Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Voltage drifting

Voltage drifting

Voltage drifting

I have a  strain gauge connected to a metallic rod hinged at one end. The system detects the bending of the beam(when I press it with my hand, as seen by increase in output voltage) but even before touching the rod, as I bring my hand close to the rod the output starts increasing (offsetting from zero point) and decreases to normal when I move away from it. The change in output voltage due to this offset is greater than that caused by bending. It seems almost as if the grounding of the system changes. I tried insulating and shielding the circuit, wires and beam(with aluminum foils, tapes etc) but still the systems offsets as soon as my hand or body comes close to the rod. I am trying to understand the reason for it and if there‚Äôs a way to solve this problem.

RE: Voltage drifting

Are you grounding yourself while running these trials?  Is it the same ground as the strain gauge?  Is the rod sensitive enough to thermal effects such that bringing your hand within close proximity induces measurable strain?


RE: Voltage drifting

PSE: I did not ground myself to the rod because that is the way it will be used in the field, the person pressing the rod will not be able to ground himself to the rod every time he presses it. However apart from the person pressing the rod, everything else(strain gauge circuit, power supply, rod ) has a common ground. Also I do not know how sensitive the rod is to thermal effect( but I believe its not that sensitive that bring hand close to it would change its temperature or measurable strain)

RE: Voltage drifting

My background is not electrical but I am still suspicious of separating the operator from the same ground as the device.  Any way to test performance with a common ground?  If it works you might be able to design a ground location on the equipment for the operator to contact while running a test.


RE: Voltage drifting

I think you need to make sure the strain gauge instrumentation works correctly when hooked up under lab conditions. Also, make sure your connections are good.  Is it possible that you might have an "open circuit"?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close