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gigohm resister uses

Discussion in 'General Electronics Discussion' started by C13isotopes, Jul 12, 2012.

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  1. C13isotopes

    C13isotopes

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    Jul 12, 2012
    gigohm resisters are used in measuring low currents, e.g. 10-9 to 10-12 amp signals in some mass spectrometers. The gigohm resistors are used in preamplifiers connected to the detector head sensor leads, converting the small currents to voltages which are amplified by VRE (vibrating reed electrometers) or similar circuits. GJ
     
  2. David Sparks

    David Sparks

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    Jul 12, 2012
    I used Hi-Voltage probes from Tektronix with a 1 Gigaohm input, as a differential pair to measure the 30,000 volt charge on the capacitor bank-based surge generator at a company I worked for. The probes were rated to 40KV, and when I opened them up I found two 500 megohm 1% ceramic resistors in series made by Dale mfg, each one rated for 20KV max. Because this was a custom ATE setup and not for a Fluke DVM, I had to disable the internal trim resistor in each of the 2 probes. I fed the resistors to a small board with 2 CA3140T op-amps (each op-amp has a 1.5 Tera-ohm input impedence). Both input's had a 100K 1% resistor to gnd (which divided the input by 10,000 - so +30KV showed up as +3 VDC at the pc), which fed a AD524CN diff op-amp, which fed a SSM2142 600 ohm balanced line driver with about a 50 foot run to my pc with an analog input card.
    I used a duplicate set of probes and circuit's to measure the charge current for the capacitor's, to check for anomalies during charge-up. 30% of my code was just to check for all the thing's that might go wrong!
    Giga-ohm resistors are mandatory when you have a hi-voltage source, common grounded or not, whether you are measuring volts (or a voltage "field", such as a lightning detector) or amps. I found this differential probe technique to be very accurate and stable as well. Added software can trim the accuracy to about .1%!
     
    Last edited: Jul 12, 2012
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