodreputations for their playback and gaming quality.

9. Write a note on Weston frequency meter. Jan13.

The main principle of working of weston type frequency meter is that "when anelectric current flows through the two coils which are perpendicular to each other,

due to these currents some magnetic fields will produce and thus the magneticneedle will deflects towards the stronger magnetic field showing the measurementof frequency on the meter".Construction of weston frequency is as compared to ferrodynamic type offrequency meter. In order to construct a circuit diagram we need two coils, threeinductors and two resistors. Given below is the circuit diagram for the weston type
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frequency meter .

Axis of both coils are marked as shown. Scale of the meter is calibrated such thatat standard frequency the pointer will take position at 45. Coil 1 contains a seriesresistor marked R1 and reactance coil marked as L1, while the coil 2 has a seriesreactance coil marked as L2 and parallel resistor marked as R2. The indcuctorwhich is marked as L0 is connected in series with the supply voltage in order toreduce the higher harmonic means here this inductor is working as a filter circuit.Let us look at the working of this meter.

Now when we apply voltage at standard frequency then the pointer will takenormal position, if there increase the frequency of the applied voltage then we will

see that the pointer will moves towards left marked as higher side as shown in thecircuit diagram. Again we reduce the frequency the pointer will start movingtowards the right side, if lower the frequency below the normal frequency then itcross the normal position to move towards left side marked lower side as shown inthe figure.
http://www.electrical4u.com/voltage-or-electric-potential-difference/http://www.electrical4u.com/voltage-or-electric-potential-difference/


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Now let us look at the internal working of this meter. Voltage drop across aninductor is directly proportion to frequency of the source voltage, as we increasethe frequency of the applied voltage the voltage drop across the inductorL1 increase that means the voltage impressed between the coil 1 is increased hencethe current through the coil 1 increase while the current through the coil 2decreases. Since the electric current through the coil 1 increases the magnetic fieldalso increases and the magnetic needle attracts more towards the left side showingthe increment in the frequency. Similar action will takes if decrease the frequency

but in this the pointer will moves towards the left side.
http://www.electrical4u.com/voltage-or-electric-potential-difference/http://www.electrical4u.com/voltage-or-electric-potential-difference/

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