I tried to design an inamp for a K-type thermocouple. In theory the gain of this amp should be 250 (close enough to 10 mV/K), and if my understanding of instrumentation amplifiers is correct the output voltage should be the difference in voltage multiplied by the gain of the amplifier(s). My problem is that no matter how I connect the tcl, or if I leave the input floating, the output is stuck high (Vsupply = +5 V, Vtcl = 7 mV (doesn't really matter since Vout does not change), Vout = 4.2 V pinned). Could it be because I'm not supplying my op with +-Vsupply, or is my multimeter not a big enough load and the output is floating or is my design outright flawed, if it is where did I go wrong and how can I fix my issue?
UPDATE 1: Tried with a +-12V supply. TCL hooked up with the correct polarity, the output is ~11V the other way the output is ~-9V. The Non inverting amplifier at the end works fine, but the inamp seems to be stuck at 0.42V on the output. I'll get a precision(or more precise) op and try again.