HCL transmitter including digital measurement value processing and temperature compensation for the continuous monitoring of the ambient air to detect hydrogen chloride concentrations. Integrated in the transmitter there is a comfortable calibration routine with selective access release. The ADT-53 possesses a standard analog output (0) 4- 20 mA or (0) 2– 10 V DC, and an RS-485 interface. 2 relays with adjustable switching thresholds are available as an option.