The commissioning process serves as a pivotal task in verifying the capability of a PLC control system to meet specified control requirements, offering an objective and comprehensive assessment of the system's performance. Prior to the operational deployment of the system, rigorous testing and commissioning of all system functions must be undertaken until the requirements are met and signed off by relevant user representatives, supervisors, designers, and others, signifying their approval for its use. Commissioning personnel should have undergone systematic and specialized training, familiarizing themselves with the composition of the control system, as well as the usage and operation of both hardware and software components.
Any issues identified by the commissioning personnel during the process should be promptly communicated to the concerned designers. Modifications can only proceed with the designers' consent, and detailed records of these changes must be maintained. The modified software must be backed up, and proper documentation and archiving of the commissioned and modified sections should be carried out. The commissioning scope primarily encompasses testing of input/output functions, control logic functionalities, communication capabilities, processor performance evaluations, among others.
Input/Output Circuit Commissioning
Carefully verify the address allocation of the I/O modules. Check if the loop power supply mode (internal or external) matches the field instrumentation. Utilize a signal generator to apply signals to each channel at the field end, typically testing at 0%, 50%, and 100% points. For AI loops with alarm and interlock values, also inspect the alarm and interlock thresholds (such as high alarm, low alarm, interlock points, and accuracy) to confirm the correctness of the associated alarm and interlock states.
Based on the loop control requirements, manually output (i.e., directly set in the control system) to check the actuators (e.g., valve positions), typically testing at 0%, 50%, and 100% points. Additionally, perform closed-loop control checks to ensure the output meets the relevant requirements. For AO loops with alarm and interlock values, inspect the alarm and interlock thresholds (including high alarm, low alarm, interlock points, and accuracy) to confirm the correctness of the associated alarm and interlock states.
Short-circuit or disconnect at the corresponding field end to observe changes in the light-emitting diodes (LEDs) corresponding to the channel addresses of the discrete input module. Simultaneously, check the channel's open and closed status changes.
Utilize the forced function provided by the PLC system to inspect the output points. By forcing the outputs, observe changes in the LEDs corresponding to the channel addresses of the discrete output module. Concurrently, check the channel's open and closed status changes
Precautions for loop Debugging
The positive logic principle is commonly adopted, which means when the input/output is energized, it is in the "ON" state with a data value of "1"; conversely, when the input/output is de-energized, it is in the "OFF" state with a data value of "0". This facilitates understanding and maintenance.
In other words, field contacts should not be directly connected to the input/output modules whenever possible.
At no time should an excessive number of points be forcibly operated simultaneously to avoid damaging the module.
Control Logic Function Debugging
The process of control logic function debugging necessitates collaboration among designers, process representatives, and project managers. This involves utilizing the testing functionality of the processor to set input conditions and verifying the correctness of output state changes based on the processor's logic, thereby confirming the system's control logic functionality. For all interlocking circuits, it is essential to simulate the interlocking process conditions, meticulously examining the accuracy of the interlocking actions, and maintaining detailed debugging records with countersignature confirmation.
The inspection process serves as the acceptance phase for the designed control program software, representing the most intricate, technically demanding, and challenging aspect of the debugging process. In particular, when dealing with patented technologies, proprietary software, or specialized applications, it is imperative to conduct an even more rigorous examination of control accuracy, allowing for operational margins while ensuring the normal functioning of process operations alongside the system's safety, reliability, and flexibility.
Processor Performance Testing
Processor performance testing must be conducted in accordance with the requirements outlined in the system specifications to ensure the system possesses the described functionalities with stability and reliability. This includes the inspection of system communication, backup batteries, and other specialized modules. For systems configured with redundancy, a mandatory redundancy test must be performed, comprehensively examining all aspects of the redundant design, such as power redundancy, processor redundancy, I/O redundancy, and communication redundancy.
Upon disconnecting one of the power sources, the system should continue to operate normally without any disturbance. The power supply that was disconnected should be able to resume normal operation upon being reconnected.
When the power to the primary processor is cut off or its operational switch is toggled, the hot-standby processor should automatically take over as the primary processor, maintaining normal system operation without output disturbance. The disconnected processor should be able to resume normal operation and return to standby mode upon being powered back on.
Select input and output points that are mutually redundant and have corresponding addresses. Apply identical input signals to the input modules, and connect the output modules to status indication instruments. Toggle (or hot-swap, if allowed) the redundant input and output modules individually, verifying that their states remain unchanged.
In accordance with the design requirements, all modules designed with redundancy must undergo redundancy checks. Additionally, system functionality inspections encompass system self-tests, file searching, file compilation and downloading, maintenance information, backups, and other functions. For more complex PLC systems, system functionality checks also include logic diagram configuration, loop configuration, and special I/O functionalities.