What does the PLC equivalent of an open contact represent?

In programmable logic controllers (PLCs), an open contact refers to a condition where the circuit is not completed, meaning that the flow of electricity is interrupted. This is characteristic of a normally open contact. When the contact is open, it indicates that the associated condition or control signal is not present, preventing current from flowing through that branch of the circuit.

In contrast, a normally closed contact allows current to pass until the control signal or condition actuates something to open the contact. Therefore, when an open contact within a PLC is referenced, it directly correlates to the behavior of a normally open contact, which only conducts when a specific input or condition is met, aligning perfectly with the definition and function of a normally open configuration in electrical circuits and PLCs.