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Need Help for Temperature Control System

Discussion in 'Electronic Basics' started by Thomas Ritche, Aug 2, 2003.

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  1. Hi All

    I want to construct a Temperature Control System myself.
    I want to use a Thermocouple to sense the Temperature.
    (Thermocouple generate 0 mv at 0 degree celcius and
    150 mv at 300 degree celcius)
    I want to control the temperature range between 0 to
    300 degree Celcius.
    I want to use analog system and controls.

    Can any tell me about a web site which showing a complete
    circuit diagram of Temperature Control System which I want.

    Thanks
    Thomas Ritche
     
  2. Fred Abse

    Fred Abse Guest

    Those temperatures are actually the difference between the "hot" and
    "cold" junctions. This means that if the temperature you want to measure
    is 0 Celsius, and your instrument (where the "cold" junction normally
    lives) is at room temperature, say 20 Celsius, you won't get zero, you'll
    get minus 20 reading. You need to incorporate circuitry that will
    compensate for the "cold" junction temperature.
    You could just use an op amp to amplify the thermocouple voltage to a
    level where you can use a comparator against a voltage derived from a
    calibrated potentiometer. That'll give you simple on-off control, or
    replace the comparator with a summing amplifier which will give voltage
    proportional to deviation from set point. If you want integral and
    derivative terms, things get complicated. There are (or used to be, it's
    been a while) devices that do the whole CJ comp / PID thing on one chip.

    Just Google. You'll probably find ready made controls which are quite
    cheap.
     
  3. Here is a start in understanding how to get a linear temperature
    reading out of a thermocouple:
    http://www.national.com/an/AN/AN-225.pdf

    A PI controller is little more than an inverting opamp with an R and a
    C in series in the feedback path. Of course the values have to be
    tuned to match the system being controlled.

    The output depends entirely on what you are controlling.
     
  4. Bob Huish

    Bob Huish Guest

    DS1620
    Measures temperatures from -55°C to +125°C
    in 0.5°C increments; Fahrenheit equivalent is
    -67°F to +257°F in 0.9°F increments

    He wants 0 to +300C

    Any other ideas?

    I need one to measure a solar cooker project.

    Bob Huish
     
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