Electronic – Calculate Current out of Function Generator

500kHz is a ways past the maximum specified frequency for square waves for this generator: 100kHz. It appears to have a single-pole RC of about 3.5µs, which would work great for a 0.35/(3.5µs)=100kHz square wave. The output may have a LPF for slew limiting. Also, it is a 50Ω source, so it should be terminated properly to avoid ringing. Try using the TTL and CMOS waveforms, too. B&K have put together this document: Function & Arbitrary Waveform Generator Guidebook .

The external CMOS inverter is not a 50Ω source -- it's source impedance is only a few ohms at most (for low currents) due to V_CC and ground impedances and FET R_ON equivalent resistances. Notice that the output duty cycle isn't 50%, and the edges are ringing.

My understanding is that the thermocouple voltage is strictly a function of the temperature. Apparently this is called the Seebeck Voltage. Like any voltage source there is an internal resistance associated with it due to "real world" effects. The short-circuit current will be determined by that internal resistance by the usual Ohm's Law calculation I_ss = V(temperature) / R_internal.