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FP 54 amplifier

Discussion in 'Electronic Design' started by Allan Adler, Aug 22, 2003.

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  1. Allan Adler

    Allan Adler Guest

    On p.348 of Ramsey's book, Molecular Beams, he mentions something called
    a FP 54 amplifier. What is that? If it has gone the way of the dinosaur,
    what would be a modern replacement?

    Ignorantly,
    Allan Adler


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    * Disclaimer: I am a guest and *not* a member of the MIT Artificial *
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  2. Phil Hobbs

    Phil Hobbs Guest

    The FP-54 was an electrometer tube from the 1930s. You're using this for a Langmuir
    probe or something like that, are you?

    If so, then depending on the sensitivity you need, you can use a CMOS op amp with a
    back-to-back parallel pair of diode-connected bipolar transistors in the feedback
    loop where the resistor usually lives, and connect the probe to the summing junction
    through a biggish resistor (not big enough to drop more than 100 mV at your design
    current, but big enough to protect the amplifier input. This will give you a
    logarithmic output. There are more accurate ways of doing it, if you have money to
    spend or a circuits guy available to help.

    Cheers,

    Phil Hobbs
     
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