Control must be carried out from the outside via a fail-safe electronic module to the respective IN P and IN M terminals. The ET 200SP 4 F-DQ (6ES7136-6RA00-0CA0) can be used for this, for example.

One channel of the 4 F-DQ module can be used to control a further 1 F-RQ module. The output signal can be looped through for this purpose: OUT P and OUT M of the first 1F-RQ module are wired to IN P and IN M of the second 1F-RQ module.