Switch-type sensor contact issues
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For switch-type sensors—such as level switches, vibration switches, pressure/differential pressure switches, etc.—the NO and NC contacts: do the terms “NO” and “NC” refer to the state when the sensor is not powered on/not in use, or to the state under normal operating conditions once it is in use? Are there any uniform regulations? Does it vary by product/manufacturer? I’ve never been able to figure it out; I’ve gotten the logic wrong several times. Do we have to check the manual or use a multimeter every time before installing and using it?
NO: Normal Open contact. NC: Normal Close contact
Generally, these switches come with both normally open and normally closed contacts. In ordinary circuits, it doesn’t matter which type of contact is used, but in fail-safe designs, it is usually necessary to use the normally closed contacts.
2# lmsa613 agrees with this; it is indeed like this in the initial state.
3# liaoshengli Thank you! But I have seen two fail-safe systems where, in one system, the pressure differential switch is connected in an open circuit configuration, while in the other system, the vibration switch is connected in a closed circuit configuration. My doubt remains: does the so-called normal open or normal closed state refer to the condition when it is not in use, or to the condition under normal operating conditions? Without knowing the internal procedural logic, it is difficult to determine whether to use an open-circuit or a closed-circuit connection, even when following the fail-safe principle.
3# liaoshengli Thank you! What does the second floor refer to? What kind of state is the “initial state” you are referring to? Status under normal operating conditions?