100 Most Important MCQ Of Measurement and Instrumentation with explanation

Answer.3. 3kW

Explanation:-

Meter constant K = Number of revolution/Kwh (rev/kWh)

Number of revolution = 10

Energy consumed when the disc made 10 revolution

= 10 × 1/600 = 1/60 KWh

Now energy consumed is equal to load in kW multiplied by time in hours i.e.

Load × 20/3600 = 1/60

Load = 3600/120

Load = 3 kW

Answer.4. 480

Explanation:-

Energy consumed in two hours = V.I.cosφ.t

Where

Voltage V = 220 V

Current I = 5 A

Power factor cosφ = 1

Time (t) = 2 hours

Number of revolution = 1056

Energy consumed = 220 × 5 × 1 × 2 = 2.2 kWh

Meter constant K = Number of revolution/Kwh (rev/kWh)

K = 1056/2.2 = 480 rev/kWh

Answer.4. 6200W

Explanation:-

The sum of two wattmeters gives the total power consumption in the three-phase load i.e

Total Power = P₁ + P₂

Reading of wattmeter 1

W₁ = 5 kW = 5000 watts

Reading of wattmeter 2

W₂ = 1200 watts

Total power = 5000 + 1200 = 6200 watts

Answer.1. 150Ω

Explanation:-

Given: I₁ = 2.0 A; I₂ =4 A; I₃ = 6 A

V = 300 V

Non-inductive resistance, R = (V/I₁) = 300/2 = 150Ω

Answer.3. Schering bridge

Explanation:-

The Schering bridge is used for the measurement of the properties of insulators, capacitor bushings insulating oil, Dielectric losses, and other insulating material.

The loss factor is given as

R₁ = R₃C₄/C₂

Dissipation factor/Dielectric loss

C₁ = C₂R₄/R₃

It is suitable for small capacitances and usually supplied from high frequency or a high voltage source.

Note:-

The Anderson’s bridge gives the accurate measurement of self-inductance of the circuit.

Wien’s bridge is used for precision measurement of capacitance in terms of resistance and frequency. It is also used to measure audio frequencies.

Answer.3. Vibration galvanometer

Explanation:-

A galvanometer is an instrument that is used to detect the presence and measure magnitudes of the small currents or voltages in the measuring circuits. Thus galvanometer term is generally used for any current or voltage indicating instrument which is not calibrated.

A.C Galvanometers: The A.C galvanometers are mainly used as a null detector in the bridge and potentiometer circuit. These are also used for measuring an effective or r.m.s. value of the small A.C current flowing in the circuit. The a.c. galvanometers are further classified as phase-sensitive galvanometers and frequency-sensitive galvanometers.

The phase-sensitive galvanometers are dynamometer-type galvanometers in which a moving system is suspended with a long suspension win a mirror attached to it. To make the instrument is highly sensitive, the moving system should be light. To protect the moving coil from the electrostatic field between fixed and moving coils it is necessary to screen the moving item properly. To increase the sensitivity of the instrument, a laminated iron core is used for the fixed coil to achieve a stronger magnetic field In this type of galvanometer, the magnetic field is setup by an a.c electromagnet.

The frequency selective galvanometer is called a tuned detector type galvanometer. It is tuned at an operating frequency and it is generally used at frequencies below 250 Hz as the galvanometer is found to be more sensitive than the telephone. The common frequency-selective galvanometer is the vibration galvanometer. 

Vibration Galvanometers

Vibration galvanometers are the more sensitive bridge detectors and are constructed in the frequency range from 5 c/s to 1000 c/s but their principal application is below 200 cps where their sensitivity is greater than telephone receiver. At power frequency, their sensitivity closely matches with those of d.c. galvanometers. Thus the response of vibration galvanometer is limited to a very narrow range of frequency. When tuned to the fundamental frequency, it will have an extremely small response to harmonics. Vibration galvanometers are of two types:

(i) Moving-magnet-type vibration galvanometer

(ii) Moving-coil-type vibration galvanometer

Answer.2. Inductance

Explanation:-

A Maxwell bridge is a modification to a Wheatstone bridge used to measure an unknown inductance (usually of low Q value) in terms of calibrated resistance and inductance or resistance and capacitance.

As in the balanced condition of the Wheatstone bridge product of opposite arms, resistance are equal i.e

R₁R₃ = R₂R₄

In Maxwell AC bridge in the two arms, there are two pure resistances so that for balance relations, the phase balance depends on the remaining two arms.

For the balanced condition of Maxwell AC bridge

Z₁Z₃ = Z₂Z₄

Where Z₁ is the unknow Impedance

Z₁ = R₁ + JX₁ = R₁ + JωL₁

Z₄ is the know Impedance

Z₄ = R₄ + JX₄ = R₄ + JωL₄

R₂ and R₃ = Known pure resistance

∴ (R₁ + JωL₁)R₃ = (R₄ + JωL₄)R₂

Equating Real and Imaginary part

R₁R₃ = R₂R₄

&

ωL₁R₃ = ωL₄R₂
L₁R₃ = L₄R₂

Hence, the unknown self-inductance can be measured in terms of the known inductance L₄ and the two resistors. Resistive and reactive terms balance independently and the conditions are independent of frequency. This bridge is often used for measuring the iron losses of the transformers at audio frequency.

Answer.2. Wein bridge

Explanation:-

The Wien bridge is one of many common bridges. Wien’s bridge is used for the precision measurement of capacitance in terms of resistance and frequency. It is also used to measure audio frequencies. It is also used in distortion analyzers as the notch filter.

Answer.2. 2

Explanation:-

The deflection sensitivity of a magnetic deflection cathode ray tube is defined as the amount of spot deflection on the screen when the potential of 1 volt is applied to the deflection plate.

In most CROs, the deflection sensitivity is expressed as the ratio of input voltage to the length of the trace.

In the electrostatic deflection, the spot la deflected on the screen by applying voltages on the vertical or the horizontal deflecting plates. The dc or peak-to-peak ac voltage applied to the deflects ing plates to displace the spot by 1 mm on the screen is termed the deflection factor. The reciprocal of the deflection factor is called the deflection sensitivity. The deflection factor la usually expressed in V/mm and deflection sensitivity in mm/V.

Deflection sensitivity of the CRO is given as

Deflection sensitivity = 1/deflection factor

Deflection sensitivity = 1/0.5 = 2 m/V

Answer.4. 10%

Explanation:-

Limiting error at full scale is

δE = ± 5% of 100

δE = ±5mv

Thus when the reading is 50 V, the error will still be 5 V. Hence the % limiting error

= (5/50)x100 = 10%

Note that the percentage limiting error is twice the mentioned value at full-scale reading. The limiting error increases as the reading of the voltmeter decrease.