How does PLC seal-in logic operate?

PLC seal-in logic operates by maintaining the state of a control circuit using a second XIC (Examine If Closed) instruction connected in parallel with the initial input condition. This configuration allows the PLC to 'seal in' or hold the output status even after the initial triggering input has gone low, thus ensuring the output remains activated until it is intentionally deactivated by another condition or input.

When the first XIC instruction is true (meaning the input is active), it energizes the output. The parallel connection of the second XIC (which is typically linked to the same output or a control signal that can represent a maintained condition) means that as long as either XIC condition remains true, the output will stay on. This is a common technique used in control systems for maintaining states, such as keeping a motor running or a light on until a different condition (like a stop button being pressed) occurs.

In contrast, other options involve different methodologies that do not effectively demonstrate the sealing logic's persistent state function. For instance, timer-based instructions can manage delays or timing requirements but do not inherently maintain an output state like the XIC parallel connection does. Similarly, using a closing relay or a series of nested instructions may complicate the logic without achieving the