The SIS specification document downloaded from Baidu Wenku – please take a look and see if the parameters are outdated
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The SIS specification document downloaded from Baidu Wenku (from Sinopec, from 2006), intended for cost inquiry purposes (for a chemical project). Please check whether the key parameters listed below are outdated The system utilizes triple-redundancy fault tolerance (TMR) technology. The communication interface with the DCS is a serial RS-232C interface, and the communication protocol is Modbus RTU. The SIS processor must be a 32-bit or higher processor with a clock speed of at least 33 MHz (is this specification no longer up to date?) ) The data processing and program execution time for the SIS host should be less than 100ms (Is this value no longer up to date? ) The scope of supply includes one control station, one operation station, and one engineer/SOE station (it seems that in some projects, a operation station is not required for the SIS?) ) All alarm circuit signal contacts in the system should be normally open signals (why normally open? Is there no definition for normally open or normally closed for interlock signals? ）
It is normally open because, in that mode, it needs excitation to function; if the circuit is interrupted, a cascade reaction occurs.
It is normally open because, in that mode, it needs excitation to function; if the circuit is interrupted, a cascade reaction occurs.
The system employs Triple Modular Redundancy (TMR) technology. TMR and QMR (Quadruple Modular Redundancy) have always been the mainstream options. The communication interface with the DCS uses the serial communication standard RS-232C, with Modbus RTU as the common communication protocol; RS-485 is also widely used. Some projects now require that Modbus/TCP SIS processors be 32-bit or higher, with a clock speed of at least 33 MHz (is this specification no longer up to date? ) The CPUs in SIS systems are still mostly 32-bit, unlike those in home computers. Tricon’s MP: Motorola MPC860, 32-bit, 50 MHz SIS – the data processing and program execution time for this host should be less than 100 ms (Is this figure no longer up to date?) ) Most SIS systems can achieve this, with some even managing to reach 50ms. However, it’s not very meaningful to emphasize this point – it depends on whether your PST package includes a control station, an operation station, and an engineer/SOE station (it seems that in some projects, an operation station isn’t required for the SIS?) ) Depending on the specific requirements on site, it is necessary for the ITCC project; generally, ESD systems are connected to the DCS. All alarm circuit signal contacts in the system should be normally open signals (why normally open? Is there no definition for normally open or normally closed for interlock signals? ) SIS designs all follow the principle of fail-safe operation.
Thank you for your patient explanations. I still have some doubts regarding the last question. Following the principle of fail-safe operation, what I understand is that, for example, when an electromagnetic valve loses power, it should exhaust air and return to a safe position. Power loss can occur due to process interlocks or circuit breaks in electrical cables; in such cases, the interlock contacts should be normally closed so that failures in electrical cables can also trigger the interlock. If they are normally open, then this will not be possible. The alarm contact is designed as an open circuit – is this also fail-safe? In that case, wouldn’t there be no alarm in the event of a fault with the electrical cables, since the circuit is already disconnected under normal conditions?
You have the wrong understanding. Whether a relay contact is normally open or normally closed refers to the condition when the coil is de-energized.