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Hi All,
I am new to arduino and am looking to use the product as a temperature controller for a furnace that runs some of our reactions in the lab. I am more comfortable on the software side of things than the hardware side of things, but basically what I want to do is mimic an Omega CN4800 temperature controller (http://www.omega.com/manuals/manualpdf/M1791.pdf). However I would also like it to be web accessible or at the very least remotely accessible through the computer nearby. The way I envision this working is the uno card with a thermostat and a relay to control the furnace with the ethernet shield. Any thoughts? recommendations? As I said before I am really just needing some help on the hardware side and trying to get everything wired up properly.

Thank you
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Just getting your furnace to turn on and off may not get it to fire up.  You may also need to send a low voltage signal to the furnace to get it to fire, it all depends on what kind of furnace it is.
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Sorry, should have specified... they are just ceramic furnaces. You send current to them and they get hot.
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Dubuque, Iowa, USA
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Provide more details on your furnace. We need to know what its voltage and current requirements are. You describe this as a "ceramic" furnace; do you mean this is like a pottery kiln?

At a minimum you'll need an ethernet shield (with a Wiznet chip, preferably), a thermocouple interface and thermocouple, and an SSR to match your voltage and amperage requirements. Not much else except some wire.
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Thanks for the help! the furnace is ceramic covered coil. It runs off 120V and 15 amp... the standard stuff.

http://www.watlow.com/products/heaters/ceramic-fiber-heaters.cfm
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Then a solid state relay would work fine and would be less than $10. One side takes a DC input (you'd connect the + side to an Arduino digital pin and the other side to the Arduino GND) and the AC goes on the other side. Make sure it's rated greater than 15A AC of course. "Fotek" is a popular (cheap) brand that you can find on Amazon or eBay. If you google for "Sous Vide" cookers you'll assuredly find lots of examples of them in use.

You can also use a typical electromechanical relay, but SSRs are getting so inexpensive it's not worth the money savings if you're just switching a single AC line. SSRs have no moving parts and are preferred if you're doing a lot of switching on/off as you might be doing if you want to keep the temperature in a very narrow band.
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I have done similar controls with different brand controllers so just one experience I want to share, keep the thermocouple wire as far away from the power wire to the heater or furnace as possible to prevent cross talk. If you want them together, find shielded cable with separately shielded strands of wire. Otherwise sudden turn on/off will create interference on thermocouple large enough to throw your control routine off.
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Here's the standard warning that building projects that involve mains voltage are potentially very dangerous, especially so if you are new to electronics. Usually, I'd suggest that you can use the power switch tail to enclose the 120V wiring, but even the mark two can only handle 15A, so you'd be operating at its limit which would make me nervous.
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Hi, General info on controlling power with Arduino here:
http://arduino-info.wikispaces.com/ArduinoPower

High power SSR's look like this:  http://goo.gl/QsK8b


DISCLAIMER: Mentioned stuff from my own shop...
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Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info

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Thanks everyone. I think that I definitely have enough to get started with and if/when I have questions I'll be back.
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