Hello Muhammad,

Refer my answer to your other question related to the DAC output. First ensure that your bridge excitation (the Drive Signal) is stable enough or not. The bridges do have some "CREEP" and many factors are associated with it. The first, as I mentioned is the excitation, other is the temperature stability or drift and third is the mechanical assembly itself. But from the description of the problem in your question it is not clear as what temperature changes the gauges are exposed to? But as I have stated in the second answer, first stabilize your drive signal then concentrate on the drift in the output. Certainly, you shall see that this drift is minimized.

And lastly, take care of your "TINY" offset voltages in the bridge amplifier. These play HAVOC!!!!

Best Luck!

Hi Prasanna,

Thankyou for your valuable suggestion.

Regarding the excitation signal, yes it is stable. For the temperature drift, as i set my bridge to the zero level(manually stetting the variable resistors). It leveled for some time but then it became unbalance again.

I am thinking of using a voltage subtractor.

Regards

Awais

Could you please confirm if the elements on the bridge as arranged are all having similar temperature characteristics.

Take a look at this paper. It might help.

http://connection.ebscohost.com/c/articles/23073192/temperature-compensation-wheatstone-bridge-magnetoresistive-sensors-based-generalized-impedance-converter-input-reference-current

Hello Muhammad,

if your problem is really caused by temperature, it can occur during several reasons. The first is the temperature stability of elements creating the brdge. Use that which have the lowest temperature coeffitint. The second one can be parasitic thermocouples on contacts of the bridge elements. Use the same materials or materials with low thermoelectric voltages for these connections. If the connections are solded, use a special soldering alloy with low thermoelectric voltage with contacted materials. The third reason can be caused by the thermal drift of the used zero indicator amplifier. Use a so called zero drift amplifier (chopper stabilized), e.g. AD8628 or similar for this purpose. Whem balancing your bridge, start with the compensation of the zero indicator voltage and current offsets. Then balance the bridge. After such balancing, the bridge should not be sensitive to the drift of the exciting voltage, but mention that eventual changes of this voltage cause the change of the measuremnt sensitivity.

I wish you success in your activity.

With the best regards

Ivan.

I have a doubt Muhamad.

What is your bridge configuration?

1) Are you using all gauges in the bridge or ,

2) From your explanation above, it seems that you are using some fixed resistive elements as part the bridge alongside the gauges. If that is the case, certainly you have temperature drift problem. So pay attention to the tempco (the Temperature Co-efficient) of these element.

3) Ideally, such a configuration is not recommended. Always use four matched gauges in your bridge configuration rather than using some fixed elements and the gauges. This is where I suspect your problem of DRIFT lies.

4) If you have all four elements in the bridge as the gauges, then these will have same tempco and the drift from one arm/section will cancel out with the other.

Hope this helps you sort out the problem!

-Prasanna Waichal