Questions & Answers of Electrical and Electronic Measurements

Two wattmeter method is used for measurement of power in a balanced three-phase load supplied from a balanced three-phase system. If one of the wattmeters reads half of the other (both positive), then the power factor of the load is

A 0-1 Ampere moving iron ammeter has an internal resistance of $ 50\;m\Omega $ and inductance of 0.1 mH. A shunt coil is connected to extend its range to 0-10 Ampere for all operating frequencies. The time constant in milliseconds and resistance in $ m\Omega $ of the shunt coil respectively are

The slope and level detector circuit in a CRO has delay of 100 ns. The start-stop sweep generator has a response time of 50 ns. In order to display correctly, a delay line of

The following measurement are obtained on a single phase load; V=220 V±1%,I=5.0 A±1% and W=555 W±2%. If the power factor is calculated using these measurements, the worst case error in the calculated power factor in percent is__________. (Give the answer up to two decimal places)

The load shown in the figure is supplied by a 440 V (line-to-line), 3-phase source (RYB sequence). The load is balanced and inductive, drawing 3436 VA. When the switch S is in position N, the three watt-meters W1, W2 and W3 read 577.35 W each. If the switch is moved to position Y, the readings of the watt-meters in watt will be:

 

Two resistors with nominal resistance values R1 and R2 have addictive uncertainties $\triangle$R1 and $\triangle$R2, respectively. When these resistances are connected in parallel, the deviation of the error in the equivalent resistance R is

A stationary closed Lissajous pattern on an oscilloscope has 3 horizontal tangencies and 2 vertical tangencies for a horizontal input with frequency 3 kHz. The frequency of the vertical input is

A 10 12 digit timer counter possesses a base clock of frequency 100 MHz. when measuring a particular input, the reading obtained is the same in: (i) Frequency mode of operation with a gating time of one second and (ii) Period mode of operation (in the x 10 ns scale). The frequency of the unknown input (reading obtained) in Hz is ____________.

An energy meter, having meter constant of 1200 revolutions/kWh, makes 20 revolutions in 30 seconds for a constant load. The load, in kW, is _____________.

When the Wheatstone bridge shown is used to find value of resistance RX ,  the galvanometer G indicates zero current when R1 = 50Ω, R2 =65Ω and R3=100Ω. If Ris known with ±5% tolerance on its nominal value of  $100\mathrm\Omega$, what is the range of RX in Ohms?

 

A (0-50 A) moving coil ammeter has a voltage drop of 0.1 V across its terminals at full scale deflection. The external shunt resistance (in milliohms) needed to extend its range to (0-500 A) is ________.

An unbalanced DC Wheatstone bridge is shown in the figure. At what value of p will the magnitude of V0 be maximum?

Match the following:

Instrument Type Used for
P. Permanent magnet moving coil 1. DC only
Q. Moving iron connected through current transformer 2. AC only
R. Rectifier 3.AC and DC
S. Electrodynamometer  

A 3-phase balanced load which has a power factor of 0.707 is connected to balanced supply. The power consumed by the load is 5 kW. The power is measured by the two wattmeter method. The readings of the two wattmeters are

A capacitive voltage divider is used to measure the bus voltage Vbus in a high-voltage 50 Hz AC system as shown in the figure. The measurement capacitor C1 and C2 have tolerances of ±10% on their normal capacitance values. If the bus voltage Vbuis 100 kV rms, the maximum rms output voltage Vout(in kV), considering toleance , is _____________.

The coils of a wattmeter have resistances 0.01Ω and 1000Ω; their inductances may be neglected. The wattmeter is connected as shown in the figure, to measure the power consumed by a load, which draws 25A at power factor 0.8. The voltage across the load terminals is 30V. The percentage error on the wattmeter reading is _________.

Power consumed by a balanced 3-phase, 3-wire load is measured by the two wattmeter method. The first wattmeter reads twice that of the second. Then the load impedance angle in radians is

In an oscilloscope screen, linear sweep is applied at the

The reading of the voltmeter (rms) in volts, for the circuit shown in the figure is __________

The dc current flowing in a circuit is measured by two ammeters, one PMMC and another electrodynamometer type, connected in series. The PMMC meter contains 100 turns in the coil, the flux density in the air gap is 0.2 Wb/m2, and the area of the coil is 80 mm2. The electrodynamometer ammeter has a change in mutual inductance with respect to deflection of 0.5 mH/deg. The spring constants of both the meters are equal. The value of current, at which the deflections of the two meters are same, is ________

The saw-tooth voltage waveform shown in the figure is fed to a moving iron voltmeter. Its reading would be close to _____________

While measuring power of a three-phase balanced load by the two-wattmeter method, the readings are 100 W and 250 W. The power factor of the load is _________.

Suppose that resistors R1 and R2 are connected in parallel to give an equivalent resistor R. If resistors R1 and R2 have tolerance of 1% each, the equivalent resistor R for resistors R1 =300 Ω and R2= 200 Ω will have tolerance of

Two ammeters X and Y have resistances of 1.2 Ω and 1.5 Ω respectively and they give full-scale deflection with 150 mA and 250 mA respectively. The ranges have been extended by connecting shunts so as to give full scale deflection with 15 A. The ammeters along with shunts are connected in parallel and then placed in a circuit in which the total current flowing is 15A. The current in amperes indicated in ammeter X is __________.

An LPF wattmeter of power factor 0.2 is having three voltage settings 300 V, 150 V and 75 V, and two current settings 5 A and 10 A. The full scale reading is 150. If the wattmeter is used with 150 V voltage setting and 10 A current setting, the multiplying factor of the wattmeter is _________.

The two signals S1 and S2, shown in figure, are applied to Y and X deflection plates of an oscilloscope

The waveform displayed on the screen is

A periodic waveform observed across a load is represented by

Vt=1+sinωt0ωt<6π-1+sinωt6πωt<12π

The measured value, using moving iron voltmeter connected across the load, is

In the bridge circuit shown, the capacitors are loss free. At balance, the value of capacitance C1 in microfarad is _________.

The input impedance of the permanent magnet moving coil (PMMC) voltmeter is infinite. Assuming that the diode shown in the figure below is ideal, the reading of the voltmeter in Volts is

A strain gauge forms one arm of the bridge shown in the figure below and has a nominal resistance without any load as Rs = 300 Ω. Other bridge resistances are R1 = R2 = R3 = 300 Ω. The maximum permissible current through the strain gauge is 20 mA. During certain measurement when the bridge is excited by maximum permissible voltage and the strain gauge resistance is increased by 1% over the nominal value, the output voltage V0 in mV is

A periodic voltage waveform observed on an oscilloscope across a load is shown. A permanent magnet moving coil (PMMC) meter connected across the same load reads

The bridge method commonly used for finding mutual inductance is

For the circuit shown in the figure, the voltage and current expressions are

vt=E1sinωt+E3sin3ωt and it=I1sinωt-Φ1+I3sin3ωt-Φ3+I5sin5ωt

The average power measured by the Wattmeter is

An analog voltmeter uses external multiplier settings. With a multiplier setting of 20 kΩ, it reads 440 V and with a multiplier setting of 80 kΩ, it reads 352 V. For a multiplier setting of 40 kΩ, the voltmeter reads

Consider the following statement
(i) The compensating coil of a low power factor wattmeter compensates the effect of the impedance of the current coil.
(ii) The compensating coil of a low power factor wattmeter compensates the effect of the impedance of the voltage coil circuit.

The bridge circuit shown in the figure below is used for the measurement of an unknown element ZX. The bridge circuit is best suited when ZX is a

A dual trace oscilloscope is set to operate in the ALTernate mode. The control input of the multiplexer used in the y-circuit is fed with a signal having a frequency equal to

A 412 digit DMM has the error specification as: 0.2% of reading + 10 counts. If a dc voltage of 100 V is read on its 200 V full scale, the maximum error that can be expected in the reading is

A wattmeter is connected as shown in the figure. The wattmeter reads

An ammeter has a current range of 0 - 5 A, and its internal resistance is 0.2Ω. In order to change the range to 0 - 25 A, we need to add a resistance of

The Maxwell's bridge shown in the figure is at balance. The parameters of the inductive coil are

The pressure coil of a dynamometer type wattmeter is

The two inputs of a CRO are fed with two stationary periodic signals. In the X-Y mode, the screen shows a figure which changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. The following inference can be made from this.

The figure shows a three-phase delta connected load supplied from a 400V, 50 Hz, 3-phase balanced source. The pressure coil (PC) and current coil (CC) of a wattmeter are connected to the load as shown, with the coil polarities suitably selected to ensure a positive deflection. The wattmeter reading will be

An average-reading digital multimeter reads 10V when fed with a triangular wave, symmetric about the time-axis. For the same input an rms-reading meter will read.

Two 8-bit ADCs, one of single slope integrating type and other of successive approximation type, take TA  and TB times to convert 5 V analog input signal to equivalent digital output. If the input analog signal is reduced to 2.5 V, the approximate time taken by the two ADCs will respectively, be

Two sinusoidal signals p(ω1t) = A sinω1t and q(ω2t) are applied to X and Y inputs of a dual channel CRO. The Lissajous figure displayed on the screen shown below :

The signal q(ω2t) will be represented as

 

The ac bridge shown in the figure is used to measure the impedance Z .

If the bridge is balanced for oscillator frequency f = 2 kHz, then the impedance Z will be

The probes of a non-isolated, two channel oscillocope are clipped to points A, B and C in the circuit of the adjacent figure. Vin is a square wave of a suitable low frequency. The display on Ch1 and Ch2 are as shown on the right. Then the “Signal” and “Ground” probes S1, G1 and S2, G2 of Ch1 and Ch2 respectively are connected to points: