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The main function of the SIS system is to enable immediate and proper responses in cases where there is a risk of failure in the production equipment itself, or when hazards are caused by human factors or certain force majeure events. It generates corresponding logical signals that allow the production equipment to be safely interlocked or shut down, thereby preventing the occurrence of hazards and the spread of accidents and reducing potential damage. A failure in the SIS system will **reduce the ability to predict risks. To ensure safe production, prevent serious equipment failures and casualties, and improve the company’s overall economic performance, it is urgent to strengthen the management of the SIS system. This article shares the key aspects of SIS system management to help instrument maintenance personnel improve their work in managing SIS systems. The task of SIS system management is to maintain the good condition of the equipment in the SIS system by strengthening professional technical management, ensure safe production, reduce unplanned shutdowns, prevent major equipment failures and casualties, and improve the company’s overall economic efficiency. So, what should we do for daily maintenance and management? Preliminary management of the SIS interlock protection system refers to all the management tasks involved in the planning, design, selection, procurement, installation, and commissioning phases; it is an important part of the overall management process. To achieve the most economical life-cycle costs and the highest overall efficiency, attention must be paid to preliminary management work. The equipment management departments should participate in the design review of the SIS interlock protection systems for projects such as new construction, modifications, and expansions, in accordance with the principles of safety and reliability, technological advancement, and economic Reasonableness. Requirements are put forward for the reliability, maintainability, suitability, cost-effectiveness, advancement, and safety of the design selection. The design of the SIS interlock protection system shall comply with the “GB 50770-2013 Design Code for Safety Instrumented Systems in Petrochemical Industry”. The acquisition of SIS interlock protection systems should adhere to the principles of good quality, excellent performance, and cost-effectiveness over their lifetime. Adhere to strict quality inspection procedures upon factory entry, and imported equipment should come equipped with the necessary maintenance parts. The Equipment Management Department should be involved in the procurement of the SIS interlock protection system, and be responsible for or participate in the drafting of technical agreements. The construction of the SIS interlock protection system must be carried out in accordance with the design requirements and the “SHT3521-2015 Technical Regulations for Construction of Petrochemical Instrumentation Engineering”. Units responsible for the construction of instrumentation equipment in new, renovated, or expanded projects must possess the appropriate construction qualifications, the capability to carry out construction in accordance with design requirements, and a sound project quality assurance system. The Equipment Management Department shall be responsible for or participate in tasks such as the completion acceptance of instrument and equipment projects. The completion acceptance must be carried out in accordance with the design requirements and relevant specifications. To ensure that all completion documents are available, the documents required for the project’s completion acceptance should include: (1) the as-built drawings of the project (including the design drawings and as-built drawings for the entire set of instruments and control systems). (2) Design modification documents and substitute material documents. (3) Documents and records of concealed works. (4) Records of SIS interlock protection system installation and quality inspection. (5) Records of cable insulation tests. (6) Records of ground resistance tests. (7) Records of purging, pressure testing, and leak testing for instrument air and pressure guiding pipes. (8) Certificates of product quality for the SIS interlock protection system and materials. (9) Records of calibration and testing for the SIS interlock protection system. (10) Records of loop tests and system tests. (11) SIS interlock protection system handover checklist. (12) Commissioning records of alarm and interlock systems. (13) SIS interlock protection system configuration record work order. (14) List of unfinished projects, etc. (15) SIS interlock protection system manual. Among them, the contents of (1), (2), (10), and (15) should be handed over to the maintenance department of the SIS interlock protection system, the management department of the SIS interlock protection system, as well as the user units, in addition to the archives department. Before putting the SIS interlock protection system into operation, the user unit and/or maintenance unit shall formulate relevant procedures based on the characteristics of the equipment, and carry out technical training and accident response drills. System management: For changes to the interlock programs in the SIS interlock protection system, adjustments to interlock settings, and changes to timing values, it is necessary to establish a system of approval by relevant specialists and technical supervisors, as well as to fill out the \"Interlock Protection System Change Approval Form\". Changes to the SIS interlock protection system due to process or equipment reasons shall be handled by the production unit; those due to instrumentation-related reasons shall be handled by the Electrical and Instrumentation Workshop. The process interlock protection system must be reviewed and approved by the unit manager ； The SIS interlock protection system for key units and other equipment is reviewed by the responsible personnel in the Equipment Department, approved by the deputy supervisor, and implemented by the instrumentation (electrical and instrumentation) specialists. Before carrying out operations on the SIS interlock protection system, it is necessary to obtain a \"Temporary Operation Ticket for Interlock Protection System\". If it is necessary to temporarily shut down the SIS interlock protection system due to process-related reasons, the process unit is responsible for handling this matter, with approval and signature from the head of the production unit; the dedicated personnel in each workshop responsible for operating the SIS interlock system are tasked with carrying out the shutdown. Due to instrument maintenance requirements, the SIS interlock protection system is temporarily taken out of service. This must be carried out by qualified instrumentation personnel, and the work can only proceed after obtaining approval and a signature from the production unit supervisor. The SIS interlock protection system, which has been temporarily shut down for the above two reasons, must be restored within a specified time frame, and both parties shall keep records of this. During production, the SIS interlock protection system must not be deactivated. In cases where deactivation is absolutely necessary due to special circumstances, it is required to have relevant professionals conduct an evaluation under the supervision of the competent authority, formulate corresponding measures, obtain professional sign-offs, and secure approval from senior management; only then can the “Approval Form for Deactivation of the Interlock Protection System” be processed. Issues arising from the process are to be handled by the process equipment personnel; those caused by instruments are to be handled by the instrumentation personnel. Instrumentation professionals carry out operations upon receiving work orders. Archived in the Production Technology Department, Process Units, and Equipment Department. Commissioning of the SIS interlock protection system after the installation of a new unit or after major maintenance of an existing unit ； To resume the use of the SIS interlock protection system after a long period of disuse, relevant professionals from areas such as production, process control, safety and environment, instrumentation, and electrical engineering must inspect each circuit one by one and provide confirmation; only after filling out the \"Interlock Protection Circuit Test Confirmation Form\" can the system be put back into use. The relevant departments, the Instrumentation and Equipment Department are responsible for archiving. The addition of the SIS interlock protection system requires the Company’s Equipment Management Department to issue task orders, along with drawings and relevant documents, to the Electrical and Instrumentation Workshop; the instrumentation team in each plant’s equipment department is responsible for carrying out this work. Before removing the SIS interlock protection, the process personnel responsible for the production unit must develop a plan and take appropriate measures, which must then be confirmed by two or more instrument operators before the interlock can be removed. After removing the interlock, it must be checked and confirmed. When dealing with issues in SIS interlock protection systems, instrumentation professionals must first determine a plan for disabling the interlocks and take reliable measures to modify, add, or delete procedures. They must also ensure that this does not affect the normal operation of the DCS, PLC, and SIS. For the testing instruments, switches, relays, interlock procedures, actuators, and their accessories involved in the problem-solving process, it is necessary for two or more persons to confirm and verify them, and then carry out the operations strictly in accordance with the operating procedures. After the problem has been resolved, and before activating the interlock protection, it is necessary for two or more instrument operators to conduct verification and confirmation. For circuits with a memory function, they must be reset. Once confirmed by technical personnel, the process engineers shall activate the interlock protection for those circuits under the supervision of someone, and they must fill out the \"SIS Interlock Protection System Operation Ticket\" promptly. The operation switches and buttons of the SIS interlock protection system are operated by personnel designated by the workshop. The sensing elements, logic units, and actuating elements used in the SIS interlock protection system must be inspected and calibrated during the major maintenance of the equipment and units. Instruments, equipment, and accessories of the SIS interlock protection system must have distinct red interlock markings ； Emergency stop buttons and switches shall be equipped with protective covers. In accordance with the reserve standards and regulations for spare parts management, the interlock protection system must have sufficient spare parts on hand. The components of its power supply system, primary sensing elements, logic units, and control instruments must be replaced regularly according to the specified service life cycles. Routine maintenance involves checking the operation of hardware and software, recording any abnormalities, and promptly fixing any faults that arise during operation. Conduct a thorough inspection of the hardware in the SIS control system; document any abnormalities and include them in the list of items to be addressed during the next maintenance session. Check the operating status of various modules in the control cabinets, the status of scan exits and any damage in different channels, as well as the operation of operator stations, control stations, and the communication network, to ensure that both primary and redundant devices are in proper working condition ； Check the power supply voltage of the Uninterruptible Power Supply (UPS) and the power supply voltage for each cabinet. The voltages of various DC power supplies and the operating status of each power supply module are monitored to ensure that both the primary power supply and the redundant power supplies are in proper working condition ； Check the operating condition of each cooling fan ； Check the temperature and humidity in the engineer’s room ； Review the records of daily maintenance and troubleshooting for computer equipment and systems, and summarize the tasks that require shutdown to be resolved ； Conduct a thorough inspection of the condition of the SIS control system software, document any abnormalities, and include them in the list of items for the next maintenance session: Ensure that complete backups of the SIS control system software and data are made. Data and files stored in volatile memory (such as RAM) should be uploaded and backed up in a timely manner ； Check that the SIS control system software is operating properly; the monitoring software can accurately track the real-time status of the equipment, the configuration software enables the creation of display screens, and it can also properly display the system’s detection information online ； Ensure that the software for recording SOE files in the SIS system remains operational during device operation (it is not necessary for ISC Trusted systems to be running), so that SOE files can be exported correctly ； Ensure that the historical trend function of the SIS system is working properly, enabling long-term monitoring of faulty variables and accurately reflecting the status of equipment or measuring devices ； Inspect the alarm system and make detailed records of any significant abnormal events (such as loss of redundancy, abnormal switching, loss of important signals, data overflow, frequent bus switching, etc.) ； Check the SIS control system operation logs and database operation alarm logs ； Check the SIS self-diagnosis system, compile the abnormal records from the system’s self-diagnosis results, and consult experts on related systems ； Maintenance tasks during operation include fixing system failures; when such failures are detected during inspections, the factors causing the alarms are carefully analyzed. Redundant devices allow for online replacement with new units. Circuits that trigger alarms are checked to resolve the issues, while unknown factors that might affect operations or cause shutdowns are addressed only after the system is shut down ； For the engineer station and operation station maintenance, in the case of software faults, reset them according to the software’s requirements or reinstall them as required; for hardware faults, ensure that all software has been backed up before carrying out any maintenance ； For the maintenance of the configuration software, any modifications to the control screens are proposed and carried out uniformly by the process workshop. The configuration software is used only for viewing the logical configurations online or offline; it does not support modifications during operation ； For the maintenance of measurement equipment, it is necessary to disconnect the relevant interlocks before carrying out maintenance; if needed, the interlocks related to various variables must also be disconnected. The process workshop must confirm that the equipment has been disconnected from the production process before maintenance can take place. After maintenance, it is necessary to check that the measurement circuit of the equipment is functioning properly, and the process workshop must give approval before the equipment can be put back into use. Interlock protection should be reactivated after observation ； Establish ledgers for recording hardware and software failures in the SIS control system, as well as ledgers for documenting software modifications. All issues that occur in the system (including error messages and text), the handling procedures, and every software modification should be recorded in detail ； To prevent the introduction of computer viruses, no other third-party software should be installed on the engineer stations; mobile storage devices must be used for specific purposes only ； Change passwords regularly and keep them securely. For shutdown maintenance, detailed inspections and repairs should be carried out on the cabinets, engineer stations, operation stations, network and interface devices, as well as the power supplies for the module system cabinets. Before starting such maintenance, the equipment must be shut down in accordance with the normal shutdown procedures of the SIS control system: the power supply should be turned off, and the power plug of the equipment to be repaired should be removed ； Cabinet maintenance: (1) Remove dust from the cabinets; assign numbers to each cabinet and slot that requires cleaning, and keep detailed and accurate records of the jumper settings. Clean the modules, cooling fans, and other components ； After the modules have been inspected and the cabinets, racks, and slots have been cleaned, the modules are installed back into their respective slots one by one, using the cabinet and slot numbers indicated on the modules. The installation must be precise and reliable ； (2) Check the backup battery of the SIS control system; replace it with a new one if its charge level is low ； (3) Module inspection contents: There should be no burn marks or damage to the electronic components in each module of the SIS control system ； The connection pins between components should be free from deformation or wear ； Straighten the pins that have become deformed due to distortion of the module mounting baseplate; any baseplate with broken pins must be replaced ； After maintenance, it is required that the base plate be firmly fixed, and the pins be intact, without any deformation or breaks ； Inspect the communication cable connectors in all I/O cabinets and intermediate cabinets of the SIS control system; separators and splitters should be connected properly, and in particular, the shielding wires inside the connectors must be firmly fixed ； Restore the system and check all I/O modules; the circuit connections and plugs should be secure with no looseness, and all setting switches (DIP switches) and jumpers should be configured correctly ； (4) After confirming that the cable connections are correct, restore power supply ； Verify that the fan is rotating in the correct direction, that the indicator lights on all modules are functioning normally, and confirm on the monitor that communication with the SIS control system is normal, with no alarms or error messages ； Maintenance of engineer stations and operation stations: (1) Remove dust from the engineer stations and operation stations, and clean the interior and exterior components as well as the cooling fans. After cleaning, it should be clean, free of dust and stains, with the cooling fan rotating smoothly. (2) After power is connected and the device is started, there should be no abnormal noises, odors, or other issues; it should be able to start up properly and enter the operating system. No error messages should appear during the self-check process, and all status indicator lights as well as the display should function normally ； Check that the cooling fan rotates properly, without any jamming, and in the correct direction ； The display image should be clear, and the buttons should function properly ； The mouse should be flexible and smooth, with correct responsiveness ； Each key on the keyboard should respond promptly and accurately ； (3) The software process for launching the application system should proceed without any abnormalities, with no error messages displayed ； (4) Check the user permission settings for each operator station, engineer station, and service station; they should meet the requirements regarding management and security ； For equipment with anti-static requirements, anti-static measures must be taken during maintenance; staff must wear anti-static grounding wristbands and should avoid touching the electrical components as much as possible ； The removed equipment should be placed on an anti-static mat, and the compressed air gun used for purging should be grounded ； The compressed air used for purging must be dry and free of water and oil, with the pressure controlled at around 0.05 MPa ； The cleaning vacuum must have sufficient power to promptly suck up the dust that is raised ； Special cleaning agents must be used for equipment cleaning ； Maintenance of network and interface devices: (1) Replace faulty network cables or optical fibers ； After maintenance, the communication cables should be free of damage or breaks, and the fiber optic cables should not have any bends ； Ethernet cables or optical fibers should be neatly tied and properly secured ； (2) Clean and inspect the interior and exterior of network devices such as switches, repeaters, and optical transceivers, and tighten connections ； After maintenance, the equipment’s exterior should be clean, free of dust and stains, and all connections and cables should be properly fitted, without any looseness or breaks ； All connectors are in good condition with proper contact ； (3) After powering on, check the status of the module’s indicator lights or use the system diagnostic functions to verify that the communication module and the communication bus system are operating properly, with no abnormal alerts. The redundant bus should be in a redundant operation mode, and the status indicators of switches, repeaters, bus modules, etc. should all show normal when powered on. Check each control system; all I/O channels and their communication status should be normal ； Maintenance of module power supplies, system power supplies, and cabinet power supplies: Clean the power supply equipment and fans; after maintenance, the equipment should be clean, free of dust and stains ； Plug in all the connectors according to the marking notes, confirm they are correct, and then power on. Power-on inspection test: After power is applied, the power supply unit should produce no abnormal noises or odors, and its temperature rise should be normal ； The fan should rotate properly, without any jamming, and in the correct direction. The various output voltages shall meet the specified requirements as per the instructions. When the entire system is started, it should operate normally without any error alerts, and the indicator lights on the power supply should show normal status. For redundantly configured power supplies, turn off any one of them and check whether the corresponding controller can function properly; if not, appropriate action should be taken or the relevant power supply should be replaced. For redundancy performance, redundancy switching tests need to be conducted on four aspects: the operator station, the main controller and modules, the communication bus, and the power supply for the modules, system, or cabinet. Redundancy switching test for the operator station: (1) For devices that operate in parallel, such as operator stations, disabling one or some of these devices should not affect the normal operation of the entire computer control system ； (2) For devices with redundant switching, once the primary operating device is brought offline through means such as a power outage or the shutdown of the application software, the secondary operating device should immediately switch to operational mode ； (3) Conduct a reverse switching test using the same method ； (4) During the aforementioned testing process, aside from fault alarms related to the testing equipment, the system shall not experience any errors or other abnormalities, and the fault diagnosis display shall be accurate. Main controller and module redundancy switching test: (1) Select one of the following methods to conduct the redundancy switching test for the main controller or module: remove the fuse of the main controller or module that is currently in use ； Remove the main controller or module that is in active operation (provided that the module can be plugged in and removed while powered on). Conduct a reverse switching test in the same manner ； (2) During the testing process, the system should be able to switch to a backup controller or module without any disruptions, and the fault diagnosis display should be accurate; aside from alerts related to module failures and loss of redundancy, no abnormalities should occur in the system. Communication bus redundancy switching test: (1) When a device connected to any node on the communication network is switched in or out, bus communication should remain normal ； (2) At any node in the communication network, by alternately cutting off one of the communication connections between the node’s equipment and the bus, the system should not experience any errors or other abnormalities ； (3) Select one of the following methods to conduct a communication bus redundancy switching test: cut off the power supply to the main operating bus module ； Pull out the plug of the main operation bus ； Disconnect the main operation bus cable or terminal matcher ； (4) Conduct a reverse switching test using the same method ； (5) During the test, the communication bus should automatically switch to operate on a redundant bus ； The indicator lights should indicate that the system is operating properly ； Check that system data is not lost, communication is not interrupted, fault alarms are accurate, and the diagnostic display matches the actual test conditions. Test for redundant power supply switching of modules, systems, or cabinets: (1) The redundant power supply systems for modules, control systems, and cabinets shall each be subjected to a redundant switching test: the active power supply circuit shall be disconnected to verify that the backup power supply activates automatically ； For a redundant power supply system, disconnect any one of the power supplies ； Conduct a reverse switching test in the same manner ； (2) During the aforementioned testing process, the control system should operate properly; intermediate data and cumulative data must not be lost, fault diagnosis displays should be accurate, and no errors or other abnormalities should occur in the system. Control performance testing includes the following aspects: analog input (AI) channels, pulse input (PI) signals, analog output (AO) signals, digital input (DI) signals, digital output (DO) signals, system configuration, and online download functionality. Analog input (AI) channel testing: Using the appropriate standard signal source, signals corresponding to 0%, 25%, 50%, 75%, and 100% of the range are applied to the respective terminals of the measurement point. The display values at that measurement point are read on the operator station or engineer station to ensure that the measuring equipment and the measurement circuitry are functioning properly. Pulse quantity input (PI) signal test: Using a standard frequency signal source, signals corresponding to 10%, 25%, 50%, 75%, and 100% of the full scale are applied to the respective terminals at the measurement point. The display values at that measurement point are read from the operator station or engineer station to ensure that the measurement equipment and the measurement circuit are functioning properly. Analog output (AO) signal testing: Using the operator station (or engineer station, or handheld controller), set the output values for each point at 0%, 25%, 50%, 75%, and 100% of the range, respectively, to ensure proper operation of the safety devices. Digital input (DI) signal testing: The state of each input point is changed by shorting/cutting the passive contacts or by adding/removing level signals; the changes in the state of these input points are checked on the operator station or engineer station (human-machine interface), to ensure accuracy. Digital output (DO) signal testing. System configuration and online download function testing: (1) Verify that the permission settings for the engineer station are correct, and log in to the engineer station using an engineer level account. (2) Modify the logical configuration of the SIS control system according to process requirements; compile and generate it when conditions permit. Functions such as configuration, online operation, downloading, and SOE operate normally. (3) Check that the permission settings on the operator station are correct, and log in to the operator station at the operator level. (4) Modify the screen according to logic; the screen editing software should function properly. Check that there are no abnormalities in various process screens, parameter setting screens, etc. The historical trend function is working properly. Archives management: The Equipment Management Department regularly organizes professionals in fields such as instrumentation, electrical engineering, and mechanics to work together with the production units to carefully review and verify the technical documents related to the SIS interlock protection systems of each unit, thereby establishing comprehensive technical archives for these systems. The technical documents available mainly include the interlock layout diagram, the SIS interlock schematic diagram, the SIS interlock program diagram, wiring diagrams, a list of SIS interlock set values, a list of time setting values, textual descriptions related to the SIS interlock protection system, as well as information on the instruments, electrical, and mechanical equipment associated with this system. Maintenance and calibration records for various instruments used in the SIS interlock protection system, etc. Documents such as the \"SIS Interlock Protection System Change Approval Form\", \"SIS Interlock Protection System Work Order\", \"SIS Interlock Protection System Deactivation Approval Form\", and \"SIS Interlock Protection Circuit Test Confirmation Form\" are kept on file by the Instrumentation Department of the Equipment Management Section.