RTD sensors are specifically for liquid or semi-solid immersion applications. The protective housing is of 304 or 316 stainless steel, depending on the process material. The sensors can be designed for high-pressure applications reaching 5,000 psi. Various lead wire materials and constructions can be used for abusive environments to meet UL/CSA requirements. Lead-wire configurations are available in two-, three- and four-wire designs. Platinum and nickel are the primary element materials for RTDs.