Valve position switch selection
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Valve position switches come in NAMUR, proximity, and mechanical types; are normally open and normally closed options available for all of them? (Some say both are available, while others say that NAMUR only offers normally closed types.) Is there a requirement regarding whether normally open or normally closed should be used? Is it the same whether to choose normally open or normally closed for DCS and SIS? Is fault safety taken into account? Is there any regulatory support?
The types of valve position switches include NAMUR, proximity, and mechanical. Normal open (NO) and normal closed (NC) are the two basic functions of valve position switches. Different types of switches may support both functions, but there are indeed some specific types of switches that only support one of them. Taking the NAMUR switch as an example, it is designed primarily to meet explosion-proof requirements, and some models or brands may only offer a normally closed function. When deciding between normally open and normally closed, safety and the specific requirements of the application are the main considerations. Generally, when choosing between normally open or normally closed, the safe state of the device in the event of a power loss or failure (Fail Safe) must be taken into consideration. For example, in certain applications with high safety requirements, a normally closed type may be chosen to ensure that the valve closes automatically in the event of a power failure, thereby avoiding potential hazards. The choice of systems to be integrated into DCS (Distributed Control Systems) and SIS (Safety Instrumented Systems) also typically needs to be determined based on the system’s Safety Integrity Level (SIL) and fail-safe requirements. For example, SIS systems may prefer to use normally closed types to ensure that the system can be shut down safely in emergency situations. As for standards, specific choices and applications often draw on relevant industry standards and safety regulations, such as IEC 61508 and IEC 61511, which provide guidance on the design, selection, and maintenance of safety instrumented systems. .
For intrinsically safe explosion protection, NAMUR is chosen, and it must be used in conjunction with a safety barrier; the rest are basically dry contacts, normally open
It’s still pretty good, isn’t it? Haha