input impedance...?

Discussion in 'Homework Help' started by KingKK, Feb 13, 2007.

  1. KingKK

    Thread Starter New Member

    Feb 13, 2007
    2
    0
    hi, i'm a dumb newbie!

    I need to find a suitable transceiver for transmitting a voltage signal (0-5 Volts) from a sensor. From the sensor's datasheet I read the following: "Please note connection considerations: Analogue output load is min. 10 kOhm, max. 20 nF."

    This means that the sensor has to be connected to a device (load) with an input impedance of at least 10 kOhm, right? But why is the maximum value given in farads?

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    That's 20 nanofarads. 2.0^-10 farads. That means that, in addition to the necessary load resistance, you can have problems if the capacitance is too great - like in a long run of coaxial cabling.

    What distance do you need to send the signal over, and is it a DC level, or some signal frequency that goes from 0 to 5 volts?
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Beenthere,

    Doesn't 2.0^-10 end up being the same as 200 picoFarads?

    hgmjr
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    All right, 2.0^-8 farads. Having been brought up on micrmicrofarads, nanofarads still give me fits on occasion (saving face here).
     
  5. KingKK

    Thread Starter New Member

    Feb 13, 2007
    2
    0
    Oh, that's what it means. Should have guessed it.
    Still, thanks a lot.

    It's a DC level signal and I only need to send it a few inches (from the sensor to the transmitter). And I'm using two separate wires, so capacitance shouldn't be that big of a problem?
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    Won't be enough to measure. I'd twist the wires together to minimize stray noise, though.
     
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