Adapting a K-Type, Wire Thermocouple Sensor  - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: November 10, 2018, 07:44:14 am
content: I have an extra K-Type, Wire Thermocouple Sensor. I want to change the connector, from a "mini-type," to a banana plug, so I can have another, to use with my DMM.1) Is it okay to shorten the length of the wire, or is the length related to the calibration?2) I would rather solder the sensor wire, to the banana plugs. Will the special wire metal types take the solder?I could go with a mechanical connection, but it would make a messy device. The tiny wires are not likely to be clamped inside the cup, by the tiny screw. So, the wire would have to be wound around the screw, on the outside of the cup.I am aware that I have to be very careful to maintain the positive and negative wire orientation.I also have the sensor that came with the DMM. It has a plastic insulation covering. The data sheet was confusing, about its safe temperature operating limits and I melted the covering, slightly. The wires were slightly exposed, but completely unhurt. I replaced it.I take it that I could just add a little heat shrink, for isolation protection, and keep using the damaged one; correct? It would be good for situations, were the likelihood of additional damage is in question.Thank you, for your help.

author: nfmax
author_rank: Super Contributor
timestamp: November 10, 2018, 08:54:07 am
content: I think you would do better making an adapter using a K type socket and a couple of very short, heavy gauge copper core leads to 4mm plugs. You will lose some accuracy because the effective cold junction will now be where the copper leads connect to the K type socket, and not at the meter 4mm sockets. So the meter's cold junction compensation, which should measure the temperature of the sockets, will be slightly wrong. Short, thick, copper leads minimise the temperature difference.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 10, 2018, 09:35:32 am
content: The type K thermocouple wires are very hard to solder. It works with special rather aggressive flux.Shortening the wire is not a problem to the calibration.For reading the temperature one should include the temperature where the thermocouple wires go to copper wires as a cold junction temperature. So using normal banana plugs is not a good idea. The yellow connectors look a little cheap, but they are actually quite good as they use special contact material that matched the thermocouple. So it's usually worth to get a suitable counterpart. One can mount a temperature senor (e.g. NTC or diode) inside the counterpart for the cold junction and than go with copper wires from there.There are also commercial electronic cold junction units available, that take the plug and add to suitable voltage to compensate the plug temperature. AFAIR they where at some $40 - 20 years ago.It's no problem to use heat shirk to repair the insulation.

author: t1d
author_rank: Super Contributor
timestamp: November 10, 2018, 11:21:17 am
content: All excellent information with things I would not have thought of. Brymen makes the needed adapter. Where to get it and how much are the questions.Thanks for the help.