Silicon Pressure Cell Fill Oil Volume Verification Methods
Confirm fill oil volume using pre- and post-injection micro-gravimetric mass checks combined with non-contact laser interferometric diaphragm dome profiling.
Zero Thermal Drift
Sensor Behavior
Metrological stability dictates how a sensor’s baseline output varies when exposed to temperature changes in the absence of applied pressure. When a pressure transmitter is heated, zero thermal drift causes the reported pressure to shift away from the actual zero value. This deviation is expressed as a percentage of the full-scale span per degree Celsius.
It is a major source of error in field measurements.
Material Balancing
Thermal expansion mismatch between the silicon sensor chip, the metal diaphragm, and the glass feedthrough creates internal mechanical stress. As this stress changes with temperature, zero thermal drift is induced due to the piezoresistive effect of the sensing elements. Minimizing this effect requires selecting materials with closely matched coefficients of thermal expansion.
Manufacturers use automated temperature chambers to characterize this drift for each sensor.
Calibration Routine
Digital compensation uses a built-in temperature sensor to measure the housing temperature and apply a correction factor in real time. To minimize zero thermal drift, the transmitter microprocessor applies a polynomial curve-fit calculated during the factory calibration. This process involves recording the zero-point output at multiple temperatures, such as minus forty, twenty, and eighty degrees Celsius.
The resulting correction coefficients are stored in the non-volatile memory of the device.
Operational Limit
Performance integrity is evaluated over the lifetime of the instrument. Excessive thermal cycling can cause the compensation parameters to shift, which requires periodic re-calibration to maintain the specified accuracy.