The Model 657C-1 Transmitter features the same circuit design as the 657-1 providing two 4 - 20 mA channels to produce separate output signals for both relative humidity and temperature. However, this model is housed in a tough die cast aluminum protective conduit enclosure with gasketed cover. An internal terminal block is provided for electrical connections. The sensor employed in the 657C-1 features a state-of-the-art integrated polymer film humidity sensor and a thin-film platinum temperature sensor to assure high reliability and rock-solid stability over years of continuous service. Stainless steel probe measures 5/16" x 9 1/10" (0.8 x 23.1 cm) and can be easily mounted to most ductwork using either of the two optional kits below.