Connecting thermocouples

[hoppyscotty]

As a bit of a project I'm building a simple control system to control my new 3 vessel RIMs system. It consists of three heating elements but I only have the power supply for two which isn't an issue as I shouldn't have to run all three elements at the same time. So I'm running two PID channels, one for the RIMS tube and the other for the HLT and Kettle elements with a switch to switch between the two. This is fine for switching the supply to the elements from the PID, but I also need to switch the thermocouples. I could just pull the thermocouple out of the thermowell of one and into the other as required, but I know it would be only a matter of time till I forgot to do that so ideally want it switched via the same switch. They are K-Type thermocouples but not sure if you can just simply connect thermocouples through a switch? Anyone have experience of a similar setup? Ta.

 

[foxbat]

Yes you can run thermocouples through switches.

 

[The-Engineer-That-Brews]

Personally I prefer to use digital temperature sensors like the ones below, as you can connect as many of them as you like at the same time via a shared serial bus; but to do that you need talk to them via a microcontroller (Arduino etc).

If you're stuck with using the K-Type analogue ones then according to What is a type K Thermocouple? the output voltage for low temperatures is really quite small (about 41 micro volts per degree). So if you use a switch it would have to be a good low-resistance one I think.

 

[The-Engineer-That-Brews]

Yes you can run thermocouples through switches.

I defer to @foxbat if it's easier than I think it is!

 

[foxbat]

I defer to @foxbat if it's easier than I think it is!

I'd agree not to use a cheapo switch. Switch and junction boxes for thermocouples are available commercially e.g. at RS. Calibration after fitting the switch should cancel out any errors I'd have thought.

 

[hoppyscotty]

thanks both. The thermocouples came with the kit I bought so have them around. The chap hadn't them connected via cat 5 cable through a number of cat 5 sockets but I'm not using the same controller he used so building my own. Can give it. go and if it doesnt work I can try something different