Transducer Part 2 - The Strain Gauge

I have chosen the strain gauge to start with since it uses some of the basic electrical principles that are taught to electrical students. Problem is that for many the theory will have been lost in some obscure part of the brain. Therefore it is time to trigger new neural pathways to this long forgotten collection of brain cells.

Before getting into the theory it was mentioned that a piece of knicker elastic can help understand strain gauges in Part 1 of transducers. With your knicker elastic or even rubber band in both hands, pull at either end. You will notice the the width of knicker elastic becomes thinner the more it is stretched.
No doubt the above demonstration will have triggered the eureka moment for many students of electricity into how the strain gauge works. I say farewell to those for whom the penny as dropped and continue on for the others.

Put these in order of lowest resistance, a 1 metre diameter of copper cable a meter long, 1 metre diameter of copper cable 10 metres long, 1 millimetre diameter of copper cable a meter long, or a 1 millimetre diameter of copper cable 10 metres long.

Did you get:-

1. metre diameter of copper cable a meter long,
2. metre diameter of copper cable 10 metres long,
3. millimetre diameter of copper cable a meter long,
4. millimetre diameter of copper cable 10 metres long.

So for the same material the resistance is proportional to both it's cross sectional area and length. Those neural pathways are now being formed, I can sense it.

Back to the knicker elastic in which when pulled gets longer and narrower (the csa reduces). Copper does have a very very tiny amount of stretch property like the elastic but so small you are unlikly to notice it, however as with the knicker elastic the more it is stretched the longer in becomes increasing the resistance and the less csa so again increasing the resistance. Once released the resistance returns back to its previous value.

The actual strain gauge that uses copper or another metal will be either a wire looped and bonded onto an insulated material or metal foil again bonded to a non metalic surface.

So hopefully you will now have the gap between your knowledge bridged with neural network links from basic theory of resistance to strain gauges and thus transducers.

Rather than filling up your head with more information about strain gauges at this point I will return later in another blog.