Connect with us

AC resistance bridge

Discussion in 'Electronic Design' started by [email protected], Jun 25, 2007.

Scroll to continue with content
  1. Guest

    Does anyone know of a SMALL and HIGH PERFORMANCE commercial resistance
    bridge similar to the
    SRS SIM921C (but preferably smaller).

    I'm looking for 1ppm short term stability and the voltage at the front
    end is probably going to be less
    than 10nV. 8-(

    Thanks for any suggestions!

    Best regards,
    Spehro Pefhany
     
  2. Guest

    P.S. The primary problem with the SRS product is the (lack of)
    stability. Excitation will
    be a relatively healthy 10uA or so, resistance is in the 1K range.
     
  3. Tim Williams

    Tim Williams Guest

    10uA * 1000 = 10mV, not nV???

    That's not hard with any sufficient op-amp, as you already know, so, I'm
    confused.

    I was checking out the manual to a piece of equipment at work, an HP high
    resistance/low current meter (I forget the number), it uses a parametric
    method -- essentially, the capacitive unbalance (and therefore change in
    oscillating frequency) of some small voltage across some very special diodes
    (probably controlled capacitance more than anything else). Frequency being
    easier to read than microvolts and nanoamps.

    If you're serious about nanovolts, that sounds like SQUID territory to me.
    Isn't thermal noise on a chunk of copper about that much?

    Tim
     
  4. What's +/-0.5ppm of that?
    For 1K at 300K it's about 4nV/Hz^0.5 Don't need much bandwidth. There
    are interesting issues with stray capacitance, even at ~1Hz
    excitation. It would be nice to find something off-the-shelf, but if I
    must...


    Best regards,
    Spehro Pefhany
     
  5. Not that hard to build yourself. An AD630 does
    this job. The datashhet has a few application
    notes.

    Rene
     
  6. Thanks, Rene, I'll look at that in detail. I think I'll need a
    transformer at the front end though. Most of the commercial designs
    seem to use multiplying DACs fed with quadrature signals to deal with
    the phase shift.


    Best regards,
    Spehro Pefhany
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-