NPL unveils dynamic test facility for pressure sensors 23 October 2013

NPL (the National Physical Laboratory) has developed a dynamic pressure sensor calibration facility, which, it says, improves confidence in high-speed sensors, such as those used in gas turbines and internal combustion engine.

The new national measurement institute facility is based on shock tube techniques and secondary equipment, and can characterise the amplitude and frequency response of pressure sensors, by exposing them to extremely fast pressure steps up to 1.4 MPa.

Andy Knott, principal research scientist at NPL, makes the point that many industrial pressure sensors are used to make dynamic measurements, yet have often only been calibrated using static pressures.

However, the dynamic behaviour of a mechanical sensor deviates from its static characteristics as the frequency increases, he warns. So the use of a sensor in a different mode from that in which it was calibrated is a significant factor affecting both the reliability and uncertainty of sensor data.

"Our new facility can be used to quantify variations between static and dynamic pressure sensitivity, and to investigate ways in which to compensate for them," states Knott.

"Testing of the sensors in more realistic conditions is also available, using either the shock tube or a secondary facility, in which the dynamic pressure is generated within a liquid," he continues.

"We want to encourage businesses to come and test the facility and guide us on the work they need help with. This will ensure that we assist them in developing safer, more reliable, and more effective products."

Knott explains that a pressure step within the shock tube of up to 1.4 MPa is obtained using combinations of gases, initial pressures and different diaphragm arrangements. The theoretical rise time for these pressure steps is a few nanoseconds, so the input's frequency content is sufficient for practically all industrial applications.

One major area for dynamic pressure measurement is in gas turbine engines. The need to meet emissions targets and improve reliability and performance sees engines running with ever-leaner fuel-air mixes, which can lead to instabilities and pressure pulsations leading to mechanical failure.

Improved dynamic pressure measurement could help lower the costs of mechanical repair, downtime and environmental fines – potentially saving millions of pounds.

As part of looking at the requirement for a dynamic pressure sensor calibration service, NPL is asking for engineers and businesses to have their say.Until 15 November, people can fill out a short questionnaire about their pressure calibration requirements. Click the link below.

Brian Tinham

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