Level-Trac LT-120 Control Units are designed to be used with any conductivity probes used for the discrimination of water and vapor (steam). The Control Unit delivers a low voltage common signal to a water column, which completes a circuit when a probe installed on the water column makes contact with water. The Control Unit provides the user with a sect of contacts for each probe, and the facility for an optional indicator. Control Units are generally installed nearby the water column, but may be installed up to 1000 feet away.