Clamp-on Meters Research Articles

A deflected ray model of the transit time difference in ultrasonic flow meters applied to non-ideal flow profiles

Transit time difference (TTD) ultrasonic meters have widespread applications due to their high dynamic range, lack of moving parts and low maintenance requirements. In earlier work, the TTD is considered to arise due to the fluid flow changing the effective speed of sound along a fixed ray path, but recent publications have introduced a new way of viewing how the TTD arises. The flow velocity in the axial direction does not affect the speed of sound in the direction normal to the pipe wall. Therefore, in a clamp-on meter with the fluid at constant temperature and pressure, the transit time in the liquid must be constant with changing flow rate. The TTD then arises due to the ray path in the water being deflected, and the received wavefront travelling some extra distance along the pipe axis, which results in a different transit through the transducer wedge than for zero flow conditions. In a meter with wetted transducers, the mechanism causing the TTD is slightly different. The deflected ray travels a different distance in the fluid along the direction normal to the pipe walls due to the transducer surface being at an angle to the flow direction, and this is responsible for the TTD that is measured.Previous work has focused on calculating the magnitude of the ray deflection effect in clamp-on meters for ideal flow conditions, where the flow velocity does not depend on the position in the pipe. In this article, the ray deflection is calculated for a series of analytic profiles, and it is shown that the two models result in the same calculated TTD for both clamp-on meters and meters with wetted transducers at low flow speeds. The hydraulic correction factors calculated using the model which considers a change in the effective speed of sound are recovered using the ray deflection models. The resulting equations for beam deflection are the same as those for the conventional fixed ray path model, but the beam deflection model is more physically realistic and presents new opportunities for calibration methods utilising carefully controlled movement of the transducers. The conventional model typically has a correction factor which is allowed to vary in cases where the flows are expected to approach the speed of sound to account for the effect of ray deflection. However, the ray deflection model automatically takes this into account, so is expected to be useful in these circumstances.

Simulation Uncertainty for a Virtual Ultrasonic Flow Meter

Ultrasonic clamp-on meters have become an established technology for non-invasive flow measurements. Under disturbed flow conditions, their measurement values must be adjusted with corresponding fluid mechanical calibration factors. Due to the variety of flow disturbances and installation positions, the experimental determination of these factors often needs to be complemented by computational fluid dynamics (CFD) simulations. From a metrological perspective, substituting experiments with simulation results raises the question of how confidence in a so-called virtual measurement can be ensured. While there are well-established methods to estimate errors in CFD predictions in general, strategies to meet metrological requirements for CFD-based virtual meters have yet to be developed. In this paper, a framework for assessing the overall uncertainty of a virtual flow meter is proposed. In analogy to the evaluation of measurement uncertainty, the approach is based on the utilization of an expanded simulation uncertainty representing the entirety of the computational domain. The study was conducted using the example of an ultrasonic clamp-on meter downstream of a double bend out-of-plane. Nevertheless, the proposed method applies to other flow disturbances and different types of virtual meters. The comparison between laboratory experiments and simulation results with different turbulence modeling approaches demonstrates a clear superiority of hybrid RANS-LES models over the industry standard RANS. With an expanded simulation uncertainty of 1.44 × 10−2, the virtual measurement obtained with a hybrid model allows for a continuous determination of calibration factors applicable to the relevant mounting positions of a real meter at a satisfactory level of confidence.

A new approach for ground resistance measurements in onshore wind farms based on clamp-on meters and artificial neural network

Monitoring the grounding resistance of wind turbine generators (WTG) over the lifespan of a wind farm is important to ensure the safety of the personnel and equipment on the facilities. Conventional methods used to measure grounding resistance are not feasible in periodic maintenance activities of onshore wind farms due to test setup complexity and associated high costs. The clamp-on meter is an alternative method proposed to measure ground resistance in multi-grounded electrical systems. However, a significant error occurs in clamp-on meters on large grounding systems, such as those found in wind farms. Hence, we propose a solution to minimize methodological errors resulting from applying the clamp-on method in wind farms based on a neural network. Besides presenting lower errors than compared methods for a real Brazilian wind farm complex, it offers even greater practicality and safety to the workers involved in the measurement, as well as less test execution time.

Investigation & Minimization of Loss in Distribution System

For efficient and reliable operation of distribution system, the reactive power and voltage should be controlled so that energy loss should be minimized, bus-bar voltage should be maintained at acceptable limit (0.95P.U min and 1.05P.U max) and three phase voltages should approach as close as to the balanced system voltage . This paper work presents study of distribution system loss in the case of Textile factory, ArbaMinch town. The study makes a detail work on power system issues such as energy loss in the distribution system and its reduction techniques, reactive power flow and its compensation, power factor and voltage quality indicators such as voltage unbalance and voltage regulation. To achieve the objective, the existing distribution system of study site is modeled by using DIgSILENT Power Factory Software and simulation is carried out for unbalanced and balanced operation conditions. Clamp-on meter measurement is used to determine the load demand and line to line voltages. The results obtained for loss, power factor, voltage regulation and voltage unbalance are compared against accepted standards of IEEE, NEC & Ethiopian Electric Power Corporation (EEPCo) and possible solutions are recommended based on results obtained.

곡관후단의 직관거리와 센서위치에 따른 초음파유량계의 오차특성

관로를 통과하는 유체의 양을 측정하기 위해 설치된 유량계는 주기적인 교정과 비교측정을 통하여 측정의 정확도와 신뢰성을 확보하고 있다. 이때 사용되는 기준기는 휴대용 즉 센서가 관로의 외벽에 부착되는 건식 초음파유량계이며 사용되는 측정센서의 수량에 따라 1회선, 2회선, 4회선으로 구분된다. 본 연구의 대상은 K-water에서 주로 사용하고 있는 유량계를 선정한 후 직관거리가 충분히 확보된 상태에서 실험대상 유량계가 갖는 고유오차와 유동교란인자인 2중 곡관 후단에서의 직관거리별 오차에 대한 특성실험을 실시하였다. 실험결과를 기준으로 허용오차를 만족하는 센서위치 즉, 관로외부에 부착하는 각도와 곡관 후단으로부터의 이격거리 및 최적의 회선수를 제시하여 유량측정기술 향상을 통한 수 처리 공정관리 및 유수율 제고기반을 마련하였다.

A correlator-based current measurement system for transmission line pole footings

The ground wire on top of a H.V. transmission line poses a unique problem when measuring the resistance of pole footings. With a multimeter most of the current is diverted away from the footing and a simple clamp-on type current meter is impractical for poles ranging in diameter from 8 to 32 in. In addition, clamp-on meters typically fail below a few milliamperes but sub-milliampere measurements are required for accurate monitoring of pole footing resistance. A correlator-based sub-milliampere current measurement system using giant magneto-resistive (GMR) magnetic field sensors is reported in this paper. A correlator-based phase insensitive algorithm was used with injected currents at 94 Hz. Experiments conducted on a pole in the laboratory indicate measurement of current values exceeding 1 mA with a standard deviation of less than 2%. Measurements were also performed with current values as low as 0.2 mA with a standard deviation of 16%. Details of the system, correlator algorithm, and results are presented in this paper.

Application of ultrasonic clamp-on flow meters for in situ tests of billing meters in district heating systems

Three methods of using ultrasonic flow meters for the purpose of testing small- and medium-sized billing flow meters in district heating subscriber stations in situ were investigated. Four subscriber stations, six billing flow meters, and three ultrasonic clamp-on meters were part of the investigation. The obtained results show that clamp-on meters have measurement accuracy problems on the ordinary steel piping in the subscriber stations. When using well defined pipes mounted in series with the billing flow meters the results are clearly better; provided that the flow rates exceed a Reynolds number of approximately 10 000. In this flow region, billing flow meter deviations >±5% can be detected. A flow rate below this Reynolds number renders the method less reliable. The useful flow range is extended when using calibration data from the clamp-on meter to correct the measured data, making it possible to determine deviations >±10% in flow rates below a Reynolds number of 10 000. The investigation also showed that not all clamp-on meters are suited for this type of in situ test.

THE CLAMP-ON WAVE FORCE METER

Because of the tremendous increase in offshore activities, a great effort has been made on obtaining information on wave forces on structural members. Several oil companies have invested large sums of money in the design and construction of full-scale systems for measuring the wave forces. The equipment used for measuring the forces have been single cantilevers or segmented piles designed to make discrete measurements along the pile. For instance, during the last five years, The California Company and California Research Corporation (subsidiaries of Standard Oil Company of California) operated an installation in the Gulf of Mexico with four segmented piles of different diameters. The wave forces were measured by three-foot high force dynamometers located at seven different elevations along the length of each test pile. Each dynamometer was constructed from a section of the cylindrical pile which was attached to a system of flexures on the inside. So far the wave forces have been measured on cylindrical piles varying in diameter from one to four feet and in water depths varying from 30 to 50 feet. As the pile diameter and water depth increase, however, the measurements of wave forces by use of a cantilever or a segmented pile become very difficult and expensive. Therefore, a need exists for investigating other means for measuring the wave forces on a pile. This paper will describe the design and operation of a force meter that may be clamped to an existing pile. In Spring 1960, California Research Corporation installed equipment incorporating eight of the clamp-on meters on an oil well drilling platform in the Gulf of Mexico. The water depth at the location is 100 feet, and two years of operation are planned.