Our Platinum Reference Temperature measurement system is used to provide a goal of +-0.1 ℃ accuracy for our sensor head calibrations.
We use a Fluke 5626 Secondary Reference PRT with ASL F250 Precision AC Bridge readout.

Under laboratory conditions, our precision sensor heads & electronics will give +-0.1 ℃ short term repeatability over 24 hours. For end user FAB conditions, these heads should yield +-0.25 ℃ repeatability. Systems must be checked and calibrated yearly to maintain the noted performance.

The Fluke 5626 has 0.01 ℃ short term repeatability, 0.009 ℃ accuracy at 0 ℃, 0.025 accuracy at 500 ℃
The ASL F250 has 0.001 ℃ readout resolution, system accuracy with PRT of 0.020℃ (-189℃ to 420℃), 0.035℃ (+420℃ to +550℃).

The various Black Body systems are used as the basis for precision pyrometer calibration. The sensor head pyrometers are calibrated here.

Three primary Black Body systems are used. The sensor head to be calibrated is moved to each station in sequence.
This M300 #1 Low Range unit is setup to calibrate from 0 to 700 ℃.

This M300 #2 High Range unit is setup to calibrate from 700 to 1,000 ℃.

This M330 #3 unit is setup to calibrate from 1,000 to 1,700 ℃.

This M365 unit can change to a new temperature quickly (with less accuracy). It is used to check (not calibrate) intermediate temperature ranges in 50℃ steps under 1,000 ℃.