O.K. I bought a pyro guage thats a stewert warner brand, from a fellow member on the site, heres the question, What thermocoupler probe do I need? Can I get one of the ones that are for sale on e-bay? they are the K"style rating or J'' style? anyhelp would be great! NOTICE: I bought this to save some money, I would like to save some money on the probe to! If anybody has one they want to part with for a price, e-mail me or pm me! thanks

 

Stewartwarner.com has technical information available. For your guage it lists the thermocouple separately form the K thermocouples. What type it is I don't know. I think you would be best off ordering the recomended thermocouple from an SW dealer.


You can also contact SW for technical support thru their website. Happy wrenching!

 

 

I would pay the money and get the thermocouple from the maker of the guage. Then it will work as designed. Yes, a type "K" thermocouple is the correct one to use but some manufacturers use amplifier boxes and such. Sometimes "bargains" really arent bargains.

 

Different composition (i,e. "J" or "K" or "R")thermocouples have different pairs of metals which generate a different millivolt output per degree of temperature across the same operating temperature range.
If your pyrometer is calibrated for a type "K" thermocouple, you can't use a type "J" and expect it to be close... It has to be matched like Evil said.
The units with electronic converter circuits must be factory calibrated for a particular TC scale so they'll be close.

The different TC's each have their origins in the application they were developed for.
"R" TC's were for REALLY HIGH temps!!! (platinum/platinum-rhodium)
"E" TC's have the highest millivolt per degree output of any thermocouple. Those are typically found in gas appliances where the thermocouple is used to generate a ~33mv signal that can be run thru a thermostat to control the on/off gas valve without external electrical power.
They are the same TC's that are used for safety cutoff when the pilot goes out!.
"K" TC's have a pretty wide range making them widely used (-200F to +2282F)
"J" TC's were pretty old and used in older industry applications (0F to +1382F)
If you're so inclined, this'll keep you reading for quite a while...
http://www.omega.com/techref/

Keith

 

Spoken like a true Instrument Tech or Electrician...... Good info.

 

Yup! Learned about TC's way back in the days when a millivolt bridge had to be used to measure and hand calibrate equipment for those tiny voltages.
Then, take the millivolt value, using a printed table based on each type of TC, convert to/from degF, degC or whatever.

Keith

 

Yeah, PITA....thank God for Fluke...

 

We got it easy nowdays! The new tech's don't appreciate it what we have now...
K.

 

This answer went above and beyound the call of duty! I was going to throw in my 2 cents, but the Rattler has already thrown in a dollar. Nice job. You must be an electrical redneck like me.

 

HURRAH! Real engineers! Now I can ask my real question... I've got a couple of Analog Devices AD595CQ Thermocouple ICs that I 'm integrating into a data logger. How do I attach the thermocouple lead wires to the circuit board with the IC on it? Do I need to use a set screw terminal or is there a special solder that I can use?

Thanks!
brandon.

 

As far as special solder, no, don't believe that there is such a thing, solder just for thermocouple wires, no. Just use standard 60/40 solder and solder it to the board as close to the chip as possible. It should work fine. Use flux so it make a good clean connection.

 

Thanks man!

brnaodn.

 

Joefarmer: Like 4x4 said, there ain't no special TC solder. But, most TC wire IS rather stiff and wiggling it around where soldered could break your solder joint.

TC integrated circuits like what you are talking about, may already have an electronic version of "cold junction compensation" built in. This is the system temperature reference to which the measuring circuit compares the incoming TC signal. If you have the product data sheet on the Analog Devices part, read up on the info concerning cold junction compensation or "reference temperature".

How accurately are you needing to measure something???

If you are measuring engine EGT's, don't sweat it, just solder the wires if you can and have fun!
The minor errors that lead solder would generate for EGT temp measurements won't even be noticeable.

But, if you are designing a system to measure relatively close to ambient temps with maximum absolute accuracy, you have to take into account all the different metal "couples" that could exist in the circuit between the measurement thermocouple junction and the millivolt A/D converter leads(constantan-to-brass, copper-to-brass, brass to lead solder, etc). These different metal "couples" add and/or subtract very minute millivolt values to the true measured signal. Like I said, this only becomes important when requiring maximum absolute temperature accuracy from a thermocouple measurement system.

Hope I didn't get too long winded!


Keith

 

You guys are awesome! I'm mostly looking for engine EGT and post-CAC air temp when greater than 200°F. Here's the datasheet for the AD595 IC:
http://www.analog.com/UploadedFiles/...7AD594_5_c.pdf

Accuracy isn't too important since I'm looking for generalized changes in values, not absolute values. Anyways, this will be a large work in progress and I'm sure I'll have more questions along the way. Thanks!!

brandon.