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Voltage meter load

  1. Jul 24, 2014 #1
    Hi every one,

    I have a HP 34401a meter that is causing some issues with a high impedance sensor input.

    when I place only the ground wire ( black ) to the input circuit ground, the sensor reading jumps quiet dramatically, this does not happen if i place only the Red wire.

    I have tried an AMPROBE 30XR-A with no issues, but it is not sensitive enough for this.

    can any one think of why this could happen. I can provide schematics of the input circuitry if needed, the sensor input is connected to an instrumentation amp.

    many thanks.
  2. jcsd
  3. Jul 24, 2014 #2


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    Science Advisor

    Are you measuring Voltage?

    Do you have two leads to make the measurement?
    What happens if you connect both leads to the transducer?

    Have you selected the input resistance in the Measurement Menu?
  4. Jul 25, 2014 #3

    Yes two leads, when both are connected i see a rise in sensor reading from the analyzer, and when i take both leads off the reading drops. i can recreate this with only the ground lead. i have selected between 10M and >10G ohms input resistance on the meter, both with same results. it feels as if the meter is at a slightly higher reference ground, and it is effecting the analyzer circuit. but i am not sure if that is possible with only one lead.
  5. Jul 25, 2014 #4


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    Science Advisor

    We really need more information here.
    What does the sensor measure. We need to know the make / model of the sensor.
    What instrument, make / model, is receiving the signal from the sensor.
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