Thermocouples?

I'm looking to get a few thermocouples but don't really know much about them so I'm turning to the collective wisdome of you GRMers.
I want to use it to monitor the tempurature of a liquid. When the temp gets above, say 180°F or so I'd like it to interrupt a 110V A/C circuit. It can either monitor the temp of the aluminum housing the fluid is in, or can come in direct contact with said fluid.
Now, to get real fancy-like I'd also like another one that would interrupt a 110V A/C circuit untill said fluid comes up to, say 150°F or so. This one isn't as important, but the upper temp limit is what I really want to achive.
So, where should I get these from, and how do I interrupt the circuit?

Thanks all!

Not sure where you would get them from, but I used them in Smoke machines. Basically they trigger a relay that inturn disconnects or connects (depending on use) the circuit you are working on.

On a theatrical smoke machine, it will not start operating until it reaches a certain temp, so it interrupts the trigger signal from the "smoke" button.

Thanks Mad. I'm also wondering, should I use a thermocouple or a thermister or LM35 sensor? I don't know much about any of this stuff so I'm reading everything I can now.

gas furnaces, dryers use them. also called a limit switch. you can get them in 10 deg increments. they would have to be used to on the aluminum housing.

you might be able to find a fan controller with remote sensors. this would open the circuit at X and close it at Y.

home thermostat could also be used. but you would need some relays (or an old furnace control board) to limit a 120VAC circuit

OK so this is something I know a lot about. I use thermocouples and RTD's every day.

What you will need is a temperature controller, a relay and your thermocouple or RTD. I prefer RTD's since they are just as accurate, don't require special extension wire and in most cases are a bit cheaper from my vendors. An RTD changes resistance at different temperatures whereas a thermocouple creates voltage when exposed to heat. For the controller go with somethign like a surplus Watlow 96 http://cgi.ebay.com/WATLOW-TEMPERATURE-CONTROLLER-96B1-CAAA-00GG-/300542164184?pt=LH_DefaultDomain_0&hash=item45f9b57cd8

These are super easy to program and setup, They work on pretty much any avaliable voltage. Their autotune feature makes them extremely accurate as well. The relay inside the watlow cannot handle enough current for any load though. It is just there to run a larger relay that you will have controlling your AC source ( I am assuming a heater)

Depending on how accurate you need or how innacurate you can get away with you could go with a mercury bulb thermostat

I personally hate these. At a 350 degree set point they will vary as much as +/-60 degrees. But they can be found cheaply. These will still require a relay.

How much current does your AC draw?

I get all my lab TC's and RTD's at
Omega Engineering

I buy from Omega all the time. Even if you come up with Plan B. good site to root around in.

http://www.omega.com/

Depending on what you're trying to do, some kind of PID temp controller may be a better fit that just high and low relay triggers.

Wow, thanks guys. I don't know why, but I'm surprised to find this much info this quick. I'll check on the current draw today or tomorrow. It's a water heater element, can't remember the wattage right now.
I like the Watlow idea, but I'm trying to go grassroots all the way. I'm sure I can find an old furnace board though. Keep the ideas coming!

Auxillary coolant/tranny fluid fan relay kit should work, too, right? Or find a thermocouple that produces a certain voltage at a certain temperature, and a relay that will trip around that voltage. Can't it be that simple?

if you are using a waterheater element.. I would see about a thermocoupler from a hot water heater.

What do I do to actually switch the power off? If this were a 12V DC system it'd be a no-brainer. Can I buy a relay made for 120V A/C?

ditchdigger wrote: OK so this is something I know a lot about. I use thermocouples and RTD's every day. How much current does your AC draw?

1000 watts, so that's about 8 amps at 120V, right?

Water heater element at 120V??

They are typically 220V.

Omega will have every variant possible, but they are almost always very proud of their stuff. Pricing gets pretty high.

What is the use? What level of accuracy do you need?

there are 120volt Hot Water heater elements. We use them in Dry Ice Foggers.

110V AC Hot water boiler controls should be in that temp range, lemme look s'more.

how 'bout this: 110VAC w/ relay and $56

http://store.antx.com/browseproducts/Digital-temperature-switch.html

What is your application... a brewery? just guessin'

With an 8amp relay built in that piece seems like a winner.

Yeah, whatch you doin'? Stewin' biodiesel?