what is the following circuit doing in strain gauge conditioner

Discussion in 'The Projects Forum' started by CrackJack, Nov 7, 2010.

  1. CrackJack

    Thread Starter Active Member

    Aug 7, 2009
    Hello Everyone,
    I found this circuit inside a signal conditioner amplifier for a strain gauge. This circuit is preceded by an instrumentation amplifier INA 128, and followed by a 2 pole butterworth filter.

    Can anyone please explain me how this circuit would operate ?? Like is it a simple difference amplifier/ non-inverting amplifier or what it is doing???
    the Vcc/Vee is +/-8 V

    thanks in advance. please check the new attachment, i wrongly posted the incorrect circuit diagram!!! sorrry
    Last edited: Nov 7, 2010
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    I don't see the 'preceded by' part. It needs to be taken in context to the rest of the circuit, likely ending up being a bias offset or zeroing component.
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    It can be instructive to look at the entire circuit. For instance, the data sheet for an INA128 says that pin 5 is the reference input pin. On page 10, the data sheet talks about using the reference pin to accomplish an offset adjustment.

    The bit with the CA3130 op amp is a means of placing a voltage on pin 5 of the INA128 to slew the output somewhat plus or minus. Normally, the load cell would be unloaded, and this adjustment made to cancel any mechanical or electrical offsets from zero.
  4. CrackJack

    Thread Starter Active Member

    Aug 7, 2009
    Guys, thank you for the information, I shall send you the entire circuit diagram, once I make it. Actually, i have the signal conditioner hardware with me, and i am tracing it backwards using DMM.