Assignment 3 – Winter 2011 Sensor Technology ELCT903 1

German University in Cairo

Sensor Technology (ELCT903)

Assignment (3)

Due Date: 3/12/2011

- Please hand in your assignment to your TA at C7-010, from 12:00 to 12:30pm .You may handle before due date at any time.

- Please print and solve in this form, other prints will not be accepted.

Name: ………………………………………… I.D. #:………..

Assignment 3 – Winter 2011 Sensor Technology ELCT903 2

Question 1 For the circuit shown, examine how the arrangement could be used to measure the displacements. Given that

XK

C =

_____________________________Solution_________________________

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Question 2

The figure shows a capacitor element construction used as an accelerator sensor

a- Mention type of capacitor, explain the sensor operation, and show by equations that the output voltage varies linearly with displacement X.

b- Draw and explain the equivalent circuit diagram for the sensor, showing

the signal conditioning circuit.

c- Plot for the signals at each stage in the circuit. _____________________________Solution_________________________

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Question 3 A capacitance transducer consists of two plates of diameter 2cm each, separated by an air gap of 0.25mm. Find the displacement sensitivity.

Solution

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Question 4 A parallel plate capacitance transducer uses plate of area 500mm that are separated by a distance of 0.2mm.

a) Calculate the value of capacitance when the dielectric is air having a permittivity of 8.85x10F/m.

b) A linear displacement reduces the gap length to 0.18 mm. calculate the change in capacitance.

Solution

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Question 5 Consider a piezoelectric crystal in the form of a disc with two electrodes plated on the two opposite faces. Draw the equivalent circuit

Solution

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Question 6 A barium titanate crystal has a charge sensitivity of 150.0 Pico-coulombs/Newton (1 PC =1x10-12 coulombs). The dielectric constant for the crystal is 1.25x10-8 farads/meter Calculate the voltage sensitivity of the crystal

Solution

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Question 7 A piezoelectric crystal has a dimension of 100mm2. its thickness is 1.25mm. It is held between two electrodes for measuring the change of force across the crystal. Yong’s modules of the crystal is 90GN/m2. charge sensitivity is 110pc/N.permittivity is 1200. the connecting cable has a capacitance of 250pF, and the oscilloscope for display has a capacitance of 40pF. What is the resultant capacitance?

Solution

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Question 8 A quartz PZT crystal has a dimension of 150mm2 having a thickness of 2mm and voltage sensitivity of 0.055 Vm/N is subjected to a stress of 1.5 MN/M2. Calculate the voltage output and the charge sensitivity.

Solution

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Question 9 It is interested to develop an instrument to measure the force exerted by the human finger. This instrument will be useful in the rehabilitation department. How will you approach the design of such instrument?

a) Identify the type of sensor, and explain its principle b) Draw a schematic diagram for such an instrument pointing on the sensor. c) How will you proceed with the data acquisition and display?

Solution

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