Electronic Meters Questions and Answers
Q1. What is the difference between an ammeter and a voltmeter?
Ammeter is a low resistance indicating instrument while the voltmeter is a high resistance one.
Q2. Why an ammeter should be of very low resistance?
Ammeter, which is connected in series with the circuit carrying the current under measurement, must be over very low resistance so that the voltage drop across the ammeter and power absorbed from the circuit are as low as possible.
Q3. Why a voltmeter should be of very high resistance?
Voltmeter, which is connected in parallel with the circuit across which the voltage is to be measured, must be of very high resistance so that the current flowing through the voltmeter and the power absorbed from the circuit are minimum possible.
Q4. How an ammeter can be changed to a voltmeter?
An ammeter or low range can be converted into a voltmeter by connecting a high resistance in series with it provided the current through the series combination is within the range of the ammeter when connected across the voltage under measurement.
Q5. What happens when an ammeter is connected across the circuit?
If an ammeter is connected in parallel to the circuit like a voltmeter, a very high current will flow through it which will produce such an excessive heat the insulation of the wire carrying the current will be destroyed. The wire may itself melt away. Thus the instrument will get damaged.
Q6. What happens when a voltmeter is connected in series with the circuit?
If a voltmeter is connected in series with the circuit, the circuit resistance will become too large and consequently a very small current will flow through it. The instrument will, however, read almost the same emf acting on the circuit.
Q7. What do you understand by ammeter shunt?
An ammeter shunt is merely a low resistance that is placed across the coil circuit of the instrument in order to measure fairly large currents.
Q8. What do you understand by voltmeter multiplier?
Voltmeter multiplier is a high non-inductive resistance connected in series with the voltmeter coil and is used for increasing the range of a voltmeter.
Q9. What is the advantage of using Ayrton or universal shunt in multi-range ammeters?
The advantage of using Ayrton or universal shunt is that it eliminates the possibility of the meter being in a circuit without a shunt.
Q10. What is VOM?
The volt-ohm-milliammeter (VOM) is another name of multimeter. It is also called AVO meter.
Q11. What is a multimeter?
The instrument, which contains a function switch to connect the appropriate circuits to the d’Arsonval movement, is often called a multimeter or ampere-volt-ohm (AVO) meter or volt-ohm-milliammeter (VOM).
Q12. Indicate the various quantities that can be measured with a multimeter.
Multimeteris used for measument of current (dc as well as ac), voltage (dc as well as ac) and resistance. With the external source, high resistance (exceeding 1MΩ),inductance and capacitance can be measured with this instrument.
Q13. What are the shortcomings of a multimeter?
It may be noted that the ac sensitivity of a half-wave ac meter is only 45% of the dc sensitivity, therefore, the loading effect is greater while measuring ac voltages than while measuring corresponding dc voltages.
The rectifying action depends upon the frequency to some extent due to capacitance effect and rectifier instruments show lower readings. Instrument indications may be in error by as much as 0.5% decrease for every 1kHz rise in frequency.
Q14. Where LCR meter is used?
LCR meters are used to measure the values of inductance (L), capacitance (C) and resistance (R) directly.
Q15. What is Q-meter?
The Q-meter is an instrument designed for measurement of Q-factor of a coil as well as for the measurement of electrical properties of coils and capacitors.
Q16. On what principle does a Q-meter operate?
The Q-meter operates on the principle of series resonance i.e, under resonant condition of an acseries, circuit voltage across the capacitor is equal to the applied voltage times of Q of the circuit.
Q17. What is Q-factor of the coil?
The ratio of the inductive reactance to the effective resistance of the coil is called the Q-factor of the coil.
Q18. What are the different parameters that can be measured using a Q-meter?
The Q-meter is used for measuring Q-factor, inductance, effective resistance, self-capacitance, bandwidth and capacitance.
Q19. What are the factors which the measurement accuracy of Q-meter?
- Factors affecting measurement accuracy are:
- Distributed capacitance or self capacitance of the coil.
- Residual inductance of the instrument.
- Conductance of voltmeter.
- Shunt resistor of Q-meter.
Q20. Why the actual Q-factor of the coil is somewhat larger than the calculated Q-factor?
Calculated value of Q-factor is somewhat smaller than its actual value because Q-factor measurement includes the losses of the resonating capacitor, voltmeter and the shunt resistance Rsh.