1 Capacitance Micrometry.

A common instrument is the capacitance micrometer. This device uses the well known

parallel plate capacitance formula:

2 Design Specification.

You are required to design a circuit to measure C in the above equation. Assume that

the measuring capacitor has a plate area of 300 mm², an initial plate separation of

0.05 mm and that the dielectric between the two plates is air at a temperature of 20 °C.

Your circuit should be designed to detect a change in the separation dof 5 x 10-4 mm.

Note that an absolute measure of distance is not required, just the change in d, and

that change is to be measured to ±5% error maximum. Use of the circuit should be as

follows: A button is pressed to indicate that the current separation of the plates is to

be the start point, the circuit should then measure the change in separation at least

once per second.

You are given aournd four weeks to complete this activity. There is no "correct" answer,

however it is obviously helpful if you can show your design will work!

A range of useful electronics circuitries for capacitive sensing are described in high-

level in the provided reference materials. You are expected to research in further

1

the details of capacitance measurement techniques (utilising online resources, lecture

notes, textbooks, and simulation) so that you can justify the approach you decide to

use for the given specifications. For example, you will need to consider as many practi-

cal design issues as possible beyond the theoretical scheme, expecially those covered

in the lecture notes (op-amp non-ideal issues, noise level, power losses, etc.). Notice

that you can use any other methods different from the provided reference as long as

they are justifiable. Use of switched-capcitor techniques is optional. This course work

trains your ability for indepedent study on a topic.

3 Assessment.

Your work will be assessed based on a final report, that must be submitted through

MyAberdeen. Don't forget the usual report structure of Introduction, Main body and

Conclusion! Appendices may be used to provide further information that doesn't fit

directly into the flow of the report and any reference material should be cited and

listed in a references section.

Marks will be awarded based on the innovation apparent in the design, the extent to

which it meets the design brief, and the supporting arguments for your design.

All analogue circuitry must be completed to detailed schematic level. Digital circuit

should be completed to block diagram level.