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Ask an Expert Forum Rms converter to match HP3400A?
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Rms converter to match HP3400A?

ggabe
ggabe over 2 years ago

What is your suggestion to match the specs of the HP3400A AC millivoltmeter’s rms converter with analog parts available today? I’m drawing a line to exclude AD conversion and digital rms calculation. So it stays analog.

Below is the spec sheet:

image

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  • ggabe
    ggabe over 2 years ago in reply to phoenixcomm +4
    My motivation is “restoration”. This is the only analog instrument I have. I like the retro vibe of the mirrored gauge. Three different rms converters in my parts box already, time to make them work all…
  • scottiebabe
    scottiebabe over 2 years ago in reply to scottiebabe +4
    .
  • scottiebabe
    scottiebabe over 2 years ago in reply to phoenixcomm +4
    .
Parents
  • scottiebabe
    scottiebabe over 2 years ago

    .

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  • scottiebabe
    scottiebabe over 2 years ago in reply to scottiebabe

    .

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  • ggabe
    ggabe over 2 years ago in reply to scottiebabe

    Two more lesser known facts about the 3400A:

    1. The input stage uses a miniature nuvistor tube. Seems reliable JFET solution was not available back in the days, when it was new in 1964.

    2. Chopper amplifier used CdS photo resistors + neon strobe lights to implement “fast” analog switches.

    The follow-on model, 3400B got a JFET replacement of the nuvistor, among many other modernization, like chopper stabilized opamp, and the bandwidth went up to 15MHz. Thermocouples stayed.

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  • phoenixcomm
    phoenixcomm over 2 years ago in reply to scottiebabe

     scottiebabe && ggable Kynix seems to have the LT1088 in stock new-old-stock.  

    scottiebabe:: Ata Girl: Wonderfull world of randomness ~~ Cris 

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  • michaelkellett
    michaelkellett over 2 years ago in reply to phoenixcomm

    It's a nice chip but (almost) unobtainable. Best offer on Ebay is $55 each.

    Gives me  a performance goal for my thermistor and pcb based solution !

    MK

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  • Jan Cumps
    Jan Cumps over 2 years ago in reply to michaelkellett

    TI has a design note for etching your resistors in the PCB copper. Then trim it with your tongue in the right angle Slight smile

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  • michaelkellett
    michaelkellett over 2 years ago in reply to Jan Cumps

    2 square inches for a 0.5W resistor (10A, 50mV example in table 1) - no wonder real resistors caught on !

    MK

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  • scottiebabe
    scottiebabe over 2 years ago in reply to phoenixcomm

    .

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  • phoenixcomm
    phoenixcomm over 2 years ago in reply to scottiebabe

     scottiebabe  This *** is just over the dam top!! You may be one of us few that can pull stuff out of nowhere.. 

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  • phoenixcomm
    phoenixcomm over 2 years ago in reply to scottiebabe

     scottiebabe  This *** is just over the dam top!! You may be one of us few that can pull stuff out of nowhere.. 

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  • javagoza
    javagoza over 2 years ago in reply to phoenixcomm

    totally agree this time

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