HIGH RESOLUTION PRESSURE MEASUREMENT

Digiquartz® Pressure Products are the highest resolution, lowest noise, and most accurate instruments available today. The transducers are based on the inherently digital, highly stable, vibrating quartz crystal technology developed by Paroscientific over the last three decades. They are designed and tested to deliver outstanding performance even under difficult field conditions.

Although many applications require both high resolution and accuracy, short-term measurements generally benefit more from our high pressure sensitivity while longer term measurements need our accuracy, stability, and insensitivity to environmental errors.

With a sensor of inadequate resolution, real signals can be obscured by noise, or sensor noise can be misinterpreted as real signals. Paroscientific transducer mechanisms, oscillator circuits, and digital interfaces are carefully designed for high resolution. Typical delivered resolution of our transducers is better than one part per million, and under stabilized laboratory conditions, resolution can approach 1 part per billion. Applications where it is important to measure small pressure changes include leak-rate testing, interference and draw-down reservoir testing of oil and gas wells, Tsunami detection, and measurements of wind-shear and atmospheric shock waves.

Figure 1. Tsunami Detection (Earthquake Generated Tidal Waves)

Figure 1 shows the filtered output of a 6000 meter depth sensor used to detect earthquake-generated tidal waves (Tsunamis).1 The real signals are resolved to 1 mm of water (1 part in 6 million) and clearly show the signature of the Tsunami which is only several centimeters magnitude at the deployed depth of thousands of meters. 

Data from an evaluation by Hutt, Holcomb, and Agnew2 of high quality sensors for use in atmospheric seismic studies are shown in Figure 2. Noise of the Paroscientific transducer is much lower than all other sensors.

Figure 2. Microbarograph Comparison
(Click here to enlarge)

Noise levels as a function of frequency are generally expressed as spectral densities. Plots of this type are used to determine whether a sensor can measure a desired signal. The goal is to have the sensor noise levels much smaller than the expected real signals at all frequencies of interest. In the tests by Hutt and Agnew, our transducers had power spectral density noise levels a factor of 100 lower (20 db) than the next best transducer.

Figure 3. Noise vs. Record Length

The ultimate resolution achievable with a transducer is limited by its noise level. Typically, the rms noise increases for longer data records because of sensor drift and because temperature and other environmental contributors to noise tend to vary more over a longer period of time. Typical rms noise levels for our transducers are shown in Figure 3. For records shorter than about 1 hour, the rms noise level is less than 1 part per million. The rms noise rises slowly with record length, reaching approximately 10 ppm for records several years long.

Applications where absolute accuracy and stability are paramount include pressure calibration systems, transfer standards, meteorological measurements of barometric pressure for weather forecasting, sea floor depth survey equipment, and long-term deployments in remote locations.  Please click here to see our long-term barometer stability test.

Generally, customers who care about absolute accuracy also need to know how well the transducer holds its accuracy over time (long-term stability) and how sensitive it is to temperature and other environmental effects. Less stable devices need to be recalibrated more often or may be incapable of performing adequately under field conditions.

Paroscientific pressure transducers typically deliver accuracy better than 100 parts per million of full scale pressure over a wide temperature range and maintain this accuracy for a long time.

Digiquartz® Instruments provide the highest resolution and most accurate, stable, and reliable measurements from a fraction of one atmosphere to thousands of atmospheres of pressure.