The request
“Create an FBD that runs pump 1 when high level and pump 1 is available, and runs pump 2 when high level, pump 1 is unavailable, and pump 2 is available.”
Then tryAdd a low-level stop input to both outputs.Add a run-hour alternation input.
What is in this drawing
Read the decisions behind it.
01Demand
High level starts the selection.
02Priority
Pump 1 is the preferred available pump.
03Fallback
Pump 2 runs only when pump 1 is unavailable.
Use as a simple selection pattern before adding interlocks, faults, and alternation memory.
More like this
Other examples in this family.
FAQ
Common questions
What is an FBD network?
It is a grouped set of function blocks that performs one part of the control logic.
Why is pump 1 negated for pump 2?
The fallback runs only when the preferred pump is unavailable.
Does this alternate pumps?
No. It selects a preferred pump; alternation needs additional state logic.