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02-20-2006, 01:13 AM #1
Seems like in the old general forum was a discussion of a temperature controller for heat treating. I cannot find anything now in a search for one in here..
Anyone know of a decent one, reasonably priced?
02-20-2006, 02:56 AM #2
there was a request in the wanted section for a analogue temperature controller. I sold the man one b/c he bought a digital but didn't like it.i still have several- what temp range are you looking for? email me if you are interested.
02-20-2006, 03:31 AM #3
This is what i use for my oven
02-20-2006, 04:20 AM #4
My partner (who's main job is designing experiments in an advanced physics lab) has picked up many Omega PID temp. controllers for cheap off of ebay over the years. They have worked great for all uses he and I have ever had for them, including a high temp. kiln.
The other day, I stopped by the shop I used to work at just to say hi, and I ended up getting roped into setting up their heat treat oven with a digital temp. controller because my little experience with them was more than their none. My old boss wanted it done immediately, and as cheaply as possible. :rolleyes: He wanted to order whatever was needed from McMaster because he needed other stuff from there, and was having it delivered next-day.
I had him order part number 7981K82 on pg. 530 (Autotuning P-I-D Temperature Controllers with Fuzzy Logic, the mini one with solid state relay voltage output) and part number 7456K14 on pg. 873 (Long-Life Medium-Amp Relays, with 3-30 VAC/VDC control voltage).
Then I got an old electrical box of some sort, a standard light switch, and a big ass heat sink (a regular ass heat sink would work fine as well, but my partner just happened to have a big assed one he was willing to give me ). I milled holes in the box for the temp. controller and switch, and a hole that would allow me to bolt the heat sink to the outside of the box with the relay (which is bolted to the heat sink) on the inside.
Then the next day the stuff came and I wired it up and installed it. It works great.
BTW, McMaster doesn't list the brand name of the controller in their catalog, but it's Fuji, in case you're interested. Also, I decided to stick with the thermocouple that was already in the oven; it seemed in just fine condition. (K-type - chromel/alumel)
edit: The light switch isn't necessary. It's just handy to be able to turn the power off to the oven instantly with the flick of a switch, rather than trying to navigate through the menus on the controller or having to unplug it.
02-20-2006, 11:01 AM #5
Thanks guys.. That should tell me most of what I want to know.
I have a thermocouple that I was using with a Honeywell digital controller b4 the controller got "funny" and I couldn't make it work right anymore.
It's two wires going thru ceramic guides, then twisted together at the end, but I don't know what kind of wires they are. Does it make a difference?
02-20-2006, 03:54 PM #6
Yes the type of thermocouple makes a difference. Each type outputs a different voltage at the same temperature. Your controller only reads the voltage. I think "K" and "J" types are the most common, and if mix them up you oven/fce is off by hundreds of degrees.
BTW, I like to weld a bead into the end on the twisted pair - they seem to work better that way. Make a new twist at the end and melt the ends together to make a small bead on the end of the twist.
02-20-2006, 04:00 PM #7but I don't know what kind of wires they are. Does it make a difference?
A thermocouple works because a junction between two dissimilar metals creates a voltage that is dependent upon the temperature. The various types of thermocouples, denoted by letters, are pairs of metals which happen to have a nice, wide voltage range over particular temperature ranges. Here's a good site explaining thermocouples.
The K-type thermocouple, which consists of a chromel wire and an alumel wire joined at one end, is the most common. It has a useful temperature range of -32 - 2300 deg. F. We have a roll of K-type thermocouple wire. You simply cut off however much you need, strip the insulation back a little from one end to expose the two bare wires, and fuse them together, somehow. We typically use the TIG to melt them together into a bead. You can use solder, but you better use one that won't melt at the temperature at which you'll be using it!
BTW, you need to run the thermocouple wires directly to your temp. controller. Don't splice in other wires, as you'll be creating other junctions which will throw off your reading! The terminal on the temp. controller will be a junction, but it will be accounted for in the instrument.
02-20-2006, 05:58 PM #8
02-20-2006, 08:25 PM #9
If you are dealing with bare thermocouple wires, identifying unknown ones can be a bit of a PITA. Make sure you have a good junction, and measure the voltage produced at various temperatures, while comparing against published curves.
If you have insulated leads, there are industry standard color codes for the different types:
02-20-2006, 08:49 PM #10
</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;"> Is there any way I can tell by looking, or a simple test, what these wires are made of?
</pre>[/QUOTE]If the wire colors don't give them away, you can determine which type you have by testing them. Attach to a good (high resistance) multimeter and read the output at a known temperature.
02-20-2006, 09:20 PM #11
That is almost definately a K type thermocouple.
It is not goin to be R or S (platinum based = expensive as heck), and J wont go high enough for kiln controllers.
02-20-2006, 10:28 PM #12
Thanks... That all sounds good to me. As soon as I get a break and can mess with it I'll get a PID and hook it up.
Thanks again all.