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Help setting up OMRON Temp Controller

Discussion in 'Electronic Basics' started by MarkMc, Jul 13, 2005.

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  1. MarkMc

    MarkMc Guest

    Hi

    I just got an OMRON temperature controller, model number EJCS-R1KJX.
    The manual which comes with it is pathetic - a duff translated affair.

    I want to use this unit to control fermentation temperatures for my
    home brewery. This involves switching on a cooling source if too hot,
    and switching on a heatin source if too cold to keep a stable
    temperature.

    I have a couple of questions about setting up the controller.

    I'm not sure if i need to use on/off mode or PID - I don't know what
    PID actually is. Can somebody explain?

    The unit provides two relay outputs one for control and the other for
    alarm. I assume I need to provide my own relay contact
    protection/suppression?

    Also, I accidentally bought the wrong model. I wanted the RTD model
    but got the thermocouple model - eBay one off, so no chance to change
    it. I know nothing about thermocouples. It looks like type K's are
    easy for me to get, but I read something about "compensating
    conductors" - what's this all about?

    Regards,
    Mark
     
  2. Tom Biasi

    Tom Biasi Guest

    You have a lot of questions but nothing specific.
    Here is a place to learn about PIDS; http://www.expertune.com/tutor.html
    Type K thermocouples are easy to find.
    Regards,
    Tom
     
  3. PID stands for Proportional, Integral, Derivative. This describes the
    three responses to process error that add (or multiply) to make up the
    controller output. Proportional response alters the output without
    regard to the frequency of the error. It is set either with a
    proportional gain constant or a proportional band constant (100/gain).
    Integral response is a low pass filter type response that
    essentially ignores short duration errors, but accumulates a large
    response if an error persists. It may be set with an integral gain or
    an integral time (reciprocal of gain). Derivative response is a sort
    of high pass filter that responds stronger if the error changes
    quickly. It is also set by either a derivative gain or time.

    On/off mode just converts the PID linear output to pulse duty cycle,
    useful for things like resistance heaters or solenoid valves.
    Continuous PID control is for things like control valves that vary
    stem position with signal (usually 4 to 20 mA = full closed to full
    open or vice versa).

    For a basic tutorial on PID tuning I wrote, based on watching a time
    based chart of process measurement and output, see:
    http://www.tcnj.edu/~rgraham/PID/popelish.html
    That is the safest bet. I doubt that you can both heat and cool with
    this controller. Those take dual control outputs. You may need a
    dual output controller that splits the output range in half, with one
    output controlling the amount of heating and the other output
    controlling the amount of cooling. You may get to use RTDs, yet.
    You have to get thermocouples that match one of the set up choices for
    your controller.

    Thermocouple signals are produced when a wire passes through a
    temperature gradient. Different alloys produce different voltages, so
    bringing a pair of dissimilar types from a couple (electrical
    connection between them) from the process temperature to the
    controller will produce a small voltage related to the difference
    between those two temperatures. The controller measures its own
    temperature and corrects for that, so that it can infer just the
    process temperature. If that pair of wires has to pass through
    significant temperature variation (relative to the controller) on its
    way between these two points, the two special alloys have to be
    maintained the whole way, for this process to work. So you normally
    use thermocouple extension wire if the controller is further away than
    the lead length, rather than using copper extension wire.
     
  4. MarkMc

    MarkMc Guest

    Thanks for the detailed responses, I've very grateful. I'll have a
    read of the link too.
    rather than a 12v output. How does PID work with this?

    I was assuming I could use the main control as the cooler and the alarm
    as the heater driver. What am I missing here? IIRC the unit will let
    me set absolute values for both. In reality, I'll probably need to
    drive a cooler in summer, and a heater in winter, but it would be
    better to be able to control both, as the temperature can drop quite a
    bit over night in summer. Perhaps good insulation can take care of
    temperature drops over night.

    Regards,
    Mark
     
  5. Tom Biasi

    Tom Biasi Guest

    I use a modified Ranco mounted to a box with a Peltier cooling/heating
    device. I set the set points for both cool and heat. A DPDT relay reverses
    polarity.
    Most units have a "window" capability if they are classified Heat/Cool.
    Google 'Rec Crafts Brewing' , many of us have described what you are doing
    many times.
    Tom
     
  6. MarkMc

    MarkMc Guest

    Hi Tom

    I am a regular on r.c.b, but for some reason, I didn't think to post my
    question there.

    Regards,
    Mark
     
  7. The PID operating a relay output produces a pulse duty cycle
    proportional to the PID numerical output. That is, if the output is
    50%, the pulse will have equal on and off times (usually, you set the
    period as part of the set up). The alarm relay outputs come on
    continuously, any time the process exceeds some value you specify. No
    PID algorithm is involved in them.
    Bidirectional control is hard with a single pulsed output.

    What sort of hardware are you using for heating and cooling (hot and
    cold water valves to a heat exchanger, resistive heating element and
    peltier cooler, heat pump)?
     
  8. MarkMc

    MarkMc Guest

    Ah, now it's starting to see what how these controllers work. Im not
    sure pulsing on my chiller is a good idea.

    For heat I'm intending to use a standard homebrewers/wine makers heat
    belt (400W IIRC) and for chilling its called a recirculating flash
    chiller. These are used in pubs/bars to chill beer or beer lines to
    stop the beer frothing. Basically the chiller is a smal refridgeration
    unit, which chills a line which passes through it (via heat exchanger).
    I intend to use it to pump (build in to unit) coolant (water) through
    some 8mm copper pipe, in to my fermenter which has a coil (another heat
    exchanger), and returns back to the unit.
     
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