Explore topic-wise InterviewSolutions in .

Correct CHOICE is (c) INPUT to a proportional voltage

To elaborate: In a digital voltmeter, a TRANSDUCER is used. In general a transducer converts a PHYSICAL quantity into an electrical SIGNAL. In a DVM the transducer converts the input signal into a proportional voltage.

Right choice is (d) to bring voltage to a suitable limit

Easiest explanation: In a DVM, signal conditioning circuit is used. It CONVERTS the input signal into an voltage of suitable limit. This is done so that the voltmeter can READ the MAGNITUDE of the signal CORRECTLY.

The correct choice is (a) True

Best EXPLANATION: A digital VOLTMETER minimizes the errors DUE to human interference, interpolation mismatch and errors due to PARALLAX. A digital display is used to show the output voltage on a FRONT panel.

The correct choice is (b) voltage, temperature, pressure, etc

Easy explanation: Digital voltmeters are used for the measurement of A.C. as well as D.C. VOLTAGES and also to measure physical quantities such as temperature, pressure, stress etc. through the USE of appropriate transducer and signal CONDITIONING CIRCUITS.

Right choice is (a) analog to digital signal

Explanation: In general digital VOLTMETERS are known as DVM. They CONVERT analog signals into digital voltage. They also display the voltage to be measured in the FORM of discrete numerals in PLACE of pointer deflection.

The correct choice is (d) zero adjustment

Explanation: INITIALLY the multimeter is short CIRCUITED and zero adjustment CONTROL is made. This is done till the meter reads zero RESISTANCE or in other words displays FULL scale current.

Right ANSWER is (c) rectification

The explanation: When the MULTIMETER is used for the MEASUREMENT of A.C. voltages, rectifier section is used. It mainly PERFORMS the conversion of the INPUT A.C. voltage into D.C. for the measurement of A.C. voltage.

Correct choice is (a) connecting series resistances

To explain: We can obtain a WIDE range of D.C. VOLTAGE from a multimeter by connecting VARIOUS series resistances in the circuit through a range selection switch. By adjusting the value of the resistance we GET the required D.C. voltage.

Correct answer is (b) False

The explanation is: A MULTIMETER is used for the measurement of A.C. as well as D.C. voltage, CURRENT and resistance. By MANIPULATING the scale with a multiplication FACTOR of 100 and 10, 000 we can MAKE use of a multimeter for measuring high resistances.

Correct choice is (d) connecting shunts

For explanation: An electronic MULTIMETER can be used as an ammeter by making USE of shunt RESISTANCES across the meter. This is achieved by range SELECTING switch.

The correct answer is (B) of d.c. amplifier

To explain I WOULD say: A.C. as well as D.C. voltage, current and resistance can be measured by making use of an electronic multimeter. The basic CIRCUIT of a multimeter is MADE up of d.c. amplifier circuit in the form of a balanced bridge.

Correct choice is (a) voltage, current and resistance

The BEST I can explain: A.C. as well as D.C. voltage, current and resistance can be measured by MAKING use of an electronic multimeter. It is also KNOWN as a voltage-ohm meter.

Correct CHOICE is (b) False

Best explanation: Crest factor LIMITS the meter reading in a true r.m.s responding VOLTMETER when complex signals are TAKEN into consideration. Also, the meter costs higher compared to average and peak responding meters. As a result the response of the thermocouples is SLOW.

The correct choice is (d) mV

To explain: By making USE of TRUE r.m.s responding voltmeter we get the SENSITIVITY of the order of mV. The voltage ranges from 100 µV to 300 V with a frequency range of 10 Hz to 100 MHz.

The correct option is (c) measuring THERMOCOUPLE and balancing thermocouple

The best explanation: The thermocouple used in the INPUT SECTION of the voltmeter is known as the measuring thermocouple WHEREAS the thermocouple used in the feedback path is known as the balancing thermocouple.

The CORRECT answer is (a) Power =E^2 rms / Rheater

For explanation I would SAY: The power consumed in a thermocouple is given by the relation

Power =E^2 rms ⁄ Rheater

where, Erms is the r.m.s value of the a.c. INPUT signal

Rheater is the resistance of the HEATER.

Right option is (B) presence of thermocouple

The EXPLANATION: Thermocouples have non-linear voltage and current characteristics. This is the major drawback of the TRUE r.m.s responding voltmeter. This is overcome in some instruments by making use of an additional thermocouple in the same THERMAL environment.

Right ANSWER is (a) ROOT MEAN square

Explanation: R.M.S VALUE indicates the Root Mean Square. It is obtained by taking the square root of the average value of the square of the input SIGNAL. It is also known as the effective value.

The correct CHOICE is (b) sensing heat power

To explain: In a true R.M.S responding voltmeter, the meter reading is obtained by sensing the heat power of the WAVEFORM. The heat power is DIRECTLY proportional to the r.m.s VALUE of the input.

Correct CHOICE is (c) USES a thermocouple

The best EXPLANATION: A thermocouple is used to measure the heat POWER in a true R.M.S responding voltmeter. Input voltage under measurement is applied to the heater to which a thermocouple is ALSO attached.

The correct OPTION is (C) doesn’t AFFECT the meter

The explanation: As transistors saturate after a certain range of OPERATING voltage and current, the value of the meter current is LIMITED. As a result, overloading does not affect the meter and it remains safe.

Correct CHOICE is (b) an ATTENUATOR

The explanation: By making use of an attenuator in a basic D.C. electronic voltmeter, we get high RANGE of VALUES for the VOLTAGE reading. Attenuator is basically a voltage divider circuit with a predefined front panel.

Right choice is (a) True

Explanation: In a PMMC VOLTMETER (Permanent MAGNET Moving Coil), the sensitivity obtained is less and of the order of a few volts. In electronic voltmeters the sensitivity is very HIGH and is of the order of at LEAST 100 times as that compared to a PMMC voltmeter.

The correct answer is (d) BIAS on Q2 increases

The best EXPLANATION: The bias on the transistor Q2 increases when the input voltage is applied. As a result a proportional amount of CURRENT flows through the meter. HENCE the deflection of the meter is directly proportional to the applied voltage within the DYNAMIC range.

The correct option is (a) True

To elaborate: Field effect transistor (FET) acts as a source FOLLOWER and provides very high input impedance. BJT along with resistors form a BALANCED BRIDGE circuit. As a result the meter circuit can be isolated from the main circuit.

Right option is (b) high

The best I can explain: In an electronic voltmeter, the INPUT impedance is maintained very high. This is achieved by MAKING use of an FET (Field Effect Transistor) at the input of an electronic voltmeter.

The correct option is (c) zero adjustment resistor

Easiest explanation: 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.

Right answer is (a) amplifiers

Easy explanation: Electronic voltmeters make USE of amplifiers to measure low voltage SIGNALS. It consists of TWO or more STAGES of D.C. amplifiers.

Correct answer is (c) BANDWIDTH

For explanation I would say: NOISE in general depends on the value of the bandwidth. VOLTMETER having a LARGE bandwidth takes up more noise. Usually, the SENSITIVITY of a voltmeter is 1mV for a bandwidth of 10Hz – 10MHz.

Correct answer is (B) False

The BEST I can explain: As the unit DECIBEL makes of the logarithmic scale, it covers a WIDE range of values of any given QUANTITY.

The correct option is (d) a.c. voltmeter

The best EXPLANATION: By making use of an a.c. voltmeter in series with resistance we can OBTAIN the CURRENT VALUE. We can also make use of the current probe METHOD to obtain the value of the current without effectively disturbing the circuit.

Correct OPTION is (a) True

To explain I WOULD say: AVERAGE responding voltmeter is USED for a.c. MEASUREMENTS for a sine wave with 10% distortion or less. Hence the average responding voltmeter is cheap and accurate.

The CORRECT OPTION is (a) 100 divisions

The explanation: In ORDER to RECOGNIZE a reading with 1% accuracy it MUST have 100 divisions on the 1 V range.

Right choice is (d) 1-3-10

To elaborate: Meter scale will have a calibration of 1-3-10 for the VOLTAGE RANGE with a separation of 10 dB. It can ALSO be in the sequence of 1.5-5-15. We can also make USE of a single scale.

Correct answer is (B) capacitance

The best I can explain: Shunt capacitance appearing across the input TERMINALS AFFECTS the input impedance. CAPACITIVE reactance of the capacitance is inversely proportional to the frequency.

Xc ∝ ^1⁄f

where, Xc is the capacitive reactance

f is the frequency.

Right option is (c) decreases

The explanation is: We KNOW that the capacitive reactance is INVERSELY PROPORTIONAL to the frequency.

Xc ∝ ^1⁄f

At high frequencies, the capacitive reactance becomes very small.

The CORRECT option is (a) nil

Easiest explanation: In an electronic voltmeter as the POWER is supplied by an EXTERNAL circuit, there is no loading effect. In a PMMC instrument, a minimum CURRENT of 50 µA is obtained from the signal that is to be measured and this leads to loading effect.

The correct answer is (b) measure LOW level signals

Easiest explanation: Electronic VOLTMETERS make use of amplifier circuits. As a result they can be USED for MEASURING low level signals.

Right answer is (d) wide

To explain I would say: When compared to conventional analog voltmeters, the dynamic range is very wide and improved in electronic voltmeters. Very low as WELL as very high INPUT signals can be MEASURED using an electronic voltmeter.

The correct option is (c) made of TRANSISTORS and DIODES

The best explanation: Nowadays in VOLTMETERS, transistors and semiconductor diodes are used. A TRANSISTOR voltmeter makes use of transistor in a voltmeter.

The CORRECT choice is (d) a VOLTMETER

Easiest explanation: Field effect transistors can also be USED at the input. Such VOLTMETERS are KNOWN as FETVM (Field Effect Voltmeter).

Correct OPTION is (b) False

To elaborate: COMPARED to ANALOG voltmeters, electronic voltmeters are very ACCURATE and precise.

Correct choice is (b) made of VACCUM tubes

Easy explanation: INITIALLY, voltmeters were made of vaccum tubes. These voltmeters were known as vaccum TUBE voltmeters (VTVM).

The correct option is (a) True

To elaborate: Voltmeters that make use of rectifiers, diodes, amplifiers, etc in order to PRODUCE a current that is in proportion to the QUANTITY that is being measured is KNOWN as an ELECTRONIC VOLTMETER.