Gas Flow Calibration Research Articles

Gas flow calibration standard device for working site

A portable on-site gas flow standard device based on the standard meter method is designed to ensure metering accuracy in the natural gas trade. The standard device is optimized using computation fluid dynamics simulation technology. The acquisition of high and low frequency pulse signals, video photoelectric signals, and manual trigger signals is realized. Non-fixed-point measurement is realized by corrected linear interpolation of fixed-point and least-squares construction of the instrument coefficient correlation. The flow rate range of the device is (0.65–650) m3 h−1 and the expanded uncertainty is 0.33% (k= 2). The device is compact, portable, and can be carried on a vehicle for on-site application. The device is compared with the bell-type gas flow standard device and the sonic nozzle gas flow standard device of Hebei Metrology Supervision and Inspection Institute. The experimental results show that the E n value of the device is 0.67, and the measurement repeatability is better than 0.12 %.

Echo signal envelope fitting based signal processing methods for ultrasonic gas flow-meter

The echo signal of the ultrasonic gas flow-meter is difficult to locate, and the computation of signal processing methods proposed by others is extensive which affects the meter’s real-time performance. Aiming at solving these problems the echo signal envelopes under different flow rates are analyzed. And three kinds of signal processing methods based on echo signal envelope fitting are proposed. The shape of the echo signal remains the “approximate spindle shape” as the flow rate increases, and the envelope gradient of the middle parts of the upper envelope’s rising section and the lower envelope’s falling section remains the same at different flow rates, so the mathematical models of the two sections are established to obtain the envelope gradient curves of the two sections. With the envelope gradient curves, the ranges of envelope and peak points that linearly distributed are obtained. The least squares fitting is performed on those peak points to obtain two feature straight lines for respectively representing the upper envelope’s rising section and the lower envelope’s falling section. According to the spatial characteristics of the feature straight lines, the points on the feature straight lines are selected as the feature points for quickly locating the echo signal. According to the offline verification and comparison, the best one of three kinds of signal processing methods is selected, and realized on the hardware system of the two-channel ultrasonic gas flow-meter. The transmitter of two-channel ultrasonic gas flow-meter is developed based on FPGA & DSP dual core structure. It utilizes the parallel processing capacity and logic control ability of FPGA to realize the controlling of the high-speed ADC & DAC and the storage of the data. At the same time, it adopts the high-speed computing capacity of DSP to implement the digital signal processing method. The gas flow calibration experiments were carried out in a national accredited testing agency to verify the effectiveness of the signal processing methods and system. The experimental results show that the improved signal processing method based on echo signal upper and lower envelope fitting can quickly and accurately locate the echo signal. And the measurable range of the ultrasonic gas flow meter based on this signal processing method is broadened to 10 m3/h to 1,300 m3/h, and the turndown ratio is broadened to 1:130.

Echo energy integral based signal processing method for ultrasonic gas flow meter

Ultrasonic gas flow meter possesses unique measurement advantages, and is especially suitable for natural gas measurement of large diameter gas pipelines. It is very important to obtain the accurate transit-time of ultrasonic signal for ensuring the measurement accuracy of ultrasonic gas flow meter. However, it is difficult to find stable feature points for determining the transit-time in ultrasonic gas flow meter signal processing. Aiming at this problem, the echo energy gradient is analyzed from the point of the echo energy integral in this paper, an echo energy integral based signal processing method is proposed, and corresponding parameter selection is put forward. First of all, the FCE (fixed cumulative energy) value is set as a standard, and the area of the EES (echo energy signal) rising section is integrated, that is, the echo energy in this period of time is accumulated. When the cumulative energy value exceeds the FCE value, the end position of the FCE value is taken as the feature point. Then the ultrasonic transit-time is obtained, and the gas flow rate is calculated. This digital signal processing method is implemented in real-time in the digital system with the FPGA (Field Programmable Gate Array) and the DSP (Digital Signal Processor) as the double cores, and the gas flow calibration experiments are conducted to verify the effectiveness of the proposed digital signal processing method.

Variable ratio threshold and zero-crossing detection based signal processing method for ultrasonic gas flow meter

Abstract Ultrasonic gas flow meter has unique advantages and good application prospects for measuring the gas flow rate in medium to large diameter pipelines. However, there is energy attenuation in the ultrasonic wave propagation process, and the propagation path of the ultrasonic wave will shift with the gas flow rate increasing, which makes it difficult for the commonly used transit-time method to determine the feature point and obtain the accurate measurement results. Therefore the characteristics of the ultrasonic echo signal are studied, and a variable ratio threshold and zero-crossing detection based digital signal processing method is proposed for ultrasonic gas flow meter. The ultrasonic echo signal is normalized, and the ratio value is used as the threshold value to determine the feature point. Based on the analysis of the amplitude of the extreme points under different flow rates, the threshold value is determined according to the intersection of the amplitude interval of the extreme points. According to the feature point, the zero-crossing method is adopted to calculate the ultrasonic wave propagation time. This digital signal processing method is implemented in real time in the digital system with the FPGA (Field Programmable Gate Array) and the DSP (Digital Signal Processor) as the double cores, and the gas flow calibration experiments are conducted to verify the effectiveness of the proposed digital signal processing method and developed system.

External calibration strategy for trace element quantification in botanical samples by LA-ICP-MS using filter paper

The use of reference solutions dispersed on filter paper discs is proposed for the first time as an external calibration strategy for matrix matching and determination of As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr, V and Zn in plants by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). The procedure is based on the use of filter paper discs as support for aqueous reference solutions, which are further evaporated, resulting in solid standards with concentrations up to 250 μg g−1 of each element. The use of filter paper for calibration is proposed as matrix matched standards due to the similarities of this material with botanical samples, regarding to carbon concentration and its distribution through both matrices. These characteristics allowed the use of 13C as internal standard (IS) during the analysis by LA-ICP-MS. In this way, parameters as analyte signal normalization with 13C, carrier gas flow rate, laser energy, spot size, and calibration range were monitored. The calibration procedure using solution deposition on filter paper discs resulted in precision improvement when 13C was used as IS. The method precision was calculated by the analysis of a certified reference material (CRM) of botanical matrix, considering the RSD obtained for 5 line scans and was lower than 20%. Accuracy of LA-ICP-MS determinations were evaluated by analysis of four CRM pellets of botanical composition, as well as by comparison with results obtained by ICP-MS using solution nebulization after microwave assisted digestion. Plant samples of unknown elemental composition were analyzed by the proposed LA method and good agreement were obtained with results of solution analysis. Limits of detection (LOD) established for LA-ICP-MS were obtained by the ablation of 10 lines on the filter paper disc containing 40 μL of 5% HNO3 (v v−1) as calibration blank. Values ranged from 0.05 to 0.81 μg g−1. Overall, the use of filter paper as support for dried aqueous standards showed to be a useful strategy for calibration and plant analysis by LA-ICP-MS.

Investigations of a method for determining pumping speed and sorption capacity of nonevaporable getters based on in situ calibrated throughput

This paper presents a gas-sorption method, based on an in situ calibrated throughput, for characterizing nonevaporable getters (NEGs) of Ti- and Zr-based alloys. The main characteristics of the method are the adjustment of a constant injected gas flow, the prompt calibration of a throughput, and the measurement of an increasing sorption pressure. It is essential that inert vacuum gauges be selected for measurements of total pressure to prevent contamination of a test gas and poisoning of an NEG under test. A capacitance diaphragm gauge is used for preparation of the injected gas flow by filling the gas reservoir with a test gas and adjusting the conductance of a variable leak valve. A spinning rotor gauge (SRG) is used for in situ calibration of the throughput by means of an integrated gas-flow calibration facility and the rate-of-pressure-rise method, and by continuous measurement of the sorption pressure in a test chamber. A getter pumping speed and a sorbed quantity are calculated while considering the throughput, the sorption pressure, and the sorption time. The throughput must be selected in accordance with both the sorption characteristics of a particular NEG type and the measurement capabilities of the SRG. At room temperature, porous thick-film NEGs and structured thin-film NEGs exhibit an initial getter pumping speed on the order of 1 and 0.1 l s−1 cm−2, respectively. The corresponding sorption capacity of a few times 10−4 mbar l cm−2 is comparable for all chemically active gases except for H2, which amounts to a few times 100 × 10−3 mbar l cm−2 in the case of porous NEGs and ∼1 × 10−3 mbar l cm−2 in the case of structured NEGs. Detailed analysis of uncertainties of SRG pressure measurements below 1 × 10−3 mbar gives an expanded uncertainty of the getter pumping speed and the sorbed quantity of 1.9% and 3.5%, respectively. While temporally interrupting the throughput, the setup enables discrete measurements of the background pressure, which increases because of the accumulation of nongetterable gases. After completion of the gas-sorption test, a qualitative determination of the accumulated inert gas composition is performed by the gas-burst method using a quadrupole mass spectrometer (QMS) mounted on a vacuum system. The quantitative analysis is enabled by the use of a QMS calibrated in situ by known amounts of a certain gas such as H2, CH4, CO, Ar and Kr.

A new approach to gas flow calibration

Primary gas flow standards create calculable flow rates using two different techniques. Displacement systems rely upon the accurate determination of the first order change in position of an object being displaced by gas flowing at a constant pressure. Pressure, volume, temperature and time (PVTt) systems provide a nearly constant mass flow of gas to an accumulation tank of known volume over a fixed time interval. Measurements of pressure, temperature and time are used to calculate flow rate. The Precision Gas Flow Calibrator (PGFC) described below represents a new and simplified approach to gas flow calibration. By setting the parameters which drive the exponential decay of pressure from a fixed volume a range of flow rates is generated which is linear to first order within measurement times sufficient for obtaining high precision data. Indeed, previous work has proven this method as effective as displacement based standards for an orifice flow calibration system [1].

1809 気体流量校正設備における新型高速弁の不確かさ解析(S24-2 流量計測の新たな展開(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

1809 気体流量校正設備における新型高速弁の不確かさ解析(S24-2 流量計測の新たな展開(2),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

On measurement uncertainty of a vortex flowmeter

The measurement uncertainty of a T-shaped vortex flowmeter was examined with a gas flow calibration facility, for Reynolds numbers, Re d , in a range of 2.56×10 4–1.56×10 5. The total uncertainty interval of the Strouhal values deduced from a Fourier spectral analysis was ±0.745%, and the linearity of the data was ±1.78%. Meanwhile, a scheme based on pulse counting in reference to the analog signals measured gave the total uncertainty interval of the meter factor as ±0.568%, with the linearity ±1.89%. Further, the flowmeter was tested in a fully developed water pipe flow facility, for Re d of 5.6×10 3–5.29×10 4. The vortex shedding frequencies were obtained with the techniques of Fourier transform and autocorrelation, respectively. At low flow rates, the autocorrelation technique gave a smaller uncertainty interval than the Fourier analysis did; at higher flow rates the situation was reversed. The linearity of the St values obtained in the water pipe flow experiment was ±0.391%, noticeably smaller than that obtained in the gas flow facility.

Portable Piston Gas Prover for Field Calibration of Flowmeters

Summary This paper describes a newly developed, unique piston-gas-prover system and its advantages for on-site gas flowmeter calibration to improve measurement accuracy. The gas prover was tested at a natural gas flow calibration facility and at the Colorado Engineering Experimental Station Inc. (CEESI) to demonstrate its measurement performance, repeatability, and accuracy. The piston prover, with a design similar to that of an existing piston liquid prover, is bidirectional and uses a special piston to move gas through a calibrated section of known volume. It is constructed to perform on-site calibration of such flowmeters as gas turbine or orifice meters at operating conditions. The unit can easily be set up in series with a field meter for calibration. Less than 4 in. of water pressure drop is required to operate the piston through the calibrated section. In the evaluation tests, a master turbine meter was calibrated on unprocessed natural gas. Test results show turbine pulse-count repeatability to be ±0.05%. The accuracy of the piston prover was also checked in series with an air calibration system at CEESI. This study showed that on-site calibration of a gas metering device can be conducted successfully with a portable piston-gas-prover system to improve flow measurement accuracy.