The model 904 control unit is used in combination with model 831 inductive contacts. The control unit consists of a power supply unit, a control element, a switching amplifier and a relay output. Certain versions are approved for the operation of inductive contacts in Ex areas.
Non-Ex areas
The direction of action is fixed for this design. The relay output is de-energised when the flag passes through the air gap. Cable break monitoring is included. In addition to the relay outputs for operating the contacts, an additional voltage output with DC 24 V (max. 20 mA) is available. With this, for example, control lamps or sensors can be supplied.
Ex areas
These intrinsically safe control units are type tested. With them, inductive contacts can be used in zone 1 or 2 Ex areas.
The switch behaviour of the control unit can be manipulated by inserting wire bridges or through slide switches. In this way, a reversal of the direction of action can be achieved: e.g. the output relay is either de-energised or energised by the flag in the slot sensor. Cable break monitoring can be switched on, as required.
