GATE Electrical Engineering Electrical and Electronic Measurements Syllabus

Electrical and Electronic Measurements syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Electrical and Electronic Measurements in GATE Electrical Engineering, not a summary of it.

1. 1

   Bridges and Potentiometers

   5 topics

   • Measurement of voltage
   • Measurement of current
   • Measurement of power
   • Measurement of energy
   • Measurement of power factor
2. 2

   Instrument transformers

   overview

   Examined as a single unit within Electrical and Electronic Measurements — no further topic split in the official outline.

3. 3

   Digital voltmeters and multi-meters

   overview

   Examined as a single unit within Electrical and Electronic Measurements — no further topic split in the official outline.

4. 4

   Phase, Time and Frequency measurement

   overview

   Examined as a single unit within Electrical and Electronic Measurements — no further topic split in the official outline.

5. 5

   Oscilloscopes

   overview

   Examined as a single unit within Electrical and Electronic Measurements — no further topic split in the official outline.

6. 6

   Error analysis

   overview

   Examined as a single unit within Electrical and Electronic Measurements — no further topic split in the official outline.

Electrical and Electronic Measurements flashcards for GATE Electrical Engineering

20 of 50 cards from the Electrical and Electronic Measurements deck — real questions with worked answers.

1. What is the basic working principle of a PMMC (Permanent Magnet Moving Coil) instrument?

   It works on the motor principle: a current-carrying coil placed in the magnetic field of a permanent magnet experiences a deflecting torque proportional to the current (T = NBIA).

2. Why can a PMMC instrument measure only DC quantities directly?

   Its deflecting torque reverses with current direction, so for AC the average torque over a cycle is zero and the pointer reads zero. It responds to the average (DC) value only.

3. How is a basic PMMC galvanometer (millivoltmeter) converted into a voltmeter for measuring higher voltages?

   By connecting a high non-inductive resistance (a multiplier/series resistance) in series with the moving coil.

4. Give the formula for the multiplier resistance Rs needed to extend a voltmeter range, where V is desired range, Im and Rm are full-scale current and meter resistance.

   Rs = (V / Im) - Rm, or equivalently Rs = Rm(m - 1) where m = V/Vm is the multiplying factor.

5. What is the 'voltmeter sensitivity' (ohms-per-volt) and how is it related to full-scale current?

   Sensitivity = 1/Ifsd (ohms per volt). It equals the reciprocal of the meter's full-scale deflection current; e.g. a 50 µA movement gives 20,000 Ω/V.

6. What is the loading effect of a voltmeter and how is it minimized?

   A voltmeter draws current from the circuit, lowering the measured voltage; the error is the loading effect. It is minimized by using a high-resistance (high ohms-per-volt) voltmeter.

7. How is a galvanometer converted into an ammeter to measure large currents?

   By connecting a low-resistance shunt in parallel with the moving coil to bypass most of the current.

8. Give the shunt resistance formula Rsh for an ammeter, where Rm is meter resistance and m is the multiplying power of the shunt.

   Rsh = Rm / (m - 1), where m = I/Im (total current / meter full-scale current).

9. For a moving-iron instrument, what quantity does the deflection depend on, and can it measure both AC and DC?

   Deflection is proportional to the square of the current (torque ∝ I²), so it reads RMS value and can measure both AC and DC.

10. What type of scale does a moving-iron instrument have and why?

    A non-uniform (cramped at the lower end, crowded scale) scale because deflection is proportional to I², making it non-linear.

11. What is the principle of an electrodynamometer (electrodynamic) instrument?

    It uses the interaction between the magnetic fields of fixed coils and a moving coil; torque is proportional to the product of currents in the two coils, allowing true RMS and power measurement on AC and DC.

12. Why is the electrodynamometer instrument the most suitable for use as a transfer instrument and as a wattmeter?

    Because its deflection depends on the product of two currents (or voltage and current), it gives identical readings for AC (RMS) and DC, making it ideal as a transfer instrument and for power measurement.

13. What is a rectifier-type AC voltmeter and what value does it actually respond to?

    It uses a rectifier (diode bridge) feeding a PMMC movement; the PMMC responds to the average value of the rectified waveform but the scale is calibrated to read RMS (assuming a sine wave).

14. What error arises in a rectifier-type instrument when measuring non-sinusoidal waveforms?

    A waveform error, because the scale is calibrated assuming the sine-wave form factor (1.11); for other waveforms the form factor differs, giving incorrect RMS readings.

15. Define the form factor of an AC waveform and give its value for a sinusoid.

    Form factor = RMS value / Average value. For a pure sine wave it equals π/(2√2) ≈ 1.11.

16. What is the basic structure used to measure power in a single-phase AC circuit with a wattmeter?

    An electrodynamometer wattmeter with a current coil (in series, carrying load current) and a pressure/voltage coil (across the supply); deflection ∝ V·I·cosφ = real power.

17. State the wattmeter reading expression for a single-phase load.

    W = V I cosφ (the average product of instantaneous voltage and current), i.e. the real/active power in watts.

18. What is the two-wattmeter method used for?

    Measuring total three-phase power in a three-wire system (balanced or unbalanced); total power P = W1 + W2.

19. In the two-wattmeter method for a balanced load, how are the individual readings expressed in terms of phase angle φ?

    W1 = VL IL cos(30° - φ) and W2 = VL IL cos(30° + φ).

20. In the two-wattmeter method, how is the power factor angle φ obtained from the two readings?

    tan φ = √3 (W1 - W2)/(W1 + W2), so φ = arctan[√3(W1-W2)/(W1+W2)].

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