I'm working on a JBC solder iron controller design which aims small size and light weight as well as USB control.
At the beginning I thought it would be easy -- nope.
I was able to get the power path sorted out, but the temperature sensing part annoys me.
As seen here:

The DC- of the heater is NOT grounded, which means if I ground the iron (which is USB ground), I need USB isolator, which is fine.
The second problem is the thermocouple connection. The TC doesn't have a Kelvin connection, which means during TC sensing, if the tip is connected to an electrical noise surface (say, a grounded case with high EMI emission), the TC readout would be a mess.
The second issue is exact the issue that brings the idea of building a controller -- my original JBC controller went crazy when I solder on ground planes connecting to my PXI box, which is noisy.
So, besides of building a custom JBC handle (which has Kelvin connection for GND), is there a solution that allows me to read thermocouple input while soldering on a noisy surface?
Also, the above mentioned diagram might be wrong -- it could have a Kelvin connection, just not I'm aware of. Does anyone have a cartridge pinout for C470 and C105?