Example Sheet 3
1. Usingadiagramandequations,brieflydescribetheoperationandlimitationsofa Linear Variable Differential Transformer
2. Discusswaysofsensingchemicaleffectswithelectronicsensors.
3. Describe how a variable gap displacement sensor works, including a discussion of the response type.
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4. A square variable gap capacitor has a relative permittivity of 2, a length of 1mm and an initial gap of 100 microns. If the object moves by 10 microns how much does the capacitance change?
5. Describe how a resistive displacement sensor works.
6. Fortheresistivedisplacementsensorsshowninfigurebelow.
(a) What is the output voltage if Vs is 10V,R = 60Komhs, dmin =0, dmax = 50cm and d = 25cm?
(b) If dmin = 5 cm what proportion of the output voltage is due to the displacement d?
(c) What is the value of R2 seen by the output in (b)? What power is dissipated by this resistance?
7. Whyisthemicrostructureofaerospacematerialsimportant?Brieflydescribea technique that can be used to measure the grain structure of materials.
8. Whyisultrasoundusefulforimaginginthebody?Howisanimagereconstructedina simple linear array ultrasound machine?
9. A quarter bridge, with a supply voltage of 5V, is used with a platinum strain gauge (100% Pt) to measure the strain on an object.
(a) if the applied strain is 100 microstrain, what is the output voltage? You may
assume the circuit was balanced before the strain was applied.
(b) If this is to be interfaced to an ADC with a +/-1V input range, how much voltage
gain do you need? (expressed in dB)
EEEE3089 Sensing system and signal processing 2020-2021
(c) Using a differential amplifier configuration suggest values for the resistors R1,R2,R3 and R4 to achieve this. Why are these values suitable is there a better way to do this?
10. Show via the use of partial derivative that the expression for the combined output for a full bridge is:
11. A bridge circuit is to be used with two identical strain gauges (platinum tungsten). The devices replace R2 and R3 in the bridge as numbered in the lecture notes. What is the output voltage if the sensors are used in the below configurations?
12. A MEMS accelerometer has the following characteristics: Active Mass = 5 ¦Ìg
Spring constant (k) = 50×10-3 Nm-1
What was the acceleration applied to the device if the extension of the spring was 1
13. A manometer is used to measure the pressure of a gas line. The height of the fluid (water ¦Ñ=1000kg.m-3) in each side of the loop are h1 = 51cm and h2 = 52 cm.
(a) what is the difference in pressure between the gas line (PA) and the reference (PB)?
(b) If the reference is atmospheric pressure (101kPa) what is the absolute pressure of the gas line?
14. The sensors shown in the figure below are used to measure the fluid flow of a lubricant oil (¦Ñ=900kg.m-3). If the pressure measured for sensor 1 is 250kPa and for sensor 2 is 251kPa, what is the velocity of the lubricant flowing past the sensors?
15. How does a Bourdon tube sense pressure? How could the output of this sensor be modified to produce and electrical signal?
EEEE3089 Sensing system and signal processing 2020-2021
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