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SCADA: Operational Philosophy & Trends

Operational Requirements

Present day RTUs are required to perform safety related tasks on their own to control tunnel fire or other such risks. This has to be independent of operator participation or master station automation. Detailed analyses of historic data as also particular industry-related analyses are required to be performed by master station software before presenting to the operator. Because of application of stringent safety requirements in the system, the safety standards for markets have to be met by the master station software.

Risk Of Failure

If the control system fails in some installation, the resultant cost including possible loss of life would be very high. The SCADA system hardware is generally made much toughened for coping with varied temperature, voltage fluctuation and vibration. But reliability in such installations can be further enhanced if standby hardware and communication channels are provided. Such backup ensures that the backup hardware can urgently identify and replace a part that has failed and can take up automatically its function without impeding the process. Mean time between failures calculated statistically indicates reliability of the system and often this time is very high highlighting risk.


Now the preference is for matching combinations of HMI/SCADA and PLC software. Mix-match is the current trend. A manufacturer of a typical DAQ/IO in the mid nineties had their own proprietary communication protocol on offer like RS-485 that could carry suitable distance. The late nineties saw continuation of the tilt in the direction of open communication. There were on offer by I/O manufacturers open message structure support in the form of Modicon Modbus replacing RS-485. By the turn of the millennium, open interfacing like Modicon Modbus on TCP/IP was being offered by most I/O makers. With rising industrial automation, factors like protocol selection, synchronization, suitable environment, etc. came to assume important role and industrial automation saw entry of Ethernet TCP/IP.

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