Wheatstone bridge offset-nulling circuit

[nitronick]

Hi all, I’m making a simple cantilever beam measurement system using 2 strain gages (120Ω).

The two gages make up one leg of my Wheatstone bridge; the other leg will be made up using 120Ω resistors.

Because of tolerances etc I will need to null the system before I add any weight to the end of the beam.

So how is best to go about this, I’ve been looking about on Google but all I can find is to add a variable resistor into the circuit, but I’m not sure where and what value to use.

Any help will be much appreciated.

 

[schip666!]

Probably about 2x the tolerance of your devices. You're mostly nulling-out the error, which is the difference in the response of the two sensors and any temperature related fluctuations. But an experiment might be the best way to figure it out...

 

[sophiecentaur]

You could start by measuring the actual resistances of the strain gauges. If there is a difference of n% then the two fixed resistors could be picked to have the same ratio. Only a small value of variable resistor would be necessary then. But the numbers would depend on what your measurements tell you.