CPCB Scientist B Paper | Central Pollution Control Board Scientist B Old Paper for Instrumentation Engineering

(Every Correct answer 1 mark, every wrong answer – 0.25 mark as a negative marking)

In a full wave rectifier circuit using centre trapped transformer, the peak voltage across half of the secondary winding is 30V. Then PIV is
(a) 30 V
(b) 60 V
(c) 5 V
(d) 10 V

The resolution of 4 bit counting ADC is 0.5 volt, for an Analog input of 6.6 volts. The digital output of ADC will be
(a) 1011
(b) 1101
(c) 1100
(d) 1110

A 6bit dual slope A/D converter uses a reference of -6V and a 1 MHz clock. It uses a fixed count of 40 (101000). Then, what will be input, if the output register shows 100111 at the end of conversion.
(a) 5.85 V
(b) 6.0 V
(c) 5.0 V
(d) 10.0 V

Which multivibrator can be used as a clock timer?
(a) Astablemultivibrator
(b) Bistablemultivibrator
(c) Any of the above
(d) None of the above

Data from a satellite is received in serial form (1 bit after another). If this data is coming at a 5 MHz rate and if the clock frequency is 5 MHz how long will it take to serially load a word in a 32-bit shift register?
(a) 1.6 ms
(b) 3.2 ms
(c) 6.4 ms
(d) 12.8 ms

An ammeter of 0-25 A range has a guranteed accuracy of 1% of full scale reading. The current measured is 5A. The limiting error is
(a) 2%
(b) 2.5%
(c) 4%
(d) 5%

Kelvin’s double bridge is used to measure low resistance because
(a) it has high sensitivity
(b) there is no thermoelectric emf
(c) resistance variation due to temperature
(d) effect of contact and lead resistance is eliminated

A moving iron voltmeter reads 250 V when connected to 250 V dc. If connected to 250 V 50 Hz, the voltmeter reading is likely to be
(a) 250 V
(b) 252 V
(c) 248 V
(d) 210 V

Two sinusoidal signals of equal amplitude and frequency are applied to X and Y plate of CRO respectively. The observed Lissajous pattern is a straight line. The phase shift between signals is
(a) Zero
(b) 90 degree
(c) Either zero or 180 degree
(d) Either 90 or 270 degree

The scale of a dynamometer is linear when used as
(a) Ammeter
(b) Voltmeter
(c) Wattmeter
(d) Both (a) and (c)

The repeat accuracy of an instrument can be judged from its
(a) static error
(b) linearity error
(c) dynamic error
(d) standard deviation of error

In a CRO, the frequency of output of time base generator
(a) is only one constant value
(b) is adjustable
(c) varies automatically
(d) either (a) or (c)

Which of these instrument does not have a control spring?
(a) Moving iron ammeter
(b) PMMC ammeter
(c) Electrostatic voltmeters
(d) Power factor meter

A ‘Q’ meter uses the principle of
(a) variation of self inductance
(b) variation of mutual inductance
(c) series resonance
(d) none of the above

The burden of current transformer is expressed in terms of
(a) Secondary winding current
(b) VA rating of transformer
(c) Voltage, current and power factor of secondary winding circuit
(d) None of the above