Seeking help with SIS interlock logic issues
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In the SIS interlock logic, isn’t it required that the contacts at the input side be in a disconnected state? Isn’t it said that SIS requires an interlock state of 0, or is it only the output that needs to be at 0 for interlocking, while the input does not have such a requirement?
Putting aside the site conditions and design, it’s possible to use either 1 unit or 0 units; in reality, it depends on the manufacturing processes and the need to ensure fault safety – it’s not fixed
The SIS design is safety-oriented; its logic can be 0 or 1, but the hardware contacts are usually 0.
As the original poster said, if a 0-series action is desired, it should be a normally closed contact, not a normally open contact. For the normally open contact, you have 1 interlock in place.
Regardless of whether it is positive logic or negative logic within the logic system, safety must be the primary consideration on site – this is the original purpose of the SIS system. Typically, a value of 1 indicates normal operation, while 0 indicates interlock activation.
The SIS system requires fail-safe operation. By fail-safe operation, it is meant that under normal conditions the input contact is closed (logic 1), while in the event of a fault it becomes open (logic 0). The purpose of this is to ensure that an interlock action is triggered even if there is a fault with the input switch (for example, if the coil burns out and causes the contact to open), as a fault in the contact itself also constitutes a fault.
Unlike DCS, SIS operates on inverse logic
You should be referring to the trigger signal; there are 1-trigger and 0-trigger types