View Full Version : Infrared Thermocouple!!!!!!
May 12th, 2002, 02:16 AM
Anybody had experience with infrared thermocouples?
Are they as accurate as your typical TC?
I have an app. where a hot part travels on a conveyor and has to be checked for temp before it can enter next step in the process.
As always, any input is appreciated.
May 12th, 2002, 07:55 PM
I don't know that I can be much help but I'll give it a shot. I just had my first experience with IR thermocouples last week. I replaced two contact t/c on internaly heated silicone rubber rollers for a laminator. I don't recall the brand used. The were purchased from McMaster Carr for $185 each. Distance is important depending on the accuracy you require. Do some research on several brands and find the one that best suits your needs. I found a 30 degree F difference in what I got from the IR and a surface probe in the same location. This can be easily rectified by using a quality temp controller that allows for compensation. If you are connecting the IR T/C to a plc analog input module, the compensation can be written in your code. Based on your application of a moving target, I'd say IR is the way to go. Also, search Google for "emissivity", it will give you a better understanding on how IR energy is radiated. Hope this helps.
May 12th, 2002, 10:53 PM
Check with Raytek, they make a whole line of IR heat gun's and sensors. They range in price from $150 and up. They do have units which can be put on a production line and give a continuous signal, but they are more money than a hand held unit. I have used both types and both units are very well made and easy to use.
May 13th, 2002, 12:54 AM
I thought I wasn't familiar with "Infrared Thermocouples" until Mike mentioned Raytek. Now I realize I am familiar with them...
A while back, we used a Raytek Thermalert sensor to confirm that hot melt glue was applied inside an aluminum tube. We basically just looked at the surface temperature rise on the outside of the tube, which was good enough for this application. This was a nice self-contained unit with simple to use programming software. I'm sure they've improved over the years as well. They seem to one of the leaders in infrared temperture measurement, so Raytek (http://www.raytek.com) should be your first stop.
May 13th, 2002, 08:45 AM
I've been doing this $#!t for awhile and I aint never seen an
infrared thermocouple. I've seen plenty of thermocouples
and plenty of IR temp detectors, but, I aint never seen an
May 13th, 2002, 09:31 AM
I think what they are reffering to is a radiation thermometer, which picks up radiant heat by means of a lens and focuses the heat waves on a thermocouple. I think they are also reffered to as a pyrometer.
May 13th, 2002, 09:59 AM
JDW is absolutely right - by definition a thermocouple (T/C) uses two disimilar metals to create voltage as a function of temperature - the Seebeck effect. To me an "Infrared Thermocouple" is an optical pyrometer that has an output signal equivalent to the output of a thermocouple at the same temperature, allowing it to be substituted one on one for a T/C in the control circuit.
I think a lot of "Infrared Thermocouples" can be calibrated against a given object at a known temperature to compensate for emisivity and similar inaccuracies. Omega Engineering - http://www.omega.com/ - has a pretty good tutorial in their catalog.
May 13th, 2002, 10:07 AM
There are optical infra red detectors that are sometime called infra red thermocouples because they do the same job but they are really not the same. Thermocoples are strips of metal. Infra red detectors are optical and non contact.
Infra detectors can be accurate to a .1 degree or better. The medical ones I worked on once were much more accurate than that. The medical infra temperature detectors used by medical personnel to detect blood flow. These thing can see through clothes but not in detail. One can certaily see all the veins and arteries close to the skin. They are also used to detect hot spots on printed circuit boards right down to the pins. The boards in your PLC had to be examined by one of these optical infra red temperature detectors to check the design before it was put in to production.
Infrared temperature sensors can be very fast because there is nothing to heat up. It is all optical.
May 13th, 2002, 01:03 PM
I do realize that there is no such thing as a IR thermocouple, but I did now what Orn was looking for. I saw no reason to be negitive about the existance of an IR thermocouple or not, I just wanted to point him in the right direction. I hope I helped Orn in his search.
May 13th, 2002, 03:39 PM
Y'all being picky with terminiology. Whether you seen one or NOT there are devices called Infrared Thermocouple. Even Tom's post to omega has info on them:
Believe what you wish but these devices also use a form of thermopile, so cant say they aint a thermocouple.
If ya been doin this s*&t that long and dont take the time to read some of the prior links and/or look around yourself, well maybe you can figure the rest out.
May 13th, 2002, 09:32 PM
Sorry, I'm just used to calling a rtd a rtd, a thermocouple a
thermocouple and an IR temp sensor just that.
Even got a few UV/IR detectors.
I wasn't trying to be mean.
March 28th, 2004, 08:03 PM
They have nifty calibrators for those devices at colepalmer they basic set a temperature across a surface area and you shoot your beam at it and calibrate the DUT to read the readout of the standard
March 28th, 2004, 11:02 PM
I set up a Raytek one last year, worked well except that the power supply went after about three weeks.
Found out after that they are rather sensitive about the supply voltage. Our was rated from 12 to 24V, so we stuck it on our standard 24V supply. Seems that even a slight increase can damage the supply. We now run it through a 15V regulator now to be sure.
March 29th, 2004, 02:59 AM
I've worked with Raytek units quite a bit and I also had good results with them. We calibrate IR Guns were I work I also do all those other items like Recorders,Sensors of all types,Displays of all types, but a side note is that Im looking to setup my dell axium 5 to be able to connect to a plc in the field and use the Screen as a susbstitue from either touch panel replacement or regular CRT.
The reason for this is that I also calibrate Analog Input cards on PLCs but usually the readout is pretty far away so a one man job nows becomes a two men job with a radio, etc. etc. you get the picture
March 29th, 2004, 08:44 AM
OOOOPS! I've seen a few Infrared thermocouples in my past life :)
In a high-vacuum application with pure carbon heating bars and magnetic amplifiers. These where old technologies but here what these thermocouples where.
They consist in a small tube equiped with a lens (Looks like a miniature telescope). At the oposite end of the lens there was a serie of thermocouples, yes, connected in serie with the cold junction outside of the tube (if I remember dismantling one correctly there was about 10 of them).
I beleive they where made of Rodium.
Hey, that was 20 years ago and those machine had wood spike brackets still in place to measure temperature. If you don't know what this means then your way to young. If you know then your way too old :)
March 29th, 2004, 08:59 AM
Another possibility why the term "Infrared Termocouple" has come up:
I guess that Termocouples are so common in many places, that it spurred the development of infrared sensors that could be put traight in as replacement of existing Termocouples.
Myself, I once tried an Exergen infrared temperature sensors that had TC output.
Today I am using Raytek TSX sensors. I have had a few units go bad over the time (approx. 5%). But I find them so cheap, that if there are more then just 2 sensors in a project, then I specify one spare to be included, just in case.