BAS-401 Visual Aid Library
Figure-use rule
Each figure is an orientation and reasoning aid, not a project drawing. Learners must pair it with the current sequence, point list, wiring/piping documents, manufacturer instructions, and as-found evidence.
Normal-rule anchor
A programmer implements current approved intent; code is not permission to redesign, defeat a safety, or conceal a conflict between requirements.
Case overlay
A project sequence says the fan shall run when occupied, while the approved safety matrix adds smoke shutdown and low-temperature lockout.
Calculation/evidence callout: Build a requirement-coverage matrix; every shall statement maps to logic, evidence, test, owner, and status, and unresolved conflicts remain open.
Normal-rule anchor
Logic that is mathematically correct can still fail when type, scan order, initialization, task rate, stale quality, or retained state is misunderstood.
Case overlay
A one-scan pulse is consumed before a downstream block sees it, and a retained mode returns after an unexpected restart.
Calculation/evidence callout: Compare task period, process time constant, pulse duration, and network update rate; state whether an event can be detected and whether aliasing or stale data is likely.
Normal-rule anchor
Displayed command, effective command, physical output, equipment action, and process result are separate states and require separate evidence.
Case overlay
A fan graphic shows AUTO and a start command, but a higher-priority value holds the BO off and the current switch remains open.
Calculation/evidence callout: Convert raw input to engineering units and reconcile all active priority slots, fallback value, command, proof, and process response.
Normal-rule anchor
Safeties and interlocks are explicit conditions with defined reset and failure behavior; burying them inside a permissive chain makes testing and diagnosis unsafe.
Case overlay
A pump request is true, but low level blocks start; after level recovers, the trip must remain latched until an authorized reset.
Calculation/evidence callout: Enumerate all input combinations for up to four conditions and prove that no unsafe combination can energize the command.
Normal-rule anchor
A timer must state what starts it, what resets it, whether it retains through restart, its time base, its permitted range, and why that duration is appropriate.
Case overlay
A compressor request chatters around a threshold, a holiday schedule is active, and a temporary occupied override has no expiration.
Calculation/evidence callout: Calculate elapsed time, minimum cycle interval, starts per hour, schedule overlap, and required sample/task rate with units and a reasonableness check.
Normal-rule anchor
Every analog expression carries units, valid range, fallback quality, limits, and a reasonableness test; correct arithmetic on bad data is still bad control.
Case overlay
A 0-10 V outdoor-air sensor represents -40 degF to 140 degF and drives a supply-air reset that must remain between 52 degF and 65 degF.
Calculation/evidence callout: Calculate slope and intercept, test 0%, 50%, and 100% input, convert units if required, and confirm output saturation and direction.
Normal-rule anchor
Tuning follows verified sensor, actuator, valve/damper, direction, authority, load, and sequence checks; gains cannot repair a wrong sensor, stuck final element, or unstable upstream process.
Case overlay
A discharge-air loop oscillates every eight minutes while the valve repeatedly reaches 0% and 100%, and the sensor is located downstream of mixed air.
Calculation/evidence callout: Determine error sign, percent span, oscillation period, settling time, overshoot, saturation time, and whether the sample interval can represent the loop.
Normal-rule anchor
If mode priority, transition rules, timeouts, and restart defaults are not explicit, the program contains hidden sequences that will emerge during abnormal conditions.
Case overlay
An AHU loses communication during warm-up, power cycles, and returns with a stale occupied request and a latched freeze alarm.
Calculation/evidence callout: Check state coverage and transition completeness; calculate timeout and restart windows and prove that every state has a safe exit or intentional latch.
Normal-rule anchor
Reusable code must make variation explicit through parameters and interfaces; copy-and-paste logic that silently diverges is a maintenance defect.
Case overlay
Eight VAV programs differ only in box size, flow limits, and reheat type, but each contains undocumented local edits.
Calculation/evidence callout: Compare duplicate block counts, parameter coverage, cyclomatic decision count, comment/revision completeness, and estimated review/test effort.
Normal-rule anchor
A successful normal case is not release evidence; critical logic must also survive negative, boundary, loss-of-proof, communication-loss, restart, and rollback tests.
Case overlay
The logic passes occupied cooling but fails when fan proof drops after start and leaves a valve command active after the test.
Calculation/evidence callout: Reconcile test cases planned, passed, failed, deferred, and blocked; verify checksums/versions and calculate response times against acceptance tolerances.