Describe based on the diagram, a PID diagram.
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As shown in the figure, could the expert explain what the control principle behind this is? Why is there an HLO (High-Level Override)? The direct liquid level is high; isn’t it possible to use a control valve? Thank you.
This post was last edited by Feng Qiu Huang on 2024-10-11 at 21:01. What does HLO mean in the legend of this set of drawings?
There’s no legend either – just a picture thrown there. Isn’t the control method supposed to be discussed in conjunction with the manufacturing process?
HLO, you translated it as high-level override； This should be understood as high liquid level locking ； Do you have a complete picture? What type of drawing is this?
I’m not familiar with the process; based on some of the drawings, it seems to be for emergency cooling – used to reduce the temperature in case the reaction liquid level in the tower bottom rises too high
It’s necessary to first understand what HLO means; here it seems to have nothing to do with overriding. A legend for the drawings should be included.
Override control refers to the mechanism by which, when an automatic control system receives abnormal signals such as accident alarms, deviations beyond acceptable limits, or failures, the override logic immediately carries out functions such as automatically switching to manual mode, prioritizing increases or decreases, prohibiting increases or decreases, etc., in order to bring the system into a pre-set safe state while simultaneously issuing alarm signals. Please understand it in light of your own manufacturing processes.
Assuming that the liquid level of this gauge fluctuates frequently (due to a faulty gauge), it is not possible to control these fluctuations in a timely manner using control valves; moreover, this may affect the opening degree of the associated control valves, thereby disrupting the water flow in that emergency pipeline. The choice of HLO here is likely intended to reduce the impact of faulty instruments on production fluctuations. Note: If there is a problem with the control instrument itself, the control loop loses the basic conditions for automatic control; in such cases, the override control mechanism will switch the control loop to manual mode automatically. Externally, it acts as a safety switch for the system. When the automatic control instruments are functioning properly but there are changes in the operating status of the main and auxiliary equipment or various automatic control systems, the override control will determine the control strategy or operating direction of the automatic control system based on the results of its evaluation logic, thereby switching to a safe mode and avoiding potential dangerous situations. The above are merely guesses and for reference only. The actual analysis will be based on the specific process.