In a simple control loop, which link is most likely to cause problems?

Let me say it first: I think the final execution link is the most likely to cause problems, because the execution valve is always moving. The control mechanism is the least likely to cause problems, because the hardware is redundant, and the probability of software problems is very small. What do you think?

Experience summed up in long-term production process: The easiest and most common place to go wrong is in the pressure and source parts.

Summary of practical work experience: In the control loop, there are three links that are most likely to cause problems. 1. Measurement process. In the measurement process, sampling points are prone to problems. 2. In the execution link (control valve assembly), the control valve is stuck. 3. The air supply to the instrument carries impurities in the air supply system, causing blockage problems in the instrument locator, echo device, etc. Once one of the above situations occurs, it will inevitably cause problems in the control loop, resulting in production fluctuations and even production accidents. Precautions: 1. In the measurement process, during the measurement process, the diameter of the sampling point of the measuring meter should be as large as possible to reduce clogging. 2. The instrument supplies air to ensure stable air source pressure, and the static air tank must maintain continuous condensation discharge. 3. Sufficient spare parts.

The actuator is most prone to problems. The valve positioning is inaccurate over time, and the air source is not regularly drained. When it gets cold in winter, the air source pipe freezes. The results can be imagined. Solution: Calibrate valves regularly and drain sewage regularly by operators.

Personal experience: 1. The measurement link is where the most problems occur. The pressure pipe is blocked due to medium reasons, overheating or frozen meters caused by northern heating problems, etc. Therefore, generally important interlocking tables usually use 2 out of 3, and important control tables also use 2 or 3 tables for redundant configuration. 2. Control link. This link is basically implemented in control systems, such as DCS, PLC, etc., and I/O mostly uses redundant structures, so the probability of problems is low. 3. In the execution link, there are many problems in this link, such as air source problems, internal leakage caused by erosion of valve internal parts, problems caused by insufficient or too tight packing, etc. 4. In addition, intermediate links, such as input and output safety barriers and intermediate lines, are also areas where problems often occur.