How are we able to know the variable of a Strain Gauge?

Hi, for a school-project I need to measure the weight of an object.
Therefore I am using an old weight-scale.
The component wich includes 2 Strain Gauges has 2 seperated wires coming out and 1 other wire conected to the Ground.

Because we can't find something changing when we measure differend kinds of things, (for example the changing resistor-value) we hope that you can help us.

The two wires coming out of the Strain Gauges are connected to an Amplifier (TL081CP).
The scale itself is a KRUPS TYP 841 ; 871-B


Whats on pin 6 of the opamp when you apply weight ? The resistance change is likely to be very small, and the circuit will be connected in a bridge with another pair of resistors, a bit like this circuit.

This was for another job, delete R1 and D and you have a simple (very) bridge sensing amplifier. You need to drive the bridge from a stable source.
zupperzipper (author)  steveastrouk7 years ago
Thanks a lot...
We couldn't see anything (a really small change in value) on the Multimeter,
but after using the oscilloscope we discovered that the scale 'transformed' a certain frequency...
The heavier the object, the more periods we saw on the screen.

 Thank you!