Hi all,

I'm finishing up a popper mod that I've been tinkering with for a while, and I'm having some issues with the ET thermocouple. Despite being the exact same model as the BT thermocouple probe (Omega TC-K-1/8NPT-U-72...overkill, I know.) and being in close proximity to the BT probe, I get hugely different values once I start to heat up the chamber (but fine at atmospheric). Both thermocouples are ungrounded and K type (hence the "K" and "U" in the model number, respectively), and they're set up as such in the Arduino sketch. Any ideas for troubleshooting? I have a few guesses as to what's happening--do any of these seem likely given these circumstances?

• Bending the probe below the hex nut caused it to ground around that point, so the temperature it reads is that of the dead space about an inch outside of the roasting chamber, but still adjacent to the heater.
• I have a weak/failing solder joint on my TC4 shield.
• The ET probe is calibrated differently than the BT probe.
• My ET placement is awful.

Here's a shot of the chamber & probe placement:


Here's what it looks like on roast:


Thanks,

Stephen