Vacuum Calibration Research Articles

A MEMS resonant vacuum gauge for high vacuum measurement

In this paper, a MEMS resonant vacuum gauge (MRVG) based on the squeezed film damping is proposed and its theoretical measurement model is established. The sensitive structure and electrodes of the MRVG were fabricated on SOI wafers and were wafer level packaged including intake hole. An resonance excitation and capacitive detection circuit consists of capacitive voltage converter (C/V) module, PLL and modulation and demodulation module was designed. Experimental tests were carried out in a standard vacuum calibration chamber, and the measurement results verified the theoretical model. The indication accuracy of the MRVG is less than ±20% in the vacuum range of 9×10−5 Pa ∼ 1 Pa. Moreover, the output voltage is still not saturated at the highest vacuum level (9×10−5 Pa), which lays the foundation for subsequent measurement of higher vacuum levels.

Instrumented baffle for the Advanced Virgo input mode cleaner end mirror

A novel instrumented baffle surrounding the suspended end mirror in the input mode cleaner cavity of the Virgo interferometer was installed in spring 2021. Since then, the device has been regularly operated in the experiment and the obtained results indicate a good agreement with simulations of the stray light inside the optical cavity. The baffle will operate in the upcoming O4 observation run, serving as a demonstrator of the technology designed to instrument the baffles in front of the main mirrors in time for O5. In this paper we present a detailed description of the baffle design, including mechanics, front-end electronics, data acquisition, as well as optical and vacuum tests, calibration and installation procedures, and performance results.

Measurements of virial coefficients of Helium, Argon and Nitrogen for the needs of static expansion method

<p>Generally, there are three primary methods in vacuum metrology: mercury manometer, static expansion method, and continuous expansion method. For the pressure below 10 Pa, the idea of the primary standard is that the gas is measured precisely at a pressure as high as possible, and then the gas is expanded to the bigger volumes; this allows to calculate the expanded pressure. An important parameter that needs to be taken care of in primary vacuum calibration methods is the compressibility factor of the working gas. The influence of virial coefficients on the realization of primary standards in vacuum metrology, especially in the realization of the static expansion method is very important. In this paper we will present the measured data for virial coefficients of three gases Helium, Argon and Nitrogen measured at room temperature and a pressure range from 3 kPa to 130 kPa. The dominating term due to real gas properties arises from the second virial coefficient. The influence of higher orders of virial coefficients drops rapidly with lower pressure, particularly for gas pressures values lower than one atmosphere. Hence, in our calculation, the series of real gas was used for the first and second virial coefficients but not for higher-order virial coefficients.</p>

Gas Expansion Process in the Dynamic Vacuum Calibration

By analyzing the gas expansion process from the upstream chamber via an orifice and a very rapid-opening ultra-high vacuum (UHV) gate valve to downstream one, the standard pressure analytical model based on the dynamic vacuum calibration apparatus in millisecond range developed by Lanzhou Institute of Physics (LIP) is deduced theoretically and corrected by real gas characteristics and temperature changes. According to the Knudsen criterion, there is no free molecular flow regime in the area in front of the orifice during the gas expansion, so the chocked flow approximation is adopted to reduce the difficulty of numerical computation. Under this approximation and the full opening of the rapid valve, the standard pressure expression is calculated theoretically, and the upstream chamber pressure and temperature changes are obtained by numerical simulation during the gas expansion from 100 kPa to 10 kPa. Also, experiments are performed using capacitance diaphragm gauges (model CDG045Dhs). The uncertainties between the measured pressure and the simulated and theoretical ones are 10% and 4.65%, respectively, which indicates that the apparatus can generate predictable pressure changes in the millisecond range and the conceptual model can better approximate the calibration results. Finally, the orifice conductance, and the correction factors of real gas characteristics and temperature change to the standard pressure are calculated according to the simulation results; the corrected standard pressure expression is obtained.

Fabrication of an efficient structured packing for hard vacuum distillation processes and calibration by Carbon tetrachloride-Benzene mixture

In vacuum distillation processes, pressure drop per unit of theoretical plate (Δp) is an important parameter because overall pressure drop of distillation column must be lower than one atmosphere (0<ΔP<1 atm.). Besides, in hard distillation processes having small relative volatility coefficient (1<αi<1.1), minimum number of theoretical plates per unit length (nmin) is another important parameter as total height of distillation column cannot exceed the maximum of technologically attainable height. Moreover, by increasing total height of the column its thermal control will be extremely hard. In this work, an efficient structured packing for hard vacuum distillation processes has been fabricated and also calibrated using the binary mixture of Carbon tetrachloride-Benzene, with very low relative volatility coefficient (1.128<αi<1.142). In hard vacuum distillation processes both parameters, Δp and nmin, are important. Therefore, the effects of three main variables including reflux volumetric flow rate, the number of distributors within the packed-bed and average height of each element of the structured packing on these parameters have been studied. The best amounts of Δp and nmin found to be 1.394 mmHg/tray and 14.2175 tray/m respectively. This vividly indicates that the newly introduced structured packing is appropriate for hard vacuum distillation processes.

Time stability characterization of quadrupole mass spectrometers

• Time stability of eight QMSs was investigated over 2-years period. • Stability of sensitivity of Faraday cup detector and SEM gain for He and N 2 . • Stability of peak position and peak width of He and N 2 . • Stability of minimum detectable partial pressure for He. • Measurements were carried out according to ISO TS 20175:2018. This study focuses on the time stability of different metrological characteristics of quadrupole mass spectrometers (QMSs). Investigated parameters were the sensitivity, when using a Faraday cup as a detector, the peak position, the peak width, the gain of a secondary electron multiplier, and the minimum detectable partial pressure. Eight different commercial QMSs were investigated at seven national metrology institutes under three different nominal calibration pressures of 5 × 10 −6 Pa, 5 × 10 −5 Pa, and 5 × 10 −4 Pa for N 2 and He. The measurements were carried out using a periodicity of approximately 3 months for a total duration of 2 years. Sensitivity calibrations were conducted either through a comparison method using calibrated ionization gauges or by applying a primary vacuum calibration system. In the case of ionization gauges, they were periodically recalibrated to ensure their stability and traceability to a primary pressure standard.

Extraction of the plasma current contribution from the numerically integrated magnetic signals in ISTTOK

ISTTOK tokamak operates in AC mode allowing to have consecutive cycles of positive and negative plasma current. The plasma centroid position is estimated from the reconstruction of the signals obtained from a poloidal array of twelve magnetic probes. In the previous setup, this reconstruction relied on a cylindrical approximation algorithm in which the error fields generated by active coils and currents in the passive structures were not taken into account, leading to some centroid position inaccuracy. Although this approach has been able to produce flat top current AC discharges with reasonable reliability, a better solution was implemented as a preferred plasma position estimator. The signals are currently corrected subtracting the contribution from external magnetic fields following a method that relies on state-space models which use data collected from a systematic vacuum calibration procedure. Also, the plasma centroid position is estimated using a multi-filament current model. Furthermore, the recent implementation of numerical integrators in the real time ATCA based data acquisition system substantially improved the real time conditioning of the magnetic signals measurements. First results demonstrate that this new approach delivers a more reliable estimation of the plasma current centroid position with noticeable improvement on control performance, which is paramount to the success ratio of the AC plasma current switching.

Nonlinear characteristics of FY-3D microwave radiation imager and an optimal calculation method

The Earth’s radiation was observed by a microwave radiation imager(MWRI) on board FengYun-3D(FY-3D) satellite at 10.65 GHz, 18.7 GHz, 23.8 GHz, 36.5 GHz, and 89.0 GHz with dual polarization. The nonlinearity of this payload, as an important parameter in calibration algorithms, is represented by the nonlinear parameter u from vacuum calibration ground tests. Therefore, an accurate knowledge on the nonlinear characteristics of MWRI is required to achieve precise remote sensing.The nonlinear parameter applied in the calibration algorithm is usually averaged over a set of u, which is calculated at corresponding observed brightness temperatures in the range between 95 K and 298 K. A t-distribution test method is proposed to screen u and further optimize the nonlinearity calculations in this study instead of conventional empirically filtering of u before averaging. The t-method examines the validity of u values at each observed brightness temperatures, and its effectivity is proven in this study.Nonlinear fitting brightness temperatures, as well as means and standard deviation of residual error, were calculated using empirically filtering method and the t-method to demonstrate the results in the nonlinearity calculation. The nonlinear parameter of MWRI is a physical parameter of the instrument, and the nonlinearity of up to 2 K at 10 GHz is mainly introduced by higher-order harmonic during detection.The nonlinear brightness temperature calculated using the t-test distribution method is improved by approximately 0.04 K with better fitting results than the ground tests, especially at 10 GHz.According to the results presented in this study, the nonlinear parameter is independent of observed brightness temperatures, and its nonlinearity is correlated to the instrument’s working condition. The proposed algorithm using the t-test distribution method can improve the nonlinearity fitting results and calibration precision. This method provides accurate nonlinear parameter for on-orbit calibration and can play a role in the total life cycle of MWRI after being launched.

High vacuum measurements and calibrations, molecular flow fluid transient effects

High vacuum pressure measurements and calibrations below ≈1 × 10−6 Torr are problematic. Specifically, measurement accuracies change drastically for vacuum gauges when pressures are suddenly lowered in vacuum systems. How can gauges perform like this? To answer this question, a brief system description is first required. Calibrations were performed using a vacuum calibration chamber with attached vacuum gauges. To control chamber pressures, vacuum pumps decreased the chamber pressure while nitrogen tanks increased the chamber pressure. By balancing these opposing pressures, equilibrium in the chamber was maintained at selected set point pressures to perform calibrations. When pressures were suddenly decreased during set point adjustments, a sudden rush of gas from the chamber also caused a surge of gas from the gauges to decrease the pressures in those gauges. Gauge pressures did not return to equilibrium as fast as chamber pressures due to the sparse distribution of gas molecules in the system. This disparity in the rate of pressure changes caused the pressures in different gauges to be different than expected. This discovery of a new theory was experimentally proven to show that different gauge designs return to equilibrium at different rates, and that gauge accuracies vary for different gauge designs due to fluid transients in molecular flow.

Prelaunch calibration and primary results from in-orbit calibration of the atmospheric correction microwave radiometer (ACMR) on the HY-2A satellite of China

The atmospheric correction microwave radiometer (ACMR) is one of the main payloads for correcting atmospheric path delay in the radar altimeter on the Haiyang-2A (HY-2A) satellite. The ACMR is a three-band microwave radiometer operating at 18.7, 23.8, and 37.0 GHz. Calibration of the ACMR is important for applying its measurements to correct for atmospheric effects on the HY-2A altimeter signal transmission in the air. Therefore, a detailed introduction to the principles and specifications of the ACMR system is given first. The thermal vacuum calibration method of the ACMR is discussed and analysed, and the microwave transfer functions and related coefficients are given, especially the nonlinear coefficients derived from a test for correcting nonlinear responses between the input of antenna temperature and the output of voltage at each channel of the ACMR. Furthermore, antenna pattern correction algorithms for removing the effects of side lobe and cross-polarization are derived and their coefficients are used for in-orbit data processing. Primary calibration results are given by comparing with the similar spaceborne Jason microwave radiometer (JMR) on the Jason-1 satellite and with the advanced microwave radiometer (AMR) on Jason-2. The results of this comparison show that the data from the ACMR match well to those from the JMR and AMR.

Global Precipitation Measurement Microwave Imager Prelaunch Hot Load Calibration

For typical scanning microwave radiometers, a significant source of calibration error arises from thermal gradients on the hot load. Even when direct or reflected solar illumination is blocked, hot load gradients arise from thermal coupling between the target and the surface facing the target which is heated and cooled as the instrument orbits the earth. For the GlobalL Precipitation Measurement (GPM) Microwave Imager (GMI), a rotating metal annular ring called the “hot load tray” serves to guard the hot load against solar intrusion, and is the surface immediately facing the hot load during the majority of the scan. The planned GMI calibration algorithm corrects for the target gradients induced by thermal coupling between the hot load tray and hot load. The correction uses an empirically derived relationship between the target gradient and the temperature differential between the target and the tray. The correction is derived using target-level and GMI system-level calibration testing. The dual calibration of GMI, in connection with thermal vacuum calibration measurements, is a key aid to determining and correcting the hot load gradients.

Preflight calibration of the Imaging Magnetograph eXperiment polarization modulation package based on liquid-crystal variable retarders.

We present the study, characterization, and calibration of the polarization modulation package (PMP) of the Imaging Magnetograph eXperiment (IMaX) instrument, a successful Stokes spectropolarimeter on board the SUNRISE balloon project within the NASA Long Duration Balloon program. IMaX was designed to measure the Stokes parameters of incoming light with a signal-to-noise ratio of at least 103, using as polarization modulators two nematic liquid-crystal variable retarders (LCVRs). An ad hoc calibration system that reproduced the optical and environmental characteristics of IMaX was designed, assembled, and aligned. The system recreates the optical beam that IMaX receives from SUNRISE with known polarization across the image plane, as well as an optical system with the same characteristics of IMaX. The system was used to calibrate the IMaX PMP in vacuum and at different temperatures, with a thermal control resembling the in-flight one. The efficiencies obtained were very high, near theoretical maximum values: the total efficiency in vacuum calibration at nominal temperature was 0.972 (1 being the theoretical maximum). The condition number of the demodulation matrix of the same calibration was 0.522 (0.577 theoretical maximum). Some inhomogeneities of the LCVRs were clear during the pixel-by-pixel calibration of the PMP, but it can be concluded that the mere information of a pixel-per-pixel calibration is sufficient to maintain high efficiencies in spite of inhomogeneities of the LCVRs.

Measurement of Long-Term Dimensional Stability of Glass Ceramics Using a High-Precision Line Scale Calibration System

Length measurement was conducted for two years on glass ceramics, Zerodur®and Clearceram®, which have a low coefficient of thermal expansion, and on synthetic quartz. Commercially available glass ceramics were used for evaluating long-term stability, or secular change. Synthetic quartz ensured longterm length measurement stability. Two line scales of 300 mm length made of each material for a total of six line scales were simultaneously manufactured and measured to evaluate dimensional stability variation of the materials over time. Measurements were conducted with a line scale calibration systemdeveloped by Nikon. The calibration system is a onedimensional laser interferometer, featuring reduced Abbe’s errors, laser interferometer paths in a vacuum and real-time wavelength calibration of laser frequency using a 633 nm iodine-stabilized He-Ne laser. Long-term quartz stability was 4.3 nm and 5.4 nm (2σ). The yearly stability coefficients of the two glassceramic scales were -0.22 and -0.23 parts per million per year (ppm/yr) for Zerodur and -0.16 and -0.16 ppm/yr for Clearceram. No significant difference in stability between the two scales was observed for Zerodur or Clearceram.

Error contributor of defocus and quadratic caustic in line scale measurement

Measurement error resulting from the defocus and quadratic caustic of a line-detecting microscope in line scale measurement was investigated. The relationship between the lateral shift and defocus was clarified and a procedure for measuring the lateral shift without changing the tilt of the line scale under measurement was proposed. An experiment was performed on line scale measurement to demonstrate the proposed measurement procedure using a line scale calibration system. The calibration system used in this experiment was a one-dimensional, laser-interferometric length measurement system for line scales developed by Nikon. The calibration system features a reduced Abbe's error, laser interferometer paths installed in vacuum and real-time calibration of the wavelength of the Zeeman laser, which is used for length measurement, using a 633 nm iodine-stabilized He–Ne laser. The line scale used for the experiment was 300 mm in length, and made of glass ceramics. The experimental result of the lateral shift stemming from the defocus and quadratic caustic of the optics of the line-detecting microscope was approximately 4 nm for a defocus range of ±10 µm. The possibility of reducing this type of error was also discussed.

Analysis of Heat Transfer in PVC Profiles during the Extrusion Calibration/Cooling Step

Abstract The external vacuum calibration of extruded thermoplastic materials is a complex process, which may hinder the production and even the quality of the parts. Process control requires a thorough knowledge and a deep analysis of the heat transfer phenomena between both the part and the calibrator during the cooling phase. This paper initially presents a detailed description of the experimental setting used to qualify and quantify the heat transfer modes. The experimental specimen is a 100-mm wide PVC strip, which represents one of the three sides of the U-profile. The development of physical models to predict plastic part thermal history during the forming process is a major industrial concern because it can reduce tooling development times and costs significantly. In the extrusion processing field, the external vacuum calibration stage often hinders productivity. The present study has been conducted to examine strip cooling phase so as to propose some thermal models for both global and detailed analyses of heat transfer modes. First, a transparent wall calibrator is used to view the behaviour of the extrudate inside the calibrator for a better understanding of the thermal phenomena at work. A second calibrator equipped with temperature sensors makes it possible to assess, using an inverse calculation method, the heat flux transferred from the extruded material to the calibrator as well as the temperature pattern throughout the tool.

Measurement of absolute radical densities in a plasma using modulated-beam line-of-sight threshold ionization mass spectrometry

Using modulated beam line-of-sight threshold ionization mass spectrometry (LOS-TIMS) we measured absolute O, O2, and Ar densities, and the average neutral-gas temperature in an O2/Ar electrical discharge as a function of pressure in the plasma chamber and the mole fraction of Ar in O2; the pressure and mole fraction range was 25–200 mTorr and 0–0.90, respectively. Although LOS-TIMS is a versatile tool for measuring absolute radical densities, it requires careful vacuum design and calibration to account for various sources of error such as the contribution to the quadrupole mass spectrometer (QMS) ion current from the background gases, the ion mass-to-charge ratio dependent sensitivity of the various QMS components, and space-charge limitations in the QMS ionizer. In addition, collisions within the molecular beam extracted from the discharge must be taken into account particularly for higher plasma chamber pressures (&amp;gt;75 mTorr). In our measurements, these effects are carefully considered and the consequences of ignoring them are discussed. The O atom density increases with pressure and O2 mole fraction in the feed gas and is in the range of 2.1×1018–2.6×1019 m−3. At low pressures, our measurements show that the O2 translational temperature is higher than that for Ar.

Ultimate determination of ScaRaB flight model 2 channel gains

The Scanner for Radiation Budget (ScaRaB) instruments are a series of Earth Radiation Budget (ERB) radiometers of which the first flight model (FM1) was launched on a Russian METEOR satellite in 1993. A second model (FM2) was launched on the Russian RESURS satellite in July 1998. The FM2 instrument worked perfectly until the failure of the platform transmitter in April 1999. Considering both missions, ERB data were obtained over sixteen months with ScaRaB. In order to obtain a good correlation between calibrations on the ground and in space in the long-wave spectral domain, the spectral response has been re-estimated using an original method. As the solar ground calibration and the integrating-sphere calibration are conducted in an enclosure purged with dry nitrogen, the detector gain differs from the gain under vacuum, and a correction factor must be applied. A new correction coefficient has been determined through analysis of the ScaRaB data sets, leading to satisfactory agreement between long-wave vacuum calibration and solar calibration.

Precision gas flowmeter for vacuum calibration

The Primary Standards Laboratory at Lockheed Martin Missiles and Space has developed an orifice flow vacuum calibration station for in-house calibration of spinning rotor and ion gages. A flowmeter supplies gas to a vacuum chamber partitioned by an orifice of calculable conductance. The pressure generated within the chamber is defined by the flowrate and the orifice conductance for molecular flow conditions. Orifice conductance is calculated from dimensional measurements, the flowrate is determined by measuring pressure drop at constant volume within the flowmeter. The design, development, and operation of the flowmeter is fully explained and illustrated. Chamber pressures as predicted from flowrate measurements are compared to those measured using a spinning rotor gage calibrated at the National Institute of Standards and Technology. Data for the extension of the calibration range beyond that of spinning rotor gages will be presented. An analysis of uncertainties inherent to the flowmeter is also presented.

Evaluation of low cost residual gas analyzers for ultrahigh vacuum applications

In recent years several low cost computer controlled residual gas analyzers (RGAs) have been introduced into the market place. It would be very useful to know the performance character- istics of these RGAs in order to make an informed selection for UHV applications. The UHV applications include extreme sensitivity helium leak detection and monitoring of the residual gas spectra in UHV systems. In this article, the sensitivity and linearity data for nitrogen, hydro-gen, and helium are presented in the pressure range 10−8–10−1 Pa. Further, the relationships between focus voltage and ion currents, relative sensitivity, and fragmentation factor are also included. A direct comparison method is used in obtaining this data. Spinning rotor and extractor gauges are the transfer standard gauges used in Jefferson Lab’s vacuum calibration facility, with which all the reported measurements here were carried out.

A primary standard high vacuum calibration station for industrial applications

The Metrology Laboratory at Lockheed Martin Missiles &amp; Space in Sunnyvale, CA, has developed a primary standard high vacuum calibration station. Maintaining an in-house capability for calibrating Bayard–Alpert gauge tubes and spinning rotor gauges (SRGs) at the primary level eliminates the need for external sources of calibration. This not only significantly reduces costs but also provides for continuous monitoring of the reference standards used to support research programs and manufacturing processes. A constant volume, pressure drop flowmeter is used to generate known pressures in a vacuum chamber partitioned by an orifice of calculable conductance. Data are presented which show vacuum chamber pressure to be directly proportional to flowmeter pressure drop in the three decades of vacuum spanned by the SRGs (10−3–10−6 Torr). Using a SRG calibrated at the National Institute of Standards and Technology, the proportionality constant is determined and shown to agree well with the constant calculated from system fixed parameters and measured pressure ratios. A new design of flowmeter is discussed. An estimate of when the system will be fully utilized as a primary reference will be made.