1. Low voltage signals in Electronic Voltmeter can be measured by ______
Amplifiers
Transformers
Transducers
Voltmeters
Answer.1. Amplifiers
Explanation:
The electronic voltmeter uses amplification or rectification (or both) to measure either alternating- or direct-current voltages.
The amplifiers in the Electronic voltmeter not only supply power; for the operation but also make it possible for low-level signals, which produce a current less than 50 µA for full-scale deflection, to be detected which otherwise cannot be detected in the absence of amplifiers.
2. What will be the reading of the voltmeter in the given figure?
100 V
150 V
0 V
50 V
Answer.2. 150 V
Explanation:
Ideally, the voltmeter has infinite resistance and the practical resistance of the voltmeter is very high.
So that no current or negligible current is flowing through the voltmeter.
The given circuit is open-circuited due to the very high resistance of the voltmeter and the current flowing through the circuit is zero.
Hence all the voltage drops appeared across the voltmeter.
∴ voltmeter reading is 150 volts.
3. Input impedance of an electronic voltmeter is ________
Low
High
Medium
Zero
Answer.2. High
Explanation:
An electronic voltmeter has very high input impedance and very low output impedance and the current drawn by the instrument for full-scale deflection is negligible. Hence, the instrument does not draw any significant current from the system whose voltage is being measured. This way the system does not get loaded at all thereby almost eliminating the loading effect.
4. A multimeter consists of
Current and Ohm meter
Voltmeter and Ohm meter
Voltmeter and Current meter
Voltmeter, current meter and Ohm meter
Answer.4. Voltmeter, current meter and Ohm meter
Explanation:
A multimeter consists of a voltmeter, current meter, and Ohm meter
Current drawn by an electronic circuit is in the order of mill amperes. We can measure this using multimeter
The supply voltage to the DC motor is around 240 V, we can measure this voltage by using a multimeter
We can do continue tests of motor winding by using a multimeter.
6. In DC Electronic Voltmeter ______ effectively isolates the meter circuit.
Amplifier
Attenuator
Electronic Switch
FET
Answer.4. FET
Explanation:
DC Electronic Voltmeter consists of an input attenuator source follower and d.c. coupled amplifier. The purpose of the input attenuator is to provide input voltage levels that can be accepted by the d.c. amplifier. A FET is used to serve as a source follower at the input stage to obtain high input impedance. FET effectively isolates the meter circuit from the circuit under measurement.
7. Thermocouple meters are AC meters that respond to the ________ of a signal.
Peak value
Instantaneous value
Average value
RMS value
Answer.4. RMS value
Explanation:
Thermal-Thermoelectric uses the thermocouple for the measurement of the temperature, current, and voltage type of instrument known as the thermocouple instrument.
It is used for both the AC and DC measurement. The thermocouple is an electric device that uses two wires of different metals.
Thermocouple meters are AC meters that respond to the RMS value of a signal.
8. In DC Electronic Voltmeter bridge is balanced by _____
Galvanometer
Oscillator
Zero adjustment resistor
Headphone
Answer.3. Zero adjustment resistor
Explanation:
The bridge circuit in a basic D.C. electronic voltmeter is balanced by making use of a zero adjustment resistor such that the pointer shows zero deflection.
The bridge balance is obtained by a zero adjust resistor such that for zero input, the pointer shows zero. The bias on Q2 is such that i2 = i3 when the input is zero. Under such conditions, the potential of point an i.e. Va, and potential of point b i.e. Vb is the same. No current flows through the meter.
9. Which of the following features are associated with the rectifier instruments?
Small power loss
High degree of measuring accuracy
High sensitivity
All of the above
Answer.4. All of the above
Explanation:
Rectifier type instruments are used for the measurement of AC voltages and currents by employing a rectifier element that converts AC to a unidirectional DC and then using a meter responsive to DC to indicate the value of rectified AC.
The indicating instrument is the PMMC instrument which uses a d’Arsonval movement.
Features of rectifier instruments:
Liner scale
High sensitivity
A high degree of measuring the accuracy
A small number of power losses
10. In DC Electronic Voltmeter what is the effect of the input voltage on the transistor Q2?
Bias on Q2 decreases
Bias on Q2 is constant
Bias on Q2 is zero
Bias on Q2 increases
Answer.4. Bias on Q2 increases
Explanation:
When the input voltage is applied, the bias on Q2 increases. This causes V, to increase hence proportional current 7, flows through the meter. Thus the deflection of the meter is proportional to the input voltage, within the dynamic range of the amplifier.
