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Circuit Design

  1. Mar 21, 2008 #1

    I am making a circuit which runs a large current through a material at intervals, heating it, which then temporarily stops to make a resistance measurement. Each individual circuit is not an issue in itself, nor the timing of it since I have a computer interface which can grab analog values and produce digitial 1s.

    The issue I need to address is the interference of each circuit's operation with the other's. Do I need to just put a power transistor on each series of connections to the material I am testing for each part of the circuit, or do I need to do something more complicated?

    So in other words can I just, let's say, turn on the circuit which measures resistance, by providing an appropriate input to that transistor(or FET) and turn off the section which provides the heating current by providing another input to the other controlling transistor, without the heating circuit significantly interfering with the measuring circuit or vice-versa?

  2. jcsd
  3. Mar 21, 2008 #2


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    Staff: Mentor

    Can you just do both simultaneously? Can you measure current and voltage being applied to the material as you are heating it?
  4. Mar 21, 2008 #3
    Well wouldn't that the changing current from my heating circuit, cause the voltage drop to be different across the material, which would in turn provide a different value than expected for my four-wire kelvin circuit, which is simultaneously hocked up to the material. Perhaps I can use relays, what is the average switching speed on those guys?

  5. Mar 23, 2008 #4


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    Staff: Mentor

    Small relays bounce for a few ms, typically.
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