What is override interlocking

Override control is selective control. One controller is used under normal conditions in the process, and another controller is used under abnormal conditions.

Override control and selective control mean the same thing. Usually, when a fault occurs during operation, there will be two sets of protection schemes. One is called hard protection, which means that once a fault occurs, there is no other emergency plan on site and the car has to be stopped for processing. The other is soft protection, which is what we often call override control. Once a fault occurs, another set of control schemes will be automatically put into use, which ensures the continuity of production and improves the safety index. Usually there is an override controller in override control, low selection or high selection, which selects one signal among multiple input signals to play its main role, thus playing the role of safety interlock. A little humble opinion

In fact, it is a protection, just understand it as protection!

For example, the control of the feed valve may be temperature control under normal conditions to ensure the temperature. When the liquid level is high, it may switch to a low-select low-select signal. The smaller value of the output from the temperature control and the liquid level control output ensures that the valve is at a small opening and ensures that the liquid level will not be super high. This is what I understand as override low-select control.

This post was finally edited by neuzkm on 2013-10-16 11:49. After reading the detailed explanation upstairs, I learned* Got it!

Override means interlock enforcement. The device operates when there is a high-level protection signal. However, the level of forced interlock execution may not be lower than that in place, depending on the production situation! The so-called override control means that when the automatic control system receives abnormal signals such as accident alarms, deviation limits, and failures, the override logic will immediately execute logical functions such as automatic manual switching, priority increase, priority decrease, prohibition of increase, prohibition of decrease, etc. according to the cause of the accident, convert the system to a preset safe state, and send out an alarm signal. In the past, most control systems composed of conventional control instruments lacked the ability to identify the status and quality of equipment inside and outside the system. As long as there is a deviation signal at the input end, the controller will take corresponding actions, regardless of whether there is a problem within the system or whether the external production equipment is working abnormally. Sometimes the control may even deviate from the given value, causing an accident. Override control can effectively suppress the above adverse consequences. Internally, it is the eye that monitors the automatic control process, detecting the quality of the transmitter signal in the control loop, input and output deviation limits, etc. at any time. If there is a problem with the control instrument itself, the control loop loses the basic conditions for automatic control. The override control will choose the automatic manual mode to automatically switch the control loop to manual; externally, it is the safety transition device of the system. If the automatic control instrument is normal and the operating status between the main and auxiliary equipment or various automatic control systems changes, the override control will determine the control strategy or operating direction of the automatic control system based on the results obtained from the judgment logic, thereby switching to a safe channel and escaping from possible dangerous conditions. Both DCS and FCS are designed with override control functions.

The explanation above is correct. Honeywell systems often use the term override.

I understand, overriding is equivalent to selective control, it’s just a different term.

I saw override control yesterday and didn't understand what it meant. Now I have a general understanding, but it seems that our system has not yet used it. I don’t know how to implement it in central control DCS? Use program blocks?