Extension lead for thermocouple

[lindsay]

Hi LO community,

I am considering mounting a PID controller 612 in a plastic box for use in Sous Vide cooking.
For convenience sake an extension lead on the PID controller’s thermocouple inputs would be a useful addition.
I imagine the screw terminals on the back of these controllers are common or garden electrical fittings so ordinary copper/ solder/ etc. materials should not compromise the sensors performance.
Is this thinking valid?

Lindsay

[richiem]

You can do this no problem. Keep the two connections of the probe wires to the extension wires as close together as you can so that they are essentially at the same temperature, and are as cool as you can get them given the environment -- these connections are thermocouples, too. Copper wire and solder connections are fine, but I think I'd use a small barrier strip with screw pads for the connections between probe and extensions.

You should probably check calibration accuracy so that you can add a correction factor if needed -- thermocouples have good resolution but are not very accurate. Use a crushed ice/water slurry in a large drinking glass to check the 32 deg F/0 deg C point, and rapidly boiling water for the 212 deg F/100 deg C point, then use the correction adjustment built into the 612 to make adjustments.

It is quite difficult to get accuracies of better than 3-4 deg F from thermocouples, which is why many sous vide cooks use Pt100 probes. Marco sells a waterproof Pt100 probe that would be perfect for what you;re doing.

[lindsay]

Hi Richiem,

Thanks very much for your guidance which seems to put into perspective the information that I have previously partly absorbed, added to it and also added the miracle ingredients knowledge and experience.
As I am an entry level DIY-er this sort of advice is hugely valuable to me
Now I wonder whether the Pt100 probe could be extended in the same manner and as I know even less about Pt100 probes, can you offer any other guidance.

Thanks so much for the advice
Lindsay

[richiem]

Yes the Pt100 leads can be extended without problems of any kind. Assuming the probe has three wires (two of one color and one of a different color) just add three extension wires -- I would use 20-gauge stranded wire for flexibility, and I would solder the connections and use heat-shrink tubing to insulate the connections. No concerns about thermocouple effects with the Pt100 probe. Try to use color-coding consistent with that of the original wires (two of one color and one of a different color) just to reduce future confusion.