Wheatstone bridge noise issue

Discussion in 'The Projects Forum' started by thomasrj, Jan 20, 2012.

  1. thomasrj

    Thread Starter New Member

    Jan 20, 2012
    I am working with a standard quarter-bridge strain gauge signal conditioning circuit. My excitation voltage is 5V DC, and my resistors are 350 ohm. I am amplifying the signal with an AD620 in-amp. I cannot get clean data, presumably due to all of the noise sources. I am using a load frame that is powered by a massive hydraulic unit that is accompanied by an even more massive transformer, several UPS's, control boxes, digital controllers, etc. Relocating the signal conditioning circuit is not a practical option.

    What is the best method of attenuating the noise in the circuit? I am assuming a lowpass filter (or several lowpass filters). I have also heard of driving the reference on the in-amp with an op-amp (I have some LF412s) or a shunt voltage reference (I have a few LM4040s) to get a cleaner reference. Any suggestions or circuit diagrams would be greatly appreciated, since I have no electronic background (I am a civil engineering graduate student working on instrumentation for my thesis).

    Also, if I use a lowpass filter, what cutoff frequency should I aim for? I am assuming since my signal is DC, I should be aiming for as low as possible, but I could be misguided.

    Thanks in advance!
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    Can you post your schematic. Also do you have proper shielding for the wires and electronics. How is your power supply. Is this clean? In such a system you will have endless posebileties for noise. Let us start with inspecting your schematics first.