Towards a standard for the dynamic measurement of pressure based on laser absorption spectroscopy

Abstract

We describe an approach for creating a standard for the dynamic measurement of pressure based on the measurement of fundamental quantum properties of molecular systems. From the linewidth and intensities of ro-vibrational transitions we plan on making an accurate determination of pressure and temperature. The goal is to achieve an absolute uncertainty for time-varying pressure of 5 % with a measurement rate of 100 kHz, which will in the future serve as a method for the traceable calibration of pressure sensors used in transient processes. To illustrate this concept we have used wavelength modulation spectroscopy (WMS), due to inherent advantages over direct absorption spectroscopy, to perform rapid measurements of carbon dioxide in order to determine the pressure. The system records the full lineshape profile of a single ro-vibrational transition of CO2 at a repetition rate of 4 kHz and with a systematic measurement uncertainty of 12 % for the linewidth measurement. A series of pressures were measured at a rate of 400 Hz (10 averages) and from these measurements the linewidth was determined with a relative uncertainty of about 0.5 % on average. The pressures measured using WMS have an average difference of 0.6 % from the absolute pressure measured with a capacitance diaphragm sensor.

Evaluation of Shock Tube Retrofitted with Fast-Opening Valve for Dynamic Pressure Calibration

“…At the national laboratory for pressure in Sweden, a future standard for dynamic pressures based on shock tube technology is under development. Shock tubes can realize pressure steps with rise time well below 1 μs and are preferred when realizing high-frequency dynamic reference pressures [ 5 , 6 , 7 ]. In calibration, shock tubes may either be used as a pure pressure generator in combination with a reference sensor or be used as a primary measurement standard [ 8 ].…”

Towards an improved helium-based refractometer for pressure measurements

“…With the new international system of units (SI), many developments are now in progress for the realization of a "quantum pascal" by means of methods such as superconductive microwave resonators [1], Rayleigh scattering, multi-reflection interferometry [2], gas phase thermometry and absorption spectroscopy methods [3] as well as Fabry-Pérot (FP) cavity refractometers [4].…”

Comparing the adiabatic and isothermal pressure dependence of the index of refraction in a drop-weight apparatus

“…It is therefore of interest to investigate whether a dynamic calibration might mitigate this difference. Several groups are working towards this goal, see for example [2,[8][9][10][11][12][13]. A particular challenge is the transfer of SI traceability from static pressure, where well established primary standards are available, to dynamic pressure, where work on providing standards with the required characteristics (pressure range, frequency range, uncertainty) is still in progress.…”

“…Several principles have been used to construct devices for the non-destructive generation of strong pressure pulses, i.e., stronger than can in general be reached by shock tubes [14,15]. They include, for example, fast opening valves [7], the use of a commercial drop-weight apparatus [16], a dropweight apparatus designed for secondary calibrations using two piezoelectric sensors [8,17], a drop-weight apparatus measuring pressure via the monitoring of the deceleration of the piston [9,18,19], an air gun [16], a pressure-tank setup [10], or optical absorption spectroscopy [11]. Diamond anvil cells [20], well known for the very high pressures they can exert on small samples, necessarily need to be smallvolume devices, too small to permit attaching a customer's transducer (typical sensor casings use M10 or M12 threads).…”