High-rangeability ultrasonic gas flowmeter for monitoring flare gas

A transit-time ultrasonic gas flowmeter for high-rangeability requirements, such as those encountered in flare-gas flow-metering, is presented. The concept of ray rescue angle for the orientation of the ultrasonic transducers in single-beam transit-time ultrasonic flowmeters is introduced to overcome the problem of ultrasonic beam drift in high-velocity flows. To overcome problems associated with noise at high velocities, a chirp signal is used. To preserve the accuracy of the meter at low velocities near zero flow, a combination of chirp and continuous-wave signals is used to interrogate the flow. Overall system performance is presented, based on results from extensive wind-tunnel tests.     

Simple monitoring method for recovery helium gas

A practical and simple method for monitoring recovery helium gas is briefly described. The method makes use of the helium hydrostatic force in the atmosphere. The system described has been performing satisfactorily during the last two years of tests.     

Hairpin fluorescence DNA probe for real-time monitoring of DNA methylation

DNA methylation catalyzed by methylase plays an important role in many biological events. However, traditional methods of methylase activity analysis by gel electrophoresis were laborious and discontinuous. In this paper, we report a new strategy to study methylase activity using fluorescent probes coupled with enzyme-linkage reactions. A hairpin DNA probe is prepared with a fluorophore and a quencher linked at the 5'- and 3'-terminus of the probe. A disturbance of the stem sequence by DNA methylation would cause the separation of the fluorophore and the quencher, resulting in the restoration of the fluorescence. We used DNA adenine methylation (Dam) methyltransferase (MTase) and Dpn I endonuclease, both having a 5'-G-A-T-C-3' recognition sequence. Dam MTase catalyzed the methylation of the sequence of 5'-GATC-3', and Dpn I cut the sequence of 5'-G-Am-T-C-3'. The fluorescence of the hairpin probe was restored when it was cleaved by Dpn I endonuclease during the course of methylation. Unlike traditional methods, this assay was done in real time and could be used to monitor the dynamic process of methylation. Our method is easy, simple, and nonradioactive, yet as efficient as gel electrophoresis in detecting the activity of methylase. It also had the potential to screen suitable inhibitor drugs for Dam methylase.     

Spontaneous anti-stokes Raman probe for gas temperature measurements in industrial furnaces.

A compact, pulsed Nd:YAG laser-based instrument has been built to measure in situ absolute gas temperatures in large industrial furnaces by use of spontaneous anti-Stokes Raman scattering. The backscattering configuration was used to simplify the optics alignment and increase signal-to-noise ratios. Gated signal detection significantly reduced the background emission that is found in combustion environments. The anti-Stokes instead of the Stokes component was used to eliminate contributions to spectra from cold atmospheric nitrogen. The system was evaluated in a methane/air flame and in a bench-top oven, and the technique was found to be a reliable tool for nonintrusive absolute temperature measurements with relatively clean gas streams. A water-cooled insertion probe was integrated with the Raman system for measurement of the temperature profiles inside an industrial furnace. Gas temperatures near 1500-1800 K at atmospheric pressure in an industrial furnace were inferred by fitting calculated profiles to experimental spectra with a standard deviation of less than 1% for averaging times of ~200 s. The temperatures inferred from Raman spectra are in good agreement with data recorded with a thermocouple probe.     

Measuring gas flow rates in respiration: The scope for conversion

Translated from Izmeritel'naya Tekhnika, No. 10, pp. 54–56, October, 1991.     

A fast response superconducting thin-film probe for detection of second-sound shock waves in superfluid helium

Fast response probes are needed for studying the formation and propagation of second-sound shock waves (and for applying such waves to special measuring purposes) in superfluid helium. Newly developed superconducting thin-film probes enable shock-front rise times of down to 0.3 μs to be detected at signal-to-noise ratios higher than about 100. Using high vacuum evaporation techniques, such probes are relatively easy to produce. Their main body consists of a cylindrical quartz glass rod 1.5 mm in diameter with one end face polished to a plane of optical quality. The sensor strip is deposited onto this plane face as a two-component film of 0.02 mm width and 1 mm length. The temperature variations due to second sound cause changes in the resistance of the film and thus, at constant bias current, variations of the voltage drop across it. The temperature where the film undergoes its steep transition to superconductance and where, therefore, the probe works at its greatest sensitivity, is primarily fixed by the ratio of the two components (tin and gold) of the film, but can be adjusted to special values via the magnetic field produced by the adjustable bias current. The high resolution in time which is achievable by this probe makes it useful for accurate measurement of even small variations of the running time of second-sound shock waves. Such variations may be caused by flows, as is shown in the case of a flow produced by a rotating vane; their measurement may, therefore, serve as a tool for flow investigation.     

Metrological support to chromatographs for monitoring natural gas

Metrological support to natural gas quality monitoring is considered. Error standards are given for the measurement of composition and properties of natural gas attained at the level of the state primary standard at VNIIM. Translated from Izmeritel'naya Tekhnika, No. 7, pp. 62–64, July, 1998.     

基于氧化锌气敏传感器的矿井气体无线监测系统

针对煤矿生产中需要对甲烷气体浓度进行监测的需求,设计一种基于新型氧化锌传感器的矿井气体无线监测系统,介绍氧化锌传感器的特性以及系统的硬件构成。系统主要由传感器、调理电路、数据采集电路、电源模块、显示模块及Zig Bee无线通信模块组成。最后通过试验测试该系统对甲烷气体的监测性能,试验结果表明:该系统可以实现对甲烷气体浓度的有效监测。     

Characterisation of CVD diamond detectors used for fast neutron flux monitoring

Natural diamond detectors (NDD) have been successfully used for fast neutron spectrometry on various fusion installations in plasma diagnostics. These detectors can work at high temperature, are radiation hard and exhibit a high energy resolution. However, the use of NDD is limited by the availability of IIa type diamonds exhibiting high electronic properties. With the recent advance in the growth of high quality chemically vapour deposited (CVD) diamond at LETI, CVD diamond appears to be a very promising material for plasma diagnostics. We present here for the first time results of the use of CVD diamond detectors for fast neutron flux monitoring on a neutron generator. The characteristics of CVD diamond detectors are compared with that of high quality NDD made by TRINITI. Pulse height spectra have been measured with CVD detectors and NDD under both 5.5 MeV alpha particles and 14.1 MeV neutrons. The quality of CVD diamond enables the recording of structured spectra allowing the distinction between the different neutron reactions on carbon. The efficiency of CVD diamond monitors and their actual limitations are analysed and discussed.     

Measuring interparticle forces: Evaluation of superplasticizers for microsilica via colloidal probe technique

Recent concretes like ultra-high performance concrete (UHPC) are comprised of large quantities of fines following a well-defined gradation to fill the voids between coarser particles, such as cement grains. The filling of voids displaces water, which positively influences the flowability. As the rheological properties of these fresh concretes depend mainly on the forces acting between the fines due to their high specific surface areas, understanding of these forces has become crucial. In this study, the atomic force microscopy technique of colloidal probes has been used to study the adhesive forces acting between individual silica particles placed in superplasticizer and electrolyte solutions, as silica exhibit the largest fraction of inner surface in common UHPC mixtures. Pairs of individual amorphous glass particles were approached and retracted from each other. Using this technique and silica particles as a model system, several commercial superplasticizers could be evaluated regarding their influence on the interparticle adhesion.     

Modelling, simulation and measurement of fast transients in transformer windings with consideration of frequency-dependent losses

For the specification of winding insulation of transformers, it is important to know the electrical stresses to which the winding can be exposed during fast transient oscillations. These oscillations occur during switching operations performed by circuit breakers, or when gas-insulated substations (GIS) are used. Therefore one of the priorities is to use a high-frequency transformer model capable to simulating fast transient oscillations in the windings. The model presented requires only information about the geometry of the winding and the core, as well the electrical and magnetic parameters for the used materials. In the transformer model, the frequency-dependent core and copper losses are included. Numerical computations are performed with and without the core losses being taken into account. Two types of measurement are taken to verify the validity of the model. First, the voltage transients are measured and computed by the application of a step impulse with a rise time of 50 ns. Then, the transformer is switched by a vacuum circuit breaker, and the multiple reignitions, which contain oscillations with a wide frequency range, are analysed. The results verify that the model is suitable to simulate the voltage distribution in transformer windings over a wide frequency range.