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  • FET voltmeter sought

    From amdx@21:1/5 to Peter Percival on Sat Sep 24 06:25:40 2016
    On 3/14/2016 7:40 AM, Peter Percival wrote:
    Reinhard Zwirner wrote:
    Peter Percival schrieb:
    Suppose a fellow wished to buy a high input impedence voltmeter
    rather accurate for low voltages (< 10v, say) but not expensive. Any
    recommendations?

    What do you mean with "high"? Digital multimeters normally have an
    input impedance of 10 MOhms; the lowest measuring range is 0.2 volts.

    50 Mohms down to 0.01 volts. Is that too much to ask?

    Best regards

    Reinhard



    You could put a 40M resistor in series and divide the reading by 5.
    0.002V x 5 = 0.01V So, I guess you would need a 4-1/2 digit multi meter.
    Or is that 3-1/2?

    Mikek

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  • From Phil Hobbs@21:1/5 to Peter Percival on Mon Mar 14 09:06:49 2016
    On 03/14/2016 08:40 AM, Peter Percival wrote:
    Reinhard Zwirner wrote:
    Peter Percival schrieb:
    Suppose a fellow wished to buy a high input impedence voltmeter
    rather accurate for low voltages (< 10v, say) but not expensive. Any
    recommendations?

    What do you mean with "high"? Digital multimeters normally have an
    input impedance of 10 MOhms; the lowest measuring range is 0.2 volts.

    50 Mohms down to 0.01 volts. Is that too much to ask?


    A 50 M precision series resistor (probably a series combination),
    measuring on the microamp range. You have 1 pA resolution there, which
    is 100 uV. You do have to watch the burden voltage, of course.

    Cheers

    Phil

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  • From Peter Percival@21:1/5 to Phil Hobbs on Mon Mar 14 13:19:16 2016
    Phil Hobbs wrote:
    On 03/14/2016 08:40 AM, Peter Percival wrote:
    Reinhard Zwirner wrote:
    Peter Percival schrieb:
    Suppose a fellow wished to buy a high input impedence voltmeter
    rather accurate for low voltages (< 10v, say) but not expensive. Any
    recommendations?

    What do you mean with "high"? Digital multimeters normally have an
    input impedance of 10 MOhms; the lowest measuring range is 0.2 volts.

    50 Mohms down to 0.01 volts. Is that too much to ask?


    A 50 M precision series resistor (probably a series combination),
    measuring on the microamp range. You have 1 pA resolution there, which
    is 100 uV. You do have to watch the burden voltage, of course.

    Cheers

    Phil

    Thank you.

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  • From JW@21:1/5 to peterxpercival@hotmail.com on Mon Mar 14 09:39:53 2016
    On Sat, 12 Mar 2016 15:53:37 +0000 Peter Percival
    <peterxpercival@hotmail.com> wrote in Message id: <nc1e25$eli$2@news.albasani.net>:

    Suppose a fellow wished to buy a high input impedence voltmeter rather >accurate for low voltages (< 10v, say) but not expensive. Any >recommendations?

    If you want fairly cheap:
    HP 3478A has an input impedance of >100Gohm on it's 3VDC or less ranges.
    HP 3456A has an input impedance of >100Gohm on it's 10VDC or less ranges,
    but size is a bit large.

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