• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 47 subscribers
  • Views 1000 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AC with Wheatstone Bridge (Auto-Zero Bridge Offset)

1985518
Prodigy 100 points


Need some help understanding a Wheatstone bridge application.  I am having a bit of trouble understanding the theory.

Currently, I have a torque meter that utilizes a full-bridge Wheatstone bridge.  It is an old torque meter and the gauges have aged and drifted.  There now exists an approximately 2.2mV/Vdc offset on the bridge at no load, but that offset may change (for intents and purposes, it is "unknown").
What I would like to do is be able to measure the change in voltage when a load is applied to the bridge, while stripping out the fixed bridge offset.
An idea I had was to excite the bridge with AC.  I was hoping this would cause the true displacement signal to be encoded in the amplitude of the AC signal (basically, an amplitude modulated signal), while the DC offset would just appear as a DC offset on the AC waveform.
Does my idea sound plausible or is there a better way to automatically remove the DC offset?
  • 0
    TI__Guru**** 166216 points

    The bridge will have the same zero offset for AC or DC.
    The 'zero' output need to be stored and subtracted from loaded measurement.
    If the zero can drift, then new zero offsets need to be taken periodically.

  • 0 in reply to Ron Michallick
    Prodigy 100 points

    Yeah, you are correct.  The zero-load offset of the bridge is due to resistor drift over time, so the bridge is unbalanced at zero load.  The offset appears indistinguishable from a true applied load, so the bridge offset will have to be measured periodically.  I see no way to automatically balance out the bridge offset while the bridge is loaded (in use).

    Thank you for your assistance.