Exercises
1
A potentiometer resistance transducer has a total resistance of 5 k  and a maximum
displacement of 2 cm. the maximum power dissipation is not to exceed 50 mW.
Determine:
I.
The maximum possible excitation voltage
II.
The output voltage when input displacement is 0.75 cm assuming the excitation in
part (a)
2
The potentiometer has the following specifications:
Type; wire wound resistance displacement potentiometer
Terminal resistance: 10 kΩ
Range:
0 -25 mm
Resolution: 0.4 %
Power rating: 0.25 W
Maximum wiper current:
15 mA
Thermal drift: 0.05 5 per oC
6
Life expectancy:
10 cycles
(a)
Explain the meaning and significant of each specification
(b)
Determine a suitable excitation voltage allowing for 5 % safety margin
(c)
If a voltmeter having an input resistance of 270 kΩ is connected used to
measure displacement, calculate the error as a percentage of fsd at 0.025 mm
intervals and plot the error against displacement.
(d)
What is the maximum error in part (c)?
3
Platinum RTD with a resistance of 100 Ω at 0 oC has a resistance of 140 at 100 oC. What
if the temperature coefficient α
4
A copper-constantan thermocouple is to be used to measure temperature between 0 and
200 oC. The emf at 0 oC is 0 mV, at 100 oC it is 4.277 mV and at 200 oC it is 9.286 mV.
What is the non-linearity error at 100 oC as a percentage of the full range if a linear
relationship is assumed between emf and temperature over the full range
5
An electrical resistance strain gauge with has a gauge factor of 2.1 and resistance of 50 Ω.
What id the change in resistance if the strain is 0.001?.
6
You are offered a choice of an incremental shaft encoder of an absolute shaft encoder for
measurement of an angular displacement.
(a)
What is the principal difference between the results that can be obtained by these
methods
(b)
A shaft encoder with a 50 mm radius tracking wheel is used to monitor linear
displacement. In the encoder produces 256 pulses per revolution, what is the
number of pulses produced by a linear displacement of 225 mm?
7
A float sensor for determination of the level of water in a vessel has a cylindrical float of
mass 2 kg, cross –sectional area 20 cm2 and length of 1.5 m, It floats vertically in the
water and presses upwards against a beam attached to its upward end.
(a)
(b)
What will be the minimum and maximum upthrust forces exerted by the float on
the beam?
Suggest a means by which the deformation of the beam under the action of the
upthrust force could be monitored