The' black boxes' mentioned above have two functions - the first is to convert the terminals from RS 422 to RS232 and the second, its main function, is as a data selector which selects each UV module in turn for polling. This is simple enough but the design is '1980's, using many chips, some in sockets, which can be sensitive to corrosion.
These boxes are then linked to the 'Modicon' bridge multiplexer units installed in the Tubex enclosure. The Modicon units convert the serial data again, this time to MODBUS format, thence to the PLC. It is not clear why these units are used inaddition to the 'black boxes'- it looks like these two parts of the system were designed in isolation. 
The data is collected from the UV modules via two types of PCB cards:-
The first card, known as the "LCA card"
This is a distribution card, which splits the incoming 240-volt power supply into the eight connections to the ballasts, and provides the feedback on whether or not the lamps are lit. It is also fitted with a microcontroller and serial port to communicate the lamp status to the DCA card, and to control a relay for the flow-pacing programme.
The flow-pacing is never used.
There are five of these cards in each module.
The second card known as the "DCA card "
This is also fitted with a microcontroller and A-D converter used to measure and record information such as: - lamp hours, lamp cycles and enclosure temperature. The measured UV intensity level is also routed through this card, which again uses serial comms under microprocessor control
This is a very complex card with unknown software, and reverse-engineering costs would be prohibitive, and the likelihood is that it would not prove successful.
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