APPARATUS FOR DETERMINING AND/OR MONITORING A PROCESS VARIABLE

摘要

An apparatus for determining and/or monitoring a process variable of a medium in a container. including: a probe unit, which has a sensor electrode and a guard electrode; and an electronics unit, which supplies the sensor electrode with an activating signal and which supplies the guard electrode with a guard signal; An amplifying unit; and a limiting element arranged in series between the guard electrode and the output of the amplifying unit. The amplifying unit supplies via the limiting element the guard electrode with the guard signal; and the amplifying unit supplies via the limiting element the sensor electrode with the activating signal. The evaluating unit is provided, which determines and/or monitors the process variable based on an electrical current signal measurable at the sensor electrode, and the activating signal and/or the guard signal.