Ultrasonic Interferometer Manometer Research Articles

Evaluation of effective area of air piston gauge with limitations in piston–cylinder dimension measurements

The air piston gauge (APG) has been established at the National Physical Laboratory, India (NPLI) for Pascal realization since 2002. The APG at NPLI has been considered a transfer pressure standard because it has been calibrated against the primary pressure standard, i.e. ultrasonic interferometer manometer. As per existing international protocol, the APG establishment as a primary standard, the effective area (A e) of piston–cylinder (p–c) assembly and masses must be directly traceable to SI units. We have calculated A e and associated uncertainty of p–c assembly using the theory of rarefaction gas dynamics, which is based on dimension measurements. The value of A e is obtained for varying temperatures and radii of piston and cylinder in their respective uncertainty limits. The variation of the cylinder's inner radius within its uncertainty limit of 0.7 µm includes the expected effective area, i.e. 3.356 775 (5) cm2. The effective area’s expected values are obtained for the cylinder’s radius of 10.338 00 (2) mm, which is approximately 0.65 µm away from the value obtained from dimensional measurements and well within the uncertainty limit. Therefore, to get the effective area of 3.356 775 (5) cm2, the uncertainty of the cylinder’s radius should be at least one order less (similar to piston’s radius) than that of the present value. The precision in dimension measurement of the cylinder's internal radius is the critical parameter for effective area calculation of p–c assembly.

Establishment of air piston gauge as primary pressure standard at CSIR-National Physical Laboratory INDIA

The air piston gauge (APG) was established at CSIR-National Physical Laboratory, India (NPLI) since 2000. Later the same piston- cylinder(p-c) assembly was calibrated in NIST USA; however, it was never published for metrology communities. As per international protocol, the establishment of the APG as a primary standard, the effective area of p-c assembly, and masses must be directly traceable to SI units. The first time we have calculated the effective area and associated uncertainty of p-c assembly using dimension and mass metrology, traceability to the SI units, i.e., meter and kilogram. To realize the APG as primary pressure standards, we have calculated the effective area of p-c assembly of APG directly from dimension metrology, which is further supported by various other methods. The effective area values obtained in the pressure range of 6.5 – 360 kPa lie in the range of 3.356729 – 3.357248 cm² due to uncertainty limitation in the measurement of dimension of internal diameter of cylinder. The expected values of the effective area which are also measured from cross-float technique against ultrasonic interferometer manometer (UIM), primary pressure standards. The accuracy in effective area measurement is possible only when the resolution in the internal radius of the cylinder should at least be up to 5th decimal order and the uncertainty is 80 nm. The expanded uncertainty was measured nearly 11 ppm at <em>k</em> = 2 by considering the uncertainty in internal radii of cylinder and radii of piston around 80 nm.

Improved Measurement Capabilities in Pneumatic Pressure Measurements at NPLI Through Re-establishment of the Traceability Chain

This work presents, in brief, the recently concluded extensive in-house inter-comparison of the pneumatic pressure standards at CSIR-National Physical Laboratory, India (NPLI) and the resulting marginal improvement in our measurement uncertainties. The measurements are traceable to the Ultrasonic interferometer manometer (UIM), our low-pressure primary pressure standard as well as to the national primary standard in pneumatic pressure, NPLI-P1. The inter-comparisons and the subsequent estimations of measurement uncertainties, starting from the UIM, were carried out in the overlapping pressures, ranging from 0.01 to 40 MPa. In addition, the large-diameter piston gauge, the pneumatic primary standard was also used to establish the traceability chain. A summarized description of the extensive exercise undertaken is given herein which describes the stability and the excellent agreement with previously reported results as well as successful improvement owing to better control over experimentation as well as environmental factors.

On long-term stability of an air piston gauge maintained at National Physical Laboratory, India

The complexity of electronics and hardware in Ultrasonic Interferometer Manometer (UIM) along with a large amount of health and environmental hazardous mercury compelled most of the national metrological institutes (NMIs) to replace UIM with easy to operate and handle based on low-pressure range air piston gauge (APG). Since most of the NMIs have kept APG at the top of traceability chain (only a few have functional UIM), it is an urgent need of time to understand the qualitative change in the effective area at 23 °C (Ae) of piston-cylinder (p-c) assembly after long-term uses in measurement. The Ae of the p-c assembly of APG has been determined using UIM over the years during six in-house comparisons, which are found in the range of 10 ppm in the pressure range 20–120 kPa, which is well within the estimated uncertainties. The quality of p-c assembly was further checked by measuring fall-rate up to the full range of APG, which provides a maximum fall rate of 2.2 mm/min at 350 kPa. The present fall rate is very close to the manufacturer reported value, which suggests long-term stability of p-c assembly after 18 years in the calibration and measurement process. The uncertainties associated with Ae have been calculated using the law of propagation of uncertainty and Monte Carlo method and are found to be 9.8 ppm and 9.5 ppm at k = 2, respectively. The standard deviation of the mean of effective areas is in the range of 10−10 m2 to 10−11 m2 over 18 years, further, confirm the long-term stability of their consistency in the pressure measurement by p-c assembly.

Evaluation of Uncertainty in the Effective Area and Distortion Coefficients of Air Piston Gauge Using Monte Carlo Method

The fixed number of trials in the Monte Carlo method (FMCM) has been employed for the evaluation of effective area along with their associated uncertainties and distortion coefficients of piston–cylinder (p–c) assembly of the air piston gauge with varying pressures ranging from 6.5 to 360 kPa. The FMCM uncertainty values are compared with the conventional method, i.e., the law of propagation of uncertainty in the experimental range 20–120 kPa using our primary pressure standard, i.e., ultrasonic interferometer manometer. It is observed that the relative uncertainty of the effective area using FMCM (~ 9.5 ppm) is lesser than that of the experimental value (~ 9.7 ppm) using the same parameters responsible for uncertainty measurement which leads to the quality enhancement in the measurement of pressure.

Uncertainty evaluation and phase variation of ultrasonic interferometer manometer: A primary pressure and vacuum standard

The ultrasonic interferometer manometer (UIM) is an apex level primary pressure standard for Pascal realization established at National Physical Laboratory India (NPLI). The performance of UIM has been evaluated from time to time by participation in key comparisons, calibration and measurement capabilities (CMC) and publications in reputed international metrology journals. The pressure is measured using time of flight technique at 44 different frequencies in ultrasonic range and the phase measurement. The phase measurement combined with the time of flight measurement using the exact fractional algorithm provides highly accurate column length hence respective pressure values. The combined process helps in lowering the uncertainty in real experimental conditions. Recently, we have also changed UIM software from tbasic to window based program with the same algorithm which provides a column length measurement study. A detailed study was carried out for variation of fringe counts or oscillations with varying pressure. Experimental and theoretical calculation for both resolution and pressure dependent part has been carried out for uncertainties involves the physical parameters. The uncertainties in lower pressure range, i.e., between 1 Pa and 1000 Pa were varying equal or sometimes higher than the theoretical resolution value 0.0092 Pa (k = 2) because of environmental conditions like vibration, temperature, atmospheric pressure, and humidity whereas for higher pressure range, i.e., 1000 Pa to 130 kPa the uncertainties were either close or smaller than the pressure dependent theoretical uncertainty value, i.e. 7.2 × 10−6 of the reading.

Measurement Uncertainties for Vacuum Standards from a Low to an Ultra-high Vacuum

The Korea Research Institute of Standards and Science (KRISS) has three major vacuum systems: an ultrasonic interferometer manometer (UIM; Section II, Figs. 1 and 2) for a low vacuum, a static expansion system (SES; Section III, Figs. 3 and 4) for a medium vacuum, and an orifice-type dynamic expansion system (DES, Section IV, Figs. 5 and 6) for high and ultra-high vacuum systems. For each system, explicit measurement model equations with multiple variables are given. According to ISO standards, all of these system variable errors were used to calculate the expanded uncertainty (U). For each system, the expanded uncertainties (k = 1, confidence level = 95%) and relative expanded uncertainty (expanded uncertainty/generated pressure) levels are summarized in Table 4. Within the uncertainty limits, our bilateral and key comparisons [CCM.P-K4 (10 Pa to 1 kPa)] are extensive and in good agreement with those of other nations (Fig. 8 and Table 5).

Establishing a Continuous Chain of Traceability for Pressure Measurements up to 40 MPa

Abstract:An Ultrasonic Interferometer Manometer (UIM) has been in use as the primary pressure standard at the National Physical Laboratory in India (NPLI) for absolute and gauge modes up to 130 kPa since 1982. However, the primary pneumatic pressure standard in gauge mode up to 6 MPa was based on the performance of controlled clearance Piston Gauges (CCPG). The uncertainty of measurements in UIM and CCPG were of great concern in establishing the primary pneumatic pressure scale of NPLI. To bridge the gap between the high vacuum, both in absolute and gauge modes, pneumatic pressure and hydraulic pressure up to 1 GPa, a conscientious attempt has been made to establish a uniform scale in the entire pressure range from 1 × 10−4 to 1 × 109 Pa that utilizes the UIM as the primary pressure standard. This paper presents the results of this entire systematic exercise up to a pressure of 40 MPa, in terms of the characterization of the piston gauges by the method of cross floating in the overlapping pressure ranges,...

Establishment of a force balanced piston gauge for very low gauge and absolute pressure measurements at NPL, India

National Physical Laboratory, the National Metrology Institute (NMI) of India is maintaining Primary standards of pressure that cover several decades of pressure, starting from 3.0E-06 Pa to 1.0 GPa. Among which a recent addition is a Force Balanced Piston Gauge, the non-rotating piston type, having better resolution and zero stability compared to any other primary pressure standards commercially available in the range 1.0 Pa to 15.0 kPa (abs and gauge). The characterization of this FPG is done against Ultrasonic Interferometer Manometer (UIM), the National Primary pressure standard, working in the range 1.0 Pa to 130.0 kPa (abs and diff) and Air Piston Gauge (APG), a Transfer Pressure Standard, working in the range 6.5 kPa to 360 kPa (abs and gauge), in their overlapping pressure regions covering both absolute and gauge pressures. As NPL being one of the signatories to the CIPM MRA, the Calibration and Measurement Capabilities (CMC) of both the reference standards (UIM & APG), are Peer reviewed and notified in the Key Comparison Data Base (KCDB) of BIPM. The estimated mean effective area of the Piston Cylinder assembly of this FPG against UIM (980.457 mm2) and APG (980.463 mm2) are well within 4 ppm and 10 ppm agreement respectively, with the manufacturer's reported value (980.453 mm2). The expanded uncertainty of this FPG, Q(0.012 Pa, 0.0025% of reading), evaluated against UIM as reference standard, is well within the reported value of the manufacturer, Q(0.008 Pa, 0.003% of reading) at k = 2. The results of the characterization along with experimental setup & measurement conditions (for gauge and absolute pressure measurements), uncertainty budget preparation and evaluation of measurement uncertainty are discussed in detail in this paper.

Establishment of High Pressure Pneumatic Standard up to 40 MPa at NPLI

The current paper describes the successful establishment of high pressure pneumatic secondary standard for the realization of national pneumatic pressure scale up to 40 MPa from the previously existing 12 MPa. The traceability as well as the uncertainty in measurement was established through a continuous chain of measurements from very low pressures starting with the ultrasonic interferometer manometer and successive extension in overlapping pressure ranges. For this purpose a piston cylinder assembly designated as NPLI-40, with a pressure range of 0.2–40 MPa was coupled to a mechanical gas booster through a high gas pressure controller. We have experimentally estimated the zero pressure effective area of piston as well as the distortion coefficient which is traceable to the international system of unit SI. The CMC for the same is now on the BIPM website. The results obtained are discussed in detail.

진공측정표준의 불확도 평가모델 개발

한국표준과학연구원(Korea Research Institute of Standards and Science, KRISS)에는 초음파간섭 수은주압력계(ultrasonic interferometer manometer, UIM), 정적형표준기(static volume expansion system, SVES), 오리피스형 정압표준기(orifice-type dynamic expansion system, ODES) 등 세 개의 주요한 국가 진공표준기가 있다. 이 장치들의 불확도 평가를 위해 각각 변수들의 측정 및 계산 모델을 개발하였다. 국제표준화기구(International Organization for Standardization, ISO) 지침에 따라 표준기들의 확장불확도(expanded uncertainty, U)를 계산하였다. The Korea Research Institute of Standards and Science (KRISS) has three major vacuum systems: an ultrasonic interferometer manometer (UIM), a static volume expansion system (SVES), and an orifice-type dynamic expansion system (ODES). For each system explict measurement model equations with multiple variables are respectively given. According to ISO standards, all these system variables errors were used to calculate the expanded uncertainty (U).

Comparison of an ultrasonic interferometer manometer and a new dynamic flow control system in the pressure range 1–133 Pa

This work is concerned with comparison of two low-pressure calibration systems at the Korea Research Institute of Standards and Science (KRISS). The ultrasonic interferometer manometer (UIM) which is a national primary standard and the dynamic flow control system (FCS) which can be used for the calibration of vacuum gauges by comparison method by generating precise and stable pressure in the range 1–133 Pa. For this comparison, a capacitance diaphragm gauge (CDG) of 133 Pa full-scale range was used as transfer standard in the overlapping range of 1–133 Pa. The behavior of two systems in the pressure range 1.37–11.5 Pa had large variations which gradually reduced above 11.5 Pa. In the range 1.37–11.5 Pa, the difference in calibration factors for the two systems was 0.0114 with relative deviations of 5.177%. However above 11.5 Pa the corresponding values were 0.0056 and 1.197%, respectively. Since in vacuum metrology, UIM is world-wide recognized as a national calibration standard, the results of this comparison will be used to validate the FCS for calibration of low vacuum gauges.

1–15,000 Pa Absolute mode comparisons between the NIST ultrasonic interferometer manometers and non-rotating force-balanced piston gauges

The National Institute of Standards and Technology (NIST) Low Pressure Manometry Project maintains and operates primary standard ultrasonic interferometer manometers (UIMs) over the pressure range of 1 mPa to 360 kPa. Over the past decade a new type of customer gauge, the non-rotating force-balanced piston gauge or FPG (model 8601, DH Instruments, a Fluke Company 1 Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding. Such identification does not imply endorsement by NIST nor does it imply that the equipment or materials are necessarily the best for the purpose. 1 ) has been introduced to the standards community that covers the range of ≈1–15,000 Pa and is capable of both absolute and differential measurement modes. Since 2002, NIST customers 2 NIST customers shall not be identified. 2 have requested that four different FPG units be compared to the NIST primary pressure ultrasonic interferometer manometer standards (UIMs). The results of the comparisons were that all four FPG units were within manufacturers stated uncertainty (0.008 Pa + 30 × 10 −6 × P for absolute mode) when compared against the NIST UIMs at pressures between 10 Pa and 15,000 Pa (absolute mode). At pressures between 5 Pa and 10 Pa, the results were generally within manufacturer’s specifications. Below 5 Pa some of the FPG units were outside of manufacturer’s uncertainty specifications. The use of an isolating capacitance diaphragm gauge (CDG) was necessary during the comparisons to prevent humidified gas from the FPG from entering the NIST 160 kPa mercury UIM primary pressure standard. The results of these four different comparison tests will be discussed in detail, along with test conditions, equipment set-up, and test uncertainty analysis.

Effect of Dissolved Nitrogen Gas on the Density of Di-2-Ethylhexyl Sebacate: Working Fluid of the NIST Oil Ultrasonic Interferometer Manometer Pressure Standard

The National Institute of Standards and Technology (NIST) Low Pressure Manometry Laboratory maintains national pressure standards ranging from 1 mPa to 360 kPa through the operation of four ultraso...

Measurement uncertainty estimation in real experimental conditions of ultrasonic interferometer manometer established at NPL, India

The National Physical Laboratory, India, has established an ultrasonic interferometer manometer (UIM) as a primary standard in the barometric pressure region. This paper reports the results of the measurement uncertainty of the UIM evaluated under experimental conditions at each pressure point through a software developed and integrated with the existing operating software program. Through the operating software program, an initial estimate of column length using time-of-flight and four predefined ultrasonic frequencies with the help of an exact fractions algorithm is made, but the final pressure is calculated from the measurements made at multiple frequencies. At a particular pressure point, 44 measurements are made at different frequencies, covering two full circles (fringes). The mean of these 44 measurements is taken as the measured pressure to minimize the uncertainty contribution due to systematic phase error. In the present uncertainty evaluation, the standard deviation of this mean is taken into account in estimating the measurement uncertainty in real experimental conditions. The uncertainty thus estimated has been compared with that uncertainty, evaluated theoretically, as per ISO Guide to the Expression of Uncertainty in Measurements. This experimental determination of measurement uncertainty has helped us in making further improvements in the measurement accuracy of the UIM, especially at low-pressure measurements.

Measurement uncertainties for vacuum standards at Korea Research Institute of Standards and Science

The Korea Research Institute of Standards and Science has three major vacuum systems: an ultrasonic interferometer manometer (UIM) (Sec. II, Figs. 1 and 2) for low vacuum, a static expansion system (SES) (Sec. III, Figs. 3 and 4) for medium vacuum, and an orifice-type dynamic expansion system (DES) (Sec. IV, Figs. 5 and 6) for high and ultrahigh vacuum. For each system explicit measurement model equations with multiple variables are, respectively, given. According to ISO standards, all these system variable errors were used to calculate the expanded uncertainty (U). For each system the expanded uncertainties (k=1, confidence level=95%) and relative expanded uncertainty (expanded uncertainty/generated pressure) are summarized in Table IV and are estimated to be as follows. For UIM, at 2.5–300Pa generated pressure, the expanded uncertainty is <4.17×10−2Pa and the relative expanded uncertainty is <1.18×10−2; at 1–100kPa generated pressure, the expanded uncertainty is <7.87Pa and the relative expanded uncertainty is <7.84×10−5. For SES, at 3–100Pa generated pressure, the expanded uncertainty is <1.77×10−1Pa and the relative expanded uncertainty is <1.81×10−3. For DES, at 4.6×10−3–1.3×10−2Pa generated pressure, the expanded uncertainty is <1.04×10−4Pa and the relative expanded uncertainty is <8.37×10−3; at 3.0×10−6–9.0×10−4Pa generated pressure, the expanded uncertainty is <8.21×10−6Pa and the relative expanded uncertainty is <1.37×10−2. Within uncertainty limits our bilateral and key comparisons [CCM.P-K4 (10Pa–1kPa)] are extensive and in good agreement with those of other nations (Fig. 8 and Table V).

Primary pressure standards based on dimensionally characterized piston/cylinder assemblies

NIST has characterized two large diameter (35.8 mm) piston/cylinder assemblies as primary pressure standards in the range 0.05 MPa to 1.0 MPa with uncertainties approaching the best mercury manometers. The realizations of the artefacts as primary standards are based on the dimensional characterization of the piston and cylinder, and models of the normal and shear forces on the base and flanks of the piston. We have studied two piston/cylinder assemblies, known at the National Institute of Standards and Technology (NIST) as PG 38 and PG 39, using these methods. The piston and cylinder of both assemblies were accurately dimensioned by Physikalisch Technische Bundesanstalt (PTB). All artefacts appeared to be round within ±30 nm and straight within ±100 nm over a substantial fraction of their heights. PG 39 was dimensioned a second time by PTB, three years after the initial measurement, and showed no significant change in dimensions or effective area. Comparisons of the effective area of PG 38 and PG 39 from dimensional measurements, against those obtained with calibration against the NIST ultrasonic interferometer manometer (UIM), are in agreement within the combined standard (k = 1) uncertainty of the dimensional measurements and the UIM. A cross-float comparison of PG 38 versus PG 39 also agreed with the dimensional characterization within their combined standard uncertainties and with the UIM calibrations. The expanded (k = 2) relative uncertainty of the effective area is about 6.0 × 10−6 for both assemblies.

A low differential-pressure primary standard for the range 1 Pa to 13 kPa

The National Institute of Standards and Technology (NIST) has completed the development of a low differential-pressure primary standard covering a range from 1 Pa to 13 kPa for operation with line pressures up to 200 kPa. The standard is based on an ultrasonic interferometer manometer (UIM) primary pressure standard and includes a test-instrument manifold with pressure control systems. The standard was found to be equivalent to low differential-pressure primary standards at three other national metrology institutes (NMIs) in a recent international key comparison. Initial performance of the standard was limited in large part by pressure instabilities. This problem has been addressed with the development of two types of active pressure control, one for calibrating pressure-measuring instruments such as capacitance diaphragm gauges, resonant silicon gauges and Bell-type micromanometers and the other for characterizing pressure-generating instruments such as conical-piston, ball and force-balanced piston gauges. The UIM is characterized by a standard (k = 1) uncertainty due to systematic effects of [(3 × 10−3 Pa)2 + (3.2 × 10−6P)2]1/2 where P is the pressure in pascal. Random uncertainties are dominated by pressure instabilities which can be controlled to a level that varies from standard deviations of 3 mPa at lowest differential pressures to about 60 mPa at full range. The NIST primary standard is described, along with results of comparisons with primary standards developed at other NMIs.

The static expansion system as a new medium vacuum primary standard in KRISS

A new medium vacuum primary standard using the static expansion method was developed in Korea Research Institute of Standards and Technology. We compared the system with an ultrasonic interferometer manometer using two capacitance diaphragm gauges with full-scale ranges of 133 Pa and 1333 Pa. The results showed that the two standards are coincident with each other within the range of uncertainty at calibrated pressures 3 Pa to 100 Pa.

Comparison of an ultrasonic interferometer manometer and a static expansion system using a capacitance diaphragm gauge

The paper describes the results of a comparison of two primary low-pressure standards, (i) the Ultrasonic Interferometer Manometer (UIM) and (ii) the Static Expansion Apparatus (SEA), maintained at the National Physical Laboratory (NPLI), India. The comparison was carried out by employing a capacitance diaphragm gauge (CDG) of 1333 Pa full-scale range as the transfer standard over the pressure range 1 Pa to 1000 Pa. For pressures of 20 Pa and above, the values of the calibration factor of the CDG obtained on the SEA deviate 0,10 % from the values by the thermal transpiration equation and this deviation increases to over 0,4 % for pressures lower than 20 Pa. For the UIM, the deviation is found below 0,05 % at pressures of 100 Pa and above, but increases to 0,8 % for pressures as low as 1 Pa. The comparison (i) establishes the mutual compatibility of the two primary standards in the region of pressure overlap and (ii) sets limits to the uncertainty of measurements made on the two systems, which are 0,2 % at 1000 Pa and 1,0 % at 10-4 Pa for the SEA and 0,0014 % at 1000 Pa and 1,4 % at 1 Pa for the UIM.