Building a fuel control circuit

Discussion in 'General Electronics Chat' started by Crclarke, Jan 25, 2016.

  1. Crclarke

    Thread Starter New Member

    Jan 25, 2016
    6
    0
    I am trying to design a basic analog fuel control circuit, I can almost see it but I can't quite put it down on paper... My electronic engineering skill is at about a 6.5 out of 10.....

    Anyway, this is what I need to do:

    I have an O2 sensor with an ideal voltage of 500mv, and a 3 wire control valve. I need a design that will open the valve at a reading of less than 500mv and close the valve at a reading of more than 500 mv. It would also be nice if it was static at 500mv. It seems so simple but I can't seem to grasp it. My initial idea was a Zener diode and a small amp to a 2 position relay, but I don't think it would work well..... Would appreciate some ideas
     
  2. sailorjoe

    Active Member

    Jun 4, 2013
    361
    64
    What are the three wires on the control valve for, please? Needed for a complete answer.
    It is correct that this is all powered by a car battery?
    If it was me, I would start with a comparator IC that would compare the 500mv signal to a 500mv fixed reference. I would add a little hysteresis to the circuit with feedback. That would prevent the valve from oscillating rapidly right at 500mv input. The output from the comparator would feed a transistor driver circuit that would connect to the control valve.
    Search for "comparator circuit designs". Find something that fits in a car, and ask more questions after you tell us about you valve.
    Welcome to AAC!
     
  3. Crclarke

    Thread Starter New Member

    Jan 25, 2016
    6
    0
    It is a standard 3 wire valve, middle wire is ground, one wire opens valve and other closes the valve, it will operate on a 12v dc system, it is for a propane blast furnace
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    8,483
    1,924
    Can you post a link to its spec? It helps to know its full electrical properties, particularly coil resistance/current ratings.
     
  5. Crclarke

    Thread Starter New Member

    Jan 25, 2016
    6
    0
    After some research, I think a comparitor circuit is exactly what I need. I can use a comparitor to essentially make a low level and a high level alarm circuit, low level set at 475mv and the high level set at 525mv, sending the output to a couple of control relays. The low level will activate the relay to open the valve and the hi level will activate the relay to close the valve, also leaving a 50mv dead zone at the nominal voltage. Sounds like it could work. Agree?

    Thanks sailer joe for the idea!
     
Loading...