# Objective Questions on Measurement – 3

1. Meggar has how many terminals

Meggar used for measurement of high resistance and it has 2 terminals line and earth.

2. Thermistor is used for measurement of

Thermistors are semiconductors which behave as resistors with a high negative temperature co-efficient of resistance and it is used for measurement of temperature.

3. Multimeter measures

Multimeter measures both ac / dc voltage and current. As well as it measures resistance.

4. A digital to analog converter with a full scale output voltage of 3.5 V has a resolution close to 14 mV. Its bit size is

Resolution of digital to analog converter R = V0 ⁄ 2N = 14 mV, Where V0 = full scale output voltage = 3.5 V and N = bit size. V0 ⁄ 2N = 3.5 ⁄ (14 × 10 - 3) = 250 or,N = 8.

5. When a signal 15 mV at 85 MHz is to be measure then which of the following instrument can be used?

CRO is best choice. It can measure very low voltages at high frequencies.

6. In single phase modulation PWM inverters fifth harmonic can be eliminated if pulse width is equal to

Pulse width = 2π/n( n = 5) or, 360 Degree / 5= 72 Degree.

7. In CRO saw tooth voltage is applied at the

In CRO sawtooth voltage is applied at the horizontal deflecting plates.

8. LVDT stands for

LVDT translate linear motion into electric signals.

9. A single phase ac voltage controller feeding a pure resistance load has a load voltage of 200 V(rms) when fed from a source of 250 V(rms).The input power factor of the controller is

Power factor = v0 ⁄ vs = 200 ⁄ 250 = 0.8

10. An analog voltmeter voltage is in the range of 0 to 8 V is divided in eight equal intervals. For conversion to 3 bit digital output. The maximum quantizing error is

Quantizing error = V ⁄ 2N = 8 ⁄23 = 1 V.

11. The sensitivity of voltmeter using 0 to 5 mA meter movement is

Sensitivity = 1 / (5 mA) = 200 Ω / Volt.

12. A zero to 300 V voltmeter has a guaranteed, accuracy of 1% full scale reading. The voltage measured by the instrument is 83 volt. The percent limiting error is

1% accuracy means that a maximum possible error of 300 × ( 1 / 100 ) = 3 may be present in any reading. Since the deflection is 83 Volt, therefore percent limiting error = (3 / 83 ) × 100 = 3.62.

13. A thermocouple ammeter gives full scale deflection of 10 Amp. When it reads one fifth of the scale, the electric current will be

Q1 / Q2 = I12 / I22 or, 5 / 1 = 102 / I22 ⇒ I2 = 4.47 Amp.

14. A certain meter has a sensitivity of 50000 Ω/V. The electric current required to defect the meter movement to full scale will be

Current = Voltage ⁄ Resistance = 1 ⁄ 50,000 = 20 μA.

15. The percentage limiting error, in case of an instrument reading of 8.3 V with a 0 to 150 V voltmeter having a guaranteed accuracy of 1% full scale reading is

Max error = 1% of 150 V = 1.5 V percentage limiting error = ( 1.5 ⁄ 8.3 ) × 100 = 18.10%.

16. An electrically deflected CRT has a final value anode voltage of 2000 V and parallel deflecting plates 1.5 cm long and 5 mm apart. If the screen is 50 cm from the centre of deflecting plate. Find the deflection sensitivity of the tube?

S = ( l × ld) / (2d × Ea) = ( 0.5 × 1.5 × 10 - 2) ⁄ (2 × 5 × 10-3 × 2000 ) = 0.375 mm ⁄ V.

17. Errors due to human mistakes are

Gross errors occur because of mistakes in observed readings or using instruments and in recording and calculating measured results.

18. Sensitivity factor of a strain gauge is normally of the order of

1.5-2.0 is the sensitivity factor of strain gauge. The strain gauge is one of the most widely used strain measurement sensors. It is a resistive elastic unit whose change in resistance is a function of applied strain. We know dR / R = Sε where R is the resistance, ε is the strain, and S is the strain sensitivity factor of the gauge material.

19. The sensitivity of a voltmeter using 0 to 5 mA meter movement is-

Sensitivity = I ⁄ IB = 1 ⁄ 5 mA = 200 Ω / Volt

20. A compensated wattmeter has its reading corrected for error due to the

A compensated wattmeter has its reading corrected for error due to power consumed in potential coil.

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