I have a problem that I can't seem to wrap my head around.
I am designing a controller for a JBC handpiece, but the cartridgess are only three pins (JBC Nano only two.) I'm trying to design a controller that would be "universal" between the two (for now just focused on the C245 pictured below.) I'm using 24-45VAC.
I would measure the thermocouple at the "zero crossing", but how would I protect the circuitry when it is not at zero crossing?
I have the basic AC MOSFET circuitry, current sensing, etc. all figured out (ready for testing,) but just can't seem to understand how I can measure the thermocouple correctly. I have seen many designs using "single ended" designs using diode protection, but wouldn't using an op amp in differential configuration be better? (Below is my rough circuit.)
Yellow = C1, green = C3, temperature goes direct to micro. (I'm using a "rail splitter" for my voltages, -5v_v is analog GND.)
I'd go into more detail but this is already fairly long.
TL/DR: How to amplify thermocouple signal when one leg is "common" to an AC heater element? Single ended vs differential vs something else.