Abstract: Corrosion of a water sensor resulting from the passage of considerable electric current through it while it is in contact with water is prevented in a motor fuel filter equipped for water separation by interrupting or greatly reducing the current passing through the sensor after the sensor has given a signal indicating the presence of water in sufficient quantity to require draining soon. The warning provided to the vehicle driver is maintained thereafter either by a signal storage circuit (flipflop) or by causing current diverted from the sensor to flow through a substitution resistor or a shunt transistor.

Abstract: Control system and apparatus for measuring and monitoring the nitrogen oxides content of internal combustion engine exhaust gases. The exhaust gases are contacted with the reducing electrode of a sensor cell having a predetermined potential established between the cell electrodes so that the reducing electrode is able to reduce both the nitrogen oxides and oxygen content of the exhaust gas. The current flowing through the sensor cell is measured to determine whether the nitrogen oxides content of the exhaust gas is sufficiently low.