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Lead/Standby


Relay microblock

The Lead/Standby microblock controls two outputs to maintain an on or off signal. If one of the output signals is interrupted by an alarm condition or an expired runtime, the other output is activated to continue the signal. The output that produces the same signal received by the go input is called the lead output. The other output is the standby output, which becomes the lead output when the lead output is inactivated. This occurs when one of the following happens:

The lead output's corresponding alarm input (a1 or a2) turns on. The a1 input corresponds to the o1 output, and the a2 input corresponds to the o2 output. Note that one of the outputs will be on even when both alarm inputs are on. For example, if a1 is on, then o2 turns on. If a2 then turns on, then o1 turns on even though a1 is still on.

The lead output's runtime expires. The maximum runtime for the lead output can be defined on the microblock's dialog or on the Properties page.

The swap input turns on. When the swap input turns off, the outputs are not affected. Note that as long as the swap input is on, the alarm inputs do not affect the outputs. For example, if o1 is on and swap turns on, then o1 turns off and o2 turns on. If a2 then turns on while swap is still on, o2 will remain on. To avoid this situation, you can send a pulse signal to the swap input that turns swap on only long enough for the outputs to change.

The lstat output turns on when the lead and standby outputs are swapped as a result of the swap input turning on. When the go input is off, both outputs are turned off.

Properties

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