The zener barrier unit (shunt diode safety barrier) should be utilised for on-line applications in hazardous areas. The zener barrier unit, which comes in a custom enclosure, and the analyser instrument must be situated in a safe area and only the moisture sensor is permitted in the hazardous area. The connection from the moisture sensor to the zener barrier is via low loss coaxial cable. The zener barrier can also be supplied without the enclosure for direct installation into an existing bus bar system.