By leveraging the elasticity, resolution, and stability of crystalline quartz, Quartzdyne has been manufacturing high accuracy quartz crystals for over twelve years. (Quartzdyne founders have been working in the quartz crystal industry for nearly thirty years.) In early 1999, we began a program to quantify and improve the long-term stability (drift) performance of our pressure transducers.
Since the rate of drift increases with temperature, we have focused our efforts on minimizing the drift at temperatures of 150 °C (300 °F) and higher. The sources of drift in the pressure measurement are (1) the quartz pressure crystal, (2) the quartz reference crystal, (3) the oscillator circuit, and (4) the bellows. Due to robust construction, design, and material/component selection, the contribution of the latter two are insignificant. The quartz pressure crystal is responsible for the majority of drift, while the quartz reference crystal makes a smaller contribution through the mixed pressure frequency (ƒp, mix = ƒp, raw - ƒr).
We have conducted over 100 drift tests and found that Quartzdyne sensor drift can be predicted--and compensated for--using an algorithm. However, piezoresistive sensor drift is unpredictable. Piezoresistive sensor drift increases exponentially with increasing temperature.
Through design and process changes, we successfully reduced the drift in our pressure transducers, typically by a factor of 4 to 10. These lower drift crystals now provide our customers with superior long term accuracy. Coincidentally, they provide us with improved yields in manufacturing and calibration, indicating that drift reduction has come without other performance compromises.
Quartz transducers are more expensive than strain or piezoresistive gauges. (Quartz crystals are made by people, not machines.) With its long-term stability and accuracy, quartz retains its value over time through extended recalibration intervals. Thus, a tool using our quartz pressure transducer will remain in service for a longer period of time than a piezoresistive tool, earning more revenue for the service provider. Hence, we emphasize life-cycle costs with our customers, not initial costs.
For more information on testing methods and improvements to Quartzdyne's pressure transducer's long-term stability see our tech note.