EI 1302 (2 MARKS) UNIT I

ELECTRONICS INSTRUMENTATION

2 Marks Questions and answers

UNIT-I

1. Define Ayrton shunt or universal shunt?
The universal or ayrton shunt eliminates the possibility of having the meter in the circuit with a shunt. The advantage is gained at the price of a slightly higher overall meter resistance.

2. What is a true RMS responding voltmeter?
Complex waveforms are most accurately measured with an rms-responding voltmeter. This instrument produces a meter indication by sensing waveform heating power, which is proportional to the square of the rms value of the voltage.

3. What are the sources of error in a Q meter?
i) Due to the distributed capacitance or self capacitance Cd
ii) Due to insertion resistor,
iii) Due to self inductance
iv)Conductance of the Q meter.

4. What is a vector impedance meter?
Vector impedance meter makes simultaneous measurements of impedance and phase angle. The magnitude of the impedance is determined measuring the current through the unknown component when a known voltage is applied across it, or by measuring the voltage across the component when a known current is passed through it. The phase angle is found by determining the phase difference between the voltage across the component and the current through the component.

5. What is a power meter?
The electrodynamometer is used extensively used in measuring power. It is used to indicate both dc and ac power for any waveform of voltage and current and it is not restricted to sinusoidal waveforms.

6. State the prime advantage of peak responding voltmeter?
When no ac pre-amplification is required the rectifying diode and the storage capacitor may be taken out of the instrument and placed in the probe.

7.What is meant by basic meter?
The motor action is produced by the flow of a small amount of current through a moving coil which is positioned in a permanent magnetic field.

8.What is the main purpose of the multiplier?
The main purpose of the multiplier is to limit the current through the movement so that the current does not exceed the full scale deflection current.

9.What is meant by full scale deflection current?
Full scale deflection current is defined as the amount of current required to deflect the basic meter to full scale.
10.What are the factors in choosing an analog voltmeter?
a)input impedance,
b)Voltage ranges,
c)Decibels,
d)Sensitivity versus bandwidth,
e)Battery operation

11.What are the general requirements of a shunt?
` a) The temperature coeff of the shunt and instrument should be low.
b)The resistance of the shunt should not vary with time.
c)It should have a low thermal emf.

12.Define Q meter?
Q meter is defined as the power dissipated in the element to the power stored in the element.

13.What is the principle operation of Q meter?
The operation is based on the characteristics of a series resonant circuit.
The voltage across the capacitor or the coil is equal to the applied voltage times the Q of the circuit.

14.What is a vector voltmeter?
A vector voltmeter measures the amplitude of a signal at two points in a circuit and simultaneously measures the phase difference between the voltage waveforms at these points.

15.List the applications of vector voltmeter?
a)Insertion loss
b)Filter transfer functions

16.Write the components of a vector voltmeter?
a)Two RF to IF converters
b)Automatic phase control unit
c)Phase meter circuit
d)Voltmeter circuit

17.Where can we use decibels?
For measurements covering a wide range of voltages , the use of the decibels can be very effective.

18.Define current ratio?
It is defined as the ratio of primary current to the secondary current.

19. What is Digital Panel Meter (DPM)?’
Digital Panel Meters are available in a wide variety of special purpose functions. They have a readout range from the basic 3 digit (999 counts) to high precision 43/4 digit ones. They accept inputs like dc voltage, line voltage, strain gauge bridges, RTDs, thermocouples and frequency inputs.

20. What is the principle of digital frequency meter?
The signal whose frequency is to be measured is converted into a train of pulses, one pulse for each cycle of the signal. The number of pulses occurring in a definite interval of time is then counted by an electronic counter. Since each pulse represents the cycle of the unknown signal, the number of counts is a direct indication of the frequency of the signal.

21. What is ratio and multiple ratio measurement?
The ratio measurement involves the measurement of the ratio of two frequencies. The measurement method used is a period measurement. In multiple ratio measurements the period of the low frequency signal is extended by a factor of 10, 100 etc by using DDAs.

22. What is the purpose of IEEE 488 bus?
The purpose of IEEE488 bus is to provide interfacing between programmable instruments. There are many instrumentation systems in which interactive instruments, under the command of a central controller, provide superior error-free results when compared with conventional manually operated systems.