4-wire sensors are proximity sensors of sensor type "E" (~3-wire). However, these sensors have a normally-closed output and a normally-open output. The use of these sensors can keep the number of sensor variants to a minimum and thus reduce storage costs. Only one sensor type must be kept in stock, because it can be used to replace both NC function sensors and NO function sensors. To date, this option has rarely been used in practice.
With this type of 4-wire sensor, the output signals of the two switching outputs are always opposite. One output is active, the other is inactive. This means that both signals can be evaluated simultaneously for diagnostic purposes. Both output signals assume the same state in the event of a lead breakage, lead short circuit, or power failure. This state immediately signals a malfunction. The use of these sensors thus increases signal safety and plant availability.
Sensors of this type are marked with a –A in the Pepperl+Fuchs order designation.
Sensors of this type are available in the following switching element functions:
Take a look at the range of Pepperl+Fuchs capacitive sensors.