Digiquartz® Pressure Instrumentation
Background
Paroscientific is the leader in the field of high-accuracy pressure measurement.
The company was founded in 1972 by Jerome M. Paros after a decade of research on digitalforce sensors. Application of this technology to the pressure instrumentation field resulted intransducers of the highest quality and superior performance.
Precision comparable to the best primary standards is achieved through the use of a special
quartz crystal resonator whose frequency of oscillation varies with pressure-induced stress. A
quartz crystal temperature signal is provided to thermally compensate the calculated pressure
and achieve high accuracy over a wide range of temperatures.
Digiquartz® Pressure Instrumentation
Paroscientific manufactures and sells a complete line of high-precision pressure
instrumentation. Resolution of up to one part-per-billion of full scale and typical accuracy of
0.01% of full scale are achieved even under difficult environmental conditions. Other
desirable characteristics include high reliability, low power consumption, and excellent longterm stability.
Over 30 full scale pressure ranges are available - from a fraction of an atmosphere to
thousands of atmospheres (+/-2 psig to 40,000 psia). Absolute and gauge transducers havebeen packaged in a variety of configurations including intelligent transmitters, depth sensors,laboratory and portable standards, meteorological measurement systems and water levelsystems. Intelligent electronics have two-way digital interfaces that allow the user to adjust
sample rates, resolution, engineering units and other operational parameters.
The Digiquartz® products are successfully used in such diverse fields as metrology,
oceanography, meteorology, process control, aerospace, energy exploration and laboratory
instrumentation.
Advantages of Digital Technology
The use of digital pressure transducers has grown dramatically with the trend towards digital
data-acquisition and control systems. Inherently digital sensors such as frequency output
devices have been combined with microprocessor based systems to provide unparalleledaccuracy and performance, even under extreme environmental conditions. The design andperformance requirements of these advanced transducers include:
1.
2.
3.
4.
5.
6.

Digital output
Accuracy comparable to primary standards
Highly reliable and simple design
Insensitivity to environmental factors
Minimum size, weight and power consumption
Ease and utility of readout

1True digital sensors have a great advantage in resolution and accuracy over traditional analog
devices because more precise measurements can be made in the time domain. Digital-typesignals are also less susceptible to interference, easier to transmit over long distances, andreadily interface to counter-timers, telemetry and digital computer systems.
Digiquartz® Pressure Sensing Technology
Accuracy, stability, and reliable performance under difficult environmental conditions are thekey performance requirement for precision pressure instrumentation. Accuracy and stability
are required to ensure data quality. Instrumentation reliability directly affects network data
integrity as well as operating costs.
The superior performance of the Digiquartz instruments is achieved through the use of a
precision quartz crystal resonator whose frequency of oscillation varies with pressure-induced
stress. Quartz crystals were chosen for the sensing elements because of their remarkablerepeatability, low hysteresis, and excellent stability. The resonant frequency outputs aremaintained and detected with oscillator electronics similar to those used in precision clocks
and counters.
Flexurally-vibrating, single or dual beam, load-sensitive resonators have been developed.
The double-ended tuning fork consists of two identical beams driven piezoelectrically in 180
phase opposition such that very little energy is transmitted to the mounting pads. The high-Q
resonant frequency, like tuning a violin string, is a function of the applied load: increasing withtension and decreasing with compressive forces. The digital temperature sensor consists ofpiezoelectrically-driven, torsionally-oscillating tines whose resonant frequency is a function oftemperature. Its output is used to thermally compensate the calculated pressure and achieve
high accuracy over a wide range of temperatures.

Force-Sensing Quartz Crystal

Temperature-Sensing Quartz Crystal

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Digiquartz® Low Pressure Sensor

Digiquartz® High Pressure Sensor

Pressure transducer mechanisms employ bellows or Bourdon tubes as the pressure-to-load
generators. Pressure acts on the effective area of the bellows to generate a force and torqueabout the pivot and compressively stress the resonator. The change in frequency of thequartz crystal oscillator is a measure of the applied pressure. Similarly, pressure applied to
the Bourdon tube generates an uncoiling force that applies tension to the quartz crystal.
Temperature sensitive crystals are used for thermal compensation. The mechanisms areacceleration compensated with balance weights to reduce the effects of orientation sensitivity.
The transducers are hermetically sealed and evacuated to eliminate air damping andmaximize the Q of the resonators. The internal vacuum also serves as an excellent reference
for the absolute pressure transducer configurations.
Microprocessor-based intelligent electronics are available with highly stable TCXO countertimer circuitry to measure transducer frequency or period outputs, and to store thelinearization and thermal compensation algorithm, calibration coefficients, and command andcontrol software that process the outputs in a variety of digital formats.
Paroscientific Intelligent Transmitters consist of a Digiquartz® Pressure Transducer and adigital interface board in an integral package. Commands and data requests are sent via twoway RS-232 or RS-485 serial interfaces. Digital outputs are provided directly in engineering
units with typical accuracy of 0.01% over a wide temperature range. Output pressure is fully
thermally compensated using a quartz crystal temperature signal. All intelligent transmitters
are preprogrammed with calibration coefficients.
Dual RS-232 and RS-485 interfaces allow complete remote configuration and control of all
operating parameters, including resolution, sample rate, choice of engineering units,
integration time, and sampling requests. The commands include: Single sample and send,
synchronized sample and hold, continuous sample and send, and special burst sampling
modes. Starting with firmware revision R5.10 (M3.0, MET4/4A) or later it is now possible toachieve parts-per-billion resolution. This feature is also enabled by software command.
When disabled, the sensor is backward compatible and works in the standard mode withtypical parts-per-million resolution. Nano-resolution is achieved by sub-sampling pressure at3

a much higher rate (typically 8 kHz) and applying digital signal processing techniques using an
IIR (infinite impulse response) filter.
Additional features include support for serial loop and multi-drop networking, user-selectablebaud rates up to 115,200 baud, synchronization of measurements with time-based integration,
2 or 4 wire RS-485 with transmission distances greater than 1 kilometer, improved high-speed
continuous pressure measurements, a power management “sleep” mode, data formatting
features, and unit identification commands.
Performance
Digiquartz® 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 four decades. They aredesigned 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 from our high pressure sensitivity while longer termmeasurements need our accuracy, stability, and insensitivity to environmental errors.
a. High Resolution
With a sensor of inadequate resolution, real signals can be obscured by noise, or sensor
noise can be interpreted as real signals. Paroscientific transducer mechanisms, oscillator
circuits, and digital interfaces are carefully designed for ultra-high resolution. Nano-Resolution,(parts-per-billion sensitivity) is available with all Paroscientific intelligent products. The noise
floor of Quartz Crystal Sensors is shown below for an isolated quartz crystal.
Noise Floor PSD Plot - Fractional Full-Scale Scaling
1E-10

Noise Floor (Fractional FS)^2/Hz

1E-11
1E-12
1E-13
1E-14
1E-15
1E-16
1E-17
1E-18
1E-19
1E-20
1E-21
1E-22
1E-23
1E-24
0.001

0.010

0.100

1.000

10.000100.000

Hz

Applications where it is important to measure extremely small pressure changes include
tsunami detection in the ocean and land-based infrasound detection of tsunamis, severe
weather, volcanic eruptions, avalanches, wind shear, wake-turbulence, and bolides. Examplesof high resolution measurements using high-range absolute sensors follow.

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A micro-tsunami was recorded by the nano-resolution pressure sensor on December 21, 2010
(M7.4 Bonin Island earthquake). Using wavelet analysis, a spectrogram was computed for thetsunami (see Figure 6). The cutoff period for tide removal is 1 hour, using Butterworth filters.
Note the color scale in the plot was set to emphasize the tsunami, so the high frequency
components are muted. The red line in the upper panel is the modeled tsunami amplitude timeseries. The tsunami appears from 645-745 minutes (indicated by white dashed line) with aperiod of about 14 minutes. The maximum tsunami amplitude is about 0.2 cm.

On 3 October 2009, an eruption of Sakurajima Volcano generated infrasound signals thatwere measured 987 km away at a nuclear test monitoring site. Note that ocean-generated
microbarom signals with amplitudes of 0.1 Pa were measured with a sensitivity of 0.0003 Pa
before and after the eruption.
Sakurajima Eruption 10/3/09 7:45 UTC
Station IS30 S/N 111244 Bandwidth 0.05 - 1.4 Hz
64

Microbaroms

Pa

2

0

-2

Sakurajima erupted at 7:45 UTC on October 3, 2009. It took
48 minutes to reach the Nano-Resolution Barometers thatwere located 987 km away

-4

-6
1950

2000

2050

2100

2150

2200

seconds after 10/3/09 8:00 UTC

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On April 20, 2010 the Space Shuttle re-entered the atmosphere over Vancouver Island in
British Colombia, Canada. Figure 9 above shows the pressure signal measured from alocation in West Seattle, approximately 150 miles away. The pressure change shown is the
typical N-Wave that is generated from supersonic flightSpace Shuttle Infrasound Pressure Signature
Measured with Paroscientific Nano-Resolution Barometers
West Seattle, WA USA--Location: 47 34 44 N 122 22 47 W

Absolute Pressure (Pascal)

99471

99470

99469

99468

99467

99466

99465

99464
4/20/10 5:57:00

4/20/10 5:57:05

4/20/10 5:57:10

4/20/10 5:57:15

4/20/10 5:57:20

4/20/10 5:57:25

4/20/10 5:57:30

Time

Figure 9b. Static Error Band
Typical accuracy of Digiquartz® Instruments is 0.01% of full scale or better. Accuracy relative
to the primary standard includes resolution, hysteresis, non-repeatability and nonconformance. Digiquartz® Instruments are calibrated across a wide operating temperature
and accuracy does not degrade as temperature changes.

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Typical static error band for Digiquartz® Instruments is achieved after meticulous testing andcalibration. Calibration is performed by applying known pressure from primary standards tomanifolds of transducers mounted in temperature chambers. Two frequency (or period)
output signals are sent from each transducer. Pressure is measured with a force-sensitive
quartz crystal whose output period changes with applied load. A second period output comesfrom a quartz crystal temperature sensor used for thermal compensation. The manifold oftransducer signals are multiplexed, measured, and the data fit to derive coefficients for the
standard equation that characterizes the transducers. The calibration coefficients areprovided with each transducer and the indicated pressure (calculated) will agree with the“true” applied pressure with a typical accuracy of 0.01 percent of transducer full scale over thefull operational range of pressure and temperatures. Digiquartz® Intelligent Transmitters store
the calibration coefficients in non-volatile EEPROM to provide fully temperature-compensatedand linearized outputs on the bi-directional RS-232 and RS-485 interfaces.
c. Environmentally Rugged and Reliable
Digiquartz® Instruments are carefully calibrated and temperature-compensated over a broad
temperature range. They are also designed to survive extremes of shock and vibration withaccurate, reliable measurements. Paroscientific transducers have been used in a variety of
applications from deep space probes to ocean bottom deployments.
All Digiquartz transducers have an internal quartz temperature sensor whose output is used tothermally compensate the calculated pressure and achieve high accuracy over a wide rangeof temperatures.

Temperature Conformance of a Typical Digiquartz® Instrument
The temperature conformance plot above shows the closeness of the indicated pressure to
the applied pressure at different temperatures over the full operational range of pressures andtemperatures.

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d. Low Cost of Ownership
Digiquartz® products provide a low total-cost-of-ownership. The long-term stability of
Digiquartz® products reduces recalibration intervals and operational costs. Ease of use
reduces the need for extensive training. Reliable operation eliminates excessive productpurchases, repair costs and loss of revenues due to process interruptions.
Quality Assurance and Test
Paroscientific, Inc., maintains a Quality Management System that is certified to therequirements of the ISO 9001 International Quality Standard. All calibrations performed at
Paroscientific, Inc. are traceable to the National Institute of Standards and Technology (NIST)
Our quality system and commitment to excellence ensure our customers of outstanding
products and services.
Facilities
The Paroscientific Inc. headquarters and manufacturing facility are located in an awardwinning building in Redmond, Washington USA. This facility contains all of the sophisticatedmanufacturing and test equipment necessary to produce the world’s most accurate pressure
instrumentation including electron-beam, laser, resistance and pulsed TIG welders, vacuum
deposition machines, mass spectrometer leak detectors, specialized quartz crystal andpressure transducer fabrication and test stations, high-vacuum evacuation and bake-out
equipment, environmental test chambers, primary standards, and automated test stands.

Paroscientific Facility in Redmond, WA

Weld Room (TIG, Laser, Electron)

Manufacturing Area

Calibration Laboratory

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Warranties, Service and Support
Paroscientific Inc. provides world-class products, service and quality. We offer a 5-year
limited warranty on all of our pressure transducers including a 3-year stability warranty on all
barometric products and a free 2-year zero adjustment with a calibration certificate traceable
to NIST on all absolute pressure instruments (<1000 psia).
Product and application support including technical reports and free software are available on
our web site at www.paroscientific.com. Paroscientific sells direct in the USA and world-widethrough the International Representative Network listed on our web site. Please contact us at
support@paroscientific.com or call us at (425) 883-8700 for our Personal Pressure SearchEngine Support.
Paroscientific, Inc.
4500 148th Ave. N.E.
Redmond, WA 98052 USA
Web: www.paroscientific.com

Telephone: (425) 883-8700
Facsimile: (425) 867-5407
E-Mail: support@paroscientific.com

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