Hollysys DCS - a common fault of DCS

1. Field instrument equipment failure:

Field instrumentation equipment includes various transmitters, various switches, actuators, loads and components of various temperatures that are directly connected with the production process. If the field instrument fails, it will directly affect the control function of the DCS system and the monitoring of process parameters by the operator, which will bring certain difficulties to the process operation. In the current DCS control system design, such faults account for the vast majority, and such faults are generally caused by the quality and life of the instrumentation equipment itself. This kind of fault is relatively intuitive, and it is relatively easy to judge and deal with, and there is generally no problem in dealing with the treatment method according to the conventional instrument. The handling of this kind of fault requires maintenance personnel to be proficient in the fault handling of conventional instruments to ensure the timeliness and accuracy of fault handling. Since this kind of fault is a single point of failure, it has little impact on the process, and the maintenance personnel do not have high requirements for DCS system knowledge, and only need to deal with it according to the conventional instrument.

2. System Failure:

This is a global fault that affects the operation of the system, and the system fault can be divided into fixed fault and accidental fault. If a system failure can be restarted to restore the system to normal, it can be considered an accidental failure. On the other hand, if the system cannot be restored to normal after a reboot and the hardware or software system needs to be replaced, it is considered a fixed failure. This failure is usually caused by improper system design or a long operating life of the system.

3. Hardware Failure:

This type of fault mainly refers to the fault caused by damage in the DCS system (I/O module). This type of fault is generally obvious and the impact is localized, and they are mainly caused by improper use or long use, and the aging of the components in the module.

4. Software Failure:

This type of malfunction is caused by a bug contained in the software itself. Software failures are further divided into system software failures and application software failures. The system software is brought by the DCS system, if the design is not well considered, once the conditions are met in the execution, it will cause failure, resulting in downtime or crash. This kind of fault is not common, the application software is programmed by the user himself, in the actual engineering application, because the application software works complexly, the workload is large, so the application software error is almost unavoidable, which requires the DCS system debugging and trial operation to be very serious, careful, timely found and solved.

5. Failure caused by improper operation and use:

In actual operation, sometimes a function of the DCS system cannot be used or a control part cannot work normally, but in fact, the DCS system is not faulty, but caused by the operator's unskilled operation or operation error. This is more common for operators who are new to DCS systems.

Once the DCS system fails, it is urgent to correctly analyze and diagnose the location and cause of the fault, and the fault diagnosis is based on experience, according to the environment and phenomenon of the fault to determine the part and cause of the fault. According to the experience and methods of system fault handling in the usual work, the DCS system fault diagnosis can be carried out as follows:

(1) Whether the fault is caused by improper use. Common faults include power supply failures, terminal wiring faults, module installation errors, and on-site operation errors.

(2) Whether the fault is caused by the operation error of the DCS system. This kind of fault is commonly caused by the setting error of a certain setting parameter and the error of a setting state.

(3) Confirm whether it is a field instrument equipment failure or a DCS system failure. If there is a failure of the instrument in the field, the corresponding field instrument will be repaired or replaced once.

(4) In the case of a system failure, confirm whether it is a hardware failure or a software failure.

(5) If it is a hardware failure, find out the corresponding hardware part and repair or replace the hardware module.

(6) In the case of software failures, it is also necessary to determine whether it is a system software failure or an application software failure.

(7) If the system software is faulty, you can restart it to see if it can be restored to normal or reload the system software, if it cannot be restored after restarting, contact the system management personnel or system manufacturer to solve the problem.

(8) If the application software fails, all the data of the program and configuration written by the user can be checked to find out the cause of the failure.

(9) Use the self-diagnostic test function of the DCS system. Each part of the DCS system is designed with a corresponding self-diagnosis function, and when the system fails, we must make full use of this function to analyze and judge the location and cause of the failure.

In practical application, the DCS system fault should be analyzed and judged according to the actual situation. In the actual use process, common system hardware failures in the field generally include the following aspects:

(1) The failure of system modules and components may be caused by poor quality of components, improper use conditions, improper adjustment, and short circuits caused by abnormal voltages introduced by wrong wiring. Sometimes system hardware failures can also occur due to factors such as temperature, humidity, dust, vibration, shock, rodent infestation, etc.

(2) Line failure: The possible cause is that the cable terminal and plug are damaged or loose, resulting in poor contact, or due to wiring error, improper temporary wiring, broken wire or jumper wire during debugging, or damage due to external corrosion, etc.

(3) Power failure: The cause of the power supply line accident can be caused by the power supply line accident, and the line load mismatch can cause the system or local power supply to disappear, or the voltage fluctuation range exceeds the limit, or a component is damaged, or misoperation and other power supply failures.

Software glitches include:

(1) Program errors, design, programming and operation may occur program errors, especially interlocking, sequential control software, many problems are caused by the process of control requirements are not met.

(2) Configuration error: An error occurs when designing and entering configuration data, which can be called up for configuration data display for inspection and modification.

Since the DCS system is equipped with self-diagnostic programs, the system can timely carry out periodic diagnosis of each circuit and functional module hanging on the bus or network. Through diagnostics, if an anomaly is found, its content is coded or the corresponding fault indication is transmitted, and the information is transmitted through the bus operating station, so that the location of the fault is displayed and reported on the CRT. After understanding the fault situation through the CRT, you should further query the fault content of the abnormal state through the display status of the card inserted in the cabinet or a series of light-emitting diodes on the module. Faults outside the card or module are checked and analyzed step by step.

Hollysys DCS - a common fault of DCS

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