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How to make a wide range of voltage to be constand

  1. Jul 31, 2011 #1
    i am working on my project but i do not have much practical experience on connecting the circuit, hence asking for help here.

    ok here's my problem.
    i have a temperature sensor LM35 which its Vout = 10mV/˚C.
    the output of the temperature sensor has to be connected to PLC input.
    when the output is higher than 270mV (27˚C), the nothing will happen.
    when the output is equal or lower than 270mV (27˚C), PLC input will receive 5V constant voltage.

    i have done research with op-amp (comparator) with negative feedback and successfully make it into a positive voltage when the temperature is lower than 27˚C.
    anyhow, the voltage is in a wide range from 5v to 50v, depends on the temperature difference.
    i have also done research with voltage regulator but most of them do not receive such a wide range of input.

    when the temperature is lower than 27˚C, how can i make it constantly 5V to the PLC input?
  2. jcsd
  3. Aug 1, 2011 #2


    User Avatar

    Staff: Mentor

    Welcome to the PF. It sounds like you are on the right track with the comparator circuit, but comparators use positive feedback, not negative feedback. The positive feedback is used to set the hysteresis of the comparator circuit.


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