Primary Pressure Standards Research Articles

Pressure calibration to 304 GPa on the basis of X-ray diffraction measurements of Pt, Fe and CsI

Abstract X-ray diffraction measurements have been carried out above 300 GPa for the first time using Pt as a primary pressure standard. The equations of state of iron up to 304 GPa and of CsI up to 302 GPa have been obtained. These materials can therefore be used as secondary pressure calibrants.

Comparison of two primary pressure standards using spinning rotor gauges

In this paper a comparative study of two primary pressure standards viz. static and dynamic gas expander systems is reported. The two systems are compared by using spinning rotor gauges as the transfer standard in the pressure region of 6×10−3 to 2×10−1 Pa. It is observed that if the pressure variation of the conductance of the orifice assembly of the dynamic system is taken into account then the two systems are found to show an agreement of ±0.3% in the overlapping pressure region. A modified mathematical analysis of the equation due to Bureau et al. for molecular conductance of the orifice assembly is also given by taking into account the exit/entrance loss based on the new short-tube transmission probability equation developed by Santeler. The molecular conductance value thus obtained is found to be in close agreement with the corresponding experimental value extrapolated from the conductance versus pressure curve. This modified formula can be used to determine the effective conductance of the orifice assembly irrespective of the position of the orifice inside the tube connecting the two chambers.

Accuracy of vacuum gauges

The performance characteristics of the following types of vacuum gauges are discussed: quartz Bourdon gauge (QBG), capacitance diaphragm gauge (CDG), thermal conductivity gauge (TCG), quartz friction gauge (QFG), spinning rotor gauge (SRG), cold cathode ionization gauge (CCG), hot filament ionization manometer (IM), quadrupole mass spectrometer (QMS) and other mass spectrometers. Depending on the pressure, the most stable gauges are the QBG, the CDG, the SRG, and the IM. In applications with modest demands on the measuring accuracy, it may be sufficient to employ an uncalibrated gauge and adopt an average gauge coefficient given by the manufacturer. In cases with higher demands on the accuracy, the calibration of individual gauges may be necessary. The highest demand arises if the gauges are used as transfer standards in intercomparisons of primary pressure standards. Here, the achievable accuracy is limited by the stability of the gauge with time. Gauges based on different operating principles and different constructions show different stabilities. Furthermore, the stability depends on the handling of the gauge. This paper compiles available data on the accuracy performance of the various gauges.

Use of strain gauge pressure transducer as working pressure standard up to 500 MPa

This paper describes the calibration of a strain gauge transducer (700 MPa full scale) against a primary pressure standard (500 MPa full scale) maintained at the National Physical Laboratory (NPL), India, over a pressure range of 500 MPa. The calibration data obtained at the NPL are also compared with the calibration data taken at Istituto Di Metrologia ‘G. Colonnetti’ (IMGC), Italy, using the primary pressure standard of IMGC in the possible overlapping pressure region of 158 – 457 MPa, with particular reference to reproducibility, hysteresis and the calibration equations. It is found that the reproducibility between the calibration factor of the standard at NPL and that at IMGC is typically ± 5 X 10 −4 and the highest difference in the pressure values of NPL and IMGC calcualted using the second-order polynomial calibration equation is well below 2 X 10 −3, the expected uncertainty for the transducer. This suggests a possible use of the strain gauge transducer as a working pressure standard in this pressure range if the accuracy required in the pressure measurement is of the order of 2 X 10. −3.

Accurate measurement of pressure

This paper briefly describes the fundamental principles of the instruments used for accurate measurement of hydrostatic pressure and in particular the use of piston gauges as primary pressure standards. Different methods for the calibration of secondary standards have been discussed and in particular, emphasis has been given to the calibration of secondary piston gauges against the primary standards by the cross-float method along with the evaluation of uncertainties attached to different correction factors associated with the measurement of pressure from these gauges. The importance of secondary pressure standards in the region 0.1 GPa to several GPa has also been defined.

Recent studies of float and stall curves in controlled-clearance deadweight testers with a simple piston

The effect of piston rotation speed and fluid viscosity on the performance of free-piston gauges with a controlled clearance was studied as part of an experimental program aiming at the better evaluation of pressure by these primary pressure standards. Calculated effective area is shown to be greatly influenced by both speed of rotation and choice of a fluid. An optimum rpm resulting in the smallest possible uncertainty in effective area should be determined experimentally for each fluid and pressure range involved. When all the pertinent parameters are properly selected an appreciable improvement in accuracy can be achieved.

The rotational frequency dependence of a pressure balance

The change in generated pressure with rotational frequency is measured for a type of gas-operated gauge-mode pressure balance which is widely used as a primary pressure standard. The results show that at low rotational frequencies (3-10 Hz) the generated pressure increases with the square of the frequency and that the extrapolated pressure for zero frequency corresponds to the calculated pressure. Also, it is shown that the force due to rotation action on the pressure balance is almost independent of load at low frequencies.

Fast Accurate McLeod Gauge System

The use of an orifice and a secondary mercury source near it as means for reducing the trap pumping error of the McLeod gauge is discussed. With the proper utilization of an orifice, trap pumping is not a serious hindrance to the use of the McLeod gauge as a primary pressure standard. Accuracy better than 1% with a time constant less than 30 sec can be achieved using a conventional McLeod gauge. Experiments that directly demonstrated a reduction of the trap pumping error gave good agreement with the theoretically expected reduction.