BAS-104 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 device is not selected by point type alone; process, range, dynamics, environment, installation, integration, service, and source authority all matter.
Case overlay
A duct sensor model meets range but not insertion depth, environment, or replacement-access requirements.
Calculation/evidence callout: Calculate requirement coverage, range utilization, accuracy impact, and unresolved source conflicts.
Normal-rule anchor
A precise sensor in an unrepresentative location creates precise bad evidence.
Case overlay
A space sensor sits on an exterior wall above equipment and reads warm while the occupied zone is cool.
Calculation/evidence callout: Calculate sensor error/offset, averaging, response comparison, insertion/coverage from supplied criteria, and control impact.
Normal-rule anchor
Sensor output depends on technology, location, maintenance, time, and context; project ventilation and health decisions require governing sources and qualified review.
Case overlay
A wall CO2 sensor near a door reads outdoor air while occupants report stuffiness in the room center.
Calculation/evidence callout: Calculate ppm difference, percent outside band, dew-point margin from supplied data, calibration offset, and sampling/occupancy timing.
Normal-rule anchor
A transducer measures the pressure relationship delivered to its ports, not necessarily the intended airflow or filter condition.
Case overlay
A hybrid VVT box reads high airflow because high/low tubes are reversed and the pickup is installed near a disturbance.
Calculation/evidence callout: Calculate DP polarity, airflow from supplied K-factor/equation, percent-of-range, error propagation awareness, and tubing/elevation reasonableness.
Normal-rule anchor
Proof must match the consequence: current may show energized load but not airflow, rotation, belt condition, or delivered capacity.
Case overlay
A fan current switch proves while a broken belt leaves airflow near zero.
Calculation/evidence callout: Calculate threshold/margin, analog scaling, delay, false-positive/negative coverage, and command-to-proof timing.
Normal-rule anchor
Command and displayed position do not prove valve travel, flow, seat closure, or heat transfer.
Case overlay
A heating valve reports 100 percent while linkage slips and coil delta T remains near zero.
Calculation/evidence callout: Calculate signal-to-position scaling, stroke time, command/feedback error, supplied close-off/torque margin, and heat-transfer response.
Normal-rule anchor
An actuator shaft turning does not prove blades move or air changes; listed smoke/fire assemblies and testing have separate authority.
Case overlay
An economizer actuator drives while a disconnected linkage leaves outdoor-air dampers closed.
Calculation/evidence callout: Calculate rotation/position, stroke timing, supplied torque margin, outdoor-air fraction, and expected airflow/temperature change.
Normal-rule anchor
BAS relays belong in approved control interfaces, not motor-power legs, and BAS logic does not replace hardwired/listed safety function.
Case overlay
A boiler enable relay is correct, but its proof point is mapped to the command contact rather than burner status.
Calculation/evidence callout: Build truth tables, calculate coil/load and contact-rating margin from supplied data, and compare command/proof timing.
Normal-rule anchor
Common, ground, reference, and shield are not interchangeable; correct signal type with wrong reference is still wrong.
Case overlay
A 0-10 V pressure sensor drifts whenever a VFD runs because its reference and shield are misapplied.
Calculation/evidence callout: Calculate voltage drop, loop scaling, source/load VA/current, expected readings, and noise/error comparisons.
Normal-rule anchor
Adjustment is not automatically correction; first establish reference quality, installation, range, repeatability, tolerance, and process impact. Online mastery supports preparation, not a false field qualification; document both evidence and limits.
Case overlay
A sensor is adjusted at one point to match a questionable handheld reference and becomes worse across its operating range. Changed case: A zone is hot with normal sensor value, full cooling command, no actuator feedback, and a kinked pneumatic-style tubing remnant near a retrofit device.
Calculation/evidence callout: Calculate error, percent span, offset/slope from supplied points, tolerance/uncertainty stack awareness, and pass/fail coverage. Calculate evidence coverage, response timing, error/range, test discrimination, artifact completeness, and temporary-state closure.