Long term stability of pressure sensors

What is long term stability of pressure sensors? Long term stability is a change in output, either zero and/or span, at two successive points in time under the same conditions. This change in output is not directly attributable to any other effect at the time of the subsequent measurements.

However, it can be affected by several factors; pressure/pressure cycles, temperature/temperature cycles or other environmental conditions the sensor has been exposed to over the interval. A long-term stability specification is typically provided as a percent of full scale (FS) over a one-year period, e.g. ±0.1% FS/annum.

Other time periods can be used so it is important to note the specification definition when making decisions on performance checks or calibration intervals.

Why is this important? Long term stability is a non-repeatable error source. Therefore, it is not possible to compensate or correct for it within the sensor itself on a continuous basis. The long-term stability performance of a pressure sensor is determined by the inherent stability of the fundamental sensor technology.

It is possible to periodically reset zero and span settings in many sensors either by ‘mechanical’ adjustment, e.g. potentiometer adjustments, or electronically in sensors that have some on-board processing capability and a facility to ‘communicate’ digitally, e.g. sending a zero and/or span reset command over a bus.

Potentiometers are inherently unstable and once adjusted can often time lead to a neverending cycle of readjustment. Electronic adjustment is perhaps the preferable method.

Electronic adjustment is also possible in the control systems to which a sensor is connected; e.g. DAQ, datalogger, PLC, Scada System, etc., again by adjusting offset and gain to balance out or remove any offset from instability. However, these methods are a temporary reset and do not eliminate drift.

For applications where this is either not desirable or practical to readjust, e.g. life cycle testing of engine components, it is crucial to select a sensor with a long-term stability specification that will not adversely impact the test results.

How does Druck address these challenges? Druck uses a silicon strain gauge technology. Silicon is a perfectly elastic material. As long as deformation, i.e. pressure is applied, is within the elastic region it will return to exactly the same state regardless of the number of iterations, i.e. pressure cycles, or the amount of time that passes.

This property lead to very high stability. Restated very low longterm stability errors.

The packaging of the silicon element into a mechanical structure that does not introduce any other aspect that would affect this inherent stability is some that Druck has been refining for the 50 plus years we have been in business.