electrical & electronics engineering department brcm ... · object: to measure self inductance...

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LABORATORY MANUAL Electrical Measurements & Measuring Instruments

EE-209-F

(3rd Semester)

Prepared By:

PRIYAJIT DASH(A.P)

B. Tech. (EEE), M. Tech. (EEE)

Department of Electrical & Electronics Engineering BRCM College of Engineering &Technology

Bahal-127028 (Bhiwani).

Electrical & Electronics Engineering Department BRCM COLLEGE OF ENGINEERING & TECHNOLOGY

BAHAL – 127028 ( Distt. Bhiwani ) Haryana, India

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Index



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S. No Name of Experiment Page No

1 Self-inductance measurements: Ammeter and Voltmeter method, Self-

Inductance Measurement by General four-arms’s bridge network method.

2 Measurement of the unknown inductance by using Hay’s bridge method

3 To measure self inductance of two coils, mutual inductance between these

and the coefficient of coupling

4 Measurement of the unknown inductance by using Maxwell bridge method

5 Measurement of medium resister by the voltmeter and ammeter method

6 Measurement of the medium resistance by using whetstone bridge method

7 Measurement of the low resistance by using Kelvin Double bridge method.

8 Measurement of the high resistance by using loss of charge method

9 Measurement of the unknown capacitance sharing bridge method

10 To study of DC potentiometer

11 ToStudy of C.R.O. Voltage measurement on C.R.O. Current measurement

on C.R.O. Frequency measurement on C.R.O. Phase difference measurement

on C.R.O

12 To study Digital Instruments – Digital Voltmeter, Digital Frequency Meter,

Digital Panel Meter, Digital Storage Oscilloscope

13 To Study the Working Principles of single phase& Three phase induction

type electronics energy meter

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Experiment no 1

OBJECTIVE :. Self-inductance measurements: Ammeter and Voltmeter method, Self-Inductance Measurement by General four-arms’s bridge network method.

MATERIAL REQUIRED :- Inductance, Ammeter and Voltmeter, General four-arms’s bridge network method

THEORY:- Inductance Meters instruments for measuring the inductance of circuits with

lumped parameters, the windings of transformers and chokes, and inductance coils. Their

principle of operation depends on the method of measurement.

The “voltmeter-ammeter” method (Figure 1) is used for measuring relatively large inductances (from 0.1 to 1,000 henrys [H]) when the resistance of the windings is significantly lower than the inductance. In this case Lx = U/(π f · I), where U is the voltage, I is the current in the circuit whose inductance is being measured, and f is the frequency of the alternating current, usually 50 hertz (Hz). Such inductance meters have an error of 2–3 percent.An AC measuring bridge (for frequencies of 100, 400, and 1,000 Hz) with standard capacitance or, much less frequently,standard inductance (Figure 2) is the main component of inductance meters. When the bridge is balanced, rx = (R1· R2)/R3Lx = Cs· R1· R2 where rx is the ohmic resistance of the wire of the inductance coil winding. Bridge measurement methods have an error of 1–3 percent; the range of measurement is 0.1 to 1,000 H.

Resonance methods are based on the resonant properties of an oscillatory circuit composed of the inductance being measured (Lx) and a standard capacitance Cs (Figure 3). By varying C„ the circuit can be tuned to resonance with the generator (at frequencies of 10 kHz to 1.5 MHz); the inductance is then calculated using the formula Lx = (2.53 ×l0)(f2

0 · c), where Lx is the inductance in mH, f0 is the resonance frequency in kHz, and C = Cs + Cc is the total capacitance of the circuit in picofarads. Resonant inductance meters have an error of 2–5 percent; the range of measurement is 0.05 µ.H to 100 mH.

For each value of Rx, find the expected value of current that will flow (assuming a voltage source of 10 V) by dividing 10 V by the value of Rx. 3- Based on the value of current expected to flow, calculate the required value of the DRB to convert the ammeter to the suitable full scale deflection (FSD). 4- Set the DRBX to the value of Rx. 5- Calculate the required value of DRBV to a value suitable for a FSD of voltage of 10 V. 6- Connect the circuit as shown in Figure 2 below. Remember that the voltmeter shown might include DRBV in series. Also remember that the ammeter shown might include DRBA in parallel.



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CIRCUIT DIAGRAM :

Figure 1. Diagram of the measurement of inductance by the “voltmeter-ammeter” method:(A) ammeter, (V) voltmeter, (Lx) inductance, (l) current, (U) voltage

Figure 2 Diagram of resonance method of inductance measurement: (Lc) coupling loop,

(Lx) inductance being measured, (Cc) self-capacitance of coil, (Cs) standard capacitance

Procedure:-

1) Study the circuit provided on the front panel of the kit. 2) Connect unknown inductance LX1 in the circuit. Make all connections to complete the bridge. 3) Put the supply ON 4) Set the null point of galvanometer by adjusting variable resistance R3. 5) Note value of R2, R3, and C4 by removing connection by patch cords. 6) Calculate theoretical value of LX1 using L=R2R3C4 7) Measure value of LX2 by LCR meter and compare it. 8) Repeat process for LX2.

Result:- The unknown inductance is measured using Hay’s bridge and is found to be___

Precautions : 1.connections should be tight. 2.Instrument should be handled carefully.

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Experiment No :-2 Object:- Measurement of the unknown inductance by using Hay’s bridge method. Apparatus:- Multimeter LCR meter Hay’s bridge kit, Patch cords. Theory:- The hays bridge is the modification of the Maxwell Bridge. This bridge uses a resistance in series with the standard capacitor. The bridge has four resistive

arms in which the arms one is consists of the resister R1, Lx .The arm 2 is consists of the variable resistance R3.The low value of the resistance is obtain

by the low resistive arms of the bridge. The value of R4 and C4 is the standard

value of the capacitor and resistance. By using the unknown inductance having a resistanceR1. R2, R3,R4-is the known non-inductive resistance and C4 is standard value of the capacitor. The unknown value of inductance and Quality factor of the Bridge is obtained by formula. Lx = (R2R3C4) /(1+ 2R42C4 2) Quality factor (Q)=(1/ 2R42C42) Basic AC bridges consist of four arms, source excitation and a balanced detector. Commonly used detectors for AC bridges are: (1) Head phones (2) Vibration galvanometers (3) Tunable amplifier detectors Vibration galvanometer is extremely useful at power and low audio frequency ranges. Vibration galvanometers are manufactured to work at various frequency ranging from 5 KHZ to 1 KHZ. But one most commonly used between 200HZ. Advantage-1) This Bridge gives very simple expression for unknown for High Q coil. 2) This bridge also gives a simple expression for Q factor. Disadvantage-1)The hays bridge is suited for the measurement of the High Q inductor. 2)It is used to find the inductor having the q value of the smaller then 10.

Procedure:- 1) Study the circuit provided on the front panel of the kit. 2) Connect unknown inductance LX1 in the circuit. Make all connections to complete the bridge. 3) Put the supply ON 4) Set the null point of galvanometer by adjusting variable resistance R3. 5) Note value of R2, R3, and C4 by removing connection by patch cords. 6) Calculate theoretical value of LX1 using L=R2R3C4 7) Measure value of LX2 by LCR meter and compare it.



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8) Repeat process for LX2.

Circuit Diagram:-

Figure 1. Diagram of a bridge for measuring inductance: (U) current

source; (G) galvanometer; (R3), (R2), and (R3) ohmic resistances; (Cx,) standard capacitance; (Lx) inductance being measured

Result:- The unknown inductance is measured using Hay’s bridge and is found to be___ Precautions : 1.connections should be tight. 2.Instrument should be handled carefully.

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Experiment no 3

Object: To measure self inductance of two coils, mutual inductance between these and the coefficient of coupling

Apparatus required: Ammeter 0-2am,0-10A MI Voltmeter 0-500V MI100V Theory:

When the two coils are connected for additive polarity the fluxes produced by

the current in the two coils will aid each other and hence the impedance is high. This

require the equivalent inductance to be very high. In this case, the mutual inductance

terms will have the same sign as that of the self inductance terms. Thus, if the two

coils having inductance L1 and L2 respectively and a mutual inductance of M between

them are connected for additive polarity, the equivalent inductance L1 = L1 + L2 + 2M – (1) When the two coils are connected for subtractive polarity, the two fluxes will oppose

each other and the inductance and hence the impedances are low. In this case the

mutual inductance terms will have the opposite sign as that of the self inductance

terms. Hence the equivalent inductance L11 = L1 + L2 - 2M – (2) From (1) and (2), we can find out M, L1 and L2. Thus the coefficient of coupling is

calculated by the formula

K

M



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L1 L2

Procedure: First the polarity is to be checked. For this connect the 0 – 10A ammeter and 0 –

500V voltmeter in the circuit. Then switch on the supply with autotransformer in its minimum

position. Then vary the autotransformer and note the variation of readings in the ammeter and

voltmeter. If the current variation is high, for a small voltage the polarity is subtractive.

Otherwise, the polarity is additive. After checking the polarity put the required range of meters

in the circuit. For additive polarity, give the rated voltage (ie 220 + 200 = 420V) and note the

ammeter and voltmeter readings.

For subtractive polarity, pass the rated current (7.5A) by adjusting the autotransformer and

note the ammeter and voltmeter readings. For measuring the resistance, keeping the current

limiting rheostat at its maximum position supply is switched on. Then the ammeter and

voltmeter readings are noted.

Circuit diagram: For additive polarity

For subtractive polarity Tabulation

Additive

Polarity

Subtractive

Polarity Resistance Measurement

V1 I1 Z1 V2 I2 Z2 V3 I3 R

Volts Amp _ Volts Amp _ Volts Amp _

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Calculation L1 = L1 + L2 + 2M ………….. (1) L11 = L1 + L2 - 2M ………….. (2) L1 + L11 = 2 (L1 + L2) L1 + L2 = (L

1 + L11) / 2 ………….. (3) (L1 - L11)/4 = M ………….. (4) Z1 = V1 / I1 Z2 = V2 / I2 R = V3 / I3

X1 Z1 2 − R 2

L1 = X1 / 2 Π f

X 2 Z 2 2 − R 2

L2 = X2 / 2 Π f

L N 2 E

1

1

1

L2

E 2

N 2 Solve for L1 L2 and M.

Coefficient of coupling

K

M

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L1 L2 Result Self inductance of primary coil L1 = __________________ Self inductance of primary coil L2 = __________________ Mutual inductance M = __________________ Coefficient of coupling K = __________________ Precautions : 1.connections should be tight. 2.Instrument should be handled carefully.

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Experiment no 4

Aim:- Measurement of the unknown inductance by using Maxwell bridge method. Apparatus:- Digital multimeter, Patch cords. R2=100 =1M , R3=9.97K , C4=1 f LX1=318mH LX2=73 mH

Theory:- The Maxwell’s bridge is used an inductance is measured by comparison with a standard variable capacitance. One of the ratio arms has a résistance and the capacitance in the parallel. In this bridge at the balance in condition there is no current is flow in the galvanometer.henced the balance equation for the bridge using the admittance of the arm 1 instead of the impedance. ZX=(Z2* Z 3*Y1) Where the Y1 is the admittance of the arm-1. Z2=R2 Z3=R3 Y1=(1/R1+j) By separating the real and imaginary term the unknown value of the resister (Rx) and the unknown value of the capacitor (Cx) has given below. Rx=(R2*R3/R1). LX= (R2*R3*C1) Advantage- 1) This bridge is very useful for measurement of a wide range of a inductance at the power and audio frequencies. 2) The frequency does not appear in any of the two equations. Disadvantage- 1) This bridge requires a variable standard capacitor, which may be Vary expensive if the calibration to a high degree of the accuracy. 2) The bridge is limited the measure the low Q value. Procedure:- 1) Study circuit on kit from panel. 2) Connect unknown inductance LX1 in circuit. Make all possible connections to complete the network. Switch the supply on. 3) Set null point of galvanometer by adjusting variable resistance R3 4) Note values of R2, R3, C4 by removing their connections. Calculate theoretical values of LX using L1=R2R3C4. 5) Measure actual value of LX1 using LCR meter. Compare this value with calculated. also calculate Q factor by using above equation. Circuit Diagram :

Electrical & Electronics Engineering Department

BRCM COLLEGE OF ENGINEERING & TECHNOLOGY


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Result:- Unknown inductance measured using Maxwell’s bridge is found to be LX1=____ Precautions : 1.connections should be tight. 2.Instrument should be handled carefully

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Experiment No-05 Aim:- Measurement of medium resister by the voltmeter and ammeter method.

Apparatus:- DC ammeter(0-500mA) DC Voltmeter (0-5V) Dc power supply (0-30V) Variable Resistance -100 ohm. Connecting wires.

Theory: - Two types of the connections are done one employed for the ammeter voltmeter method as shown in the figure voltmeter and ammeter are connected in series, where ammeter measures the total current flowing through the circuit and voltmeter measures the voltage across the unknown resistance .The voltmeter should have ideally infinite resistance and ammeter should have ideally zero resistance so that it will measure total current flowing

through the unknown resistance. But practically it is not possible and measured value Rm of the resistance is the sum of resistance of ammeter and actual resistance. Rm=R1+Ra Where R1=Actual resistance. Ra=resistance of the ammeter. It is clear from the expression that the value of measured resistance is equal to actual resistance when ammeter has zero resistance.

Procedure:- 1) Make the connections as per circuit diagram. 2) Switch on the supply and note down the readings of ammeter and voltmeter. 3) Calculate the value of the unknown resistance by ohms low. 4) Perform the procedure for the other case similarly. Circuit Diagram:-

Observation Table:-

Electrical & Electronics Engineering Department BRCM COLLEGE OF ENGINEERING & TECHNOLOGY BAHAL – 127028 ( Distt. Bhiwani ) Haryana, India

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Result: - Hence we study the measured and the actual vale of the unknown resistance is found.

Precautions : 1.connections should be tight. 2. Instrument should be handled carefully

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Experiment No.-6 Aim: - Measurement of the medium resistance by using whetstone bridge method.

Apparatus: - Power supply,Resistor: - 10K_-1no, 5K_-1no, 11K_-1no Unknown resistor=100_, Pot =1K-1no. Wheat stone bridge kit. Digital multimeter-1no, Patch codes.

Theory- A very important device used in the measurement of medium resistances is the Wheat stones bridge .it is an accurate and reliable instrument .The wheat stone bridge is an instrument based on the principle of null indication and comparison measurements. The basic circuit of a wheat stone bridge is shown in fig . it has four resistive arms, consisting of resistances P,Q,R and S together with a source of emf and a null detector , usually a galvanometer G or other sensitive current meter is used. The current through the galvanometer depends on the potential difference between point’s b and d .The bridge is said to be balanced when there is on current through the galvanometer or when the potential difference across the galvanometer is zero. this occurs when the voltage from point ‘b’ to point ‘a’ equals the voltage from point ‘d’ to point ‘a’ or by referring to other battery terminal , when the voltage from point ‘d’ to point ‘c’ equals the voltage from point ‘b’ to point ‘c’. For bridge balance; I1P=I2 R ……………. .1) I1=I3=E/P+Q ………………………………(2)

I2=I4=E/R+S………………………………… (3) E=emf of battery. Combining equ (1) and (2) we get P/P+Q=R/R+S……………………… (4) QR=PS Equ ……………………………………………………………. (5)

Shows the balance condition of wheat stone bridge. If three of the resistances are known

then fourth may be determined by formula… R=S*P/Q Where R is the unknown resistance, S is called the standard arm resistor and P and Q are called the ratio arms.

Procedure: - 1) Connect the patch cord as per the circuit diagram. 2) Note the resistance of P and Q using multimeter. 3) Adjust the resistance of P, Q, R, S 4) Switch on the power supply and adjust the resistance S such that galvanometer shows the zero deflection. 5) Now calculate R, R=P*S/Q

Circuit Diagram:-


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Observation Table: -

Result:- Hence we have studied the low resistance by using whetstone bridge.

Precautions:1. Connections should be tight. 2. Instrument should be handled carefully

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Experiment No:-07 Aim: - Measurement of the low resistance by using Kelvin Double bridge method.

Apparatus: - Regulated dc supply-1no Standard resistance coil-1no Kelvin’s double bridge kit. Digital multimeter-1no, Patch codes.

Theory: - Kelvin’s bridge is a modification of whetstone’s bridge and always used in measurement of low resistance. It uses two sets of ratio arms and the four terminal resistances for the low resistance consider the ckt. As shown in fig. The first set of ratio P and Q. The second set of ratio arms are p and q is used to connected to galvanometer to a pt d at an Approx. potential between points m and n to eliminate the effects of connecting lead of resistance r between the known std. resistance ‘s’ and unknown resistance R .The ratio P/Q is made equal to p/q. under balanced condition there is no current flowing through galvanometer which means voltage drop between a and b, Eab equal to the voltage drop between a and c, Eamd. Now Ead=P/P+Q ; Eab=I[R+S+[(p+q)r/p+q+r]] -------------- (1) Eamd= I[R+ p/p+q[ (p+q)r/p+q+r]] --------------------------- (2) For zero deflection->Eac=Ead [ P/P+Q]I[R+S+{(p+q)r/p+q+r}]=I[R+pr/p+q+r] ---- (3) Now, if P/Q=p/q Then equa… (3) becomes R=P/Q=S - (4)

Equation (4) is the usual working equation. For the Kelvin’s Double Bridge .It indicates the

resistance of connecting lead r. It has no effect on measurement provided that the two sets of

ratio arms have equal ratios. Equation (3) is useful however as it shows the error that is

introduced in case the ratios are not exactly equal. It indicates that it is desirable to keep r as

small as possible in order to minimize the error in case there is a diff. between the ratio P/Q

and p/q. R=P/QS Circuit Diagram: -

Observation Table: -


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Procedure: - 1) The circuit configuration on the panel is studied. 2) Supply is switched on and increased upto 5v. 3) The unknown resistance is connected as shown . 4) The value of P,Q was selected such that a. P/Q=p/q 5) S was adjusted for proper balance and balance value of s was balanced. 6) The value of known resistance was calculated.

Result- The observed value of unknown resistance is

Precautions- 1) Check all the connections before turning ON the power supply. 2) Do not exceed the value of 5v. 3) Note the readings accurately.

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Experiment No-08 Aim:- Measurement of the high resistance by using loss of charge method. Apparatus:- Multimeter –1no Ammeter-(0-200ma)-1no

Voltmeter –(0-30v)-1no Capacitor-10uf-1no Resister-100K-1no Power supply-(0-30v)-1no .

Theory:- In this method the resistance which is measured is connected in parallel with the capacitor C and the electronic voltmeter V. The capacitor is the charged up to some suitable voltage by means of the battery having the voltage V and is then allowed to discharge through the resistance. The terminal voltage is observed over the considerable period of the time during discharge. Let ,

V=initial voltage on the charged capacitor. .v=instantaneous discharging voltage. I=the discharging capacitor current through the unknown resistor at time “t”. Q=the charge still remaining in the capacitor. I=dq/dt=-cdv/dt since[I=V/R] V/R+C dv/dt=0 (1) 1/RC dt+1/V.dV=0 integrating both sides t/RC+logev+K=0 (2) K is const. of integration At initial condition When T=0 , v=V from equ. (2) K=-logeV now equ. (2) Becomes t/RC+logev-logeV=0 therefore. Loge (v/V)=-t/RC v/V=e-t/RC v=V*e-t/RC Taking log on both sides logev=logeV+logee- t/RC R=t/C*loge(V/v) R=0.4343*t/C*log10(V/v) Procedure:- 1) Connections are make as per the circuit diagram. 2) Close the switch s and keep s2 open the capacitor charge by own leakage method. 3) New open reading and voltmeter .as its own resistance.

4) Note down the reading of the voltmeter Vs equal interval of the time


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Circuit Diagram:- Observation Table:- Result:- High resistance of the resistance is calculated by using loss of charge method.


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Experiment no-9 Aim:- Measurement of the unknown capacitance sharing bridge method. Apparatus:- Sharing bridge kit digital multimeter, patch cords, Theory:- The schering bridge one of the most important ac bridge is used the

extensively for the measurement of capacitors. In the schering bridge the arm 1 now contains a parallel combination of the resistor and the capacitor and standard arm contain only one capacitor. The standard capacitor is usually a standard high quality mica capacitor. in the balance condition of the bridge the sum of the phase angles of the arms 1 and 4 is equal the sum of the phase angle of arms 2 and 3.at the balance in condition there is no current flow in the galvanometer. The balance equation is derived in the usual manner, and by substituting the corresponding impendence and the admittance the value of the unknown capacitor and the resister is find as given below. Cx=C3(R1/R2). Rx=R2(C1/C2)

Procedure: - 1) Study the circuit provided on the front panel on the kit. 2) Connect the unknown capacitance of the position given. 3) Set the null point of galvanometer by adjusting the variable 4) Calculate the value of unknown capacitance by formula given Circuit Diagram Result: -The values of unknown capacitance is measured by shearing bridge



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Experiment no-10 Aim:- To study of DC potentiometer. Apparatus:- Power supply,(0-50v) Battery,(0-30V) Resister-100 Theory:- The potentiometer although not consider a bridge has circuit that using a simple circuit thermo becomes identical to the whetstone bridge. The potentiometer is a device for measuring the voltage while presenting a very high impedance to the voltage source under the Test. The variable resister R1 is the precision device that can be set to an accurate value. the resister is adjusted so that no current is flow through the galvanometer. which is the similar to balancing the bridge. At this point the zero current flow several important characteristics of the potentiometer cab be determine. Circuit Diagram Result:- To study the working of the DC potentiometer. . Precautions- 1) Check all the connections before turning ON the power supply. 2) Do not exceed the value of 5v. 3) Note the readings accurately.


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Experiment no 11

OBJECTIVE: ToStudy of C.R.O. Voltage measurement on C.R.O. Current

measurement on C.R.O. Frequency measurement on C.R.O. Phase difference

measurement on C.R.O.

APPARATUS REQUIRED: Cathode-ray oscilloscope, millimeter, and oscillator.

Theory

INTRODUCTION: The cathode-ray oscilloscope (CRO) is a common laboratory instrument that provides accurate time and amplitude measurements of voltage signals over a wide range of frequencies. Its reliability, stability, and ease of operation make it suitable as a general purpose laboratory instrument. The heart of the CRO is a cathode-ray tube shown schematically in Fig. 1.

The cathode ray is a beam of electrons which are emitted by the heated cathode

(negative electrode) and accelerated toward the fluorescent screen. The assembly of

the cathode, intensity grid, focus grid, and accelerating anode (positive electrode) is

called an electron gun. Its purpose is to generate the electron beam and control its

intensity and focus. Between the electron gun and the fluorescent screen are two pair

of metal plates - one oriented to provide horizontal deflection of the beam and one pair


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oriented ot give vertical deflection to the beam. These plates are thus referred to as the

horizontal and vertical deflection plates. The combination of these two deflections

allows the beam to reach any portion of the fluorescent screen. Wherever the electron

beam hits the screen, the phosphor is excited and light is emitted from that point. This

coversion of electron energy into light allows us to write with points or lines of light

on an otherwise darkened screen. In the most common use of the oscilloscope the

signal to be studied is first amplified and then applied to the vertical (deflection) plates

to deflect the beam vertically and at the same time a voltage that increases linearly

with time is applied to the horizontal (deflection) plates thus causing the beam to be

deflected horizontally at a uniform (constant> rate. The signal applied to the verical

plates is thus displayed on the screen as a function of time. The horizontal axis serves

as a uniform time scale. The linear deflection or sweep of the beam horizontally is

accomplished by use of a sweep generator that is incorporated in the oscilloscope

circuitry. The voltage output of such a generator is that of a sawtooth wave as shown

in Fig. 2. Application of one cycle of this voltage difference, which increases linearly

with time, to the horizontal plates causes the beam to be deflected linearly with time

across the tube face. When the voltage suddenly falls to zero, as at points (a) (b) (c), etc...., the end of each sweep - the beam flies back to its initial position. The horizontal deflection of the beam is repeated periodically, the frequency of this periodicity is adjustable by external controls.

To obtain steady traces on the tube face, an internal number of cycles of the

unknown signal that is applied to the vertical plates must be associated with each cycle

of the sweep generator. Thus, with such a matching of synchronization of the two

deflections, the pattern on the tube face repeats itself and hence appears to remain

stationary. The persistance of vision in the human eye and of the glow of the

fluorescent screen aids in producing a stationary pattern. In addition, the electron beam

is cut off (blanked) during fly back so that the retrace sweep is not observed.

CRO Operation: A simplified block diagram of a typical oscilloscope is shown in

Fig. 3. In general, the instrument is operated in the following manner. The signal to be

displayed is amplified by the vertical amplifier and applied to the verical deflection

plates of the CRT. A portion of the signal in the vertical amplifier is applied to the

sweep trigger as a triggering signal. The sweep trigger then generates a pulse

coincident with a selected point in the cycle of the triggering signal. This pulse turns

on the sweep generator, initiating the sawtooth wave form. The sawtooth wave is

amplified by the horizontal amplifier and applied to the horizontal deflection plates.

Usually, additional provisions signal are made for appliying an external triggering

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signal or utilizing the 60 Hz line for triggering. Also the sweep generator may be

bypassed and an external signal applied directly to the horizontal amplifier.

CRO Controls

The controls available on most oscilloscopes provide a wide range of operating conditions and thus make the instrument especially versatile. Since many of these controls are common to most oscilloscopes a brief description of them follows.

CATHODE-RAY TUBE

Power and Scale Illumination: Turns instrument on and controls illumination of the

graticule.

Focus: Focus the spot or trace on the screen.

Intensity: Regulates the brightness of the spot or trace.

VERTICAL AMPLIFIER SECTION

Position: Controls vertical positioning of oscilloscope display.

Sensitivity: Selects the sensitivity of the vertical amplifier in calibrated steps.

Variable Sensitivity: Provides a continuous range of sensitivities between the

calibrated steps. Normally the sensitivity is calibrated only when the variable knob is

in the fully clockwise position.

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AC-DC-GND: Selects desired coupling (ac or dc) for incoming signal applied to

vertical amplifier, or grounds the amplifier input. Selecting dc couples the input

directly to the amplifier; selecting ac send the signal through a capacitor before going

to the amplifier thus blocking any constant component.

HORIZONTAL-SWEEP SECTION

Sweep time/cm: Selects desired sweep rate from calibrated steps or admits external

signal to horizontal amplifier.

Sweep time/cm Variable: Provides continuously variable sweep rates. Calibrated

position is fully clockwise.

Position: Controls horizontal position of trace on screen.

Horizontal Variable: Controls the attenuation (reduction) of signal applied to

horizontal aplifier through Ext. Horiz. Connector.

TRIGGER The trigger selects the timing of the beginning of the horizontal sweep.

Slope: Selects whether triggering occurs on an increasing (+) or decreasing (-) portion of trigger signal.

Coupling: Selects whether triggering occurs at a specific dc or ac level.

Source: Selects the source of the triggering signal.

INT - (internal) - from signal on vertical amplifier EXT - (external) - from an external signal inserted at the EXT. TRIG. INPUT. LINE - 60 cycle triger

Level: Selects the voltage point on the triggering signal at which sweep is triggered. It also allows automatic (auto) triggering of allows sweep to run free (free run).

CONNECTIONS FOR THE OSCILLOSCOPE

Vertical Input: A pair of jacks for connecting the signal under study to the Y (or

vertical) amplifier. The lower jack is grounded to the case.

Horizontal Input: A pair of jacks for connecting an external signal to the horizontal

amplifier. The lower terminal is graounted to the case of the oscilloscope.

External Tigger Input: Input connector for external trigger signal.

Cal. Out: Provides amplitude calibrated square waves of 25 and 500 millivolts

for use in calibrating the gain of the amplifiers.

Accuracy of the vertical deflection is + 3%. Sensitivity is variable.

Horizontal sweep should be accurate to within 3%. Range of sweep is variable.

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Operating Instructions: Before plugging the oscilloscope into a wall receptacle, set the controls as follows:

(a) Power switch at off (b) Intensity fully counter clockwise (c) Vertical centering in the center of range (d) Horizontal centering in the center of range (e) Vertical at 0.2 (f) Sweep times 1

Plug line cord into a standard ac wall receptacle (nominally 118 V). Turn power on. Do not advance the Intensity Control. Allow the scope to warm up for approximately two minutes, then turn the Intensity Control until the beam is visible on the screen.

PROCEDURE: I. Set the signal generator to a frequency of 1000 cycles per second. Connect the output

from the generator to the vertical input of the oscilloscope. Establish a steady trace of this

input signal on the scope. Adjust (play with) all of the scope and signal generator controls

until you become familiar with the function of each. The purpose for such "playing" is to

allow the student to become so familiar with the oscilloscope that it becomes an aid (tool)

in making measurements in other experiments and not as a formidable obstacle. Note: If

the vertical gain is set too low, it may not be possible to obtain a steady trace.

II. Measurements of Voltage: Consider the circuit in Fig. 4(a). The signal generator is

used to produce a 1000 hertz sine wave. The AC voltmeter and the leads to the vertical

input of the oscilloscope are connected across the generator's output. By adjusting the

Horizontal Sweep time/cm and trigger, a steady trace of the sine wave may be displayed

on the screen. The trace represents a plot of voltage vs. time, where the vertical

deflection of the trace about the line of symmetry CD is proportional to the magnitude of

the voltage at any instant of time.

To determine the size of the voltage signal appearing at the output of terminals of the signal generator, an AC (Alternating Current) voltmeter is connected in parallel across these terminals (Fig. 4a). The AC voltmeter is designed to read the dc "effective value" of the voltage. This effective value is also known as the "Root Mean Square value" (RMS) value of the voltage. The peak or maximum voltage seen on the scope face

28

(Fig. 4b) is Vm volts and is represented by the distance from the symmetry line CD to the maximum deflection. The relationship between the magnitude of the peak voltage displayed on the scope and the effective or RMS voltage (VRMS) read on the AC voltmeter is

VRMS = 0.707 Vm (for a sine or cosine wave).

Thus

Agreement is expected between the voltage reading of the multimeter and that of

the oscilloscope. For a symmetric wave (sine or cosine) the value of Vmmay be taken as 1/2 the peak to peak signal Vpp

The variable sensitivity control a signal may be used to adjust the display to fill a

concenient range of the scope face. In this position, the trace is no longer calibrated so that you can not just read the size of the signal by counting the number of divisions and

multiplying by the scale factor. However, you can figure out what the new calibration is an use it as long as the variable control remains unchanged.

Caution: The mathematical prescription given for RMS signals is valid only for sinusoidal signals. The meter will not indicate the correct voltage when used to measure non-sinusoidal signals.

III. Frequency Measurements: When the horizontal sweep voltage is applied, voltage

measurements can still be taken from the vertical deflection. Moreover, the signal is

displayed as a function of time. If the time base (i.e. sweep) is calibrated, such

measurements as pulse duration or signal period can be made. Frequenciescan then be

determined as reciprocal of the periods.

Set the oscillator to 1000 Hz. Display the signal on the CRO and measure the period

of the oscillations. Use the horizontal distance between two points such as C to D in Fig. 4b.

Set the horizontal gain so that only one complete wave form is displayed.

Then reset the horizontal until 5 waves are seen. Keep the time base control in a calibrated position. Measure the distance (and hence time) for 5 complete cycles and calculate the frequency from this measurement. Compare you result with the value determined above.

Repeat your measurements for other frequencies of 150 Hz, 5 kHz, 50 kHz as set on the signal generator. IV. Lissajous Figures: When sine-wave signals of different frequencies are input to the horizontal and vertical amplifiers a stationary pattern is formed on the CRT when the ratio of the two frequencies is an intergral fraction such as 1/2, 2/3, 4/3, 1/5, etc. These stationary patterns are known as Lissajous figures and can be used for comparison

29

measurement of frequencies.

Use two oscillators to generate some simple Lissajous figures like those shown in

Fig. 5. You will find it difficult to maintain the Lissajous figures in a fixed configuration because the two oscillators are not phase and frequency locked. Their frequencies and phase drift slowly causing the two different signals to change slightly with respect to each other.

V. Testing what you have learned: Your instructor will provide you with a small oscillator circuit. Examine the input to the circuit and output of the circuit using your

oscilloscope. Measure such quantities as the voltage and frequence of the signals. Specify if they are sinusoidal or of some other wave character. If square wave, measure

the frequency of the wave. Also, for square waves, measure the on time (when the voltage is high) and off time (when it is low).

Result:- Study is completed

Precautions: 1.Operate cro carefully

2.Take all reading carefully 3.Use correct power supply

30

Experiment no 12

Objective. To studyDigital Instruments – Digital Voltmeter, Digital Frequency

Meter, Digital Panel Meter, Digital Storage Oscilloscope Theory: Digital Voltmeter.

A voltmeter is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a

scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.

Voltmeters are made in a wide range of styles. Instruments permanently mounted in a

panel are used to monitor generators or other fixed apparatus. Portable instruments,

usually equipped to also measure current and resistance in the form of a multimeter,

are standard test instruments used in electrical and electronics work. Any

measurement that can be converted to a voltage can be displayed on a meter that is

suitably calibrated; for example, pressure, temperature, flow or level in a chemical

process plant.

General purpose analog voltmeters may have an accuracy of a few percent of full

scale, and are used with voltages from a fraction of a volt to several thousand volts. Digital meters can be made with high accuracy, typically better than 1%. Specially

calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million. Meters using amplifiers

can measure tiny voltages of microvolts or less.

Part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. In laboratories, the Weston Cell is used as a standard voltage for precision work. Precision voltage references are available based on electronic circuits.

Digital Instruments

Digital Frequency Meter,


EMMI LAB Laboratory

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A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. Frequency is defined as the number of events of a particular sort occurring in a set period of time. Frequency counters usually measure the number of oscillations or pulses per second in a repetitive electronic signal.

Operating principle

Most frequency counters work by using a [counter] which accumulates the number of

events occurring within a specific period of time. After a preset period (1 second, for

example), the value in the counter is transferred to a display and the counter is reset to

zero. If the event being measured repeats itself with sufficient stability and the frequency

is considerably lower than that of the clock oscillator being used, the resolution of the

measurement can be greatly improved by measuring the time required for an entire

number of cycles, rather than counting the number of entire cycles observed for a pre-set

duration (often referred to as the reciprocal technique). The internal oscillator which

provides the time signals is called the timebase, and must be calibrated very accurately.

If the thing to be counted is already in electronic form, simple interfacing to the

instrument is all that is required. More complex signals may need some conditioning to

make them suitable for counting. Most general purpose frequency counters will include

some form of amplifier, filtering and shaping circuitry at the input. DSP technology,

sensitivity control and hysteresis are other techniques to improve performance. Other

types of periodic events that are not inherently electronic in nature will need to be

converted using some form of transducer. For example, a mechanical event could be

arranged to interrupt a light beam, and the counter made to count the resulting pulses.

Frequency counters designed for radio frequencies (RF) are also common and operate on

the same principles as lower frequency counters. Often, they have more range before they

overflow. For very high (microwave) frequencies, many designs use a high-speed

prescaler to bring the signal frequency down to a point where normal digital circuitry can

operate. The displays on such instruments take this into account so they still display the

correct value. Microwave frequency counters can currently measure frequencies up to

almost 100 GHz. Above these frequencies the signal to be measured is combined in a

mixer with the signal from a local oscillator, producing a signal at the difference

frequency, which is low enough to be measured directly.

Digital Panel Meters Digital Panel Meters are used to perform digital processing and display of voltage, current, pulse signal and others. They can also compare input values to set values, transfer data and perform other functions. OMRON Digital Panel Meters feature a high tech

backlight LCD display that gives excellent read-out of values in dual color, thus provides

intuitive feedback of value

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.

Digital Panel Meter

Digital Storage Oscilloscope

An oscilloscope (also known as a scope, CRO, DSO or, an O-scope) is a type of electronic

test instrument that allows observation of constantly varying signal voltages, usually as a

two-dimensional graph of one or more electrical potential differences using the vertical or

'Y' axis, plotted as a function of time, (horizontal or 'x' axis). Although an oscilloscope

displays voltage on its vertical axis, any other quantity that can be converted to a voltage

can be displayed as well. In most instances, oscilloscopes show events that repeat with

either no change, or change slowly.

Oscilloscopes are commonly used to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can show distortion, the time between two events (such as pulse width, period, or rise time) and relative timing of two related signals.[1]

Oscilloscopes are used in the sciences, medicine, engineering, and telecommunications industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for such purposes as analyzing an automotive ignition system, or to display the waveform of the heartbeat as an electrocardiogram.

Originally all oscilloscopes used cathode ray tubes as their display element and linear

amplifiers for signal processing, (commonly referred to as CROs) however, modern

oscilloscopes have LCD or LED screens, fast analog-to-digital converters and digital

signal processors. Although not as commonplace, some oscilloscopes used storage CRTs

to display single events for a limited time. Oscilloscope peripheral modules for general

purpose laptop or desktop personal computers use the computer's display, allowing them

to be used as test instruments.

Digital Storage Oscilloscope

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Basic Oscilloscope Description Display and general external appearance The basic oscilloscope, as shown in the illustration, is typically divided into four sections: the display, vertical controls, horizontal controls and trigger controls. The display is usually a CRT or LCD panel which is laid out with both horizontal and vertical reference lines referred to as the graticule. In addition to the screen, most display sections are equipped with three basic controls, a focus knob, an intensity knob and a beam finder button.

The vertical section controls the amplitude of the displayed signal. This section carries a Volts-per-Division (Volts/Div) selector knob, an AC/DC/Ground selector switch and the vertical (primary) input for the instrument. Additionally, this section is 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. Also included 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 to automatically restart after each sweep or it can be configured to respond to an internal or external event. The principal controls of this section will be the source and coupling selector switches. An external trigger input (EXT Input) and level adjustment will also be included. In addition to the basic instrument, most oscilloscopes are supplied with a probe as shown. The probe will connect to any input on the instrument and typically has a resistor 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 cable from the signal being measured. Some probes have a switch allowing the operator to bypass the resistor when appropriate.[1]

Result: Study is completed

34

Electrical & Electronics Engineering Department

BRCM COLLEGE OF ENGINEERING & TECHNOLOGY


EMMI Lab

Experiment -13

Aim:-To Study the Working Principles of single phase& Three phase

induction type electronics energy meter Electrical

Energy meter or watt-hour meter or is an electrical instrument that measures the amount of

electrical energy used by the consumers. Utilities is one of the electrical departments,

which install these instruments at every place like homes, industries, organizations,

commercial buildings to charge for the electricity consumption by loads such as lights,

fans, refrigerator and other home appliances.

Watt-Hour Meter

The basic unit of power is watts and it is measured by using a watt meter. One thousand

watts make one kilowatt. If one uses one kilowatt in one hour duration, one unit of energy

gets consumed. So energy meters measure the rapid voltage and currents, calculate their

product and give instantaneous power. This power is integrated over a time interval, which

gives the energy utilized over that time period.

Two Basic Types of Watt-Hour Meter The energy meters are classified into two basic categories, such as:

Electromechanical Type Induction Meter

Electronic Energy Meter

Watt hour meters are classified into two types by taking the following factors into

considerations:

Types of displays analog or digital electric meter.

http://www.elprocus.com/electrical-2/

http://www.elprocus.com/control-home-appliances-using-land-line/

http://www.elprocus.com/wp-content/uploads/2014/07/Watt-Hour-Meter.jpg

http://www.elprocus.com/prepaid-energy-meter/

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Types of metering points: secondary transmission, grid, local and primary

distribution.

End applications like commercial, industrial and domestic purpose

Technical aspects like single phases, three phases, High Tension (HT), Low

Tension (LT) and accuracy class materials.

The electricity supply connection may be either single phase or three phase depending on

the supply utilized by the domestic or commercial installations. Particularly in this article

we are going to study about the working principles of single-phase electromechanical

induction type watt- hour meter and also about three-phase electronic watt hour meter

from the explanation of two basic energy meters as described below .

Single Phase Electromechanical Induction Watt Hour Meter

It is a well-known and most common type of age-old watt-hour meter. It comprises a

rotating aluminum disc placed on a spindle between two electromagnets. The rotation

speed of the disc is proportional to the power, and this power is integrated by the use of

gear trains and counter mechanism. It is made of two silicon steel laminated

electromagnets: shunt and series magnets.

Series magnet carries a coil which is of a few turns of thickness wire connected in series

with the line; whereas the shunt magnet carries a coil with numerous turns of thin wire

connected across the supply.

Braking magnet is a kind of permanent magnet that applies the force opposite to the

normal disc rotation to move that disc a balanced position and to stop the disc while power

gets off.

Single Phase Electromechanical Induction Energy meter

Series magnet produces a flux which is proportional to the flowing current, and shunt

magnet produces a flux proportional to the voltage. These two fluxes lag at 90 degrees due

to inductive nature. The interface of these two fields produces eddy current in the disk,

utilizing a force, which is proportional to the product of instantaneous voltage, current and

the phase-angle between them. A braking magnet is placed over one side of the disc,

which produces a break torque on the disc by a constant field provided by using a

permanent magnet. Whenever the braking and driving torques become equal, the speed of

the disc becomes steady.

http://www.elprocus.com/wp-content/uploads/2014/07/electromechanicl-induction-energy-meter.jpg

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A Shaft or vertical spindle of the aluminum disc is associated with the gear arrangement

that records a number proportional to the revolutions of the disc. This gear arrangement

sets the number in a series of dials and indicates energy consumed over a time.

This type of energy meter is simple in construction and the accuracy is somewhat less due

to creeping and other external fields. A foremost problem with these types of energy

meters is their proneness to tampering, which necessitate an electrical-energy-monitoring

system. These series and shunt type meters are widely used in domestic and industrial

applications.

Electronic energy meters are accurate, precise and reliable type of measuring instruments

when compared to electromechanical induction type meters. When connected to loads,

they consume less power and start measuring instantaneous. So, electronic type of three

phase energy meter is explained below with its working principle.

3-Phase Electronic Watt Hour Meter This meter is able to perform current, voltage and power measurements in three phase

supply systems. By using these three phase meters, it is also possible to measure high

voltages and currents by using appropriate transducers. One of the types of three phase

energy meters is shown below (given as an example) that ensures reliable and accurate

energy measurement compared to the electromechanical meters.

3-Phase Electronic Watt Hour Meter

It uses AD7755, a single-phase energy measurement IC to acquire and process the input

voltage and current parameters. The voltage and currents of the power line are rated down

to signal level using transducers like voltage and current transformers and given to that IC

as shown in figure. These signals are sampled and converted into digital, multiplied by one

another to get the instantaneous power. Later these digital outputs are converted to

frequency to drive an electromechanical counter. The frequency rate of the output pulse is

proportional to the instantaneous power, and (in a given interval) it gives energy transfers

to the load for a particular number of pulses.

http://www.elprocus.com/wp-content/uploads/2014/07/3-Phase-Electronic-Watt-Hour-Meter.jpg

http://www.elprocus.com/working-procedure-on-how-do-transformers-work/

37

The microcontroller accepts the inputs from all the three energy measurement ICs for three

phase energy measurement and serves as the brain of the system by performing all the

necessary operations like: storing and retrieving data from EEPROM, operating the meter

using buttons to view energy consumption, calibrating phases and clearing readings; and, it

also drives the display using decoder IC.

Till now we have read about the energy meters and their working principles. For a deeper

understanding of this concept, the following description about the watt hour meter gives

complete circuit details and its connections using a microcontroller.

http://www.elprocus.com/eeprom-features-applicaitons-circuit-diagram/

http://www.elprocus.com/encoders-and-decoders/

electrical & electronics engineering department brcm ... · object: to measure self inductance...

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