The 5636 and 5628 are idea for use with temperatures points above normal PRT temperatures. The 5626 is nominally 100 Ω and the 5628 is nominally 25.5 Ω. Both instruments have a temperature range of 200°C to 661°C. Using regular PRTs at temperatures above 500°C exposes the platinum to contamination; the 5626 and 5628 have been designed to reduce the contamination risk through internal protection.