Resistance Tomography Sensor Research Articles

Electrical resistance tomography-based multi-modality sensor and drift flux model for measurement of oil–gas–water flow

This paper proposes a novel method to measure each constituent of an oil–gas–water mixture in a water continuous flow, typically encountered in many processes. It deploys a dual-plane electrical resistance tomography sensor for measuring dispersed phase volume fraction and velocity; a gradiomanometer flow density meter and a drift flux model to estimate slip velocities; with absolute pressure and temperature measurements. These data are fused to estimate constituent volume flow rates. Other commonly used operational parameters can be further derived: water cut or water liquid ratio (WLR) and gas volume fraction (GVF). Trials are described for flow rates of water 5–10 m3 h−1; oil 2–10 m3 h−1 and gas 1–15 m3 h−1. The comparative results are included with published data from the Schlumberger Gould Research flow facility. The paper proposes the use of the described configuration for measurement of volume flow rates in oil–gas–water flows with an absolute error of ±10% within GVF 9%–85% and WLR > 45%.

Investigation of Multi-Plane Scheme for Compensation of Fringe Effect of Electrical Resistance Tomography Sensor.

Conventional electrical resistance tomography (ERT) sensors suffer from the fringe effect, i.e., severe distortion of the electric field on both ends of the measurement electrodes, leading to a 3D sensing region for a 2D sensor. As a result, the objects outside an ERT sensor plane affect the sensing and hence image, i.e., deteriorating the image quality. To address this issue, a multiple-plane ERT sensor scheme is proposed in this paper. With this scheme, auxiliary sensor planes are used to provide references for the fringe effect of the measurement plane, for compensation by subtracting the weighed influence of the fringe effect. Simulation results show that the proposed scheme, either three-plane or two-plane sensor, can compensate for the fringe effect induced by objects outside the measurement plane with a variety of axial object distributions, i.e., several non-conductive bars or conductive bars placed at different cross-sectional and axial positions inside the sensor. Experiments were carried out. Images obtained with single-plane and multiple-plane ERT sensors are compared, and the proposed compensation scheme has been hence verified.

An adaptive electrical resistance tomography sensor with flow pattern recognition capability

The all traditional electrical resistance tomography (ERT) sensors have a static structure, which cannot satisfy the intelligent requirements for adaptive optimization to ERT sensors that is subject to flow pattern changes during the real-time detection of two-phase flow. In view of this problem, an adaptive ERT sensor with a dynamic structure is proposed. The electrodes of the ERT sensor are arranged in an array structure, the flow pattern recognition technique is introduced into the ERT sensor design and accordingly an ERT flow pattern recognition method based on signal sparsity is proposed. This method uses the sparse representation of the signal to express the sampling voltage of the ERT system as a sparse combination and find its sparse solution to achieve the classification of different flow patterns. With the introduction of flow identification information, the sensor has an intelligent function of adaptively and dynamically adapting the sensor structure according to the real-time flow pattern change. The experimental results show that the sensor can automatically identify four typical flow patterns: core flow, bubble flow, laminar flow and circulation flow with recognition rates of 91%, 93%, 90% and 88% respectively. For different flow patterns, the dynamically optimized sensor can significantly improve the quality of ERT image reconstruction.

A New Design of Electrical Impedance Tomography Sensor System for Pulmonary Disease Diagnosis

AbstractAs an advanced process detection technology, electrical impedance tomography (EIT) has wide application prospects and advantages in medical imaging diagnosis. However, a series of issues need to be addressed before applying EIT for bedside monitoring. Medical diagnosis and bedside monitoring are dynamic measuring process, where the positions of measuring electrodes and the shape of the detected field are changing dynamical. Due to the inability to cope with the changeable electrode positions and various dynamic fields, existing EIT systems are mainly used for industrial detection in condition of static measurement and visualization. In this paper, we investigate the dynamic measurement and visualization of human breast in EIT field, describe the design of the measuring sensor system, and expound the measuring principle. The main component of the hardware system is a built-in servo electrical resistance tomography sensor with capacitive sliding rod, which can adapt to the crowd of different chest contour and the change of chest shape in the dynamic process of breathing. The corresponding measuring principle is extracting all real-time positions of measuring electrodes, then obtaining the dynamic boundary, finally dividing the detection field rapidly. Experimental results confirmed that the proposed system can obtain real-time location of boundary sensor and dynamically solve the problem of arbitrary-shape boundary measurement. The imaging results validate the availability of designed sensor system and the effectiveness of the corresponding measuring principle.

Electrical Resistance Tomography Sensor for Highly Conductive Oil-Water Two-Phase Flow Measurement

Oil-water two-phase flows are encountered in various process industries, such as petroleum and chemical. The measurement of oil volume fraction and its distribution is of particular importance for managing oil production and water disposal and/or water reinjection. The water phase in these environments always has high electrical conductivity, which incurs significant difficulties for oil volume fraction measurement using electrical resistance tomography (ERT). In this paper, a method of solving this problem is introduced. A pilot plant scale flow loop at TUV NEL Ltd. was used to measure oil distribution and oil volume fraction in the range of 0–0.4. The total volumetric flow rate of oil and water was 30, 60, and 90 $\text{m}^{3}$ /h. High-electrical conductivity of water in 27.6 mS/cm was applied as continuous phase. The measurement results from ERT were validated by the readings of NEL’s references and flow patterns were compared with visual observation, which demonstrated that ERT was able to visualize the oil phase distribution and monitor the local and overall oil volume fraction up to 0.4.

Design and implementation of a multi-sensor system for gas–water flow measurement

Gas–water two-phase flow is commonly encountered in industrial processes. It is still a challenging problem to accurately measure the flow parameters due to complex flow mechanics of the two-phase flow. This paper presents the design and implementation of a multi-sensor system for accurate measurement of gas–water flow in a horizontal pipe. Information detected from spatially distributed sensors can be analysed and integrated to extract effective information and obtain complete description of the gas–water flow, which is more reliable than that is estimated with a single sensor. The multi-sensor system included a dual-plane electrical resistance tomography sensor, a six-electrode conductance sensor, a dual-cone flowmeter, a pressure gauge and a temperature sensor. The position and distribution of the multiple sensors was investigated according to their measurement properties and the multi-sensor system was designed based on the combination of PXI modular instrument and FPGA technique. Experiments were conducted to study the performance of the multi-sensor system. Experimental results indicated that the proposed multi-sensor system could be used to investigate characteristics of the gas–water two-phase flow. This study underpins further study for the multi-sensor data fusion of two-phase flow measurement.

Evaluation of fringe effect of electrical resistance tomography sensor

A conventional electrical resistance tomography (ERT) sensor uses pin electrodes for current injection, and the electric field spreads far beyond the electrode plane, as a result of “soft field” nature. This phenomenon is referred to as “fringe effect” and would cause measurement errors and image distortion. The impact of fringe effect on measurement and reconstructed images depends on the object distributions, the conductivity contrast and others. It is not trivial to evaluate the fringe effect of an ERT sensor and its impact on the measurement and the reconstructed images. In this paper the fringe effect of an ERT sensor is evaluated for central core and off-central core distributions at different axial positions and with different axial dimensions and conductivity contrasts. Then, how to compensate for the fringe effect of the ERT sensor is discussed and a method proposed for improving the measurement accuracy and image reconstruction. Finally, the findings and methodology is verified by experiment.

Fringe effect of electrical capacitance and resistance tomography sensors

Because of the ‘soft-field’ nature, all electrical tomography sensors suffer from electric field distortion, i.e. the fringe effect. In electrical resistance tomography (ERT) sensors, small pin electrodes are commonly used. It is well known that the pin electrodes result in severe electric field distortion or the fringe effect, and the sensing region of such an ERT sensor spreads out of the pin electrode plane to a large volume. This is also true for electrical capacitance tomography (ECT) sensors, even though it is less severe because of larger electrodes and grounded end guards used. However, when the length of electrodes in an ECT sensor without guards is reduced to almost the same dimension as those in an ERT sensor, the fringe effect is equally obvious. To investigate the fringe effect of ERT and ECT sensors with and without guards, simulations were carried out with different length of electrodes and the results are compared with the corresponding 2D simulation. It is concluded that ECT and ERT sensors with longer electrodes have less fringe effect. Because grounded end guards are effective in reducing the fringe effect of ECT sensors, we propose to apply grounded guards in ERT sensors and integrate ECT and ERT sensors together. Simulation results reveal that ERT sensors with grounded guards have less fringe effect. While commonly current excitation is used with ERT sensors, we propose voltage excitation instead to apply the grounded guards. The feasibility of this approach has been verified by experiment. Finally, a common structure for reducing the fringe effect is proposed for ECT and ERT sensors for the first time to simplify the sensor structure and reduce the mutual interference in ECT/ERT dual-modality measurements.

Air–water two-phase flow measurement using a Venturi meter and an electrical resistance tomography sensor

A method for air–water two-phase flow measurement is proposed using a Venturi meter combined with an Electrical Resistance Tomography (ERT) sensor. Firstly, the real-time flow pattern of the two-phase flow is identified using the ERT sensor. Secondly, the void fraction of the two-phase flow is calculated from the conductance values through a void fraction measurement model, developed using the LS-SVM regression method. Thirdly, the mass quality is determined from the void fraction through void fraction-quality correlation. And finally, the mass flowrate of the two-phase flow is calculated from the mass quality and the differential pressure across the Venturi meter. Experimental results demonstrate that the proposed method is effective for the measurement of the mass flowrate of air–water flow. The proposed method introduces the flow pattern information in the measurement process, which minimizes the influence of flow pattern on the conventional differential pressure based methods. In addition, the mass quality is calculated from the void fraction, so the difficulty to obtain the mass quality in conventional methods is also overcome. Meanwhile, the new method is capable for providing concurrent measurements of multiple parameters of the two-phase flow including void fraction, mass quality and mass flowrate as well as an indication of the flow pattern.

Measurements of gas–liquid mixing in a stirred vessel using electrical resistance tomography (ERT)

The non-invasive measurement of mixing inside a stirred vessel in 3-D, using an 8×16 array of resistance tomography sensors, provides powerful opportunities for characterising and quantifying the process complexities [R. Mann, F.J. Dickin, M. Wang, T. Dyakowski, R.A. Forrest, P.J. Holden, Chem. Eng. Sci. 52 (1997) 2087–2097; P.J. Holden, M. Wang, R. Mann, F.J. Dickin, R.B. Edwards, A.I.Ch.E. JI. 44 (1998) 780–790]. Using the UMIST pilot plant 1.5m stirred vessel, new results are presented for gas–liquid mixing which can distinguish differences in liquid mixing behavior between water (low viscosity) and relatively viscous 0.05% carbopol solution. The slower liquid phase tracer mixing rates for the viscous case compared with water, as well as differences in the pattern of mixing, can be readily observed and portrayed in 3-D using linear back projection for the reconstruction. In addition, the variation of local gas hold-up (voidage) can also be simultaneously measured by identifying regions within the vessel which have high or low local conductivity/resistivity. Electrical resistance tomography (ERT) can thus provide simultaneous detailed information on two aspects of gas–liquid mixing, involving the isolation of liquid phase mixing when gas–liquid mixing is taking place. The ERT results can be processed to provide the local mixing curve, hence mixing times, for any nominated pixel.