The Field Communication Unit (FCU) is a data concentrator that continuously polls data from field devices such as Radar Tank Gauges, Data Acquisition Units and Remote Display Units and stores them in a buffer memory. Whenever a request for data is received, the FCU can immediately send data from a group of tanks from the updated buffer memory.

The FCU acts as a slave on the group bus and as a master on the field bus. The unit has six communication ports. The ports can be individually configured as either group bus ports or as field bus ports.

There are three possibilities:

1. 4 field bus ports, 2 group bus ports.
2. 3 field bus ports, 3 group bus ports.
3. 2 field bus ports, 4 group bus ports.

Each field bus can connect maximum 16 devices
(however max. 8 are recommended).