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Excom Remote I/O
System Overview   

             

             

Excom is an intrinsically safe Analogue and Digital remote I/O which is bus system compatible for use in hazardous areas. The system physically consists of a compact 18 way I/O module rack, with power supplies, gateways, and I/O modules, which is mounted in a stainless steel enclosure in a Zone 1 area. The enclosure may be opened during use and all I/O cards have hot-swappable I.S. connections. Defective devices can be exchanged during operation. The system automatically checks whether the new module accords to the defined slot assignment. The system supports substitute value programming.
 

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).

The internal cycle time of a fully assembled system is below 5 ms for binary processing and below 20 ms for analogue signals. The
response time also depends on the type of PLC and fieldbus used in the application. The system supports connection of HARTŪ-
compatible field devices. Consistent HARTŪ communication up to the PLC is possible via the PROFIBUS-DPV1.