PRACTICAL CONTROL OF DYNAMIC METERING SYSTEM AND DATA ACQUISITION

Transcription

1 International Journal of Industrial Engineering & Technology (IJIET) ISSN Vol. 3, Issue 4, Oct 2013, TJPRC Pvt. Ltd. PRACTICAL CONTROL OF DYNAMIC METERING SYSTEM AND DATA ACQUISITION A. HARROUZ, A. BENATIALLAH 1 & O. HARROUZ 2 1 Department of Electrical Engineering, Adrar University, Energy and Environment Laboratory Information System, Adrar, Algeria 2 Department of Water Institute of Nature Sciences and Agroalimentaire of Bordeaux (ISNAB), Bordeaux, French ABSTRACT Measurement is the basis of scientific and industrial research. It allows us to understand the phenomena we observe in our environment by means of experimental deduction and verification. One of the most difficult problems facing the instrument engineer is the accurate calibration of dynamic metering system of fluid (liquid or gas). The purpose of this paper is to review the essential definitions, roles and characteristics of metering system of fluid. We discuss measurement and metrological control of a signal sensor from dynamic metering systems. After that, we present descriptive way of calibration instruments with more detailed discussions to the reference standards for method of test. This paper describes experimental evaluation of the error on metering system. Also included are procedures using for validation test, after compared this error with the maximum errors tolerated defined by specifications and standards. KEYWORDS: Component, Data Acuisition, Ramp Metering, Flowmeter, Sensors, Errors Tolerated, Control, Measurement INTRODUCTION Flow measurement has a history of about 3000 years. It has been studied only in the last 200 years and in the last 30 years all the new techniques have evolved. There is now a wide variety of methods available to measure the flow of liquids, solids, gases and vapors [5]. From the plant operator's point of view, "automation" is nothing more than a means of running processes economically and to a discerning level of quality [2]. Big round-dial instruments, hand wheels, manually operated valves and peepholes used hi in order of the day, up until the nineteen-fifties [2]. A production plant's intelligence was in the head of an experienced employee who kept tabs on everything. Measurement and control were done by "eyeballing" on an as-needed basis. Correct measurements are crucial to the field of instrumentation. No matter what sensor is being used, many influence parameters or disturbances such as temperature, pressure, mechanical constraints and electromagnetic environment can contribute to measurement error. These kinds of problem are intrinsic to sensors. Furthermore, the acquisition chain must link an electronic device that can condition information and send it to a transducer. This information relates to the variable to be measured and provides the closest possible representation of the observed physical phenomenon [6]. Most analog possessing of a signal sensor contains filtering and amplification functions (Figure 1). These functions help us retrieve relevant information from signal sensors and take it to a compatible and sufficient electric level so that the information can be then used by the system or equipment [6]. This process assures

2 50 A. Harrouz, A. Benatiallah & O. Harrouz Figure 1: Simplified Functional Scheme of a Measurement Chain FLOW METER SYSTEM Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. Positive-displacement flow meters accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow. Other flow measurement methods rely on forces produced by the flowing stream as it overcomes a known constriction, to indirectly calculate flow. Flow may be measured by measuring the velocity of fluid over a known area. Figure 2: Dynamic Metering System Metering System consists of flow meter, flow calculator panel, application softwares. Flow calculator panel has flow computer and controller. Flow computer performs calculation of flowing density, volume correction, mass flow rate, corrected volume flow rate and energy flow rate by referring to gas component, pressure, temperature in case of natural gas. Calculator performs automatic meter run switching or manual valve operation. Also flow calculator communicates with upper control system. The control procedures and methods of calculation used for every measurement instrument will be developed according to the conditions of working and material available on site, based on the instructions of National Texts, recommendations and international standards. CONTROL DATA ACQUISITION OF SENSOR Electrical signals generated by transducers often need to be converted to a form acceptable to the data acquisition hardware, particularly the A/D converter which converts the signal data to the required digital format [3]. In addition, many transducers require some form of excitation or bridge completion for proper and accurate operation. The principal tasks performed by signal conditioning are: (Filtering, amplification, linearization, isolation and excitation). Figure 3: Data Acquisition of Measurements

3 Practical Control of Dynamic Metering System and Data Acquisition 51 Control the process is by which digital control signals from the system hardware are convened to a signal format for use by control devices such as actuators and relays. These devices then control a system or process [3]. Where a system is referred to as a data acquisition system, it is possible that it includes control functions as well. Transducers and sensors provide the actual interface between the real world and the data acquisition system by converting physical phenomena into electrical signals that the signal conditioning and/or data acquisition hardware can accept. Transducers available can perform almost any physical measurement and provide a corresponding electrical output. Control of Temperature Sensor In practice, a temperature is not directly measured; instead a physical magnitude that depends on it (strength, volume, voltage, etc) is measured, so the temperature is estimated based on some model [2]. Manufacturers usually try to reproduce a temperature rather than actually knowing the thermodynamic temperature involved in their manufacturing procedures and chains of measurement [3]. Probes are often used in industrial environments where pollutants it is not possible to maintain a high level of purity platinum wire [2]. For reasons of robustness outer sheath of the probe will be metallic. Heat exchange between the sensing element and the media at a temperature other than the temperature can be considered important and substantially affected the outcome. Figure 4: Control of Temperature We sending values f temperature using box decade on the site metering standards next we look at the display of the calculator these values at the metering cabinet in the room of supervision. For our work, we have implemented hardware and means (reference standards) as thermometer, decade of resistance, multimeter and temperature thermostatic bath. Table 1: Transmitter Temperature Simulated Test Results Temperature «ºC» Voltage «V» Temperature «ºC» Error «ºC» MPE «%»

4 52 A. Harrouz, A. Benatiallah & O. Harrouz Control of Pressure Sensor The absolute pressure transmitters measure the pressure using the pressure sensor to a micro load cell to the silicone in the probe. This micro pressure sensor converts the resistance change, and the change in resistance is converted into a signal of 4 to 20 ma proportional to the pressure. This measurement signal is transmitted to the remote receivers with the same two cables which carry the current to the transmitter electronics. These sons also carry bidirectional data signals between the transmitter and the computer. Common receivers while providing digital communications by smart transmitter using a HART Communicator. Figure 5 shows the connections necessary to power a transmitter and put in communication with the HART Communicator. A HART Communicator may be connected at any point of connection of the loop. Figure 5: Cabling between Sensor and the HART Communicator Table 2: Results of Control Simulated Test Results Pressure «bar» Tension «V» Pressure «bar» Error «bar» MPE «%» Table 2 show that the error between the measured values and the calculated values are within the range of the maximum error defined by recommendation R117 [11]. Flowmeter The flow meter operates by alternatively transmitting and receiving ultrasonic signal pulses between the two transducers. The ultrasonic signals are first transmitted in the direction of the fluid and then against fluid flow [10]. The transducers are clamped to the outside of a closed pipe at a specific distance from each other (Figure 6). Figure 6: Transducer Placement in a Reflection-Type Ultrasonic Meter

5 Practical Control of Dynamic Metering System and Data Acquisition 53 Since sound energy in a moving liquid is carried faster when it travels in the direction of flow than against it, a time difference between the signals time-of-flight will occur. If the fluid is not moving, the time difference is zero and the flowmeter will indicate zero flow [10]. The transit-time of the signals is accurately measured in both flow directions and the difference in time calculated. L = c * dt +v*dt (1) Where L = distance between emitter-sensor dt v c = runtime = flow velocity = speed of sound Control Panel The proposed system is designed with the following features: One flow computer per metering run accommodates the signals from the transmitters: The Temperature Transmitters The Pressure Transmitters The pulse transmitters It manages the flow control valve through an integrated control function. Figure 7: Calculator Flow Computers The flow computer provides automatic calculations or instantaneous liquid flow as per API for pressure correction, and per API 54A for temperature compensation. Determination of Liquid Volume The Gross Standard Volume (GSVm) for meters is the meters indicated volume (IVm) or registration, corrected for the meter s performance factor (MF) and the effect of temperature (CTL) and pressure (CPL) on the liquid density [7]. This can be expressed as the following equation: GSVm = IVm (CTL x CPL x MF) (2) Correction for the Temperature on the Liquid (CTL) When petroleum liquid is subjected to changes in its temperature, its density will increase or decrease as the temperature falls or rises. This change is proportional to the thermal coefficient of expansion of the liquid, which varies

6 54 A. Harrouz, A. Benatiallah & O. Harrouz with base density and the liquid temperature. Correction for the Pressure on the Liquid (CPL) When petroleum liquids are subjected to changes in pressure, its density will increase or decrease as the pressure increases or decreases [8]. This effect necessitates an adjustment to reflect reference conditions, which is called CPL [7]. This CPL factor is a function of the liquid s compressibility (F), base pressure (Pb), equilibrium vapor pressure (Pe) and the weighted average pressure (PWA). The basic correction factor for the effect of pressure on the liquid is calculated from the following equation: CPL = 1/ (1 [PWA (Pe Pb)] x [F]) (3) Meter Factors A meter s performance will change over time, this change can be due to mechanical wear or to a change in the physical properties of the liquid being metered. Therefore a meter is proved or verified to establish its meter factor (MF), which is used to adjust the indicated volume of a meter during a transfer [8] A meter factor is calculated for each run and if within the specified tolerance, the average is the resultant meter factor used for that transfer [8]. Therefore the meter factor (MF) can be expressed as the following base equation: MF = NPV NMV (4) Where: MF NPV NMV = Meter Factor = Net Prover Volume = Net Meter Volume Each proving run shall be of sufficient volume to discriminate volume units to 1 part in In the case of loading rack meters, each proving run should depict the start up, shutdown, and interim flow patterns of a normal loading. If electronic counters and high resolution meter transmitters are used to register metered volume, at least 10,000 pulses must be collected during the proving run [9]. Table 3: Variable Range Criteria for ± Random Uncertainty in Average Meter Factor Number of Proving Runs, n Moving (Variable) Range Limit For low volume locations such as small units where five runs within a range of may not be practical or cost effective, three runs within a range of may be practiced.

7 Practical Control of Dynamic Metering System and Data Acquisition 55 Table 4: Proving Report Runs Day and Start Time: 14/06/2013 3:07:34 p.m. Flow: 187 m3 / h, Base Density (15 C, bars): kg/m3 Pilot Turbine Controlled Turbine Pulses K-factor base (pulse/m 3 ) Meter Factor med Pressure med. (Brag) Temperature med. ( C) CTL med CPL med Net Standard Volume (m 3 ) Meter Factor The Table 4 show the standard proving report and calibrations of turbine metering, we have testing net standard volume with three proving runs to see if they have deviation of turbine and to determine the new Meter factor. CONCLUSIONS This paper outlines the operating principles and application of hydraulics flow metering for custody transfer. Basic principles and underlying equations are discussed, as are considerations for applying flow meter technology to station design, communications systems, installation, factor of correction and calculation. After, we have developed a model of metrological verification and control for dynamic metering system on site. REFERENCES 1. A. Harrouz, A. Benatialah, and O. Harrouz, Experimental study of control and verification of dynamic metering system, IEEE Xplore, pp. 1 5, Juin 2013 [Eighth International Conference and Exhibition on Ecological Vehicles and Renewable Energy, Monaco, France, March 27-30, 2013]. 2. Endress. Hauser, Flow Handbook, 3rd ed., vol. 9. Reinach: Switzerland, 2006, pp J. Park and S. Mackay, Practical data acquisition for instrumentation and control systems, in Technologies, pupished Elsever, vol. I, Jordan Hill. Oxford: Academic, 2003, pp A. Patrick, Lowery, Thordarson, Petur, Laragione, Robert."Mass flow meter systems and methods, United States, Flowmatrix, Inc , N. Asyiddin, Fluid flow measurement, 2013, pp D. Placko, Fundamentals of instrumentation and measurement, 2and edit., Library of Congress Cataloging-in- Publication Data, 2007,ISTE USA, pp P. Kosewicz, Calculation Of Liquid Petroleum Quantities, The University of Texas -- PETEX, Houston, Texas, 2008, pp P. Donnelly, Fundamentals of gaz mesurement, NiSource Energy Distribution, American Meter,2009, pp API MPMS, Proving Systems: Operation of Proving Systems (R2007), American Petroleum Institute, Chapter 4.8, Handbook, published 11/01/1995, pp M. Arora and P. Bhargava, Flow metering tutorial - Part 4: Ultrasonic flow meters, Freescale Semiconductor, Inc. - July 31, R OIML, Dynamic measuring systems for liquids other than water, 2 nd ed., 2007.

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