Abstract: Abstract: To reduce the influence of air-flow changes on differential-pressure alarms in desulfurization ash pipelines, a fixed-constriction, single-phase air reference section was studied. Differential pressure was normalized by mass flow and a fixed healthy baseline; validity checks, hysteresis and independent protection priority were combined for graded outputs. Three methods were compared using four calibration conditions, eight independent conditions and identical artificial perturbation arrays. Across flow rates at unchanged geometry, the differential-pressure range relative to the intermediate-flow reference was 50.29%–56.55%, compared with 6.50%–13.50% for resistance. The validity-and-hysteresis method yielded conditional false-positive and false-negative rates of 7.72% and 0.99%, with 79.54% coverage and a 21.27% missed-or-rejected fraction among positive inputs. These results characterize the trade-off between erroneous alarms and valid coverage and support interpretation of measurement-section resistance anomalies.