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Water Bath

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  • 12-10-2010 3:06am
    #1
    Iguana Bob
    Closed Accounts Posts: 208 ✭✭


    How can i make a water bath and regulate the temp. i know i could use a plc with a thermocouple and a power controler. but think this is overkill and dont have this much money.
    can you get a variable resistor that can take upto 1000v?
    That way i could get an element fron a kettle wire in the variable resistor and simply plug it in. note the temps at certain positions and have a thermocouple on hand. doesnt need to be perfectly accurate just within a few deg
    any idea?


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    #2
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,536 Mod ✭✭✭✭2011


    I used a phase angle controller for this in a project a few years ago. It was very effective.


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    #3
    Iguana Bob
    Closed Accounts Posts: 208 ✭✭Iguana Bob


    Not that up on my electronics, how would you set this up.


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    #4
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,536 Mod ✭✭✭✭2011


    Not that up on my electronics, how would you set this up.
    It is quite simple really. The one I used works like this:
    1) Connect 230VAC to the supply side of the phase angle controller

    2) Connect the heating element to the load side. With the unit I used the maximum current < or = 20A

    3) An analogue output from the PLC was configured to supply 0 to 5 VDC corresponding to a count value of 0 to 1000

    The phase angle controller would "chop" the output. How much it would chop would depend on the value of the control voltage that was supplied by the AO from the PLC. An output of 0 VDC gave an output of 0 watts, 2.5 VDC gave 1 kW, 5 VDC 2 kW (approximate values, although the relationship was not linear it was very close). So by writing a count value to the AO I could accurately control the output from the heating element.


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    #5
    Iguana Bob
    Closed Accounts Posts: 208 ✭✭Iguana Bob


    any chance you you remember where you got it had a look around and cant find one. what plc were you using
    thanks looks like a good solution


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    #6
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,536 Mod ✭✭✭✭2011


    Any PLC that can be configured to output 0-5VDC will work.

    I think the phase angle controller came from Radionics. Will look into it for you.


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    #7
    Iguana Bob
    Closed Accounts Posts: 208 ✭✭Iguana Bob


    thanks 2011
    might as well do some home automation while im at it. you can get son very cheap allen bradley one on ebay, these are the only ones i used so far. they are pretty easy to progran with rslogics


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    #8
    DublinDilbert
    Registered Users Posts: 5,367 ✭✭✭DublinDilbert


    Why do you need a plc? Do you need to perform other functions?

    How tight are you trying to control you set point? Will on/off control do? Or do you need linear control of the element?

    RS supply stand alone temperature controllers with relay and triac outputs. If the triac output is not powerful enough you can use an external triac.


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    #9
    Iguana Bob
    Closed Accounts Posts: 208 ✭✭Iguana Bob


    no dont have to use a plc. the simpler the better, on.off would probably do linear control would be nice but not nessasary basically just want to controle the temp of a waterbath to keep it around 37 degC. i thought about using a line voltage thermostat but cant find any that are used for water


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    #10
    DublinDilbert
    Registered Users Posts: 5,367 ✭✭✭DublinDilbert


    'around 37c' with on/off control you'll probably get an over/under shoot of a few degrees either side. Every immersion heater has a thermostat built in, but I don't think they can be set that low, maybe they can. Would be worth looking into.

    How much are you looking to spend on the setup? You can spend anywhere from €30 to €3000, depending on how accurate you need it.


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