The Price Curve between Accuracy Grades in One Product Family
Sensor accuracy price curves scale exponentially because higher tiers demand longer thermal chuck dwell times, lower silicon yields, and guard-banded calibration.
Long Term Drift
Stability Measure
Gradual changes in the output of a measurement instrument over an extended period occur even when the environmental conditions remain constant. Measuring long term drift allows engineers to predict how much an instrument will deviate from its calibrated state over a year or more. This parameter is usually expressed in parts per million or a percentage of the full scale.
Mechanical Aging
Stress relaxation in the materials used to construct the sensor element is a primary cause of these slow changes. Over time, the internal structure of a silicon diaphragm or a metal strain gauge will shift slightly as the residual stresses from the manufacturing process are relieved. This movement results in a slow shift in the zero point or the sensitivity of the device.
Calibration Interval
Setting the frequency of recalibration requires an understanding of how quickly the long term drift will pull the instrument out of its allowed tolerance. An instrument with a low drift rate can remain in the field for several years without needing adjustment. In contrast, a less stable device might require semi annual calibration to ensure the accuracy of the data it produces.
Environmental Influence
Storage conditions also play a role in the stability of the device even when it is not powered on. High temperatures or humidity can accelerate the aging processes that lead to drift.