Analog And Digital METERS (14MARKS) Unit-2 Analog And Digital METERS (14MARKS) Mrs.V.S.KharoteChavan,E&Tc,PC poly 1

Mrs.V.S.KharoteChavan,E&Tc,PC poly . classification of analog meters:4M The main types of instrument used as ammeters and voltmeters are as follows: Permanent magnet moving coil instrument (PMMC) Electro dynamometer type instruments. Moving Iron type instruments Attraction type moving iron instruments. Repulsion type moving iron instruments Thermocouple instruments. Electrostatic instruments. Induction instruments. Hot wire Instruments. Mrs.V.S.KharoteChavan,E&Tc,PC poly 2

Mrs.V.S.KharoteChavan,E&Tc,PC poly D Arsonval movement Mrs.V.S.KharoteChavan,E&Tc,PC poly 3

Basic d’Arsonval meter movement. Mrs.V.S.KharoteChavan,E&Tc,PC poly 4

Mrs.V.S.KharoteChavan,E&Tc,PC poly PMMC instruments Mrs.V.S.KharoteChavan,E&Tc,PC poly 5

Mrs.V.S.KharoteChavan,E&Tc,PC poly Construction: A coil of thin wire is mounted on an aluminum frame (spindle) positioned between the poles of a U shaped permanent magnet which is made up of magnetic alloys like alnico. The coil is pivoted on the jewelled bearing and thus the coil is free to rotate. The current is fed to the coil through spiral springs which are two in numbers. The coil which carries a current, which is to be measured, moves in a strong magnetic field produced by a permanent magnet and a pointer is attached to the spindle which shows the measured value. Mrs.V.S.KharoteChavan,E&Tc,PC poly 6

Mrs.V.S.KharoteChavan,E&Tc,PC poly Principle of Operation When a current carrying conductor is placed in a magnetic field, it experiences a force and tends to move in the direction as per Fleming’s left hand rule. Mrs.V.S.KharoteChavan,E&Tc,PC poly 7

Mrs.V.S.KharoteChavan,E&Tc,PC poly Advantages of PMMC meter: It has uniform scale.  Power consumption is low  It can be obtained in wide ranges.  High sensitivity & accuracy It is unaffected by external magnetic field.  Additional damping device not required.  Hysteresis problem is not there. Mrs.V.S.KharoteChavan,E&Tc,PC poly 8

Mrs.V.S.KharoteChavan,E&Tc,PC poly Torques which deflect the pointer from its zero position is known as deflecting torque. The deflecting of pointer is directly proportional to quantity to be measured. The deflection torque produced due to current flowing through coil. Let length of coil be L meter and width of coil be d meter. Assume, I is the current flowing through coil having N turn. B is consider as flux density produce in air gap. Therefore the force exerted by coil is Where, A = l x d = Area of coil former. F= BiL The deflecting torque is given by Td = Force x distance Td = F x S = B x l x I x N x d -----------------(1) Td = B x A x I x N -----------------(2) Where, A = l x d = Area of coil former. Mrs.V.S.KharoteChavan,E&Tc,PC poly 9

Mrs.V.S.KharoteChavan,E&Tc,PC poly Disadvantages of PMMC meter: 1.It is suitable for d.c. measurement only.   2.Comparatively highcost than moving iron type instrument. 3. Ageing of permanentmagnet & spring introduce errors. 4. Friction due to jewel- pivot suspension. Mrs.V.S.KharoteChavan,E&Tc,PC poly 10

Mrs.V.S.KharoteChavan,E&Tc,PC poly Applications: Ammeter: Voltmeter: Ohm Meter: Mrs.V.S.KharoteChavan,E&Tc,PC poly 11

Mrs.V.S.KharoteChavan,E&Tc,PC poly Moving Iron Instruments Attraction type Repulsion type Mrs.V.S.KharoteChavan,E&Tc,PC poly 12

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Mrs.V.S.KharoteChavan,E&Tc,PC poly LCD characteristics They are light scattering they do not actively generate light and depend for their operation on back lighting. LCD operates at low voltages 1-15V They operate on reflective or transmissive configuration Mrs.V.S.KharoteChavan,E&Tc,PC poly 16

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Mrs.V.S.KharoteChavan,E&Tc,PC poly Analog meters are characterized by the fact that they use a pointer and scale to indicate their value. One of the common types of meters uses the d’Arsonval type of meter movement. Analog meters use a moving coil placed between the poles of a magnet. Mrs.V.S.KharoteChavan,E&Tc,PC poly 30

Mrs.V.S.KharoteChavan,E&Tc,PC poly Shunt resistance ammeter. Mrs.V.S.KharoteChavan,E&Tc,PC poly 31

Mrs.V.S.KharoteChavan,E&Tc,PC poly The basic movement of dc ammeter circuit consists of D’ Arsonval galvanometer. When large current is to be measured then some extra modification is required. For measurement of large current by using same movement a shunt resistor is connected as shown in circuit. The value of shunt resistor is very small so that most of the current pass through it and only small current allow to pass through the coil. The coil winding of basic movement is small and light therefore it carries very small current. Mrs.V.S.KharoteChavan,E&Tc,PC poly 32

Mrs.V.S.KharoteChavan,E&Tc,PC poly The voltage across the shunt and movement must be same. Vsh=Vm   IshRsh=ImRm Rsh=ImRm/Ish · Rsh=ImRm/(I-Im) Mrs.V.S.KharoteChavan,E&Tc,PC poly 33

Mrs.V.S.KharoteChavan,E&Tc,PC poly A 2mA meter with an internal resistance of 100Ω is to be converted to 0-150mA ammeter. Calculate the value of shunt resistance required. Given: Im=2mA, Rm= 100 Ω, I= 150mA To find: Rsh=? Solution: m= I/Im= 150mA/ 2mA= 150/2 =75 Rsh= 1/ m-1 x Rm   1/ 75-1 x 100 100/74 Rsh= 1.35Ω Mrs.V.S.KharoteChavan,E&Tc,PC poly 34

Mrs.V.S.KharoteChavan,E&Tc,PC poly Calculate the value of multiplier resistance on the 50V range of a dc voltmeter that uses a 200μA meter movement with an internal resistance of 100Ώ. Mrs.V.S.KharoteChavan,E&Tc,PC poly 35

Mrs.V.S.KharoteChavan,E&Tc,PC poly Given: Ifsd = Im = 200 μA = 200X 10-6 A Rm = 100Ώ V = 50V solution: RS1 = V/ Ifsd – Rm (50/ 200 X 10-6 ) – 100 250000 – 100 249900 249X 103 Ώ RS1 = 249 kΏ Mrs.V.S.KharoteChavan,E&Tc,PC poly 36

Mrs.V.S.KharoteChavan,E&Tc,PC poly Why ammeter never connected across source of emf ? Justify. Mrs.V.S.KharoteChavan,E&Tc,PC poly 37

Mrs.V.S.KharoteChavan,E&Tc,PC poly While connecting an ammeter across the emf source always a series resistance should be used. This is necessary to limit the current passing through the meter movement maybe damaged. This is because the meter is having a small internal resistance. So it maydraw very high current from the emf source. 3. The polarity of the meter should be first observed and then it should be connected Mrs.V.S.KharoteChavan,E&Tc,PC poly 38

Mrs.V.S.KharoteChavan,E&Tc,PC poly MULTIRANGE AMMETER Mrs.V.S.KharoteChavan,E&Tc,PC poly 39

Mrs.V.S.KharoteChavan,E&Tc,PC poly Aytron shunt type ammeter Mrs.V.S.KharoteChavan,E&Tc,PC poly 40

Mrs.V.S.KharoteChavan,E&Tc,PC poly When switch is at 100mA range position , the series combination of R1,R2,R3 is in parallel with meter resistance Rm. Hence I1(R1+R2+R3) = Im Rm--------------------------(1) When switch is at 500mA range position, The resistor R2 and R3 are in parallel with R1& Rm Hence I2(R2+R3) = Im( R1+ Rm )---------------------(2) when switch is at 1A position The resistor R3 is in parallel combination with R1+R2+R3 Hence I3(R3) = Im (R1+ R2 + R3 )---------------------(3) Mrs.V.S.KharoteChavan,E&Tc,PC poly 41

Mrs.V.S.KharoteChavan,E&Tc,PC poly Design a multi range DC ammeter using a basic movement with an internal resistance Rm =50Ω and full scale deflection current Im = LmA. The range required are 0-10 mA, 0-50 mA, 0-100 mA, 0-500mA. Ans Given= Rm =50Ω Im =10mA-…… Consider I1= 10mA, I2= 50mA, I3= 100mA, I4= 500mA Rsh1=? , Rsh2=? Rsh3=? Rsh4=? m1= I1/ Im= 10 mA/ 1mA = 10   Rsh1= Rm/ m1-1= 50/ 10-1= 50/9= 5.55Ω m2= I2/ Im= 50 mA/ 1mA = 50 Rsh2= Rm/ m2-1= 50/ 50-1= 50/49= 1.02Ω Mrs.V.S.KharoteChavan,E&Tc,PC poly 42

Mrs.V.S.KharoteChavan,E&Tc,PC poly m3= I3/ Im= 100 mA/ 1mA = 100 Rsh3= Rm/ m3-1 = 50/ 100-1 = 50/39= 0.505Ω m4= I4/ Im = 500 mA/ 1mA = 500 Rsh4= Rm/ m4-1 = 50/ 500-1 = 50/9= 0.100Ω Rsh1 = 5.55Ω Rsh2= 1.02Ω Rsh3= 0.505Ω Rsh4= 0.100Ω Mrs.V.S.KharoteChavan,E&Tc,PC poly 43

Mrs.V.S.KharoteChavan,E&Tc,PC poly A basic D’Arsonval movement withan internal resistance of 50Ω and a full scale deflection current of 2mA is to be used as multirangevoltmeter. Design a series of string of multipliers to obtain the voltage ranges of 0-10V, 0-50V. Given: Rm= 50Ω Ifsd= Im= 2mA To find: a) Rs1 b) Rs2 Mrs.V.S.KharoteChavan,E&Tc,PC poly 44

Mrs.V.S.KharoteChavan,E&Tc,PC poly For range (0-10V), V1=10V Therefore, Rs1= V1/ Ifsd – Rm = 10/ 2x10-3 -50 5000-50 4950Ω Rs1= 4.95kΩ For range (0-50V), V2=50V  Therefore, Rs2= V2/ Ifsd – Rm = 50/ 2x10-3 -50  25000-50  24950Ω Rs2=24.95kΩ Mrs.V.S.KharoteChavan,E&Tc,PC poly 45

Mrs.V.S.KharoteChavan,E&Tc,PC poly Sensitivity is high as compared to normal shunt type ammeter Mrs.V.S.KharoteChavan,E&Tc,PC poly 46

Mrs.V.S.KharoteChavan,E&Tc,PC poly Basic DC voltmeter Mrs.V.S.KharoteChavan,E&Tc,PC poly 47

2.4: A DC VOLTMETER A basic D’Arsonval movement can be converted into a DC voltmeter by adding a series resistor (multiplier) as shown in Figure . Im =full scale deflection current of the movement (Ifsd) Rm=internal resistance of the movement Rs =multiplier resistance V =full range voltage of the instrument + Im Multiplier V Rm _ : Basic DC Voltmeter Mrs.V.S.KharoteChavan,E&Tc,PC poly 48

Mrs.V.S.KharoteChavan,E&Tc,PC poly From the circuit of Figure Mrs.V.S.KharoteChavan,E&Tc,PC poly 49 49

Mrs.V.S.KharoteChavan,E&Tc,PC poly A basic D’ Arsonval movement with a full-scale deflection of 50 uA and internal resistance of 500Ω is used as a DC voltmeter. Determine the value of the multiplier resistance needed to measure a voltage range of 0-10V. Solution: Mrs.V.S.KharoteChavan,E&Tc,PC poly 50

Mrs.V.S.KharoteChavan,E&Tc,PC poly Sensitivity and voltmeter range can be used to calculate the multiplier resistance, Rs of a DC voltmeter. Rs=(S x Range) - Rm From example 2.4: Im= 50uA, Rm=500Ω, Range=10V Sensitivity, So, Rs = (20kΩ/V x 10V) – 500 Ω = 199.5 kΩ Mrs.V.S.KharoteChavan,E&Tc,PC poly 51

2.5: MULTI-RANGE VOLTMETER A DC voltmeter can be converted into a multirange voltmeter by connecting a number of resistors (multipliers) in series with the meter movement. A practical multi-range DC voltmeter is shown in Figure 2.6. Im V2 V1 V3 Rm + V4 _ Figure 2.6: Multirange voltmeter Mrs.V.S.KharoteChavan,E&Tc,PC poly 52

Mrs.V.S.KharoteChavan,E&Tc,PC poly Basic d’Arsonval meter movement with rectifier to change AC voltage to DC voltage. Mrs.V.S.KharoteChavan,E&Tc,PC poly 53

Mrs.V.S.KharoteChavan,E&Tc,PC poly Sensitivity AND Loading effect of voltmeter. The sensitivity of voltmeter means the response given by a voltmeter to input signal.  It is the ratio of total resistance (RT) to the voltage range S = RT / V Where, RT – Total resistance…… RT = RS + Rm  V= Voltage range. OR It is also defined as the reciprocal of full scale deflection current of the basic movement. S = 1 / Ifsd Ifsd = full scale deflection current. Mrs.V.S.KharoteChavan,E&Tc,PC poly 54

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Mrs.V.S.KharoteChavan,E&Tc,PC poly Rectifier type AC voltmeter Mrs.V.S.KharoteChavan,E&Tc,PC poly 56

Mrs.V.S.KharoteChavan,E&Tc,PC poly Basic rectifier type AC voltmeter is a general rectifier type of voltmeter. In this case for the rectification action two diodes namely D1 and D2 are used. An a.c input signal to be measured is applied. If a current passing through the diode is small then there is a non- linearity problem. But for higher current the diode shows linearity. So to increase the current passing through diode; a resistance R2 is connected in parallel with the meter. Now during positive half cycle of input signal, diode D1 is forward biased with the polarities.   Mrs.V.S.KharoteChavan,E&Tc,PC poly 57

Mrs.V.S.KharoteChavan,E&Tc,PC poly While the diode D2 is reversed biased. So during this cycle the current passes the deflection.rough diode D1 and the meter. Thus the meter shows During the negative half cycle diode D1 is reversed biased and diode D2 is forward biased. So the current flows in opposite direction. In this case the meter is bypassed. Because of the diode action an a.c input signal is converted into pulsating dc. Thus the meter shows average value of an input signal. Mrs.V.S.KharoteChavan,E&Tc,PC poly 58

Mrs.V.S.KharoteChavan,E&Tc,PC poly full wave rectifier type AC voltmeter. Mrs.V.S.KharoteChavan,E&Tc,PC poly 59

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Mrs.V.S.KharoteChavan,E&Tc,PC poly Here high stabilized amplifier is used to provide the amplification. The one terminal of stabilized amplifier is connected to the attenuator network which consists of five resistors. The other terminal is connected with feedback path. Capacitor is used to block d.c entering into stabilized non –linearity problem created by diodes. Also the variation in impedance meter is compensated by negative feedback. · The D.C. milliammeter is calibrated in terms. The average reading is obtained by filtering the signal coming gives from the rectifier. Thus for meter movement gives response to average value. Mrs.V.S.KharoteChavan,E&Tc,PC poly 62

Mrs.V.S.KharoteChavan,E&Tc,PC poly Analog Multimeter. Mrs.V.S.KharoteChavan,E&Tc,PC poly 63

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