What is an independent safety instrumented system?
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This post was last edited by Concave Blade Hero on 2019-6-6 15:11. What is an independent safety instrumented system? What does it mean to be independent? If the SIS system transmits data to the DCS system using a specific protocol, or if the SIS instruments feed data to the DCS system, is the SIS system still considered an independent system? Please provide the relevant specifications or standards. “Wealth is already ready”
The independent pointer is separate from the DCS; field instruments and logic operators cannot be shared with the DCS.
Independence means developing a separate SIS system, with points that are not shared with the DCS, although the status can be shared
As an independent safety instrumented system, SIL2 and above cannot share on-site equipment. Generally, if it is necessary to use both the safety interlock signals from the SIS and the monitoring signals from the DCS, the SIS signals are transmitted to the DCS via communication; however, the DCS can only read these signals but not operate them. All operations must be carried out by the SIS, meaning it remains an independent instrumented system. For shared on-site equipment such as control valves, the DCS is used for regulation, but the shutdown function is handled by the SIS, and the operating level of the SIS must be higher than that of the regulation function. In other words, if the SIS sends a signal, the regulation function of the DCS is disabled and overridden, ensuring that all safety functions remain independent.
Check GB50770. . Pay close attention to Chapters 5 through 8. You have the answer you want.
There are no specific guidelines. But some companies will establish an internal rule based on the circumstances. The reliability of safety systems is determined through various evaluations and calculations. For example, GBT 21109 (IEC61511) \"Functional Safety of Safety Instrumented Systems in the Process Industry\" provides the following guidance regarding communication interfaces: Some companies (such as subsidiaries of Sinopec and CNPC), either because they are not sure whether the DCS will have an impact on the SIS or to prevent personnel from using communication links without proper evaluation, prohibit certain types of communication between the DCS and the SIS through directives or regulations.
SIS must exist completely independently of the DCS, from the instrument channels to the control logic. It is not allowed to send signals from separate instruments on-site to both the DCS and SIS, nor is it permissible for the DCS to transmit data to the SIS for logical processing. If both the SIS and DCS operate on the same controlled device, the control system should be used to ensure that the commands issued by the SIS take precedence over those from the DCS. In terms of safety, SIS is always at a higher level than DCS, and data communication between DCS and SIS can only occur in one direction, from SIS to DCS.
The Safety Instrumented System (SIS) is independent of the basic process control system (which includes DCS); by independence is meant that a DCS failure does not affect the SIS. It consists of three main components: sensing elements, logic processors, and actuators. According to GBT50770-2013 for SIL1 level, the sensing elements and actuators can be shared, but the logic processors should be separate (although the standard uses “should,” in principle they must be independent to be considered such). When a single sensing signal is divided into two paths, one going to the DCS and the other to the SIS, this implies that the sensing elements are shared. To meet the requirements for an independent safety instrumented system, at least the logic processors must be independent
Independence means being like coffin planks – you on one side, he on the other, with no one holding hands with anyone else. Answer completed. Drink drink drink
Independence consists of three aspects: 1. independence of measuring instruments, 2. independence of the control system, 3. independence of control valves. However, independence is not absolute: SIS of SIL1 should be separated from the DCS, SIS of SIL2 should be separated from the DCS, and SIS of SIL3 must be separated from the DCS (thus the control system is independent) ； However, the measuring instruments and control valves can be shared, often in a redundant configuration ； For communication here, the RS485 and MODBUS protocols are used, with a redundant setup. DCS can send reset and bypass signals to SIS (these are basic control signals) ； Apart from basic control, SIS and other systems should be controlled via hardwiring (through relays, safety barriers (1-to-2)) ； Detailed review of GBT 50770-2013