Hello everybody,
I am very thankful to everyone who gave answers to my previously posted questions.
I need your help one more time.
Previously, I was working on DC excitation bridges but thermal noise is an issue as the number of strain gauges are greater (approx. 30) so which one would be a better option: AC or DC?
If it's AC, could any of you provide me a good research paper to have a look at that could be useful for me?
Looking forward to your reply
Regards,
Awais
AC excitation would be better where you are trying to detect a very small signal in the presence of noise (or temperature drift). You would build a sychronous detector that is synchronised to the AC source driving the bridge - same principle as using a lock-in detector or amplifier.
I found this paper which I think is really useful:
http://ieeexplore.ieee.org.ezproxy.uow.edu.au/xpl/articleDetails.jsp?tp=&arnumber=4998013&matchBoolean%3Dtrue%26searchField%3DSearch_All%26queryText%3D%28%28AC+bridge%29+AND+strain+measurement%29
AC excitation (as people suggested here) is the best way to eliminate both perturbing effects (thermal drifts, thermocouple effects) and 1/f noise terms present at the analog signal. You can build a synchronous detector/ demodulator using an analogue multiplier with a low pass filter or use a dedicated demodulator chip such as AD620.
AC bridges have many advantages, but just one word of caution regarding inductive and E-field crosstalk that can occur in multichanel measuring systems such as Yours. Make sure Your amplifiers use a syncronized AC bridge excitation signals and use proper shielding and grounding of longer wire runs. This is also very important for inductive AC transducers such as differential transformers. It can be a mess to iron out these problems if not doing it correctly to begin with.
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