Capacitance Manometer Research Articles

Saturation vapour pressure measurements of refrigerant R1224yd(Z) from 274 K to 338 K

A new generation of refrigerant fluids, such as hydrofluorolefines (HFOs) and hydrochlorofluorolefines (HCFOs), has been recently introduced in order to increase the availability of zero-ODP (Ozone Depletion Potential) and low-GWP (Global Warming Potential) refrigerants. Among the HCFOs, the refrigerant HCFO-1224yd(Z) captured more attention due to its very low GWP (<1), negligible ODP (0.00023), non-flammability, low toxicity, and good chemical and thermal suitability. Due to its novelty, there is still a lack of thermodynamic property data about this refrigerant including, e.g. the saturation vapour pressure measurements that have been performed only in few experimental works, one of them used to develop the first equation of state in 2017. At INRIM, saturation vapour pressure measurements of the HCFO-1224yd(Z) were carried out in the temperature range from 274 K to 338 K, improving the measurement accuracy of previously available works. The experimental approach was based on a static method where the set-up consisted of a sample cell immersed into a temperature-controlled calibration bath with millikelvin stability, connected to a precision capacitance manometer with a measurement full scale of 0.5 MPa operating at a constant temperature of 373 K. The experimental work and the measurement results are reported together with a comprehensive uncertainty budget and a comparison against measurement data available from previous works.

Absolute pressure and gas species identification with an optically levitated rotor

The authors describe a novel variety of spinning-rotor vacuum gauge in which the rotor is a ∼4.7−μm−diameter silica microsphere, optically levitated. A rotating electrostatic field is used to apply torque to the permanent electric dipole moment of the silica microsphere and control its rotational degrees of freedom. When released from a driving field, the microsphere’s angular velocity decays exponentially with a damping time inversely proportional to the residual gas pressure and dependent on gas composition. The gauge is calibrated by measuring the rotor mass with electrostatic co-levitation and assuming a spherical shape, confirmed separately, and uniform density. The gauge is cross-checked against a capacitance manometer by observing the torsional drag due to a number of different gas species. The techniques presented can be used to perform absolute vacuum measurements localized in space, owing to the small dimensions of the microsphere and the ability to translate the optical trap in three dimensions, as well as measurements in magnetic field environments. In addition, the dynamics of the microsphere, paired with a calibrated vacuum gauge, can be used to measure the effective molecular mass of a gas mixture without the need for ionization and at pressures up to approximately 1 mbar.

Development of a temperature controlled container for high accuracy capacitance manometers

National Institute of Metrology of Turkey (UME) has developed a new temperature-controlled container for high accuracy capacitance manometers (CDG). In the proposed design, due to the direct (metal-metal) contact of the temperature-controlled plate of the container with the aluminum shell of the sensor, the influence of the temperature of the electronics on the pressure sensor is minimized. Inside the aluminum shell, the temperature of the pressure sensor can be controlled at any fixed temperature with stability of ± 2 mK in the temperature range from 15 °C to 30 °C. The use of a pressure sensor inside an appropriate container minimizes the effect of the ambient temperature on the sensor, eliminates the need for correction for the effect of thermal transpiration and thus improves sensor accuracy. CDGs inside containers showed excellent short-term stability at zero pressure, which does not exceed ± 5 mPa as well as a maximum drift rate of 0.03 mPa h−1. The measurement results of ambient temperature influence on CDG’s zero showed a maximum change of 0.001% of full scale per degree Celsius. Control of CDG at ambient temperature significantly reduces the effects of thermal transpiration, which increases slightly to a maximum of 0.3% at the lowest pressures.

Integrated band intensities and absorption cross sections of phosgene (Cl2CO) in the mid-infrared at 199, 250 and 300 K

Integrated band intensities and absorption cross-sections of phosgene (Cl2CO) have been measured at different temperatures (199, 250 and 300 K) to support remote sensing applications, particularly for an accurate quantification of Cl2CO in the Earth's atmosphere. To our knowledge and prior to this study, no previous work has examined the temperature dependence of the phosgene integrated band intensities. Series of N2-broadened spectra of phosgene were recorded from 525 to 2400 cm−1, at a resolution of 0.1 cm−1, using a Bruker IFS125HR Fourier transform spectrometer located at the LISA facility in Créteil, France. The pressure of each phosgene vapor sample was measured using high precision capacitance manometers and a minimum of six sample pressures were recorded for each temperature. The samples were introduced into an especially designed, short optical path length (5.10 ± 0.01 cm), coolable cell, that was mounted inside the spectrometer. From these spectra, integrated band intensities for six spectral regions corresponding to the ν2/ν4, ν5, ν2 + ν6, ν2 + ν5, 2ν5 and ν1 bands were obtained from room temperature down to 199 K. We discussed and quantified error sources and, on average, the estimate accuracy for the measured integrated band intensities is equal to 4%. Measurements at room temperature were compared with previously reported values. Our results at 300 K, show an excellent agreement (better than 4%) with the Hopper et al. J Chem Phys (1968) values, agree reasonably well with those from the PNNL database (better than 9% for the stronger ν1 and ν5 bands of atmospheric interest), but depart strongly from the measurements of Lovell and Jones J Mol Spectrosc (1960) for which there are differences between 20 and 43%. In addition, our results at low temperatures show a non-negligible temperature dependence (7.5 to ∼31%, depending on the bands, between 300 and 199 K), probably due to the presence of hot bands and possible overlapping neighboring bands such as overtones and combination/difference bands. To better understand these temperature variations a detailed high resolution investigation of pure Cl2CO spectra over a wide range of temperature would be necessary.

Measurement of transient neutral gas puff pressure in the NUDT_IPPTx by a fast ionization gauge

A gas injector was designed for the 400 J/pulse prototype of the planar inductive pulsed plasma thruster (IPPT) developed by the National University of Defense Technology (NUDT_IPPTx). As the gas puff distribution over the coil surface is critical to the NUDT_IPPTx functioning efficiently, a fast ionization gauge was developed to investigate the neutral gas pressure profiles to seek the critical time when the thruster is ignited. The gauge was calibrated for argon by using a capacitance manometer. Time-resolved pressure profiles have been acquired in the condition of the gas puff mass matching with the discharge energy and the drive coil parameters of the NUDT_IPPTx. It is demonstrated that the gas injector can supply a gas puff with a sufficiently steep (dp/dt ≈ 770 kPa s−1) leading and trailing edge, and the gas puff can be compressed against the drive coil as expected. The critical ignition moment is considered to appear at some instant between 525 μs and 650 μs after the valve trigger.

Focus on test, measurement, software, and instrumentation

Focus on test, measurement, software, and instrumentation

Design and test of a simple fast electromagnetic inductive gas valve for planar pulsed inductive plasma thruster.

In support of our planar pulsed inductive plasma thruster research, a fast electromagnetic inductive valve for a gas propellant injection system has been built and tested. A new and important design feature is the use of a conical diaphragm as the action part, which greatly contributes to the virtue of simplicity for adopting the resultant force of the diaphragm deformation as the closing force. An optical transmission technique is adopted to measure the opening and closing characters of the valve while the gas throughput is determined by measuring the pressure change per pulse in a test chamber with a capacitance manometer. The experimental results revealed that the delay time before the valve reaction is less than 40 μs, and the valve pulse width is no longer than 160 μs full width at half maximum. The valve delivers 0-2.5 mg of argon gas per pulse varied by adjusting the drive voltage and gas pressure.

Recommended Best Practices for Process Monitoring Instrumentation in Pharmaceutical Freeze Drying\u20142017

Recommended best practices in monitoring of product status during pharmaceutical freeze drying are presented, focusing on methods that apply to both laboratory and production scale. With respect to product temperature measurement, sources of uncertainty associated with any type of measurement probe are discussed, as well as important differences between the two most common types of temperature-measuring instruments—thermocouples and resistance temperature detectors (RTD). Two types of pressure transducers are discussed—thermal conductivity-type gauges and capacitance manometers, with the Pirani gauge being the thermal conductivity-type gauge of choice. It is recommended that both types of pressure gauge be used on both the product chamber and the condenser for freeze dryers with an external condenser, and the reasoning for this recommendation is discussed. Developing technology for process monitoring worthy of further investigation is also briefly reviewed, including wireless product temperature monitoring, tunable diode laser absorption spectroscopy at manufacturing scale, heat flux measurement, and mass spectrometry as process monitoring tools.

Measurement of neutral gas pressure in the D-module of GAMMA 10/PDX by using ASDEX type fast ionization gauge.

In the divertor simulation experiments in the GAMMA 10/PDX tandem mirror, pressure of the neutral gas was investigated by using a fast ionization gauge. The gauge was absolutely calibrated for hydrogen gas by using a capacitance manometer. Change of the gauge sensitivity due to the magnetic field of GAMMA 10/PDX was also evaluated. The typical gas pressure measured in detached plasma experiments was 0.1-10 Pa. The degree of plasma detachment determined from the reduction of heat flux was enhanced as the gas pressure increases. Rapid increase of the gas pressure under the plasma flow was also observed.

Multi-species sensing using multi-mode absorption spectroscopy with mid-infrared interband cascade lasers.

The application of an interband cascade laser, ICL, to multi-mode absorption spectroscopy, MUMAS, in the mid-infrared region is reported. Measurements of individual mode linewidths of the ICL, derived from the pressure dependence of lineshapes in MUMAS signatures of single, isolated, lines in the spectrum of HCl, were found to be in the range 10–80 MHz. Multi-line spectra of methane were recorded using spectrally limited bandwidths, of approximate width 27 cm−1, defined by an interference filter, and consist of approximately 80 modes at spectral locations spanning the 100 cm−1 bandwidth of the ICL output. Calibration of the methane pressures derived from MUMAS data using a capacitance manometer provided measurements with an uncertainty of 1.1 %. Multi-species sensing is demonstrated by the simultaneous detection of methane, acetylene and formaldehyde in a gas mixture. Individual partial pressures of the three gases are derived from best fits of model MUMAS signatures to the data with an experimental error of 10 %. Using an ICL, with an inter-mode interval of ~10 GHz, MUMAS spectra were recorded at pressures in the range 1–10 mbar, and, based on the data, a potential minimum detection limit of the order of 100 ppmv is estimated for MUMAS at atmospheric pressure using an inter-mode interval of 80 GHz.

Constraints on the noble gas composition of the deep mantle by bubble-by-bubble analysis of a volcanic glass sample from Iceland

Contamination of samples by air-derived noble gases is a well-known problem in noble gas geochemistry, and, as a result, determining the true neon and argon isotopic ratios of the mantle is not straightforward. Here, we directly target individual bubbles in an Icelandic volcanic glass, DICE 11, with a 193nm excimer laser in order to reduce air-contamination, and analyze He and Ar isotopes, plus 22Ne abundances, on a Helix SFT mass-spectrometer. The CO2 content of the bubbles was measured with a capacitance manometer. In addition, new He, Ne and Ar compositions obtained by crushing on similar samples (DICE 10 and DICE 11) are presented.Our analyses show that 3He/4He ratios are homogeneous in all the vesicles in this glass sample at 17.4±0.4 Ra and are consistent with analyses by crushing. Precise 40Ar/36Ar isotopic ratios were obtained on the largest vesicles only, due to high blank contributions to the smallest vesicles, and are 8600±700, i.e. the highest values measured so far in primitive basalts from Iceland. Considering that the Ar and He isotopic compositions obtained for individual vesicles (by laser ablation) are representative of the true mantle source values, not contaminated by air, we can precisely correct the Ne isotopic analyses obtained by crushing for air contamination; the corrected 20Ne/22Ne ratios are consistent with the presence of neon-B in the sub-Icelandic mantle, which is consistent with the hypothesis that neon in the OIB source region has an irradiated meteorite origin rather than purely solar. In contrast to He and Ar isotopic compositions (which are homogeneous), the relative He–Ne–Ar–CO2 abundances in the different bubbles are heterogeneous and show strong correlations which are compatible with equilibrium degassing of the magma. Because He and CO2 do not fractionate during this degassing, we can precisely constrain the CO2/3He ratio of the mantle source at 6.7±0.5∗108, at the lower end of the MORB range. Therefore the deep mantle below Iceland is not enriched in carbon compared to the upper mantle (via recycling, for example).

Hybrid co-deposition of mixed-valent molybdenum–germanium oxides (MoxGeyOz): A route to tunable optical transmission

Mixed-valent oxides of molybdenum and germanium were deposited simultaneously using reactive magnetron co-deposition within an oxygen–argon environment. The films' stoichiometry, optical, and physical properties were varied through changes in oxygen partial pressure induced by systematic variation of the potential applied to the molybdenum cathode. The oxygen partial pressure was determined from the drop in pressure as measured by a capacitance manometer, assuming constant argon partial pressure. To facilitate deposition, a constant power of 100W DC was applied to the germanium cathode, while power was applied to the molybdenum target using a modulated pulse power supply. Modulated pulse power magnetron sputtering was used due to its ability to generate high target power densities, allowing for rapid reduction of oxygen on the surface of the “oxygen poisoned” molybdenum cathode, as well as for its highly metallic plasma resulting in increased oxygen-gettering capability. Changes in the modulated pulse power supply's capacitor bank voltage load, stepped from settings of 300 to 380V, resulted in films ranging from mixtures of transparent GeO2 (Ge4+) and MoO3 (Mo6+) to the introduction of various absorptive ionic species including Mo5+, Mo4+, Ge2+ and Ge0, as determined from X-ray photoelectron spectroscopy. The presence of each of the aforementioned ions results in characteristic changes in the films' band energies and optical absorption. As deposited MoxGeyOz thin films grown using this method have been shown to have optical gap energies that are able to be tailored between 3.57eV and 0.18eV, spanning useful ranges for devices operating in the visible and near-infrared.

Ultimate limits in the gas composition determination within small sealed volumes by quadrupole mass spectrometry

Miniaturization of modern sealed vacuum devices and higher demands for their stable operation require accurate determination of the gas composition in the early stage of their operation as well as after a long operational period. Among a few highly sensitive gas methods, quadrupole mass spectrometry seems to be the most appropriate one for this task as gas amounts are well below 1·10−4 mbar L. In this paper, a new approach, how to prepare a quadrupole mass spectrometer for routine quantitative analysis of small gas amounts, is described. In the first stage, it was calibrated by an innovative in-situ procedure using three different gases: nitrogen, argon and neon. Each gas was admitted into a chamber with a precisely determined volume equipped by a capacitance manometer. By opening the variable leak valve, ion current versus flow rate dependence was determined over three orders of magnitude. Non-linear response at very low flow rates was detected. In the next stage, gas quantities from 3·10−5 mbar L to 6·10−7 mbar L of pure gas were admitted, which proved that by numerical correction of non-linearity, the achieved accuracy of gas quantity determination could be noticeably improved. Rather poor results were on the contrary obtained when synthetic gas mixtures were analysed. Additional calibrations with gas mixtures revealed a strong interference provoked by argon. It enhanced the instrument's sensitivity for nitrogen for a factor of up to 2.3, depending on argon fraction. Considering this effect, further corrections led to a substantially improved accuracy of the nitrogen fraction determination in small gas amount mixtures. In general, quantification of very small gas amounts needs a careful analysis of all contributions influencing the accuracy, as the number of data points is limited and mostly recorded in the non-linear mode of the instrument's operation.

Measurements of metal alkylamide density during atomic layer deposition using a mid-infrared light-emitting diode (LED) source.

A nondispersive infrared (NDIR) gas analyzer that utilizes a mid-infrared light emitting diode (LED) source was demonstrated for monitoring the metal alkylamide compound tetrakis(dimethylamido) titanium (TDMAT), Ti[N(CH3)2]4. This NDIR gas analyzer was based on direct absorption measurement of TDMAT vapor in the C-H stretching spectral region, a spectral region accessed using a LED with a nominal emission center wavelength of 3.65 μm. The sensitivity of this technique to TDMAT was determined by comparing the absorbance measured using this technique to the TDMAT density as determined using in situ Fourier transform IR (FT-IR) spectroscopy. Fourier transform IR spectroscopy was employed because this technique could be used to (1) quantify TDMAT density in the presence of a carrier gas (the presence of which precludes the use of a capacitance manometer to establish TDMAT density) and (2) distinguish between TDMAT and other gas-phase species containing IR-active C-H stretching modes (allowing separation of the signal from the LED-based optical system into fractions due to TDMAT and other species, when necessary). During TDMAT-only delivery, i.e., in the absence of co-reactants and deposition products, TDMAT minimum detectable molecular densities as low as ≈4 × 10(12) cm(-3) were demonstrated, with short measurement times and appropriate signal averaging. Reactions involving TDMAT often result in the evolution of the reaction product dimethylamine (DMA), both as a thermal decomposition product in a TDMAT ampoule and as a deposition reaction product in the deposition chamber. Hence, the presence of DMA represents a significant potential interference for this technique, and therefore, the sensitivity of this technique to DMA was also determined by measuring DMA absorbance as a function of pressure. The ratio of the TDMAT sensitivity to the DMA sensitivity was determined to be ≈6.0. To further examine the selectivity of this technique, measurements were also performed during atomic layer deposition (ALD) of titanium dioxide using TDMAT and water. During ALD, potential interferences were expected from the evolution of DMA due to deposition reactions and the deposition on the windows of species containing IR-active C-H stretching modes. It was found that the interfering effects of the evolution of DMA and deposition of species on the windows corresponded to a maximum of only ≈6% of the total observed TDMAT density. However, this level of interference likely is relatively low compared to a typical chemical vapor deposition process in which co-reactants are introduced into the chamber at the same time.

Gettering of hydrogen and methane from a helium gas mixture

In this study, the authors developed an approach for accurately quantifying the helium content in a gas mixture also containing hydrogen and methane using commercially available getters. The authors performed a systematic study to examine how both H2 and CH4 can be removed simultaneously from the mixture using two SAES St 172® getters operating at different temperatures. The remaining He within the gas mixture can then be measured directly using a capacitance manometer. The optimum combination involved operating one getter at 650 °C to decompose the methane, and the second at 110 °C to remove the hydrogen. This approach eliminated the need to reactivate the getters between measurements, thereby enabling multiple measurements to be made within a short time interval, with accuracy better than 1%. The authors anticipate that such an approach will be particularly useful for quantifying the He-3 in mixtures that include tritium, tritiated methane, and helium-3. The presence of tritiated methane, generated by tritium activity, often complicates such measurements.

Quantification of hydrogen in a gas mixture of noble gases

Quantification of hydrogen fraction in the gas mixture with inert gases kept in a small enclosure of the gas surge arrester (GSA) is a challenging task. Hydrogen greatly influences device properties, but as an omnipresent gas it represents also the background of any mass spectrometer. Hydrogen fraction in a particular GSA was quantified after its puncture in an evacuated batch inlet and subsequent introduction to a pumped chamber housing a quadrupole mass spectrometer (QMS). Its calibration was performed by an innovative in-situ calibration procedure which should yield high accuracy. In the first stage, a pure gas (Ar, Ne, H2) contained in a calibrated volume was set by a leak valve to flow into the UHV system. The pressure change reading of the capacitance manometer over time gives the flow rate which is directly correlated to the ion current of a specific mass peak in the span of 3 orders of magnitude. The extracted calibration curves of the QMS for each gas species are applied in the second stage of the calibration when known gas mixtures are prepared in the calibrated volume to verify the gas composition determination procedure based on the fractionation. Such procedure is revealed fairly accurate at high (above ∼6 × 10−5 mbar L/s) flow rates, however a significant error appeared at lower flow rates. Possible explanations for erroneous hydrogen determination at very low fluxes by the QMS in the mixture with argon are presented.

Spinning rotor gauge based vacuum gauge calibration system at the Institute for Plasma Research (IPR)

The Steady-state Superconducting Tokamak (SST-1) is an indigenously built medium sized fusion device at IPR designed for plasma duration of 1000 seconds. It consists of two large vacuum chambers – Vacuum Vessel (16 m3) and Cryostat (39 m3) which will be pumped to UHV and HV pressures respectively using a set of turbo molecular pumps, Cryo-pumps and Roots pumps. The total as well as the partial pressure measurement in these chambers will be carried out using a set of Pirani gauges, Bayard Alpert type gauges, Capacitance manometers and Residual Gas Analyzers (RGA). A reliable and accurate pressure measurement is essential for successful operation of SST-1 machine. For this purpose a gauge calibration system is set up in SST-1 Vacuum laboratory based on Spinning Rotor Gauge which can measure absolute pressure in the range 1.0 mbar to 1.0 × 10−7 mbar. This system is designed to calibrate up to five gauges simultaneously for different gases in different operating pressure ranges of the gauges. This paper discusses the experimental set-up and the procedure adopted for the calibration of such vacuum gauges.

JET divertor diagnostic upgrade for neutral gas analysis

With installation of the ITER-like wall in JET a major diagnostic upgrade to measure the neutral gas pressure and composition in the sub-divertor region has been completed, to characterise retention and outgassing of the new metallic first wall. The upgrade includes two new magnetically shielded systems consisting of sensitive capacitance manometers and residual gas analysers, both capable of providing data during plasma operation. These enable absolute pressure and gas composition measurements (pressure range: 10(-5)-10(-1) mbar, mass range: 1-200 amu, respectively) and have been used to characterise the neutral gas behaviour under various plasma conditions.

The Effect of Dryer Load on Freeze Drying Process Design

Freeze-drying using a partial load is a common occurrence during the early manufacturing stages when insufficient amounts of active pharmaceutical ingredient (API) are available. In such cases, the immediate production needs are met by performing lyophilization with less than a full freeze dryer load. However, it is not obvious at what fractional load significant deviations from full load behavior begin. The objective of this research was to systematically study the effects of variation in product load on freeze drying behavior in laboratory, pilot and clinical scale freeze-dryers. Experiments were conducted with 5% mannitol (high heat and mass flux) and 5% sucrose (low heat and mass flux) at different product loads (100%, 50%, 10%, and 2%). Product temperature was measured in edge as well as center vials with thermocouples. Specific surface area (SSA) was measured by BET gas adsorption analysis and residual moisture was measured by Karl Fischer. In the lab scale freeze-dryer, the molar flux of inert gas was determined by direct flow measurement using a flowmeter and the molar flux of water vapor was determined by manometric temperature measurement (MTM) and tunable diode laser absorption spectroscopy (TDLAS) techniques. Comparative pressure measurement (capacitance manometer vs. Pirani) was used to determine primary drying time. For both 5% mannitol and 5% sucrose, primary drying time decreases and product temperature increases as the load on the shelves decreases. No systematic variation was observed in residual moisture and vapor composition as load decreased. Further, SSA data suggests that there are no significant freezing differences under different load conditions. Independent of dryer scale, among all the effects, variation in radiation heat transfer from the chamber walls to the product seems to be the dominant effect resulting in shorter primary drying time as the load on the shelf decreases (i.e., the fraction of edge vials increases).

Choked flow and importance of Mach I in freeze-drying process design

Occasionally the freeze drying cycle conditions are developed on a small scale dryer that result in a water vapor flux during primary drying that the full-scale equipment cannot handle, resulting in loss of the ability to control chamber pressure. A primary cause of loss of pressure control is a phenomenon commonly described as “choked flow”, where the required mass transfer through the duct connecting the drying and condenser chamber cannot be maintained at the control pressure. Water vapor flow rate increases as the condenser pressure decreases, but it can continue to do so only until the velocity of water vapor reaches speed of sound (i.e., Mach I) at the duct exit. The flow is then said to be choked, and any further increase in water vapor flow rate results in an increase in chamber pressure (i.e., loss in chamber pressure control). Sublimation tests were carried out in Lyostar II freeze-dryer (SP Industries, NY) to predict the occurrence of choked flow. A capacitance manometer was installed in the “condenser chamber” and differential pressure ( P c − P cd ) was measured as a function of sublimation rate ( P c =chamber pressure and P cd =condenser pressure). Water vapor flow rate was measured by Tunable Diode Laser Absorption Spectroscopy (TDLAS) methodology, with a check by gravimetric data. Flow of water vapor in the duct connecting chamber and the condenser was modeled using computational fluid dynamics software (Fluent 6.3). The critical pressure ratio ( K⁎= P c / P cd ) has been identified as an important variable that determines the onset of choked flow during primary drying. This ratio can be calculated given the mass flux. For our freeze-dryer, K* greater than 2.5 (for P c <150 mTorr) resulted in choked flow. The gas velocity indeed reaches Mach I limit at the duct exit under the choked flow conditions, as modeled by Fluent. Using the differential pressure measurements, the throat connecting the chamber and the condenser can be used as an “in process” mass flow meter to measure sublimation rate under non-choked flow conditions during primary drying without interrupting the process. Also, TDLAS is a useful tool for determination of sublimation rate even at very high mass flux.