What is a drift/check procedure for instruments?

• A. Periodically verify instrument response against a stable standard to detect drift and perform recalibration if necessary.
• B. Ignore drift and continue sampling.
• C. Calibrate only at purchase and never again.
• D. Use drift as a measurement metric.

Answer: (A)

Regular calibration and drift checking are essential to keep instrument readings accurate over time. Instruments can slowly wander from their true response due to sensor aging, fouling, temperature changes, or electronic drift. To catch this, you periodically expose the instrument to a stable standard—such as a zero air or a calibration gas with a known concentration—and compare the reading to the expected value. If the response has shifted beyond your allowed tolerance, you recalibrate so the instrument once again matches the standard. This practice protects data quality between calibration events and is a fundamental part of QA/QC for air monitoring.

Ignore drift, rely on calibrating only at purchase, or treat drift as a measurement metric would all fail to maintain accuracy. Drift isn’t something you want as a measurement target; it’s a problem to detect and correct to ensure the data you collect reflect the true environmental conditions.