Equipment Setup, Calibration, and Quality Control
Calibration is a daily, documented act
Calibration establishes the relationship between a known input and the signal the device records. Verification (the "calibration check") proves that relationship still holds. Candidates blur the two; exam items do not.
Daily, before patient testing, perform a volume calibration check with a 3-L syringe: three slow, complete injections across the flow range. Acceptance is within ±3.5% of the syringe volume (about 0.105 L on a 3-L syringe), with newer ATS/ERS standards tightening the limit to ±3%. Record the date, syringe volume, measured volume, percent difference, technician initials, and any corrective action.
Also verify: no leaks in the circuit, timer accuracy (within 1% over 24 hours), and correct BTPS conversion, which requires measured ambient temperature and barometric pressure. Let the syringe equilibrate to room temperature; a cold syringe delivers a different gas volume than the spirometer assumes. Linearity checks with 1-L increments and flow checks are performed periodically (commonly weekly) and after any repair, relocation, or unexplained shift.
Biological control: a healthy nonsmoking staff member performs maneuvers regularly, plotted on a control chart; drift beyond the established limits triggers troubleshooting before patients are tested.
Trap: passing the 3-L check does not prove linearity - a device can be accurate at 3 L and wrong at 1 L or at high flow.
Worked example: three injections read 2.94, 2.97, and 2.95 L. Mean = 2.953 L; difference from 3.000 L is −0.047 L, or −1.6% - comfortably within ±3.5%. Accept and document.