BAS-305 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 number cannot be calibrated in the abstract; define measurand, location, state, reference, tolerance, and time.
Case overlay
A space sensor is compared to a handheld reference immediately after entering the room.
Calculation/evidence callout: Calculate expected range and stabilization window from supplied process limits and response-time data.
Normal-rule anchor
High display resolution does not guarantee accuracy, and a reference must be better enough for the stated acceptance decision.
Case overlay
A ±0.5°F sensor is checked with a ±1.0°F reference that is near the end of its range.
Calculation/evidence callout: Combine supplied device and reference uncertainty using the stated course method and compare to acceptance tolerance.
Normal-rule anchor
Correct raw signal with wrong engineering units points toward configuration, scaling, or representation before sensor replacement.
Case overlay
A 12 mA signal on a 4–20 mA, 0–2000 ppm input displays 2000 ppm.
Calculation/evidence callout: Use fraction = (signal−low signal)/(high−low), then EU = low EU + fraction×span.
Normal-rule anchor
Agreement at one point does not prove span, response, placement, or performance across the operating range.
Case overlay
A wall sensor reads warm only when afternoon sun strikes the wall cavity behind it.
Calculation/evidence callout: Calculate error, percent span when authorized, dew point, response lag, and two-point offset/span pattern.
Normal-rule anchor
Damper position or pressure alone does not equal airflow; tubing, pickup, range, density, and K-factor must match.
Case overlay
A VAV airflow value remains high with the fan off and one pickup tube is reversed.
Calculation/evidence callout: Use the supplied relationship such as flow = K×√ΔP only when K, units, density basis, and pickup geometry are defined.
Normal-rule anchor
A 3–15 psi branch signal is an analog control signal, not proof that the actuator reached position or the process responded.
Case overlay
A 3–15 psi actuator remains closed at 9 psi while the EP transducer output matches command.
Calculation/evidence callout: For a linear 3–15 psi signal, percent = (psi−3)/12×100; compare command, branch pressure, stroke, and process separately.
Normal-rule anchor
Current proof does not prove airflow, and CO2 does not measure total IAQ or certify ventilation by itself.
Case overlay
A fan current switch proves on while the belt is broken and the CO2 sensor reports a plausible but stale value.
Calculation/evidence callout: Calculate current threshold margin, data age, sensor error, and supplied indoor-outdoor CO2 differential without health claims.
Normal-rule anchor
A front-end offset can hide one displayed error while leaving failed span, location, tubing, or process causes unresolved.
Case overlay
A sensor agrees at 70°F but is 4°F high at 90°F and 3°F low at 50°F.
Calculation/evidence callout: Calculate errors at each point, best-fit offset/span indication, hysteresis, noise range, and drift rate.
Normal-rule anchor
Correct the cause within authority; do not use software to make one display agree while corrupting alarms, resets, or analytics.
Case overlay
A discharge-air sensor bias affects economizer logic, low-limit alarm, reset, trend, and energy analytics.
Calculation/evidence callout: Quantify before/after error and enumerate affected control, alarm, trend, graphic, calculation, and analytics consumers.
Normal-rule anchor
Calibration interval comes from source requirements, criticality, environment, history, and risk—not a universal annual rule.
Case overlay
Three years of comparable records show increasing drift on a critical mixed-air sensor.
Calculation/evidence callout: Calculate drift per comparable interval and separate observed history from unsupported extrapolation.