Anyone make temp probes?
- Thread starter VanceT.
- Start date
Bob Bass
TVWBB Gold Member
Vance, You are a brave soul !
For many years I, along with my fellow electricians, made our own thermocouples. They were anywhere from 18" long to 8 foot long. We used 10 awg thermocouple wire, mainly Copper, Constantan, Iron, Chromel, and Alumel. Slide on ceramic thermocouple insulators were used to protect and insulate the entire thermocouple lenghts. The finished thermocouples were installed in 1/2" rigid steel pipe with a screw-on weather tight heads containing the terminations. Of course, these were meant to be extremely heavy duty thermocouples. After all, this was in the mining industry. These were both time consuming to build and maintain. We later had Honeywell build them for us as well as certify their accuracy and repeatability.
Wishing the very best in your quest to build your own !
For many years I, along with my fellow electricians, made our own thermocouples. They were anywhere from 18" long to 8 foot long. We used 10 awg thermocouple wire, mainly Copper, Constantan, Iron, Chromel, and Alumel. Slide on ceramic thermocouple insulators were used to protect and insulate the entire thermocouple lenghts. The finished thermocouples were installed in 1/2" rigid steel pipe with a screw-on weather tight heads containing the terminations. Of course, these were meant to be extremely heavy duty thermocouples. After all, this was in the mining industry. These were both time consuming to build and maintain. We later had Honeywell build them for us as well as certify their accuracy and repeatability.
Wishing the very best in your quest to build your own !
Bob's just a bit further out on the duty requirements than most. Thermocouples, conceptually, are nothing more than 2 dissimilar metals joined at one point. That junction generates a microvoltage that varies as a function of temperature. Picking different metals results in different temperature ranges. 40 years ago, we built a couple of hundred Type K thermocouples for grain bin instrumentation, the junctions weren't even encapsulated. @WBegg has built them for use with HeaterMeters, he has posts about on this site about how he welded the junction, what wire, capsules and encapsulation material he used, etc.
Thermistors.... IIRC, those do have components for temperature sensing, but can also be "read" with fewer electronics than a thermocouple.
Thermistors.... IIRC, those do have components for temperature sensing, but can also be "read" with fewer electronics than a thermocouple.
Bob Bass
TVWBB Gold Member
Our's were indeed heavy duty applications.
If, after reading my post, you still wish to make your own termperature monitoring devices, a great start can be had at Omega Engineering.
If, after reading my post, you still wish to make your own termperature monitoring devices, a great start can be had at Omega Engineering.
Heh...... bet your old employer doesn't customarily mention mining in their name anymore, do they?
Nope....
Really..... I was pretty sure they'd branched out into tape (from Scotlan...) and sticky notes.
Most people who work in labs work with a lot of thermocouples.
The junction at tip should be welded, but believe it or not.....it works just twisted together.
Ive found many thermocouples in process plants....just twisted together wires stuck in a thermowell. Now, these are heavy wires, not the cheap tiny gauge wires you see in your cheap home devices.
Bare wires work fine. But temp is jumpy , mass of a probe smooths this out.
Now, theres also shielding and grounding to avoid noise pickup. Your looking at very small mv differences.
But if it uses a jack, its not a thermocouple....its a thermistor. A less accurate resistance based measurement.
If you dont have a means to calibrate a probe resistance offset in your device ...you are stuck using their probes if you want any accuracy. I wouldnt expect a mfg to give you that option...their goal is to sell you stuff.
The junction at tip should be welded, but believe it or not.....it works just twisted together.
Ive found many thermocouples in process plants....just twisted together wires stuck in a thermowell. Now, these are heavy wires, not the cheap tiny gauge wires you see in your cheap home devices.
Bare wires work fine. But temp is jumpy , mass of a probe smooths this out.
Now, theres also shielding and grounding to avoid noise pickup. Your looking at very small mv differences.
But if it uses a jack, its not a thermocouple....its a thermistor. A less accurate resistance based measurement.
If you dont have a means to calibrate a probe resistance offset in your device ...you are stuck using their probes if you want any accuracy. I wouldnt expect a mfg to give you that option...their goal is to sell you stuff.
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Its not
Unless you want it to read correctly with the device you have
Mfg produce items designed to work together.....so you dont have to worry about it.
On the heatermeter probe screen below....see the probe variables that are needed.
Each resistance probe has a curve, that curve is fit to variables to relate temp to resistance. Different thermistors from different mfgs have different curves. Even wire length can make a difference. Then other things are used to calibrate it to this device as well. You will be way off without knowing , and controlling what you are doing. Pony up the $, imo.
If you want to use any probe, calibrate it to your device, should have gotten a heatermeter
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Bob Bass
TVWBB Gold Member
And there will be calibration issues if a thermocouple uses an audio 3.5mm jack in it's circuit.
It will introduce a tc junction that is not the cold junction.
Proper TC jacks are readily available from sources such as in the link I posted earlier.
My first posting might have left you feeling that my "experience" was only with brute force items.
Farthest from the truth. Sorry about that.
Totally agree with Martin....
It will introduce a tc junction that is not the cold junction.
Proper TC jacks are readily available from sources such as in the link I posted earlier.
My first posting might have left you feeling that my "experience" was only with brute force items.
Farthest from the truth. Sorry about that.
Totally agree with Martin....