Level Sensor

The level sensor in the function unit provides the level value for the entire active reservoir. The level sensor in the active reservoir operates in accordance with the same principle as the level sensors in the passive reservoir. In this case, however, there is only one sensor with several contacts that extend at different levels into the active reservoir.

The sensor makes use of the conductivity of the urea-water solution. A total of four contacts project into the reservoir. When these contacts are wetted with urea-water solution the circuit is closed and current can flow, thus enabling a sensor signal.

Three contacts are responsible for signalling the different levels. The fourth contact is the reference, i.e. the contact via which the electric circuit is closed. This reference contact cannot be seen in the figure as it is located directly behind the "Empty" contact (3).

The level sensor sends its signal to an evaluator. This evaluator filters the signal and recognizes, for example, sloshing of the ureawater solution and transfers a corresponding level signal to the digital diesel electronics.

Fig 1: Cutaway View Of Level Sensor

Courtesy of BMW OF NORTH AMERICA, INC.