Drift

Table of Contents

In metrology, drift can be defined as the variation caused in the output of an instrument, which is not caused by any change in the input. Drift in a measuring instrument is mainly caused by internal temperature variations and lack of component stability. It also represents a static characteristic of an instrument.

A change in the zero output of a measuring instrument caused by a change in the ambient temperature is known as the thermal zero shift. Thermal sensitivity is defined as the change in the sensitivity of a measuring instrument because of temperature variations. These errors can be minimized by maintaining a constant ambient temperature during the course of a measurement and/or by frequently calibrating the measuring instrument as the ambient temperature changes. Drift may be classified into three categories:

  1. Zero drift: if the whole calibration gradually shifts due to slippage, permanent set, or due to undue warming up of electronic tube circuits, zero drift sets in.
  2. Span drift or sensitivity drift: if there is a proportional change in the indication all along the upward scale, the drifts are called span drift or sensitivity drift.
  3. Zonal drift: in case the drift occurs only a portion of the span of an instrument, it is called zonal drift.
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