A change in what an instrument reads over time, steady or in jumps, that comes from the instrument itself, such as a Zener reference wandering a ppm or two per year or a pressure transducer's zero creeping as its sensor ages. Drift is estimated from a run of calibration results and enters the budget as a separate component covering the time since the last calibration. Predictable drift can be corrected; erratic drift shortens the calibration interval.
Plot the last five cals on the 10 volt, the drift is a steady plus 0.8 ppm a year, so we can predict it.
Also heard as
- long-term drift
- aging
Do not mix it up with
- Stability: Stability describes how well an instrument holds its properties; drift is the measured change when it does not.
Related terms
Stability
The ability of an instrument or standard to hold its calibrated values as the weeks and months pass.
Calibration interval
The scheduled time between calibrations of an instrument, set to keep the chance of drifting out of tolerance low.
Check standard
A stable item measured regularly to confirm a measurement process still behaves as it did when characterized.
Offset
A constant error that shifts every reading by the same amount, most often seen as a nonzero reading at zero input.
Imported uncertainty
The uncertainty carried into a measurement from the calibration certificate of the reference standard used.