The ACI Relative Humidity Duct utilizes a thermoset polymer capacitive sensing element with a factory ­fitted hydrophobic fi­lter to improve its moisture resistance. The sensing elements multilayer construction also provides excellent resistance in applications where dust, dirt, oils and common environmental chemicals are found. The RH duct sensors include on board DIP switches which allow the user to select the desired output signal (0-5 VDC, 0-10 VDC, & 4-20 mA). Each unit also contains 0%, 50%, and 100% test options to verify that the transmitter is both working and wired properly. Field calibration can be performed by using the increment and decrement calibration DIP switches without the need to replace the sensing element. These enhancements provide increased flexibility and outstanding long-term reliability without the need to replace the sensors in the ­field. Duct configurations feature a weatherproof  enclosure with a gasketed cover and conformally coated circuit boards for increased moisture resistance in high humidity environments. NIST Calibration Certificates are available for all RH TTM part series. Applications: Humidi­fication, Dehumidifi­cation, Supply / Discharge / Return Air, Economizers, Clean Rooms, Data Centers, Process Control, Schools, Hospitals, Office Buildings