What does the term 'drift' mean in relation to measuring instruments?

The term 'drift' in relation to measuring instruments refers to the gradual change of the output signal over time. This phenomenon can occur in various types of sensors and measurement devices, where the readings may shift away from the true value even though the conditions being measured remain constant. Drift can happen due to various factors such as changes in temperature, humidity, or even aging of the components within the instrument.

Understanding drift is crucial for ensuring accurate measurements over time. Without proper calibration and adjustment, the reliability of the data obtained from the instrument can be compromised, leading to inaccuracies in process control and monitoring. Thus, recognizing and compensating for drift is an essential part of maintaining measurement integrity in instrumentation.

The other options describe different concepts: initial error at calibration refers to errors present at the moment of calibration rather than changes over time, the speed of measurement is related to how quickly an instrument can take readings, and delay in response pertains to the time taken for an instrument to react to changes in the measured parameter. Each has its own significance but does not capture the essence of 'drift' as effectively as the correct option.