Buying and calibrating thermocouples, one way to do it

I guess this fits in the Fab shop. Anyway, here goes:
I hate to admit it but I have been buying cheap thermocouples.
Steve U had suggested some time ago that my T/C’s were either incorrectly located or were not reading correctly.So here I attempt to show how I test them to see if they are accurate enough for my work. I have also finally located a source for long enough T/C’s so I can be certain that I will be readiing the temperature in the right spot. (The last 2 of them are still on their way (I hope the ship doesn’t sink!)

Go here:

Pete Stanaitis


Sean French has the tried & proven high quality thermocouples that you are looking for.

The reading will be different on each system depending on placement. There is a differance between the readings on my truck and Carl Zinn’s truck but we are using very close to the same TC’s. Once you get everything going you will get to know what the best readings are for you truck. I think Carl refuels at a lower hopper reading than I do but that is just the placement of the TC. Carl has one at the grate but I do not.

To Peter Coronis: BTW, are you Lithuanian?
I forgot to mention that I am a cheapskate about some things. The thermocouples I have been buying cost between $6 USD and $16 USD.
For that difference in price, I can afford to monkey around, besides, it is a sorta new hobby for me. You have probably seen my Arduino-based datalogger. I probably have a couple hundred dollars invested in it by now, but it reads, displays and records 8 pressures and 3 temperatures right now and has room for a lot more stuff. It can also drive relays, valves and solenoids. It’s my version of the GEK GCU:

I wish I was to the point where I could worry about some differences between one device and another. My application is a stationary
woodgas-to-electric system and my below-grate temp is only about 600 degrees F, so I am not even close yet (at least from what I have been seeing). The only thing that saves my engine is the water filtration system.
This is a Chinese JXQ-10 gasifier. I don’t think I have ever seen an “above-grate” temp over 1000 degrees F, either, so I am about 1000 degrees too low.

Pete Stanaitis

Pete, No, I am Greek

Hi Pete,
Thank you for the most informative and well presented article. I read it with great interest. Nice to have the zip files downloaded to my Thermocouple folder now.
I am finally at a point that I want/need to know the temps at my restriction and at the center of the glowing char cone. Am I correct in presuming that I need a sheathed type for this? I think the 2200 Degrees F is the limit I need. My head is wired F also.
I also need the Arduino data logger. Is this the same as or in addition to the Arduino timer? I’ll have to watch your Youtube stuff a little more closely now. This is new territory for me. Should be interesting. Hope Santa gets my letter.

You are welcome, Pepe.
Yes, you do need sheathed thermocouples.

I have tested my “cheapies” up to around 2000 degrees, but I can’t get much over 1000 degrees in my gasifier, so I don’t know what would happen for long periods of time at twice that temp.
I have had sheathed T/C’s that are as large as about 1/2" in diameter, but they don’t react as quickly to actual temperature changes as do the small diameter ones. Currently mine are about 3/16" diameter. Seem to work pretty well. BTW, to mount them, I have been drilling and tapping into the side of the gasifier for 3/8" or 1/2" pipe. Then I use a bushing in that hole that is 1/8" pipe. Then I buy an appropriate compression fitting and ream both the fitting and the ferrule to be a snug fit. Reaming the fitting is easy, but it takes 3 or 4 swear words to get the ferrule opened up. Once done, however, it is easy to install and inspect the T/C as needed.

It has just recently occurred to me that I may be reading my “above grate” temperature too close to the grate. I may be reading at the point where the endothermic reactions that produce the CO are far below the temperatures in the hottest part of the oxidation zone. Maybe I will add a T/C another inch higher. I have 4 extra T/C amplifiers just “chomping at the bit” to get out of their packages.

Pete Stanaitis

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I just bought 4- TM902C K Thermometer Thermal Coupler Probe -50C +1300C for $11 each. This should be good enough? Is it a good price? Do I need more than 4?

Sorry about the dumb subject, above. I don’t know how to change it.

eBay item number: 290944898245

If this is the item you bought, it is a complete temperature measuring meter, complete with T/C. But the T/C is not sheathed, nor does it have any way to connect it into the hot part of the gasifier. I have one of those and I use it for quick readings of a hot outer surface or for reading gas streams that are no hotter than about 500 degrees F. The insulation on that T/C is probably fiberglass-bearing material and it probably can’t stand much over about 750 degrees or so. If you look at all the T/C’s at the top of the page in the article on my website, you will see the metal sheaths on those TC’s. I am sorry if I misled you here.
You could buy the kind of sheathed T/C’s that I use and wire them to the connector that comes with the T/C on the meter, or you could buy a package of Type K Mini connectors, they will fit this meter:
eBay item number: 111052555115
The sheathed T/C’s can be found in many places. You will have to decide on the length you want/need, but here’s one example:
eBay item number: 150624152323
This one is the latest T/C that I am using. It can be inserted as little as about 2" into the hot Zone or as far as about 6". Again, if you decide to use this approach, you will have to remove the spade lugs that come with this T/C and connect them to the “mini” connector listed above.

Price for that meter? I see them as low as about $5 on Ebay and as high as $10 or $12, plus whatever shipping is.

What have I missed?
I hope this helps to clarify the issue for you and for anybody else who might be watching. If not please do reply back so we can make sure you get what you need.
Or, you can reach me directly at: [email protected]

Pete Stanaitis