The purpose of a primary laboratory realising ITS-90 is to calibrate SPRTs at fixed temperatures, by comparing their resistance to a fixed and known resistance. The fixed temperatures come from ITS-90 fixed point cells, usually a device with an ingot of pure metal that can be melted and frozen in a metrology furnace.
We have a full range of ITS-90 Fixed Point cells for both NMIs and smaller laboratories with apparatus to maintain and operate the standards. In this section we also have our Primary Standard Platinum Resistance Thermometers, SPRTs. Our thermometry bridges have their own section; microK Thermometry Bridges