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Electrical Engineers: Need help with thermostat output options.

  1. Nov 24, 2012 #1
    I'm working on a project were I will be using Heating Plug Element-
    http://www.omega.com/ppt/pptsc.asp?ref=CSS_CSH&Nav=head01

    I want to be able to control temperatures up to 1000 F using something likes this:
    http://www.omega.com/Manuals/manualpdf/M4636.pdf

    I would like to be able to control the temperature of the plug heaters so that I am able to set a maximum temperature, which is held for a period of time before shutoff. Nothing overly elaborate. There will be no other electrical components, just the plug heater and the thermostat controller.
    I'm not clear on how controllers of this type work. The output for the controllers is either DC Pulse, Relay, or 4-20mA (is up to the buyer). For my described application which output would be the simplest? What additional hardware would I need for what is suggested?
    Thanks!
     
  2. jcsd
  3. Nov 24, 2012 #2

    dlgoff

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    The idea of a controller is to maintain its set-point temperature by minimizing the error signal (difference between set-point and measured temp), so you're going to have to have either a thermocouple (TC) or resistive thermal device (RTD) to get the measured temp.

    You need to give more detail about what you are wanting to do. By "control temperatures up to 1000 F", do you mean just ramp the temp up to set-point value? And if so, how long do you want to maintain this temp? Sounds like you may need other electronics.

    As far as to which type of output to use depends on what exactly you want to do.
     
  4. Nov 25, 2012 #3
    I would like the temperature to ramp up until it reaches a desired set temperature, where it would remain until manually shut off. An automatic shutoff after x minutes would be nice, but it is not a necessity.

    My confusion stems from the description of the temperature control unit.
    -Do I need a separate power supply, or can I wire the controller directly to 110Vac?
    -The output options allow you to choose a 5-20mA relay option, is SPDT relay built in, or is that something that must be independently connected?
    -What is the difference between functionality of a relay output and DC pulse out put? Which is better for my described application?

    Sorry for my vague-ness, I'm fairly new to designing parts with electrical components.
     
  5. Nov 25, 2012 #4

    dlgoff

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    -No, you don't need an additional power supply. You can wire it directly to a 100vac to 240vac source with the line on terminal 11 and the neutral on terminal 12 (see page 6 of the Omega bulletin).

    -The Short Cartridge Heaters can be bought for either 120vac or 240vac operation so you would need to supply that through a relay output as opposed to a dc pulse which would not drive the heater.

    (see Current Loop)

    edit: Check out how your proportional–integral–derivative controller (PID controller) works. It might be an overkill here. Just sayin'
     
    Last edited: Nov 25, 2012
  6. Nov 25, 2012 #5
    Thanks!
    The PID controller is most definitely overkill for what I plan on using it for, but figured I might use it for different applications in the future.

    I had a feeling that the heating elements would have to be connected through a relay, rather than the DC pulse.
     
  7. Nov 25, 2012 #6

    dlgoff

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    You could use dc pulses as a input to a Solid State Relay that switches the ac to the heater however. Depending on the wattage of the heater you chose determines at what current rating you would need for one of these:

    458px-Solid-state-relays.jpg
     
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