So there seems to be little to no consensus as to the type of thermocouple used in the C245 cartridges for the JBC T245 handles.
I have seen some references to Copper-Nichrome with a seebeck Coefficient of 18.5uV/c and some mention of 40uV/c elsewhere with everyone questioning everyone else's measuring methodology.
I'm designing a base station for the Jbc T245 handle and wanted to have measure temperature with some modicum of accuracy. I finally got it decided to test the temp coefficient at work after hours using a
Keithley 2110 5&1/2 digit multimeter with Thermocouple input,
Keithley 2000 6&1/2 digit multimeter with 100nV resolution
,
K type probe,
Metcal MX5000 soldering station,
Kapton tape,
and little confidence in anything I do ever.
The Keithley 2110 was used to measure the K-type probe which was strapped as close to the tip of the C245 cartridge directly (T245 handle not included). The voltage across the unknown thermocouple was measured simultaneously with the Keithley 2000. The system was initially set-up and then left to equalise over some arbitrary amount of time until it reached a stable state. I used this as the cold junction measurement which ended up being 24.14c with 30.3uV.
Then comes the hot part. I used the Metcal soldering iron to heat up the C245 tip and let the system equalise. The Metcal station does not display temperature only input power into the attached iron. After the temperature stopped changing at around 274c the voltage was 7510uV. The soldering iron and tip were connected with molten solder blobs to ensure optimum transfer.
Now it becomes interesting. I couldn't be arsed writing a script to log results and setting all that up in the soldering section of the lab with a loaner work laptop since it would have been too much of a pain especially since I haven't done much logging with meters. I decided instead to save time simply record what happened next with my phone pointed at the two screens of the meters. Then I simply turned the metcal iron off and moved it away and let the C245 cartridge cool passively in the lab while recording the readings on my phone using video. The cartridge cooled back down to room temp after about 11 or 12 minutes or so. After I got home I scrubbed through the video and added the data to an excel sheet and graphed it. here's the graphed data up to about 275c and then with a dotted linear trend line just to demonstrate linearity.
Afterwards I averaged the uV/c rating of each reading which came out to be roughly 40uV/c as someone stated previously in another post. the trend seems to be quite close to 40uV/c with roughly 7uV/c over the range measured 23c-275c. I believe this corresponds to a Nichrome-Nickel thermocouple which has a seebeck coefficient of a combined 40uV/c (25uV/c-(-15uV)).
I'm quite happy with this result and believe its good enough to use for fairly accurate measurements. Anyone have any objections?