Thermistor operation

Discussion in 'The Projects Forum' started by Oxbo Rene, Jan 26, 2013.

  1. Oxbo Rene

    Thread Starter AAC Fanatic!

    Feb 20, 2009
    Hi guys, long time ........
    I am working on a new project and need some clarification on a thermistor's operating characteristics.
    My friend has built a fog machine and wants me to design it for an Industrial application, I have managed to draw it's circuit.
    And, the way I see it, the thermistor is a "short" until the atomizer heats up, thus heating thermistor to a point that it becomes an "open".
    That's the best way I see it operating.
    However, I look up "thermistor" and it's definition is that it is an "open" until heated to a spec temp then becomes a "short".
    Perhaps I'm dealing with a totally diff component that I don't know the name of.
    I'm sure it's not a thermocouple.....
    But, thought I'd pass this by you guys and see if you can clarify the component for me, etc, etc .......
    It only has two terminals and is mechanically mounted on the atomizer, that gets pretty hot etc ........
    See attached drawing.....
  2. antonv

    Active Member

    Nov 27, 2012
    Negative temperature coefficient (NTC) thermistors' resistance goes down non-linearly as temperature goes up. They are used as temperature sensors and are not designed to pass large currents. Positive temperature coefficient (PTC) thermistors' resistance goes up with temperature, usually abruptly and can be designed to act like fuses: open when hot, short when cool.
    In-rush current limiters are like NTC thermistors but their resistance changes more abruptly and they are designed to handle larger currents. They have a high resistance (but are not "open") when they are cool and change to a low resistance when hot.

    There may be other similar devices out there too..
  3. #12


    Nov 30, 2010
    Your logic is perfectly good. You just didn't know the name of it. Look for NTC inrush limiters or start surge limiters. There are other ways to set a start delay time, but the NTC surge limiter is the simplest and cheapest way to do it.
  4. Oxbo Rene

    Thread Starter AAC Fanatic!

    Feb 20, 2009
    Alrighty now ! !
    I think I'm looking at a PTC Thermistor......
    Thanks so much for your help .......