Why is a normally closed signal used for the module instead of a normally open one?
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This post was last edited by wwwhaowww on 2015-8-19 07:32. It is a vertical temperature measurement rod device, with two proximity switches at the top and bottom, both of which are normally open type. On the input module in Diagram 2, the normally open switch has been changed to a normally closed one, but I think it should be normally open; I’m not sure why. Does anyone know how to resolve this?
This requires considering the requirements of the process operating conditions
Is the temperature sensing rod device on site essentially a temperature switch? From a fail-safe perspective, the contacts need to be disconnected when the temperature reaches the interlock value. Therefore, the high-temperature interlock is connected to the normally closed circuit, while the low-temperature interlock is connected to the normally open circuit. Since there are drawings, why not upload screenshots of them? Only then can everyone help you analyze and solve the problem.
I don’t understand; what kind of processing module is this? Generally, this situation is related to the manufacturing process.
The proximity switch should have both normally open and normally closed contacts, so that homeowners can choose according to their needs, right? On the drawing, it shows a normally closed contact; that must be a requirement of the manufacturing process.
Generally, it is necessary to consider system safety; therefore, \"fail-safe\" type contacts are usually chosen, so that any electrical faults in the equipment can be detected.
In addition to the drawings on the 3rd floor, please send the model of the proximity switch, or a photo of it. This allows for a comprehensive analysis.
In the case of SIS systems as well, fail-safe functionality is categorized; for ESD systems, the safe state is 0, and power is cut off in the event of a failure； For the FGS system, the safe state is 1; an alarm is triggered in case of a fault. It is necessary to determine what constitutes the safe state based on the process requirements.
Our system is equipped with a manual emergency stop button; no mechanical limit protections or other such devices have been installed in the automatic control system. Finally, the proximity switch for the lower limit was changed to a normally closed type, so that it can still provide some level of safety even if it fails
Thank you, brother. The problem has been solved~
Yes, you can choose between normally open and normally closed