All inputs and outputs are galvanically isolated, intrinsically safe for Zone 0 use. I/O cards are
available for I.S. sensors, switches, solenoid valves/actuators, transmitters
(including Hart), temperature inputs and analogue outputs. This results in up
to 128 I/O being available at each Excom location in the field. Smaller racks are also
available. A single power supply is sufficient for correct system
operation. In order to
enhance system availability, it is possible to connect a second supply unit
(redundancy) when using the
module rack type MT18.
The gateway communicates with a Profibus DP Master (usually a card in the PLC/DCS)
over a Profibus DP network cable (1 pair) through an
I.S segment coupler
(bus barrier) and the Excom system is a Slave system controlled by the Master.
The Master is provided with a downloadable
Profibus GSD file which provides all necessary
data to enable it control the Excom. Greater functions are available if the
Master supports Profibus DPV1 functionality. The communication protocol is
industry standard. The racks may be supplied via one or two power supply cards
fitted on the rack itself. A second power supply card offers full power
redundancy and may be supplied from a different source in the plant. Changeover
is seamless in the event of failure of power source or the power supply card and an
alarm signal is issued. Similarly, the communications gateway can be via one or
two cards. Again, the communications changeover is seamless in the unlikely
event of communications card failure. These features provide a redundancy
capability and consequent security and reliability.
The inputs and outputs serve
to connect field devices in protection type EEx ia IIC.
Up to 16 I/O modules may be operated in conjunction with a single module rack.
The backplane provides the intrinsically safe supply of
the I/O modules - an additional power supply is not needed. Connection of
modules is easily accomplished: gateways, power supplies
and I/O modules are simply plugged into the rack. After establishing the
internal connections, the field components are connected. Modules can be plugged
into and removed from the rack during operation (hot swapping).