Water Triple Point Cells and SPRTs

SPRTs should be regularly checked in a Water Triple Point Cell. The temperature curve of an SPRT is more stable than the absolute resistance so users work with the ratio (W) of the resistance at a particular value to the resistance at the water triple point, RTPW. The latest RTPW value should be used and can be programmed into a suitable instrument. Checks at the water triple point also give confidence in-between calibrations and can help determine when an SPRT requires recalibration. For many laboratories, a two-year recalibration period is suitable but only with regular water triple point updates. There is little value in using a high quality SPRT without a water triple point cell.