The THERMOFLEX CF/CR Series standard heat detectors are available in single or multiple circuits with open or closed contact configurations. THERMOFLEX CF/CR Series detectors are available in 1350F, 1650F, 2000F, and 2850F versions. THERMOFLEX CR Series The CR Series detectors are combination Rate-of-Rise and Fixed Temperature. The Rate-of-Rise function allows the detector to operate when the temperature at the detector increases at a rate of 150F per minute. The Fixed Temperature portion will cause the detector to operate when it reaches the applicable temperature. The Rate-of-Rise portion of the detector is restorable; however the Fixed Temperature portion is non-restorable.