Consultation on the definition of “interlock” for those not majoring in instrumentation
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I’ve heard that the key to interlocking lies in the word “lock.” For example, if a reaction vessel overheats, the valve controlling the feed pipeline is closed – this is what is meant by interlocking. Once the valve is closed, it remains locked and cannot be opened automatically; human intervention is required. In another scenario, if the reaction vessel overheats, the valves in the hot medium pipelines will close. If the temperature returns to normal and those valves are opened again, then this situation is not considered a \"interlock\", is that correct?
This post was last edited by superme84 on 2020-4-22 09:45. This person has a decent level of understanding, but it’s not yet complete. Interlocks can be classified by purpose into process interlocks and safety interlocks. Many process interlocks do not require manual reset, as their main function is to ensure the continuous operation of production. Most safety interlocks require manual reset to confirm an abnormal condition. Both are forms of interlocking; the only difference is whether human confirmation is required.
In other words, the high and low limit alarm signals from the instrument itself are interlocked with other control devices in the plant, such as valves; when these limits are exceeded, the valves or other devices will act to ensure production safety or to keep the process parameters within acceptable ranges.
Interlocking means that measures must be taken when the interlocking conditions are met – opening valves, starting pumps, stopping pumps, starting machines, shutting down machines….
This post was last edited by stone_HOTO on 2019-11-8 09:48. The key to interlock systems lies in the word “lock”; therefore, interlocks are protection mechanisms that come into action when process values exceed safe limits, such as activating valves, stopping pumps, or shutting down devices. There are three ways to achieve this, depending on the process and operations as well as safety requirements: 1. Manual emergency shutdown, which involves human judgment; after the interlock protection is activated, it triggers an automatic response. 2. It is an automatic interlock protection system controlled by DCS or PLC; once the interlock is triggered, manual reset is required for the system to operate normally. 3. It is also an automatic interlock protection system controlled by DCS or PLC, but in this case no manual reset is needed – once the process parameters return to normal, the interlock is automatically deactivated and the system can operate normally
Interlock, the English term for this concept, is composed of the prefix Inter- and the word lock; the prefix Inter- indicates mutual connection, while lock means to secure something in a safe state. ‘’Interlocking’ refers to the mechanism of locking the production process into a safe state by taking emergency actions such as shutting off or opening valves, stopping or starting pumps or fans, based on interconnected events; these actions are taken once such events occur. When the interrelated events cease, normal operation can be automatically restored or manually returned to its usual state.