Electrostatic Discharge protection on high sample rate I/O line

Discussion in 'The Projects Forum' started by StudentResearcher, May 3, 2013.

  1. StudentResearcher

    Thread Starter New Member

    May 3, 2013
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    I am working on a project to produce a pulsed detonation engine. I am using a spark plug to ignite the fuel mixture and measuring the wave speed using capacitive discharge microphones sampled at 25 kHz. I am concerned that the high voltage signal produced by the spark plug may travel down the I/O, 5 volt, and ground lines running from the microphones to the DAQ. I have done what I can to shield the microphones from the spark but there is the chance that the engine temperature could erode the insulation and form a closed circuit with the mics.

    I originally looked into TVS diodes but found that they cause signal degradation on high sample rate sensors. Do TVS diodes exist that would suit my experiment?

    A colleague has suggested using capacitors in the pico-Farad range on all of my lines into the DAQ. I have tried 222pF, 15pF, and 1pF capacitors and found that the microphones appear to be unresponsive with the 15pF and 1pF capacitors when I observe the voltage signal produced. How do I go about finding the proper sized capacitor for my application?

    Are there alternatives for ESD protection on high sample rate signals? I am worried that the spark duration will overload the capacitors if there is a closed circuit. I am working on a very small budget since it is being funded out of my own pocket.

    Thank you very much for your assistance.
     
  2. #12

    Expert

    Nov 30, 2010
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    Have you thought about input protection diodes like this?
     
  3. StudentResearcher

    Thread Starter New Member

    May 3, 2013
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    I have very limited understanding of ESD protection equipment. What allows this to not interfere with my high sample rate I/O line when TVS diodes cause signal degradation?
     
  4. #12

    Expert

    Nov 30, 2010
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    If the signal completely collapses with 1pf in parallel with it, this is a foolish suggestion. Sorry.
     
  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Just out of curiosity, what is the engine temperature?
     
  6. StudentResearcher

    Thread Starter New Member

    May 3, 2013
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    Pulsed Detonation Engines typically melt aluminum after a few minutes of operation. I'm trying to avoid this during testing by limiting it to short duration runs. I am not certain how rapidly the temperature will climb per pulse. There is a thermo-couple attached and I intend to avoid going over 4-500 degrees.

    I put the 1pf capacitor in series with the signal line. If it needs to be in parallel for ESD protection I will test the signal input again. It just seems to me that the capacitor in parallel wouldn't stop the ESD from reaching the DAQ.
     
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