Agilent U1253B - curious input impedance problem.

Discussion in 'General Electronics Chat' started by BrianH, Sep 29, 2012.

  1. BrianH

    Thread Starter Active Member

    Mar 21, 2007
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    Hi everyone,

    I have recently been experiencing some problems whilst taking some high voltage measurements with an Agilent U1253B and a high voltage probe. This has lead me to investigate its claimed input impedance. If you're interested, have a read and let me know what you think! If you can provide any explanation your thoughts would be most welcome:

    http://www.brianhoskins.co.uk/website/agilent-u1253b-input-impedance-problem/
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    What is the model number of the insulation tester?
     
  3. BrianH

    Thread Starter Active Member

    Mar 21, 2007
    43
    0
    Hi Ron,

    That's a pretty good question actually! There doesn't seem to be a model number or even a manufacturer printed on it. When I get back to the office on Monday I'll look it up on the asset register.

    I don't doubt it's readings though - it's a calibrated instrument and provides reliable measurements in lots of other applications. Also, the apparent 5MΩ input impedance of the Agilent U1253B would explain some voltage measurement inaccuracies I've recently experienced, which is actually what started this whole thing.

    I don't know why the insulation tester reports a different input impedance to the multimeter though. That's weird.

    Brian.
     
  4. BrianH

    Thread Starter Active Member

    Mar 21, 2007
    43
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    Oh wait, just found a manufacturer printed on the unit - it's an AVO. Still no model number though, will have to get back to you on that.
     
  5. BrianH

    Thread Starter Active Member

    Mar 21, 2007
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    0
    Someone just pointed out a note in the manual to me. This explains my problem.

    It's rather silly though - they're basically saying it's a 10MΩ input impedance for the VDC range, but only if you're measuring between -2V and +3V!

    Check it out:
     
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