I'm going to withdraw a comment I made earlier in this thread. I bought the really cheap 2-wire WZP sensor that claimed to be PT100 and didn't like what I saw when I checked them. I decided it was long overdue to do some more testing on them.
In ice water, they measured 99R8 or -0.3C on my PM2534. That's where the '100' in PT100 comes from. The sensor should be 100R @ 0C. As the temperature increases, so does the resistance.
I then wrapped the sensor in one of those soft heat-conducting pads you often find in laptops and taped it to the side of a power resistor. I measured the temperature of the flat metal end of the WZP sensor with my Fluke 80T-150 probe. I wrapped everything in some old towels for insulation.
As the resistor heated up, I tracked the two temperature measurements. Between room temperature and 90C, the difference between them was rarely more than 1C and never more than 2C. Above 90C, there may be more error, but my limited technology and even more limited patience made the readings suspect.
Therefore, within the limits of my technology, calibration and patience I have to say that the WZP sensor seems to be in the ballpark for a standard PT100 sensor. I would be very interested if someone else with better capabilities could make some measurements. Are there any temperature-nuts around here?
Ed