thermistor protection

Discussion in 'General Electronics Chat' started by roadey_carl, Jun 10, 2010.

  1. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
    116
    5
    Hey folks,

    I've made a adjustable duel thermometer using a lm393n. I got a pack of thermistors but they don't come protected against liquids... is there any kind of resin I can dip them in without it changing the sensitivity of the thermistor to much?

    Thanking yourselfs!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You know that an LM393 is a dual comparator, right?

    You could use conformal coat to protect them, or clear lacquer. It will reduce their sensitivity a little, but not too much. They simply won't respond quite as quickly.
     
  3. Bychon

    Member

    Mar 12, 2010
    469
    41
    I dipped one in clear epoxy and then put shrink tubing on it (and the cable it was attached to) before the epoxy hardened. That slowed the response time down from a few seconds to most of a minute, but it was for a water bed heater where time is considered in terms of hours.
     
  4. roadey_carl

    Thread Starter Active Member

    Jun 5, 2009
    116
    5
    I think maybe the lacquer might do the trick then... if I use one thats already incased it makes the relay judder for several seconds ...even if I adjust the hysteresis. But it seems to work fine with one that isnt incased!
     
  5. Bychon

    Member

    Mar 12, 2010
    469
    41
    This is a perfect example of, "post a schematic to get good answers quickly".
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    The problem with your "juddering" is because you do not have hysteresis in your comparator circuit.

    If you would post a schematic diagram of your circuit, we could tell you how to fix it to avoid the "juddering".
     
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