Baseline Output
The residual electrical signal generated by a pressure sensor when no external physical force or pressure is acting upon its diaphragm is an essential metric in instrument qualification. This value, known as piezoresistive zero offset, is measured during initial calibration to establish the starting point for all subsequent measurements. Ideally, the sensor output should be zero volts or a nominal reference value under zero-load conditions.
However, tiny manufacturing variations in the resistor network create a non-zero baseline that must be accounted for. Engineers measure this baseline to ensure it falls within acceptable factory limits.
Strain Influence
Internal packaging stresses act directly on the microscopic resistors embedded in the silicon, altering their baseline resistance. These stresses contribute substantially to piezoresistive zero offset even before any pressure is applied to the sensor. The mounting adhesive or gel encapsulation can also exert slight pressures that shift the baseline.
This shift must be minimized by careful sensor design.
Calibration Adjustment
Software algorithms and resistor trim networks are used to null out these unwanted starting voltages during the final production stages. This process corrects the piezoresistive zero offset to ensure accurate readings from the very first measurement. It is performed at the wafer or package level to optimize accuracy.
Modern sensors utilize digital signal processors to execute this correction dynamically.
Thermal Stability
Temperature shifts can cause the baseline signal to drift, requiring active compensation across the operating range. If the piezoresistive zero offset is highly temperature-dependent, the sensor will lose accuracy when the environment heats up. This drift is compensated for using on-board temperature sensors.
