I need to connect a precision 100 Ohm resistor to my boards to calibrate the zero Centigrade point offsets for my PT100 circuit (the only other way being a water triple point cell AFAIK). So, I have selected a through hole mount precision resistor of 0.005% accuracy with a 2ppm temperature coefficient. This is specified at around 25 degC. The rated power is 600mW, but I will only be putting about 500uA through it at most.
The questions are:
Is this good enough? On paper it looks like it could calibrate to 13 milliKelvin equivalent accuracy.
How do I mount such a resistor? I intend to put it into a sealed box with terminal connections for the 4 wire PT100 and keep it in an enclosure that is temperature controlled to within a tenth of a degree. I am planning to have it hanging in the air with the two ends soldered to the terminals of the current carrying wires, and soldering connections for the sense wires close to the body. Any special precautions or advice on this? Has anyone done anything similar?
Best Answer
I would hold out for a Z-series Vishay metal foil resistor, which are available in 100\$\Omega\$, nominal 0.2ppm/degree C.
Mount with the recommended (see mfr application data) lead length to the Y connections, heat sink during soldering and fill your box with dielectric foam (eg. Urethane) to keep air currents off. If you are paranoid, use low thermal EMF solder, but try to keep everything as symmetrical as possible in any case. You can/should get it calibrated by a lab if it's important.