Instrumentation and Measurement

Hong Kong Institute of Vocational Education EG114701 HD in Mechanical Engineering (Full-Time)

Instrumentation & Measurement MBS3151

Assignment AY17-18 (TM Campus) Page 1 of 3

Assignment

1. A technician measured a 5V voltage source using a DMM and a VOM and the results are recorded in the table as shown below. Compare the two sets of data

in terms of accuracy and precision.

DMM 4.99V 5.01V 5.00V 4.99V 5.00V

VOM 4.9V 5V 5.1V 5V 5V

15%

2. An unknown resistor R is measured by the ammeter-voltmeter method as shown in Fig Q2. Calculate:

(a) the measured value of R; (b) the true value of R; (c) the percentage error of the answer in (a). (d) Comment on the use of the circuit in measuring resistance. (e) If measurement of voltage is made by a 3½ digital meter

DMM of accuracy ± (0.5% reading + 1 digit), what is the possible guaranteed limit?

18%

3. It is required to convert a moving coil micro-ammeter into an ammeter of full

scale 4A. The micro-ammeter has a full scale of 100A and an internal

resistance of 500. Sketch the circuit arrangement that should be made for the

conversion and calculate the value of resistor required.

14%

4. Suggest the most suitable instrument for the following measurements:

(a) to measure the angular displacement of a dc motor; 2%

(b) to measure the air pressure exerted inside air vessel; 2%

(c) to measure the relative humidity in a room; 2%

(d) the measure the temperature in the furnace to melt the silica sand and 2%

(e) to measure the force on the surface of a beam under compression. 2%

5. An inductive pick-up has 2000 pulses per shaft revolution. If the rotational speed of the shaft is found to be 3800 rpm, determine the

number of pulses produced in time interval of 15s.

8%

Reading 15V

Resistance 120kΩ

Reading 0.1A

Resistance 10Ω

A

V R

Figure Q2

Hong Kong Institute of Vocational Education EG114701 HD in Mechanical Engineering (Full-Time)

Instrumentation & Measurement MBS3151

Assignment AY17-18 (TM Campus) Page 2 of 3

6. An oscilloscope with x1-probe is use to examine an input sinusoidal AC

voltage signal. The setting of the vertical sensitivity and the horizontal time

baseline of the scope are 2V/div and 1ms/div. The display of the input signal is

shown in the following figure.

Determine the peak voltage, the frequency of the signal and calculate the phase

angle in rad when the input AC voltage (v) = +2V in the first time.

8%

7. The following diagram shows a series ohmmeter.

(a) What is the value of R2 to set meter at 100% FSD.

(b) Calculate RX if the meter reading is at 90% FSD.

Given R1 = 1 kΩ, meter with FSD = 1 mA and Rm = 100Ω ,

and the battery Eb = 3 V

18%

Hong Kong Institute of Vocational Education EG114701 HD in Mechanical Engineering (Full-Time)

Instrumentation & Measurement MBS3151

Assignment AY17-18 (TM Campus) Page 3 of 3

8. Figure Q8 shows a bridge circuit. RX is an unknown resistor.

G

Fig. Q1

RA

Power Supply

RB RS

Rx

Figure Q8

(a) When the galvanometer is null, the bridge is balanced. Derive the value of RX in terms of the other component values in the circuit.

(b) If RA = 200 k, RB = 50 k, and RS is a standard resistance with

adjustable range from 50 to 150 k, what is the resistance measurement

range of the bridge?

9%

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