Pressure sensors

Question:

I'm building a sensor at the moment. What I want to use is a pressure pad to measure pressure. But I can't explain how this works.

Answer:

Here are two or three ideas:

(a) resistance – some materials (such as some forms of carbon) change their resistance if they are compressed. This means that if the pressure pad is squashed the two sides get closer tighter, the resistance changes and this change can be measured and used to calculate the pressure if the instrument is calibrated. I used to use a variable resistance in one of the schools in which I taught where you had to screw a set of carbon plates together to change its resistance.

(b) capacitance – the capacitance of a capacitor changes if the two plates are brought closer together. Imagine the pressure pad contains two plates (in the form of say aluminium sheet) separated by a rubber sheet that can be squashed. As the pressure is increased these two sheets get closer, the capacitance changes and this can be used to calculate the pressure if the instrument is calibrated.

(c) the simplest form is of course an air filled bag with a pressure gauge attached to it!