Response Change
The gradual alteration of the relationship between an input signal and the resulting output of an instrument characterizes a common form of measurement error. Occurring over long periods, sensitivity drift leads to a loss of accuracy even if the zero point of the sensor remains stable. The rate of this change determines how often a device must be recalibrated to maintain its specified performance level.
Degradation Mechanism
Physical changes in the sensing element, such as oxidation, material migration, grain growth, or mechanical fatigue, are primary causes of this shift. In piezoresistive sensors, changes in the dopant concentration or the structural integrity of the bridge resistors can alter the gain. These processes are often accelerated by exposure to high temperatures or corrosive chemicals.
Calibration Verification
Detecting this error requires a multi-point calibration that checks the sensor response at several different levels within its full scale range. A simple check at zero is insufficient because it cannot identify changes in the slope of the transfer function. When the measured sensitivity falls outside the manufacturer’s tolerance, the sensor must be adjusted or replaced.
Monitoring the trend of these changes over multiple calibration cycles helps operators predict the end of a sensor’s useful life.
Compensation Strategy
Modern digital instruments use internal software algorithms to correct for known drift patterns based on operating hours and temperature history. This approach extends the time between manual checks and improves the overall reliability of the data.
