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1. 19 2 5 NOUS T CON TO a 20 2 5 1 VET OCC UO TOPLESS ar ao 20 2 5 2 NTFoducnion ge CADA C 21 LEE mmm 22 3 1 S O e 22 3 1 1 llu sdcucWegM 23 3 1 2 Amplitving gn EE uuu uuu uu iia 25 3 1 3 Converting voltage to current iii 26 3 2 The Programmable Logic Controller DLC 28 3 2 1 leet gg lee IT 29 3 2 2 Ladder logic programming eiii iaa ai 32 3 3 Human Machine Interface HMI rr 40 3 3 1 Control PALOS PA Vinnie 41 3 3 2 Started DO CC ege 41 3 3 3 Graphic windows of the GSCADA 45 Me TA a oa ANAIS casino ode 51 4 1 EE 51 4 1 1 ME WPAN SOUCEE tana 51 4 1 2 The A eier EE 56 4 1 3 The current to voltage circuit Converter 59 4 2 Testing the ladder logic programming 60 4 3 Jl eE C C DA 63 5 CONCISO ee 66 Oe Recommendations tra T 68 Ta ROTO TNC O RE 69 lt A 72 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme List of Figures Fig 1 1 Vertical water pipes in the E12 Fig 1 2 Block diagram of the project Fig 2 1 Magnetic buoy 3 Fig 2 2 Conduit sensor 3 Fig 2 3 Hydrostatic sensors 3 F Fig 2 5 Capacitive sensor 3 g 2 4 Ultrasonic sensors 3 Fig 2 6 Radioactive sensor 4 Fig 2 7 Variation with depth 1 F
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4. Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 4 Testing amp Analysis Now the design of the project is finished so it is the time to develop and test the level sensing system designed Firstly the sensor output will be tested Then the amplifying circuit will be simulated and implemented After that the ladder program will be verified and download to the PLC Finally with the aid of the RSLinx for the communications the SCADA windows will be run 4 1 Sensor 4 1 1 The transducer Firstly once the sensor had been chosen and purchased the first step was to get its output function In order to do that the laboratory environment was tried to be reproduced in a room at home Below it is possible to see some photos of the assembly W dreemt S Ya Sie MESE a ia P IN T Y AW W e a y I Fig 4 1 Water pipe at home In the image it can be seen the water pipe used to test the sensor it measures 2 10 metres and similarly to the one in the laboratory a transparent tube has been attached to control the level Similarly to the laboratory one it is filled from the top and at the it LL Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme bottom a tap has been installed to empty it In the image it is possible to appreciate that the pipe has been marked with the height and th
5. 20 mA Current Loop Ke e A 4 20 mA di Current Transducer Measuring DAQ Power Supply Device Fig 3 2 Depth sensor setup 15 3 1 1 The transducer One of the main objectives of the project was developing a new depth sensor In order to do that a research on pressure transducers was carried out The decision was to use the piezoresistive silicon pressure sensor SSCSANNOO5PGAAS from Honeywell Fig 3 3 Pressure transducer 16 This code shows e SSC Series e S SIP Single Inline Package e AN Pressure Port Axial single port e N No diagnostics e 005PG Pressure Range 0 psi to 5 psi Gage e A Output type Analog Voltage 23 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme e A Transfer function 10 to 90 of Vsupply e 3 Supply Voltage Range 3 3V The transfer function for this sensor with A calibration is the following 0 8 V Output Volts M Papvlied Pa 0 10 Vsuppty Equation 3 1 TL max Pmi Since pressure depends lineary on height it is possible to transform the equation to the one below 0 8 V Output Volts amsa a Mesa aia T OLOV uppi Equation 3 2 max I nin Transfer Function Limits A Calibration 10 to 90 Output D Vsup ply ww h B d B NH Preasura a Fig 3 4 Sensor transfer function 16 Knowing that the vertical water pipe is 3 2m
6. Where everything is in Sl units therefore e Fis in Newtons N e Area is in squared metres m e Pressure is in Pascals Pa Nim 12 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 3 2 Units As it has already been shown the Sl unit for pressure is the Pascal Pa but it is very small for pressures which usually appear in real problems Therefore the kilopascal 1 KPa 103 Pa and the megapascal 1 MPa 106 Pa are more used 2 Other units which are very used include 1 atm 101 325 KPa 1 01325 bars 760 mmHg at 0 C 1 03323 kg f cm 14 696 psi 14 696 Ib f in 2 3 3 Types It is possible to define a few types of pressure depending on the reference value of zero 2 e Absolute pressure refers to real pressure which is measured referenced against a perfect vacuum In an ideal vacuum the measure would be zero e Differential or relative pressure is the difference in pressure between two points Atmospheric pressure which is necessary to define the next type of pressure is the pressure exerted by the weight of air above Earth s surface It changes under pressure and temperature 2 e Manometric or gauge pressure is a particular case of relative pressure and its reference value is the atmospheric pressure It is very common for example when measuring the pressure in a car tyre Po Paps Patm Equation 2 4 Glyndwr Universit
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8. window will be closed ass L _ Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme T RSView32 Works 100K ex File Edit View Objects Arrange Attributes Animation Window Help el Di ki of Alles ze ajaj ale kel N Iw IO IC o Alem ER EI aaa aa goe r main Display PRA HHHH SSSsSssSS5 View alarms Monitor tags v a GA Clar Clear al Polyline Press ctrl For horizontal or vertical lines NUM Jra a v QE_____ i Fig 3 31 Main window In the image above it is possible to see the main windows in the editing mode This is the most important window and therefore the most interesting to analyse Graphically it tries to represent the environment in the E12 lab in which there is a big vertical water pipe with a smaller transparent pipe attached to it in order to control the level This pipe is filled from the top when the pump is connected to the power supply and is emptied the tap in the bottom is opened the water is both taken from and released to a deposit below the pipe The other part of the assembly is related to the sensor which is connected to the input module of the PLC The final connection is between the PLC and the PC Besides it is possible to see many arrays of s and which indicate string and numeric displays The main displays in this window are the ones in the cent
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10. SOURCE which indicates that the file type is an input from the first slot and the terminal number is O e F8 1 H height which indicates that the file type is a float number the file number is the eight and the bit number is 1 So in that direction the height will be directly calculated Below it is possible to see exact explanation of the addressing format I 1 0 P e Terminal No Input QS Bit delimiter EIER elatio delimiter In this function the input memory direction with its maximum and minimum the scaled maximum and the scaled minimum must be declared as well as the output memory direction Data File H dec INPUT 1736 NId3 Channel Input Module 1746 NI4 Channel Input Module 17436 NI4 Channel Input Module 1746 NI4 Channel Input Module Ea Radix Decimas Symbol gt Desc D Properties Forces Help Fig 3 17 Input data file window Once the height is known and considering that the desired data are height pressure and volume it is pretty easy to calculate the rest of magnitudes in different new rungs As stated before in this project P p g h and there are two ways of calculating that the first one would be using the multiplying function from the math toolbar but as it is 35 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme only useful to multiply A B that procedure has been dismissed The othe
11. which is a predefined function from RSView32 but the information displayed must be selected In this case that information is e lagname e Tag value e Analog Level e Alarm Time e Alarm Type e ag Description In the windows below the tag monitor window is shown in both editing modes This is also a predefined function but the tags which are going to be monitored must be written in the first column after double clicking on the table This table will show the current value the state and a description of the tag FS tag monitor Display Ex 2 error height value from PLC error pressure value from PLC error volume value from PLC 0 valid setpoint fixed by the user Return to Main page Fig 3 34 Tag monitor window gg Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez QUIS lt Supervisor Reg Holme The last window is datasheets and it should allow the visualization of the datasheets from the two sensors and the installation instructions and user manual of the 1746 NI4 the input module of the PLC E datasheets Display Return to Main page Fig 3 35 Datasheets window The problem with this is that this ActiveX function also requires Visual Basic and it is not available in the laboratory computer This also explains the reason why it has not been possible to implement a list box instead of using plain text acting as hyperlinks i sl
12. 1 2 x Where knowing that n219 TL 1 gt Vi Equation 4 2 i 1 y 0 94 n 1 X gt Xj Equation 4 3 i l 53 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme gt l E o Ne n 1 Syy X Zoe Xy Equation 4 4 i 1 Syy 0 175387812 2 _ i 1 Xi m Sy X Equation 4 5 s 0 32094183 Substituting in equation 4 1 and simplifying o 04 0175387812 ncm y 094 932094183 7109 y 0 94 0 54647851x 0 5956615759 y 0 54647851x 0 344338421 Where y is the voltage in volts V and x the height in metres m It is also possible to compute the correlation coefficient r which shows the quality of the approach If r is around 1 the approximation will be very good and if the coefficient is near to O the deviation will be quite important Sxy r Equation 4 6 Sy Sy Being Sy 0 56651728 n E sy m y Equation 4 5 SS 0 09589666 Sy 0 30967186 Substituting Ul Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme H 0 175387812 m 0 56651728 0 30967186 r 0 999734108 This means that the quality of the approximation is very good Next the data will be plot using MS Excel which also allows knowing the regression so it is possible to check the hand computed one Sensor output Output Voltage V 080 1 00 1
13. 10 TYP 0 370 0 250 0 270 MAX 0 260 s GLASS 0 238 A 0 012 0 008 DETAIL A DETAIL A Tm 0 250 PIN 1 IDENT W10A REV E 0 045 MAX TYP 10 Lead Ceramic Flatpak W Order Number LM741W 883 LM741WG MPR or LM741WG 883 NS Package Number W10A National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications For the most current product information visit us at www national com LIFE SUPPORT POLICY NATIONAL S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION As used herein 1 Life support devices or systems are devices or systems which a are intended for surgical implant into the body or b support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in a significant injury to the user BANNED SUBSTANCE COMPLIANCE 2 A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness National Semiconductor certifies that the produc
14. 17 PM 1 43 12 PM 1 43 11 PM height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC height value from PLC Return to Main page gt 4 Ack Current Ack Page Ack All Silence Cur Silence Pge Silence All Fig 4 19 Alarm summary window running o 6 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The last important window is the trend which can be seen below lt plots the evolution of the selected tags The y axis shows the magnitude of the current selection which can be changed by clicking on the tags below the graph it can also be zoomed and scrolled using the buttons on the right The x axis shows the time which can be moved using the buttons at the bottom of the screen r trend Display 1 43 35 PM 1 43 55 PM 1 44 15 PM 1 44 35 PM 4 20 2011 4 20 2011 4 20 2011 4 20 2011 v Reset Y Axis Oldest Scroll Scroll Newest Data Backward orward Data Return to Main page Time Range seconds Reset 5 Emm 300 Fig 4 20 Trend window running d 6 IL Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Sup
15. 20 1 0 1 0 Water level m Fig 4 4 Sensor output function It is also possible to use excel to obtain other regressions e Exponential regression y 0 4305 e This has a correlation coefficient r 0 9772921774 Polynomical of 2 order y 0 0053x 0 5576x 0 3373 e Polynomical of 3 order y 0 0119x 0 0414x 0 5867x 0 3325 e Polynomical of 4 order y 0 0007x 0 0145x 0 0447x 0 588x 0 3324 e Polynomical of 5 order y 0 0762x 0 3846x 0 6712x 0 4571x 0 461x 0 3348 e Polynomical of 6 order y 0 1718x 0 9828X 2 0869x 2 0252x 0 896x 0 7069x 0 3337 It can be seen easily that linear regression is better than exponential since the graph is much more similar to a straight line than an exponential function On the other 55 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme hand the higher the polynomial is and the better the approximation will be but it has been demonstrated that first order polynomial which is the linear regression is good enough 4 1 2 The amplifying circuit The first test after designing the amplifying circuit was to simulate it on the computer For that purpose the PROTEUS software by Labcenter Electronics has been used Since the sensor was not in the library a voltage source has been placed doing its function It is noticeable that a 24 kQ has been us
16. E mM YN WO jw P Password Account 1INMK T gt IO I IIIIHN k L m n o AAA Y Y Y Y Y Y Y Y Y Y Y Y Y Y Y YYYYNNNNNNNNNNN Fig 3 26 User accounts configuration Now graphic images which can represent plant devices can be created using the drawing tools Clicking on the display folder a new work screen will appear similar to that shown below Edit Mode Fig 3 27 New graphic window The screen is resized to nearly the maximum it is useful to leave a small margin to the right of the screen enabling to see the edge of the file tree so it can then be quickly brought back to the foreground when required Now the project is ready to start being programmed graphic images can either be drawn or obtained from the inbuilt libraries Images can simply represent the appearance of the plant i e just a picture that has no other function or they can represent a plant device that has a control or data acquisition purpose a programme is built up with a mixture of the two The control philosophy will determine the way in which the images function 23 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The difference between an image which represent an appearance and the images or text with a function is that these ones need to be linked to an address the term used for this is tag This tag may be a real I O add
17. Fern ndez Supervisor Reg Holme 1 4 Block diagram The element to be controlled is the level in the vertical pipe which is filled with the aid of the water pump Level is controlled with a depth sensor and the signal it generates is sent to the PLC which is the brain of the system and will compute the input to obtain height pressure and volume The computed data will be sent to a PC and displayed using a SCADA software LEVEL SENSOR VV PC SCADA CONTROL VALVE WATER PIPE CONTROL VALVE Fig 1 2 Block diagram of the project Sean Z uol ejuasaid euy ay auedaug MA yom Bulo8 uo y00g30 aui aedalg Sy9aM p podas palold ay jo UOISI3A jeun ay aJedag syaam g WO 3jeJp podas paloid ay auedaig Josuas anssasd au suIdO aAaq Yavas ay suiuuleJdoJg 21d au SuruuieJ804g uoneiuasald 1541 ay a1edaug yooqso ay eedaJg yoda wayu ay aJedaJg The project has two main phases The first stage will last until Christmas and will include the introduction and research After Christmas the programming of the PLC and SCADA as soon as the design and development of the depth sensor will take place The project report o lt o O cC Q ajenos Fld Apnys E Josuas aunssaud yidap au 1noqe ayesysaay un1easaM Le 9 19Jdey aM E C ydB3sal EJauac B on x o 0 y uononpomu i E gt E 1 131deu2 aM E tc E O ido o S d E p palud e jo au jeu e
18. Instrumentation and Control Online Available http www instrumentacionycontrol net es curso completo instrumentacion industrial 217 medidores de nivel un interesante resumen y muy completo html 5 TDK 2007 February Powder level sensors Online Available http www tdk co jp tefe02 eb461 ts pdf 6 G Bass 2000 October The principles of level measurement Online Available http www sensorsmag com sensors leak level the principles level measurement 941 7 S M Labat S M Rodrigo Level measurements Lecture Notes Spain Zaragoza University Available http www scribd com doc 7192985 Apunte de Medicion de Nivel 8 A Franco Fluid Statics Lecture Notes Spain Basque Country University Available http www sc ehu es sbweb fisica fluidos estatica introduccion Introduccion htm Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 9 A Creus Industrial Instrumentation 5th ed Brazil Marcombo 1993 pp 63 79 10 Manometers and barometers Online Accessed November 2010 Available http www kentchemistry com links GasLaws manBar htm 11 Science experiments 2006 November Bourdon tube Online Available http science experiments info 2006 1 1 bourdon tube 12 Diaphragm pressure gauges Introduction Online Accessed November 2010 Available http www efunda com designstandards sensors diaphragm
19. a synthesis of the actions carried out for the construction of the liquid level measuring system lt is structured in five chapters that explain the steps for the realisation of the project Knowing the content level of liquid in tanks is very important in industry although accuracy demands vary according to business requirements Therefore it becomes extremely important to monitor and control the level of tanks vessels reservoirs etc In this project a liquid tank is analysed with a pressure sensor and is monitored with the aid of a PLC and a SCADA software Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Acknowledgements owe a great many thanks to the people who helped and supported me during the realisation of this project would like to dedicate this dissertation to them Firstly want to dedicate it to my parents who have always supported me both personal and academically and who have always encouraged me to continue studying Besides want to dedicate it to my sister to encourage her to go to the university too Secondly want to dedicate it to Reg Holme my project supervisor for sharing his valuable time and giving me helpful information to finish the project Finally would also like to thank the Erasmus programme and Glyndwr University for giving me the opportunity to study and live in a foreign country which has become one of the best
20. be solved before continuing programming When a new project is created the chassis and the processor must be selected and then the IO configuration meaning that all the inputs and outputs modules must installed must be declared in the RSLogix The result is e Rack 1 1746 A10 10 slot rack e Slot 0 1747 L532C D CPU 5 03 Memory 16K OS302 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme e Slot 1 1746 NI4 4 analog channel input module e Slot 2 1746 OB8 8 digital channel output module it will not be used in this project but as it is installed in the rack it has to be declared Configuraci n E 5 UI Hacks 1 1746 410 Ackde 10 ranur sl Tarjetas actuales disponibles Filtrar Todos las 10 e 2 Rack E S no instalado zl Pate N gt Descripci n Jl Leer config E 5 i i 3 Rack E75 no matalado Cualg m dulo de entrada discr de Spt 1746 1476 Cualg m dulo de entr discr de 16pt UR IER Cualg m dulo de entr discr de 32pt 1746 0 8 Cualg m dulo de sal dizcr de 8 pts 146 076 Cualg mod de sal discr de 15 pts 1746 0 32 Cualg mod de sal discr de 32 pts AMCUI 153 M dulo de resoluci n AME Serie 1500 AMICI 1561 Mod de resaluc SMC Sere 1551 1746 545 5701 M dulo BASIC 500 5 01 1746 645 5702 Mod BASIC c capac MOM 1r45 BAS5 T M dulo BASICO 500 5 01 1746 B4 5 T M dulo BASICO Capacidad MOM
21. by the university and once the project worked another of the objectives was to design and build a new depth sensor The sensor is connected to a PLC which can be seen as a little industrial computer highly specialized in getting some inputs reading its control program and with some mathematic calculus controlling some outputs With the use of a SCADA Supervisory Control and Data Acquisition the data is sent to a PC which allows an operator to manage and control it Fig 1 1 Vertical water pipes in the E12 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 1 2 Aim The intention of this project was to monitor the level in a water pipe with the use of a submersible depth sensor Once it worked a new depth sensor was built The sensor data is sent to a PC using a SCADA system which connects the PLC to the computer 1 3 Objectives In order to achieve the aim a set of objectives have been planned as follows Research about fluids Study pressure Research on level sensors and pressure measuring Research on principles of control engineering and apply them to the project Design a program for a PLC Programmable Logic Controller Design a SCADA system Monitoring and analysis of the pressure data given by the provided sensor Design and develop a pressure sensor Glyndwr University Project Title Level sensing system Name Javier Garc a
22. class then there is a high possibility the system will clog up too much data to be collected within too short a period Therefore consideration should be given as to which devices really need a fast scan and for which devices would a slower scan be acceptable User inputs in the form of a mouse click require a fast scan so as not to be missed hence the default setting for class A to a fast setting will be changed as shown below i x Select Scan Class Name A Foreground Period seconds Background Period 01 UU seconds Name Foreground Background Cancel Help Fig 3 25 Scan class selection The remainder of the system set up can be left for now as a basic SCADA program will function with the parameters at default But in this project also the user accounts option has been configured Apart from the DEFAULT user which has all the security di 4 LL Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme codes allowed two more user profiles ADMIN and USER have been created ADMIN has the same conditions that the DEFAULT user and its password is admin this will be required as soon as the project is run The USER only has access to tags and options labelled with codes A D E User Accounts A F Security Code Account ID DEFAULT Ay lv A v B v s m D Login Macro Si ai d ad ai II Logout Macro KS wl feu mk iw L
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24. in metres m e pand dp pressure and differential of pressure are in Pascals Pa e p density is in kg m e S surface is in m Given that the density of the fluid p is constant and provided the gravity g is equal to 9 81 mie the balance of forces in the y axis is as follows pS dy g pS p dp S Equation 2 5 dp p g dy Equation 2 6 Now integrating this equation with the random limits B A Ap p g Ay Equation 2 7 Finally changing the height Ay by depth Az fundamental law of hydrostatics is obtained Ap p g Az Equation 2 8 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Where e Ap is in Pascal Pa e p density is in kg m e g gravity is in m s e Z depth is in m Pa m Equation 2 9 m 2 3 5 The hydrostatic paradox It has already been demonstrated that pressure only depends on depth and it is Independent of the vessel shape However there may be temptation to think that the pressure is bigger in a vessel in which there is a bigger volume of water 8 Fig 2 9 Hydrostatic paradox 8 The hydrostatic paradox states that the force due to the pressure exerted by a fluid in the base of a vessel can be bigger or smaller than the weight of the liquid that contains the vessel 8 This means that in each of the vessels given a fix level there is a fix pressure value no matter how the vesse
25. indicator e Glass window e Float levels Indirect methods e Conduit levels e Pressure e Ultrasonic impulses e Capacitor levels e Radioactive levels e Vibrant sheets levels e Piezoelectric levels Before taking the decision of which is right for the intended application some different type of level measuring devices will be studied Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 2 1 Magnetic lateral and bulb buoys The main characteristics are that It is easy to install operation and calibration are not affected by foam gases vapours or variations in the fluid characteristics like dielectric constants or conductivity lt is ideal when a trusted and cheap solution is wanted 3 Fig 2 1 Magnetic buoy 3 The measurement is started either by a pushbutton or a timer The float is connected to a cable at rest over the liquid The magnitude which is actually sensed is the variation of the cable tension The level indication is provided by an electrical circuit associated to the engine which pulls up and down the cable 4 2 2 2 Conduit sensor They are mainly used in applications involving control detection of conduit liquid levels in tanks deposits or profound shafts Easy to install and without mobile parts so there is no need of constant maintenance There are two versions rigid or flexible 3 S M oe GE e To Fig 2 2 Condui
26. industries simply connecting more sensors to the PLC inputs and adding objects in the SCADA to monitor the level this allows an operator to supervise with no risk a great number of tanks SCADASs are very powerful tools for real time monitoring and control of an industrial plant But the final operator must always be taken into account when designing it since the easiest to use it is the least errors there will be The alarm configuration allows being proactive with possible risks of both very full or too empty tanks in real time and take actions to correct the incidence avoiding undesirable consequences like non programmed stops Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme From an economic point of view this application allows supervision from a control room of as many levels as desired This is an important advantage if the levels to monitor are in an industry big enough to employ more than one operator to supervise everything With this application human resources could be sent to other tasks which improve quality for both the professional task of the operator and the company From a safety point of view this application allows supervision of the level regardless it is inflammable corrosive etc from a distance safe enough for the operator As a remarkable experience in the development of this application it is noticeable the behaviour between both theoretic
27. the visual interface to do that the PLC must be online Next from the bar above the status must be changed from stop to running by clicking on the following button Fig 4 15 SCADA stop run button Now some of the screens will be shown while running 20 4 2011 Espa ol Fran ais 1 37 28 Height 1 587 m 5 206 t Pressure Fix setpoint 2 258 psi i ao Continue filling Volume the pipe 0 02804 m3 28 041 49 Plot trend View datasheets FE Main EG 20 4 2011 I Espa ol Fran ais 1 38 12 Height 3 169 m 10 396 ft Pressure Fix setpoint 31 084 KPa 4 508 psi L Run the tap until I ES ar E PLE SSK volume desired level 0 05599 m3 ES cue eit Plot trend View Monitor tags datasheets CAUTION The level is over 3 1m and the limit is 3 2m Fig 4 17 Main window running 2 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme It is possible to see that all the main window displays worked well and the programmed messages too In the first image since the setpoint is 2 m and the level is 1 587 m it encourages the operator to fill the pipe until the desired level In the second screen the level is 3 169 m so an alert message has appeared at the bottom of the screen since the limit is very close Besides as the desired level is still 2 m the recommendation to the ope
28. tree channel and node configuration windows 3 25 Scan class selection 3 26 User accounts configuration 3 27 New graphic window 3 28 Tag database window 3 29 Graphic windows 3 30 Welcome window 3 31 Main window 3 32 Trend window 3 33 Alarm summary window 3 34 Tag monitor window 3 35 Datasheets window 4 1 Water pipe at home 4 2 Sensor breadboard assembly 4 3 Measuring the sensor output 4 4 Sensor output function 4 5 Amplifying circuit running in PROTEUS 1 4 6 Amplifying circuit in PROTEUS II 4 7 Amplifying circuit on breadboard 4 8 Final sensor assembly 4 9 Fitting the sensor hose into the pipe 4 10 Converting OV to 4mA 4 11 Converting 10V to 20mA 4 12 RSLogix verify buttons 4 13 RSLogix online bar 4 14 Ladder logic running 4 15 SCADA stop run button 4 16 Main window running 1 4 17 Main window running 2 4 18 Tag monitor window running 4 19 Alarm summary window running 4 20 Trend window running Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 1 Introduction 1 1 Background This project consists in monitoring depth in a vertical water pipe Fig 1 1 in the Avionics with Instrumentation amp Control laboratory E12 For that purpose it has been used a submersible sensor within the pipe which in the real world it would be suitable for use in rivers reservoirs tanks boreholes vessels or channels The sensor was provided
29. visual there are two arrows moving along the grey pipe showing where the level is this is an automatic option that RSView offers which only needs a tag in this case the tag used has been obviously heightdisp The other effect is in the transparent pipe next to it in which the water will also be as high as the level To make this easier the grey pipe is 320 pixels high and the transparent is 290 pixels starting at 30 pixels from the base trying to copy as much as possible the real pipes in the laboratory This effect has been made by drawing two rectangles the white rectangle in the back copies the transparent pipe and there is an animated blue rectangle in front of it which simulates the water This blue rectangle has the height animated with the following code Heightdisp 100 30 Although the code is quite simple the key to make it work correctly has been to initially give the blue rectangle the maximum height The reason for this code is that since the height ranges 0 3 2 and the pipe is 320 height it needs a 100 multiplying factor Besides the transparent pipe starts 30 cm from the base of the grey one so it is only 290 pixels height and the difference needs to be subtracted In order to interact with the SCADA there are also string and numeric inputs In this main window there is a numeric input on the left hand side below the Fix setpoint label actually this tag has been defined setpoint and must be a number betwe
30. with the divide function from the math toolbar and the result is stored in F8 0 e F8 0 MULTIPLIER which indicates that the file type is a float number the file number is the eight and the bit number is 0 So in that direction the scaling factor is stored The rest of the program is pretty similar to the one for the current sensor It is studied below PT Calcular Dest Fa 1 0 5707833 Expresi n t H70 M7 2 Feo Dest FR 35637385 Expresi n 9 81 1000 0 F amp 1 Fa 3 0 006552089 Expresi n 63 1415 0 075 0 075 7 F2 1 Fig 3 23 Ladder program for the voltage sensor 320 gt Y Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Firstly in rung 0003 the compute function is used again to calculate the height this calculation is made by subtracting the minimum value to the input true value which enters the PLC and then by multiplying the result times the scaling factor The result of this computation is the height which is stored in F8 1 like in the current ladder program Next the procedures in rungs 0004 and 0005 are the same that the ones for the current sensor ladder program so the memory directions used in this more complex program are going to be listed now e 1 0 MY INPUT input ranging 3277 to 16384 e N7 0 INPUT input ranging 3277 to 16384 stored in an integer file e N7 1 MAX maximum value that the inpu
31. 1r47 B5M M dulo Esc ner de reserva 1745 BTM M dulo de temperatura del barril 114 D0CHMm 1 4 Mod Adapt Modos 1 4 Rack 1r47 DCM 1 2 Mod Adapt Modos 1 2 Ack 1r47 DCM 3 4 Mod Adapt Modos 3 4 Rack 174 0CM FOLLM d Adapt Modos Rick cornpl 114 D5N 4 Esc ner E 5 distrib 7 blog E S 1r47 DS5N 30 Esc ner E S distrib 30 blog E S 1746 F1041 entr anal g r p 2 can sal carr 2 car sl M dulo de entrada 4 can anal gico Ayuda Ocultar todas las tarj Fig 3 15 I O Configuration In order to enter the logic program the instruction toolbar must be used Initially the program file will only have the end rung so a new rung must be added using the icon from the user toolbar In this project two programs files have been programmed One program per each sensor so firstly the program for the current output sensor will be shown In this first case the SCP Scaling with Parameters function has been used In this function the input memory direction with its maximum and minimum the scaled maximum and the scaled minimum must be declared as well as the output memory direction 16384 D lt Scaled him DU D lt Scaled Dz 32 ER F3 1 0 8000614 Fig 3 16 SCP function 34 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme In the print screen above it is possible how addressing to the memory directions is done e 1 0
32. 3 3 2 Starting a project To start a New project some parameters must be set up using the file tree Firstly the cannel configuration must be selected Next if RSLinx is running configured and online with the PLC in use the node configuration should be as easy as selecting the appropriate PLC This will read the node address of the PLC and check the first stage of the SCADA communications a failure here would indicate a fault with the set up Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme HMI Project EN Channel E Channel Network Type DH 485 D Messages 3 f System 2 up Channel 7 m Primary Communication Driver de Node AB_DF1 1 DI D Scan Class Secondary Communication Driver E Tag Monitor User Accounts DI Security Codes E elt Activity Log Setup 5 Activity Log Viewer Data Source Direct Driver C OPC Server C DDE Server w Startup i BJ Command Line Name one Iw Enabled Graphics E Alarms Channel 1 DH 485 E Data Log e Station U E Logic and Control El Type SLC 5 Enhanced D Timeout 3 000 seconds Fig 3 24 RSView32 file tree channel and node configuration windows From the file tree select scan class the setting within this screen will determine the sample rate for given classes lt should be noted that if there are many devices within a system and they are all on a fast scan
33. 3 St Steel body with 316 St Steel Sensing Diaphragm nterim ranges are available if required All dimensions in mm e 230 nominal gt 30 v J N Cable uPVC Self Flushing Removable Stainless IP68 Cable Exit Nose Cone Steel Housing Ordering Information The product part number is coded Pi9911 Product series type 4 20mA output to assist with ordering as follows 5mWG Range to be set for normal use CIO Cable length in metres i e 10 metres Optional 4 BSPP female thread for tapping to pipe A nose cone is supplied as standard AN APPLIED MEASUREMENTS LIMITED pu CY Continuous product development may result in minor changes to published specifications unuululul Saj9A9 UO 4 UOHIPUO GE re POYPN 4e0c Q LS TIIA wopue D 7 02 MV SAND YZ0Z 0LS 1N DUISUSpuos u0u HH 86 01 0 911S119I98 18y9 Buisues ujoo amA uoy MMM Z 69 1 y9ous UOol elqIA piwny 13 3U1B 18dg suoneoyioeds E 3ueuluoJiIAUu a1qe L s TOTO uonnios r ndino SSI 2 gt 1 gt Dome 1849 SSA Go OF O S ee Aoeinooy wax s Tun urddo jndino Jamo Max S146 d muy Buddo yndhno Jedd su j J J j eum Suodsoti su j S i Apes Brep or dn Jemod eum dnueis H5 Teese mo eBuer emiereduis Bugeiedo Glo els Wo gt abue eme edusi peresueduioo E Aiddns A 0 S Vu Le 9I NEN K ddns A g g juauno Ajddng pojoojas jopou uo paseq A 0 S JO
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35. 41 Physical Dimensions inches millimeters unless otherwise noted Continued 959 159 TYP www national com fie 0 009 0 015 0 229 0 381 0 280 7 112 0 290 0 320 0 310 0 410 0 180 e MIN 0 300 0 320 7 62 8 128 0 045 0 015 1 143 0 381 BOTH ENDS I 0 018 0 003 TYP TYP _ a um 0 400 MAX NN RO 010 TYP ES I 0 220 0 310 MAX 0 291 GLASS R0 025 TYP 0 045 0 065 P GLASS SEALANT 0 200 0 020 MAX 0 060 0 150 0 125 MIN 0 200 909 1 4 TYP 0 055 MAX 0 100 0 010 TYP JOBA REV K Ceramic Dual In Line Package J 95 sal 0 125_ Pris 8 175 DIA NOM 0 325 0 325 Tune AN 11 0 255 1010 s SA a 0 040 1 016 0 050 1 270 270 NOBE REV F Order Number LM741J 883 NS Package Number J08A 0 373 0 400 9 474 10 16 0 090 0 032 0 005 0 813 0 127 0 250 0 005 RAD 6 35 0 127 PIN NO 1 A me a OPTION 2 0 039 0 145 0 200 205 1 3 Le 0 991 3 683 5 080 0 125 0 140 3 175 3 556 0 020 90 49 0 508 TYP MIN 0 018 0 003 0 457 0 076 JL 0 100 0 010 T c 2 540 0 254 0 060 1 1 524 Dual In Line Package N Order Number LM741CN NS Package Number NO8E Physical Dimensions inches millimeters unless otherwise noted Continued 0 080 0 270 MAX 0 055 0 050 0 005 m 0 005 MIN TYP 0 035 TYP 0 026
36. Circuit Duration Continuous Continuous Continuous Operating Temperature Range 55 C to 125 C 55 C to 125 C 0 C to 70 C Storage Temperature Range 65 C to 150 C 65 C to 150 C 65 C to 150 C Junction Temperature 150 C 150 C 100 C Soldering Information N Package 10 seconds 260 C 260 C 260 C J or H Package 10 seconds 300 C 300 C 300 C M Package Vapor Phase 60 seconds 215 C 215 C 215 C Infrared 15 seconds 215 C 2150 2150 See AN 450 Surface Mounting Methods and Their Effect on Product Reliability for other methods of soldering surface mount devices ESD Tolerance Note 8 400V 400V 400V Electrical Characteristics note 5 Parameter Conditions LM741A LM741 Units Typ Max Min Typ Typ Input Offset Voltage 2 0 mV mV TAMAX Tamin S TA 3 Min Max Min Typ Max 1 0 5 0 3 0 Rs lt 500 4 0 V Rs lt 10 kQ 75 mV Te Average Input Offset Voltage Drift Input Offset Voltage Adjustment Range Input Offset Current a El ser 20 E nA Average Input Offset Current Drift Input Bias Current msc 9 0 s 60 s00 m Meme pop bmp p psp Lope iA EH 5 MO mesc o L e v a O Input Resistance S TA lt Tamax Input Voltage Range www national com 2 Electrical Characteristics note 5 Continued Conditions LM741A LM741 LM741C Units Parameter Large Signal Voltage Gain Output Voltage Swing Output Short Circuit Curren
37. Fern ndez Supervisor Reg Holme e F8 3 VOLUME which indicates that the file type is a float number the file number is the eight and the bit number is 3 So in that direction the volume will be stored in cubic metres m which is the SI unit END Fig 3 20 End rung Finally each program has to finish with an end rung like the one above So the full program with comments on the function on each rung would look like this Input haer 16354 0 15384 D lt Scaled In DU D ns Scaled hix 33 ER F3 1 0 20006 l 0001 pa lt Expression i 10000 9 38 y F3 1 0002 FS e Expression ex 14159 0 0751 0 075 14 F3 2 0003 END Fig 3 21 Full program for the current output sensor 37 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Summarising in a list the memory directions used for this program 1 1 0 SOURCE input ranging 3277 to 16384 F8 1 H height in metres m F8 2 PRESSURE in Pascals Pa F8 3 VOLUME in cubic metres m Next step is to make a similar ladder program for the voltage output sensor which has been developed in this project In this case the scaling has been done step by step instead of using a function which automatically performs it 0001 0002 Fig 3 22 Ladder scaling step by step In the first rung 0000 the input from the sensor ranging 3277 to 32767 is moved fro
38. Fig 2 9 Hydrostatic paradox 8 g 2 8 Fundamental law of hydrostatics demonstration 8 Fig 2 10 Basic manometer 10 Fig 2 11 Bourdon tube 11 F Fig 2 13 Nozzle plug system 9 F F F Fig 3 3 Pressure transducer 16 F Fig 3 5 Non inverting amplifying circuit F Fig 3 7 Voltage to current converter 18 Fig 3 8 PLC SLC 500 Fig 3 9 Communications module 1747 L532 F F Fig 3 12 Current input module wiring 20 g 2 12 Diaphragm sensor 12 g 2 14 Electronic pressure sensors 9 g 3 1 Depth sensor 15 g 3 2 Depth sensor setup 15 g 3 4 Sensor transfer function 16 g 3 6 Voltage to current converter 17 g 3 10 Input module configuration 20 g 3 11 Voltage input module wiring 20 Fig 3 13 Converting analog input data 20 Fig 3 14 RSLogix 500 main screen 21 Fig 3 15 I O Configuration Fig 3 16 SCP function Fig 3 17 Input data file window Fig 3 18 Pressure CPT function Fig 3 19 Volume CPT function Fig 3 20 End rung Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig Fig 3 21 Full program for the current output sensor 3 22 Ladder scaling step by step 3 23 Ladder program for the voltage sensor 3 24 RSView32 file
39. Glyndwr University 3 Blyndwr BEng Hons Aeronautical and Electronic Engineering Avionics Final Project Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Year 2010 2011 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Author s Declaration Statement 1 This work has not previously been presented in any form to Glyndwr University or at any other institutional body whether for assessment or for any other purposes Save for any express acknowledgements references and or bibliographies cited in the work confirm that the intellectual content of the work is the result of my own efforts and no other person Statement 2 It is acknowledged that the author of this work shall own the copyright However by submitting this copyright work for assessment the author grants to the Institute a perpetual royalty free license to do all or any of those things referred to in section 16 l of the copyright designs and patents act 1988 viz to copy work to issue copies to the public to perform or show or play the work in public to broadcast the work or make an adaptation of the work Signed Date Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Abstract This report is to present the design and development of a liquid level sensing system based on SCADA system lt is
40. I AE 2809 OM SM TM EM ZM TM TT xse O o nm Be ES B 2 3 amp oe c H o x a S O GG gt 5 O SESS e a0 O G x gt O c o9 9 5 gt 5 GO O z o o Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 Research 2 1 Fluids Fluids include liquids and gases Liquids flow under gravity until they fill the lower zones of the vessel they are in In a liquid molecules are joined and they make a force between them which could be compared to the force that join atoms in order to form molecules so there is an interaction between the molecules like in solids Molecules in a liquid create short range links transitorily which are broken due to the kinetic energy in the molecules and then they are formed again These links are responsible of the liquid union or else liquid would evaporate immediately as vapour does The magnitude of this force depends on the molecule 1 2 1 1 Density An important property of any substance is the quotient between its mass and its volume which is called density Therefore it is possible to write density as mass m Density p Volume V Equation 2 1 Where e p density is in kg m e m mass is in kilograms kg V volume is in cubic metres m Since the gram is defined as the mass of 1 cm of water water density is 1 g cm in the cgs system If we make the conversion to the International System of U
41. PU which is also the communications module In this case the power supply module is the 1746 P1 which allows 110 240V input and 2 A of output Besides the controller module is the 1747 L532 with the CPU SLC 5 03 which has the following features 19 28 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Instruction Controller Series Iy Words 8 K 16 K or SLC 5 03 32 K Max UO UO Points Options Local I O SE remote I O Built in Ports DH 485 RS 232 C ASCII or DF1 Additional Features Connects to external intelligent devices using the RS 232 port without additional modules Also in this case the communications will be through the RS232 port which has a DE 9 pin connector It is possible to see a photo of the module below Fig 3 9 Communications module 1747 L532 3 2 1 Theinput module The input module is the 1746 NI4 which is an analog module containing 4 analog input channels that are user selectable per channel for voltage or current to support a variety of monitoring and controlling applications 20 Each analog input channel can be configured for either voltage or current The NIA has 4 individual DIP switches that control the input mode of input channels 0 through 3 A switch in the ON position configures the channel for current input A switch in the OFF position configures the channel for voltage input These switches can be
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44. The decision is basically made due to the initial cost and the suitability of a certain technique for a given application However the decision should considerate that a low initial cost may be accompanied by high maintenance costs or loss of accuracy over time Suppliers often provide recommendations based on process material material characteristics process information vessel function or power requirements 6 Level measurement technologies Seven RF I I nductivity Hydrostatic Radar Ultrasonic considerations capacitance Point measurement Non conductive Continuous measurement liquids 1 1 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Average product cost m Continuous Point RF Conductivity Hydrostatic Radar Ultrasonic Capacitance The final decision has been to use a hydrostatic head Firstly because the sensor provided by the university was of this type and the intention was to develop a similar sensor Secondly because it is the cheapest and it has the easiest working principle So this method which uses pressure Is going to be further studied now 2 3 Pressure 2 3 1 General definition The pressure is defined as the normal force of a fluid per unit area Pressure is only for fluids while its equivalent for solids is normal stress So mathematically it is written 1 Force F Pressure P Area A Equation 2 3
45. akes some help Information on what everything on the screen does when the operator clicks on it and it makes that help messages disappear when he clicks again The other four buttons Plot trend View datasheets View alarms and Monitor tags will be explained one by one because their function are to display new windows which will be explained next FR trend Display HA MM SS HH MM SS HH MM SS HH MM SS Dh Y RAS ERAS RAS Oldest Scroll sssssss Scroll Newest Data Backward Forward Data Return to Main page Time Rande seconds Heset B E Fig 3 32 Trend window In this window a predefined trend window has been imported from the library sit i has only been necessary to include the tags to monitor height pressure and volume Buttons allow moving and resizing both magnitude and time axis as well as pausing resuming the monitoring The other three buttons apart from the return to the main page button have already been explained ag Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme ES alarm summary Display EILEEN Sle se Tag Description Tag Value Analog Level Alarm Type Tag Description Return to Main page gt Wes ke a ES 4 Ack Current Ack Page Ack All Silence Cur Silence Pge Silence Fig 3 33 Alarm summary window In the image above the alarm summary window can be seen There is a big table
46. al and practical work Firstly according to the datasheet of the sensor it should give a voltage as a function of measured pressure which after the development of the sensor and the data acquisition has been proved experimentally how the change in the behaviour is almost 50 less with respect to the expected values in the sensor datasheet Another remarkable experience in this topic is related to the problem with the negative supply of the Opamp although theoretically it is not necessary if the output does not require negative voltages in practice the opamp saturates when trying to amplify very low voltages To sum up the development of this application fulfils the initial objectives of supervision since the desired functionality was obtained It allows registering the tank filling It detects maximum and minimum levels and warns the operator with an alarm to allow him take real time decisions and solve conflictive situations Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 6 Recommendations As future work it would be important to fully automatize the process to control the level By doing that the operator could both fill and empty the tank according to the current need This would be a great improvement since time and fatigue would be reduced for the operator and hence money would be saved In order to do that an initial investment is required to change the water pu
47. ams They can be used with a wide range of materials like water inflammable and corrosive liquids and granulated solids like lime concrete flour or sawdust 3 Pulse reflected from surface Cathode ray oscilloscope Circuit Pulse reflected from base Ultrasonic Ultrasonic transmitter receiver Reflection AA from surface T Reflection from base Fig 2 4 Ultrasonic sensors 3 There is a hydra wave transmitter which generates a high frequency wave 20 40 KHz which propagates through the gas until it collides with the liquid Then it reflects and reaches the receiver located in the same place as the transmitter The time between transmission and receipt is inversely proportional to the level As propagation depends on temperature time will have to be corrected for very accurate measurements lt is essentially a radar method 4 Advantages are that it has no moving parts hence no wear and tear it is a non contact technology and it is easy to calibrate Disadvantages are that it is affected by powders heavy vapours surface turbulence and foam it cannot operate in vacuum or high pressure and it needs good reflective surface Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 2 5 Capacitive level sensor They have no mobile parts and due to its operation principle RHF Radio High Frequency they are extremely multipurpose with the possibili
48. atible with SLC 500 and MicroLogix programs created with any of Rockwell Software s programming packages The main screen in RSLogix 500 is r e i HT PIE Menu bar _ Fie Edt Ves Seach Comme Took Window Help Icon bar OSB G O 25 v8 ARO AM ow A Notar aj 0T A Deep Jet zess Node lo user f A Tmerkouter A resta A Compare j UNTITUI PES ESLAD 2 SEN I gt Si ken MD gt Z Project tree Gemengen E ere Corpsen D wacoze mres j aroga so e Cj Onte fies LU force Pies E Custom Data Mondo J Omon Graph Monito J feces Mordor LJ rra Y bb non Results pane Verity besos ch Besuk 41 D Status bar Fts mef Ladder view Instruction toolbar Fig 3 14 RSLogix 500 main screen 21 32 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme A brief explanation of these bars is found in the RSLogix Getting Results Guide e Menu bar Select functionality from the menus that appear as you click each selection on this bar 21 e Icon bar The icon bar contains many functions that you will use repeatedly as you develop and test your logic program lf you want to know what any of the icons represent RSLogix 500 can tell you Move your cursor over the icon and floating ToolTip window appears to tell you what the icon is used for 21 e Online bar See at a glance the processor mode and whethe
49. d This would greatly depend upon where the Control of the system lies and what is required from the SCADA system The different methods of control are 23 Full SCADA Control This method entails the control being passed over to the PC and the SCADA software running All of the logic and sequential control normally done by a PLC programme is processed by SCADA Inputs to the system may be real plant devices which are simply passed through a PLC acting like an expensive data bridge onto the PC where the SCADA programme reads the inputs Similarly real plant output devices may be driven via a PLC but controlled by the SCADA programme Thus the PLC does not have any decision making within this type of control Philosophy Besides utilising real l O mimicked I O can be created using graphics within the SCADA programme Full PLC Control The PLC will have full control of the plant actions and the PLC programme will determine the plant operation The SCADA programme will simply be used as a data collection point and display information for the user operator However the user operator cannot control the plant from the PC SCADA neither can data nor parameters be changed within the PLC programme Shared Control This is a mixture of the two above methods and is the most common way to utilise SCADA In this project no control is done and only monitoring is made due to the kind of pump installed which cannot be automatized
50. diaphragm_intro cfm 13 Rocatek S A S undated Online Accessed November 2010 Available http www rocatek com forum php 14 L A Bryan and E A Bryan Programmable controllers Theory and Implementation 2nd ed USA Industrial Text Company 1997 15 Applied Measurements LTD 2008 2009 Pi9911 Field Re Rangeable Submersible Level Depth Sensor Transducer Transmitter Online Accessed April 2011 Available http www appmeas co uk pdf level and depth sensors Pi991 1 pdf 16 Honeywell July 2009 SSCSANNOOSPGAAS SENSOR TRUSTABILITY 5PSI 3 3V SIP Online Accessed April 201 1 Available http www farnell com datasheets 578749 pdf 17 Texas Instruments September 2009 XTR110 Accessed April 201 1 Available http focus ti com lit ds symlink xtr1 10 pdf 18 Electronic design undated Voltage to current circuit converter Online Accessed April 201 1 Available http archive electronicdesign com files 29 2985 figure 01 gif Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 19 Rockwell Automation undated SLC 500 Controllers Online Accessed April 2011 Available http ab rockwellautomation com Programmable Controllers SLC 500 Controllers 20 Allen Bradley June 2004 SLC 500 4 Channel Analog I O Modules Online Accessed April 201 1 Available http literature rockwellautomation com idc groups literature docume
51. e litres so there were two magnitudes to take as reference Furthermore the transducer input was connected to a small hose with a weight on the tip so it sank to the bottom of the pipe Apart from that since the transducer pins are quite easy to bend it was installed on a breadboard placed on a shelf near to the top of the pipe so power supply and output wires ran from the top of the pipe until the voltage source and the amplifying circuit Images below try to show these concepts Fig 4 2 Sensor breadboard assembly Now everything was prepared to make some measurements and deduce the output function of the sensor Just as a reminder the sensor must be fed with 3 3 Vdc Fig 4 3 Measuring the sensor output Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The results are shown in the table below the voltage values were taken each 10 cm of depth With this data the first step was to do a regression analysis as expected trend is linear linear regression analysis has been carried out The method used will be the least squares consisting on minimizing the sum of the squares of the difference between experimental and theoretical values The solution will be of the form y ax b in this case y will be the voltage and x will be the height To get the equation the following formula must be substituted Sxy e x Xx Equation 4
52. ed instead of the 25 kQ because that is the standardized industrial value isis opamp ISIS Professional Animating Ele View Edit Tools Design Graph Source Debug Library y Template System Help De SOO 80 4999 9 qm B GER x B f Ue T sE SENSOR 0 33V TEXT 7oq H 9870H u gt gt H I B 2Mesages ANIMATING 00 01 04 150000 CPU load 23 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme EM a ee OF SR SARE Bee A EAS BEES Du LN SENSOR at OG gt ri E s GS Yi gt ur amp s F im E er OF CR LR O 7 Menage A cad T3 70 ERR F Fig 4 6 Amplifying circuit in PROTEUS II 6 81 V 3 405 2V vV Once the simulation proved the circuit was correct it was implemented on a breadboard supply Gro Fig 4 7 Amplifying circuit on breadboard This caused a lot of problems although theoretically it should work On practice it did not it worked well with big voltages but with an input below 2 V approx it did not d 5 Ll Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez T SA Supervisor Reg Holme amplify correctly the output stabilized at 6 7 V approx The problem was that since it does not require negative voltages it should work perfectly but reali
53. en 0 and 3 2 so the setpoint will be the level in metres Once a setpoint is introduced a message will appear below indicating the operator if he has to fill the pipe empty it or if the level is in a range of 10 cm of the fixed one That message has been programmed with the following function If heightdisp setpoint 0 1 Then Continue filling the pipe Else If heightdisp gt setpoint 0 1 Then Run the tap until desired level else You have reached the desired level Another string display is at the bottom of the page This will only appear showing caution messages when the level is both over 3 10 m and below 10 cm If not no message will appear and this lower part of the screen will remain in blank The code for this message is the following If heightdisp 3 1 Then CAUTION The level is over 3 1m and the limit is 3 2m else If heightdisp lt 0 1 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Then CAUTION The level is below 10cm else M Il Next analysing the rest of the screen buttons and information it is possible to see the last numeric display in this screen is the one in the upper left corner which shows the time and date In the upper right corner there are two hyperlinks which display the main window in Spanish and French On the lower right corner there are two buttons the first one is for printing the current screen and the second one m
54. ervisor Reg Holme D Conclusions The aim of this project was designing and developing a level sensing system The hardware consisted on a pressure sensor measuring from a vertical water pipe and connected to a PLC which converted the input in height pressure and volume and sent it to a PC The conclusions obtained for this project are For this project the choice was to use the simplest principle to measure level so a pressure transducer was used Using pressure to measure the level is advisable regardless the dimensions and shape of the tank One of the obtained conclusions with the implementation of this level sensing system is the acquisition of that reading safely and with a greater reliability than the one obtained by an operator An operator would give a subjective reading since in order to read the level correctly it is necessary to be at the same height of the level So it would be necessary a ladder or a mechanism to observe the tank level accurately enough when reading above 2 metres height Besides this implies a risk for the operator which is completely solved with this application Another factor which can affect to a false reading is the mental fatigue of an operator when doing a repetitive task like reading tank levels especially in those cases when the number of tanks is very high Another conclusion of this project is the flexibility to increase the number of tanks allowing this application to be used in several
55. evel 2 when the level is over 3 10 m because the limit is 3 20 m and there is a risk of water overflowing the pipe e Level 3 the higher level of alarm declared when the level is over 3 20 m because surely the water is overflowing the pipe 44 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 3 3 3 Graphic windows of the SCADA In this project seven graphic displays have been designed They are listed below in the tree file HMI Project Edit Mode III Scan Class Tag Database Tag Monitor User Accounts t Security Codes e Activity Log Set E Activity Log Vie D welcome Startup BJ Command Line s Parameters Recipe E Alarms Data Log Logic and Control E Fig 3 29 Graphic windows The initial window is the welcome display which should allow the user selecting the language between English Spanish and French So the flags are the first example of images acting as buttons in this case they link the user to the main screen r welcome Display Fig 3 30 Welcome window To configure that it is necessary to right click on the image and select animation gt touch there it is possible to touch which action the image will perform when pressed repeated and released In this case the option chosen has been from the navigation group when pressed the main window will be displayed centered on the screen and the welcome
56. experiences in my life Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Table of Contents AUTOS Declara E i e Ee E ii PC IO WS CS EMON E iii Tabe or CO i ip uu T T TT dona ei iv L OT EE vi o On 1 1 1 O PRENNE RR TR 1 1 2 Fill PE 2 1 3 Biet A uu A E E 2 1 4 LO aider n u ba 3 1 5 GAME CNA enanas 4 La OO O EE 5 2 1 la 5 2 1 1 DoD er 5 2 2 Mea urne Ce zi i i MEM 6 2 2 1 Magnetic lateral and bulb bugs 7 2 2 2 AA T 7 2 2 3 e eE o o mm 8 2 2 4 nn O DIE o o KHEN EVE 9 22 5 Capacitive level Sensor secando ooo 10 2 2 6 Miete eg KE TE 10 2 2 7 Selecting the best method EE 11 2 3 xii qe 12 2 3 1 cener e OOO u E 12 2 3 2 Bil re 13 2 3 3 Ke A 13 2 3 4 Ec WE o RR 14 2 3 5 TRE e Te Eege De ele uuu u u G L u a s 16 2 4 FIG g ese OT u u 16 2 4 1 Mechanical pressure meters dia 17 2 4 2 Pneumatic pressure meters a 19 IV Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 4 3 Electromechanical and electronic pressure meters
57. ject which can be seen below y Br Fig 4 12 RSLogix verify buttons Next one the problems found have been solved the online bar status must be changed from OFFLINE to DOWNLOAD ASLogix 500 Untitled File Edit View Search Comms Tools Dem el sae lt OFFLINE W NoForces Go Online Forces Disabled Download Upload ie Controller Properties SC E Processor Status ae E Channel Configuration i E hiritipoint Monitor LO Program Files i E AA Nata Files Fig 4 13 RSLogix online bar The software will now load the RSLINX driver for downloading and communication to the CPU The screen will bring up a series of prompts for the operator to acknowledge Now the system should be REMOTE RUN but there is the possibility that it stays in the REMOTE PROGRAM mode from the same list box the GO ONLINE option must be selected After that the PLC must be online an example of the program running can be seen below 60 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme RSLogix 500 Starter LADDER File Edit View Search Comms Tools Window Help Sejo ell XJ JJdQ mf amp amp vmejgaenoni lje No Forces 4 H TT 3E t lt gt 4 4 ABL ABS D T Node 1d XI user 6t X Timericourter K npulOupa X Compare LADDER Project 23 Help Controller i Controller Prope
58. l Reference Connection see text Qe P Channel MOSFET see text Vin 0 to 10V gt Adjust lo 4 to 20mA gt Span Adjust 4mA Span 16mA Span Fig 3 6 Voltage to current converter 17 The other option is found in textbooks The voltage to current converters feeding to grounded loads circuit is the following dak PI OD d TI DC 100k Fig 3 7 Voltage to current converter 18 27 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme This conventional circuit gives 4 to 20 mA of output for an input of O to 10 V First it is necessary to adjust P1 for zero 4 mA and then P2 for span 20 mA The circuit needs a positive and negative supply which depend on the operational amplifier but typically are 15V Finally this part was not developed the reason is related to the resolution of the PLC and will be further studied later So the sensor developed in this project gives a voltage output ranging 1 10 V depending on the pressure 3 2 The Programmable Logic Controller PLC The PLC has already been introduced so now the specific model used in this project will be analysed It is the SLC 500 with 10 slot rack from Allen Bradley AB which is a chassis based modular family of controllers and I O Fig 3 8 PLC SLC 500 In order to make a PLC work it is necessary at least one power supply module and one controller C
59. l is or the volume of water it has inside 2 4 Pressure sensors here are several kinds of instruments to measure pressure mechanical pneumatic electromechanical and electronic sensors Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The principle of operation is as follows e Pressure transducers with deformation meters work with a diaphragm deviation due to pressure difference between the two chambers When the diaphragm enlarges due to pressure change the deformation meter enlarges and a Wheatstone bridge amplifies the signal A capacitance transducer works with the same principle e Piezoelectric transducers work based on the principle that an electric potential is generated in a crystalline structure when this is under mechanic pressure They are faster and more suitable for high pressure applications than diaphragm sensors although they are not as sensitive 2 4 1 Mechanical pressure meters The most basic and old of the instruments is the manometer invented by Torricelli in 1643 It is based on height to measure pressure according to the principle above lt is a U shape tube which contains mercury water alcohol or oil depending on the expected pressure differences 2 9 atmospheric pressure E mercury fas pressure 5H n j Pas lt Pan e Lm h Fig 2 10 Basic manometer 10 Glyndwr University Project Title Level sensing sys
60. m the 1 1 0 the source to an integer memory direction N7 0 N7 0 INPUT which indicates that the file type is an integer number the file number is the seven and the bit number is 0 So in that direction the input ranging 3277 to 32767 will be stored In the second rung 0001 the SPAN is calculated with the subtract function from the math toolbar this function operates A B In this case A is the integer stored in N7 1 and B is the integer stored in N7 2 The result of this operation is saved in N7 3 38 0003 0004 0005 ogis Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme e N7 1 MAX which indicates that the file type is an integer number the file number is the seven and the bit number is 1 So in that direction the maximum input possible 32767 is saved e N72 MIN which indicates that the file type is an integer number the file number is the seven and the bit number is 2 So in that direction the minimum input possible 3277 is saved e N7 3 SPAN which indicates that the file type is an integer number the file number is the seven and the bit number is 3 So in that direction the input span which is 29490 is stored Finally in the third rung 0002 the scaling factor which will multiply every input is calculated This factor is obtained dividing the 3 2 m of height which has the water pipe between the span stored in N7 3 This is computed
61. mp and the filing and emptying valves Apart from that to improve the SCADA it would be advisable to include Visual Basic options which improve a lot the visibility of the interface and which would allow for example to create a window to display datasheets Besides with an internet connection a remote supervision could be possible This would allow an operator to connect everywhere to monitor the process or send him an e mail or a sms to the mobile phone whenever an alarm appears Another improvement would be the implementation of a database with the purpose of saving the register of levels and alarms to study trends and correct repetitive errors Finally the sensor with its amplifying circuit should be built on a PCB or even make it waterproof and convert it into a submersible depth sensor with no need of a hose with a weight on the tip to introduce it in the pipe O A Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 7 References 1 P A Tipler and G P Mosca Physics for Scientist and Engineers 6th ed Barcelona Revert 2010 pp 365 371 2 Y A Cengel and M A Boles Thermodynamics An Engineering Approach 6th ed Mexico McGraw Hill 2009 pp 21 31 3 J E Barrios Deluquez Industrial Control Il Lecture Notes Colombia Pamplona University Available http www scribd com doc 490864 EL ENTORNO DEL PLG 4 J C Villajulca 2010 May
62. nges from 1 10V The opamp that will be used will be the LM741CN from National Semiconductor the most important characteristic for us is that the supply voltage is 18V 3 1 3 Converting voltage to current The final step to make the sensor similar to the one provided would be converting the voltage output ranging 0 10 Vdc to a current ranging 4 20 mA with 4 mA representing the lowest end of the range and 20 mA the highest Since the circuit is a few metres far from the sensor the voltage gets attenuated due to the resistance of the wires Converting the voltage signal to current using the technique known as the current loop improves the accuracy of the signal which is not affected by voltage drop in the wiring whatever the electrical resistance in the wiring is So in order to make the conversion it is possible to use an integrated circuit like the XTR110 a precision voltage to current converter designed for analog signal transmission lt accepts inputs of O to 10V and can be connected for outputs of 4mA to Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 20mA The main problem of these IC s is the price which ranges from 20 to 100 GBP and the complexity of its design The other possibility is to design a circuit which performs the conversion in order to do that it is possible to look at the internal circuit of the XTR110 Vcc 13 5 to 40V 10V Ed
63. nits we obtain that p 1000 kg m Precise measurements of density must take into account temperature and pressure since density in most of materials varies with temperature and pressure changes The given value of water is for 4 C and 1 atm of pressure Generally speaking liquids are essentially incompressible and their variation with pressure is insignificant For example at room temperature 20 C water density changes from 998 kg m at 1 atm to 1003 kg m at 100 atm this is only 0 596 Density relies more on temperature than on pressure For example if we fix the pressure at 1 atm water density changes from 998 kg cm at 20 C to 975 kg cm at 75 C this is a 2 3 so it can also be ignored in most of engineering calculus This is very well known from the ideal gas law 2 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme P okt Equation 2 2 Where e P pressure is in Pascals Pa e p density is in kg m e H mass isinJ kg K e l temperature is in Kelvin K Although the cubic meter is the SI unit for volume the litre L is very common especially for liquids and it is defined as 1 L 1 dm 10 m So the density of water is 1 kg L 2 2 Measuring the level Level is defined as a position line or flat surface according to which height is measured Some of the most commonly used liquid level measurements methods are 3 Direct methods e Hook
64. nts um 1 746 um005 en p pdf 21 Rockwell Automation January 2007 RSLogix 500 Getting Results Guide Online Accessed April 2011 Available http www plctrainer net RSLogix500 pdf 22 Rockwell Automation August 2007 RSView32 Getting Results Guide Online Accessed April 2011 http samplecode rockwellautomation com idc qroups literature documents gr vw 32 gr001 en e pdf 23 Holme R Lecture Notes United Kingdom Glyndwr University Quick Start Guide to RSView32 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 8 Appendices e Appendix Pi9911 Level Sensor Datasheet e Appendix ll SSCSANNOOSPGAAS Pressure Sensor Datasheet e Appendix Ill LM741CN Opamp Datasheet 72 5 1 Turndown O30mm Field Rangeable Submersible Pi99 DEPTH SENSOR Series a Depth Ranges 150mmWG to 200mWG E Sealed to IP68 200mWG E Robust Construction E Field Adjustable 5 1 turndown m Lightning Surge Protection to EN61000 4 5 E Excellent Long Term Stability E Temperature Compensated a Outstanding Performance B 3 YEAR WARRANTY Options Available Special Ranging consult factory Extended Temperature Ranges Different Cable Length DESCRIPTION The Pi99 submersible 2 wire 4 20mA Depth Sensor offers great flexibility with its two piece body design providing ease of access to the 5 turndown facility DIL switches and zero amp span po
65. o the LM741 LM741A except that ers which feature improved performance over industry stan dards like the LM709 They are direct plug in replacements pin eegen A o EE Ena for the 709C LM201 MC1439 and 748 in most applications P p ge u i i The amplifiers offer many features which make their appli cation nearly foolproof overload protection on the input and Features Connection Diagrams Metal Can Package Dual In Line or S O Package OFFSET NULL INVERTING INPUT vt OUTPUT NON INVERTING OUTPUT INPUT 5 OFFSET NULL _ V OFFSET NULL 00934102 00934103 Note 1 LM741H is available per JM38510 10101 Order Number LM741J LM741J 883 LM741CN Order Number LM741H LM741H 883 Note 1 See NS Package Number J08A M08A or N08E LM741AH 883 or LM741CH See NS Package Number H08C Ceramic Flatpak OFFSET NULL 00934106 Order Number LM741W 883 See NS Package Number W10A Typical Application Offset Nulling Circuit 00934107 O 2004 National Semiconductor Corporation DS009341 www national com Jeyidury euonelado LEIT LM741 Absolute Maximum Ratings note 2 If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Note 7 LM741A LM741 LM741C Supply Voltage 22V 22V 18V Power Dissipation Note 3 500 mW 500 mW 500 mW Differential Input Voltage 30V 30V 30V Input Voltage Note 4 15V 15V 15V Output Short
66. obstructed by a plug the position of which depends on the output 9 n b T R v p js ro asa P ge La K gt i a ki Fd d ul x Fig 2 13 Nozzle plug system 9 2 4 3 Electromechanical and electronic pressure meters Electronics has also changed the pressure measuring Pressure transducers convert the pressure change to a voltage magnetic resistance inductance or capacitance change They are lighter faster more sensitive trustworthy and precise that their mechanic equivalents They also have a great range varying from a millionth of 1 atm to some thousands of atm 2 Fig 2 14 Electronic pressure sensors 9 LO Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme e Manometric pressure transducers use atmospheric pressure as a reference and they give a zero output signal at atmospheric pressure whichever the altitude is e Absolute pressure transducers give a zero output value when in vacuum e Differential pressure transducers measure the difference between two pressure values directly instead of using two pressure transducers and calculating the difference 2 5 Industrial Control 2 5 1 Introduction to PLCs PLCs Programmable Logic Controllers are solid state members which use integrated circuits instead of electromechanical devices to control in real time a sequential process in an industrial environment They p
67. of height it is possible to calculate the maximum pressure that will be applied Panax D 9 himax 1 psi 6 8948 KPa kg m Pax 1000 s 9 81 3 2 m 31 392 KPa 4 553 psi Now it is known that pressure values will vary from 0 psi 4 553 psi Therefore the output voltage values will be 24 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 0 8 3 3 I V Output mar Volts Bcc 4 553 psi 0 10 3 3 V 2 734 V Output min Volts 0 10 3 3 V 0 33 V 330mV 3 1 2 Amplifying the signal Since the intention was to develop a similar sensor than the one provided by the university the next step was to amplify the output voltage to a range of 0 10 Vdc In order to do that firstly the gain needed was calculated 10V 373V EEN Then a very common circuit to amplify without inverting the signal was used V Y Va Fig 3 5 Non inverting amplifying circuit Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The main characteristics of this circuit are Rin re OO Rout 0 R Vo 1 d Vin Equation 3 3 i Equation 3 4 So as a gain of 3 66 is needed Rr Av 3 66 1 gt l R f 2 66 R l Ry 2 66 R Taking a value of 10 kQ for Ri the value obtained for Rf is approximately 25 kO Now the output voltage ra
68. papuajul ae sjosues salas NSS oul a1aydsoul e OI suoneueA egnssaJd oj jeuoraodoud indino ue epi oJd pue ainssaid oueudsouue oj p 2u 1 J 1 9Je SUOISISA punoduuoo pue aber whesydeip Buisues eui Jo epis Jong o eunsseud jo uoneoi dde moje SUOISJOA enueJegyiq elmssaud einjosqe oj jeuoniodoud en eA indino ue pue aouaJajal WNNDEA euJe ui Ue ney SUOISJOA ejnjosqe ay seinsseJd oDeD pue enualayip einjosqe einseeuJ sjosues s u O9M SUOH ebue ermjeladwe 4 S8L 01 do t Do 98 01 Do OZ J9NO pejesueduJoo eJnje1eduje pue Buiuonipuoo NISY UOISIDSI 4 indino Boj eue 1q z 9ujeuoneH uonduunsuoo JeMod mo jawax4 oBeyoA Bunejedo wo ebexoed ul eco x u eg 0 ww OL x ww 0 anelu suoneoyioeds eoueuuoged Buipee AyJSnpul wes y yum qe suondo pue sajAjs eBexoed jo AjeueA e sjeujojsno Joo UBISSP ejqixej pue e npolN unuixeuw ueds ajeos Um ZF Jo pueq 10118 10 1948 SSA 96 SZ 0 Jo oeinooe jun Ajeuedx3 Auges uuo1 Buo Buipea 1snpu Sauniuivad OPA 0 S JO OPA g g Jayya Jo Addns 1ewod Buis e woz uorejedo 10J pezuejoejeuo si 1osu s eu l S8L 01 do t Do S8 01 Do OZ jo aBue alnjeladua y Jano payesqijed si SUES OSS ey ZH jeyewuixoldde ye payjepdn aie ainssaid JO senjeA 1ndino payesquey 9 Sy ynan payelbBaju oyioeds uoneoiddy preoq uo ue Buisn Ajueeur uou pue sjo9ye alnjeradula AjAnisues JaS JO JOSUSS JO pajesuaduoo 2 njesadula pue payesqujed Ant si sales OSS
69. r way of calculating pressure is by using the compute CPT function Compite Dest FS 2 U Us Express Lore i 10000 951 F3 1 Fig 3 18 Pressure CPT function Since it is known that the liquid which is going to be measured is water and that the measurement is going to take place in the earth s surface density and gravity can be taken as parameters equal to 1000 kg m and 9 8 m s respectively Therefore the function is written directly these two parameters times the height gives the pressure which is allocated in F8 2 e F8 2 PRESSURE which indicates that the file type is a float number the file number is the eight and the bit number is 2 So in that direction the pressure will be stored in Pascals which is the SI unit After that in a new rung the final magnitude which is volume will be computed The procedure is the same using the next formula V m r h Equation 3 5 Now the known parameters are pi which equals 3 14159 and the radius of the water pipe which is 3 inches approximately 7 5 cm It has to be noticed that in order to make the equation have the right result everything must be in Sl units so although pi is an adimensional number the radius must be written in metres resulting in r 0 075m Therefore the compute function in the ladder would look like this Dest Expresi n Fig 3 19 Volume CPT function 36 Glyndwr University Project Title Level sensing system Name Javier Garc a
70. r you have online edits or forces present You can also view the communications driver and node number 21 e Project tree This view contains all the folders and files contained in your project You can usually click an icon in this tree and then click the right mouse button for a menu that applies only to the icon selected For example if you click the right mouse button on a program file you see options to rename the program file open the program file hide the program file or reveal properties of the program file 21 e Status bar Look here for ongoing status information and prompts as you use the software 21 e Results pane Displays the results of a Find All search or a verification procedure You can hide this pane or place it anywhere on your screen 21 e ladder view This is where you edit your ladder logic You can view several program files at the same time 21 e Instruction toolbar Displays instruction mnemonics in tabbed categories When you click on a category tab the instruction toolbar just above it changes to show that category of instructions Click an instruction to insert it in your ladder program 21 Communications from RSLogix 500 take place through another software package called RSLinx Classic To do this the RSWho function in RSLinx is very useful the remote device shown must be opened if everything is OK the processor should be seen now If not there is a communication problem which must
71. rator is to run the tap Once the main window is opened tags are started to monitor and their status can be checked with the button on the lower right corner The window mentioned can be seen below CS tag monitor Display 1 heightdisp 0 0527365 valid height value from PLC 517 345 valid pressure value from PLC 0 000931904 valid volume value from PLC pressuredisp 3 volumedisp Fig 4 18 Tag monitor window running After increasing and decreasing the level very fast the alarm summary window has the following appearance Alarms are saved whenever the level is below 10cm with an alarm level of 1 when the level is over 3 10 m with an alarm level of 2 and when the level is over 3 20 m with the highest level of alarm since the water must be falling to the floor The time when the level comes back to allowed values is also saved CG alarm summary Display Tagname Tag Value Analog Level Alarm Time Alarm Type Tag Description heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp heightdisp 0 877097 0 275076 0 99136 0 0640217 2 84842 3 15844 2 82716 3 1057 2 58517 3 2 0 575327 0 0882197 0 326945 0 091041 0 242848 0 354181 1 43 40 PM 1 43 39 PM 1 43 33 PM 1 43 32 PM 1 43 31 PM 1 43 30 PM 1 43 29 PM 1 43 28 PM 1 43 26 PM 1 43 25 PM 1 43 20 PM 1 43 19 PM 1 43 17 PM 1 43
72. re next to the vertical pipe There will be displayed the level in metres for that purpose the tag heightdisp has been created It gets directly the height datum from the PLC memory F8 1 Just below it another numeric display indicates the height in feet since it is the imperial unit very extended in the UK The same tag heightdisp is used for this and the conversion is made directly in the SCADA dividing that tag by 0 3048 m which is the equivalent to 1 ft Pressure and volume displays are made in the same way For pressure the tag pressuredisp has been created but in this case since it comes in Pascals which is a very little unit it is displayed multiplied by a 1000 factor making the display unit Kilopascals which is much more used For the pounds per square inch psi the pressure is obtained in pascals and converted to psi using the equivalence 1 psi equals i 4 Le Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 6 894 757 Pa In the case of volume the tag is defined volumedisp and it is displayed directly in the first case But for liquid volumes litres are much more common and volume is also displayed in this unit To do that the volumedisp is multiplied by a 1000 factor since there is 1000 in a cubic metre of water Finally another numeric display shows the percentage of filling of the tank Apart from that in order to make the level more
73. ress within a PLC or a memory address within the PC In the image below different tags can be seen and the way to configure them in the particular case of this project The most important thing is to declare the data source which in this case is the device called one which refers to the PLC and the address stated in the ladder programming Apart from that minimum and maximum values unit and data type are important for the correct display of the tag Bl Tag Database Tag M ame Type Security Clo Description height value from PLE Minimum 0 0 Scale 1 0 Units Im He M aim 32 Offset 10 0 Data Type Floating Point He Data Source Type e Device Memory H Made Mame one El Scan Clazz A Address IEN E As Search Cor NEE pressuredisp nalog pressure value setpoint Analog setpoint fixed b EI volumedisp Analog volume value fi CC controltag CT datasheet 771 sustem Fig 3 28 Tag database window It is possible to see that in this project four tags have been created they will be further explained later Another important characteristic which can be declared for each tag are alarms there are several levels of importance of alarms In this project three levels of alarm have been created for the height tag e Level 1 when the level is below 10 cm because there is the risk that the application for which the tank is being used runs out of water e L
74. roduce an output to the information provided by the sensors of the automatized system They implement control functions so they are capable of storing instructions such as sequencing timing counting arithmetic data manipulation and communication to control industrial machines and processes 13 14 The idea was born in 1968 when General Motors specified the design criteria for the first PLC to substitute high cost relay controlled systems Their main characteristics are the survivability in industrial environments ease of program and maintain by engineers and technicians and reusable Apart from that the price had to be competitive with current relay systems and it had to interact with a central system By the end of the year the first PLC had been developed They met the requirements of modularity ease of install reduced space programmability reusability and capability of use in an industrial environment The programming was a little tedious but the ladder diagram format standard had been developed By 1971 the use of PLCs had spread to other industrial sectors Nowadays PLCs have improved in areas like speed of operation interfaces or data processing but the main requirements are the same of their predecessors The improvements are not only in hardware but in software too Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme This section is just an introduction
75. rties e Processor Status JU IO Configuration bis Channel Configuration E Multipoint Monitor gg Program Files B syso SYS1 ZS Lanz gg Data Files Cross Reference D 00 OUTPUT E n INPUT Dec eraus D B3 BINARY E T4 TIMER D ce COUNTER E R6 CONTROL D N7 INTEGER Fa FLOAT Cavan Ciana Controller i Controller Properties A Processor Status JU IO Configuration he Channel Configuration E Muttipoint Monitor Program Files DER 00001085114 lt amp Dest ER 08279417 lt SYS1 Expression N7 0 N7 2 F3 0 LAD2 3 2 3 Data Files 7 Cross Reference D 00 OUTPUT E n INPUT D s2 status 8122 108 lt i 83 BINARY Boression 981 10000 F8 1 E 14 TIMER D c5 COUNTER R6 CONTROL D N7 INTEGER F8 FLOAT Dest P3 c Ea Cavan Bilan E 001463051 Fig 4 14 Ladder logic running A random set of samples have been recorded they have been represented in the following table Voltage input V Bit input Height m 3550 0 028 2 6602 1 0 36 o Odal Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Using Excel to plot the results and get the linear regression Height m 3 00 4 00 5 00 6 00 Input voltage V Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 4 3 Testing the SCADA Finally it is the time to test
76. s Geng xo dos dor Fdo di SE enusla ua mor w vido vso vso vedo deet mseor w vso vm vdor wsdo avor mseor w vso vdor em vsio avow mseor w vPdon vedo wsdoe vsio avom zzo w vmo wsdoe vea vedo dVsio mseor w vsio vso weds vedo ava einjosqy 9 9JnSSaJd opo O9 SZ Y 0001 opow s 94nSSaJd y 94nssead Eroa Ayiqeis sing I9AQ uu9j Buo SD ebuey eunssaJd inss iqd suoieoyioads abuey ainssaig 9 qe L eunsseJd oueudsoue ye jes SI uug einssejd quaiquie oueudsouure pue ejnsseJd padde usemjeq e9usJayip eui o jeuoraodoud si 3ndino ZHOd od Je yes vonouny JejsueJ Jo jurod 09 ZUOd Luog uod uoee o paljdde seinssejd ay uesmjeq s9usJayp eui oj jeuoraodoud si 1ndin einssejd oueudsouue 0 pasuaJajal 5 Sd GL Je 16s SI uuq aunssaid juaiquie oueudsoue pue ejnsseJd padde usemjeq eouaiJaJip eui 0 jeuoruodoud si 1ndin uunnoeA nj eunsseud 018Z einjosqe je jes si uud UNN9EA 0 92u919J91 ut inq e pue einssaJd paiydde usemjeq eouaiJoJiip eui oj jeuoruodoud si inding abbey jenueJeyig punodwoy ejniosqy uonduoseg ad eunssaJd sed 1osues 9 qe L J9eANIIY pJepuejS saliag ISS SIOSUIS aJnssaJd U03IHS A AM Ies G 0 3002 pue Bulsuas am suoy Bisd inss iq 00 06 08 DJ 09 0S or 0 0c OL 0 INT Jong EO SS Z Aidans 9 ndino
77. se N A N A 25 CAN N A Note 4 For supply voltages less than 15V the absolute maximum input voltage is equal to the supply voltage Note 5 Unless otherwise specified these specifications apply for Vs 15V 55 C x TA lt 125 C LM741 LM741A For the LM741C LM741E these specifications are limited to 0 C x Ta lt 70 C Note 6 Calculated value from BW MHz 0 35 Rise Time us Note 7 For military specifications see RETS741X for LM741 and RETS741AX for LM741A Note 8 Human body model 1 5 kQ in series with 100 pF Schematic Diagram yt NON INVERTING INPUT OFFSET NULL 3 OFFSET y 00934101 www national com 4 Physical Dimensions inches millimeters unless otherwise noted 0 350 0 370 lt 890 9 398 DIA 0 315 0 335 DIA 8 001 8 509 i MAX 0 165 0 185 165 0 185 10 635 DE S 4 191 4 4 191 4 699 REFERENCE PLANE AS 0 035 A DE SEATING PLANE 0 500 0 889 889 f 0 381 1 016 7 HII gt Le 0 016 0 019 0 016 0 019 DUE 0 406 0 483 0 195 0 205 DIA 4 953 5 207 P C 0 029 0 045 A 0 737 1 143 0 028 0 034 0 711 0 864 X e EQUALLY SPACED Metal Can Package H Order Number LM741H LM741H 883 LM741AH 883 LM741AH MIL or LM741CH NS Package Number H08C 0 115 0 145 2 921 3 683 DIA HO8C REV E www national com LDZIN1 LM7
78. seen in red in the photo below 29 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme ee ON Configures channel for current input EI d woos wu ear ol I Off C fi h f I AAA Hp dl re Qo C BES 1 L Lontigures Channel for voltage input A vumm a A Current 1231 Switch 1 Channel 0 0 Switch 2 Channel 1 i I I I I Switch 3 Channel 2 Switch 4 Channel 3 Voltage Fig 3 10 Input module configuration 20 The wiring of the module would be like this for the voltage wiring NM analog source analog source Ae I IN 2 4 ground N i Jumper unused ANL COM Inputs IN 34 IN 3 ANLCOM Fig 3 11 Voltage input module wiring 20 And since the current sensor has positive and negative supply plus earth wires the connection would look like this for the current input 3 Wire Transmitter Transmitter supply signal GND Fig 3 12 Current input module wiring 20 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The table below identifies the current and voltage input ranges for the input channels the number of significant bits for the applications using input ranges less than full scale and their resolution Voltage Current Range Resolution per LSB 10V de to 10V de 1LSB 305 176 V Fig 3 13 Converting analog input da
79. sing system Name Javier Garc a Fern ndez Supervisor Reg Holme 3 Design In this chapter the whole system design will be done Firstly a sensor provided by the University will be used as a benchmark to test the software Then a new sensor will be designed with the purpose of getting a cheaper solution to the system This sensor output will be treated in a PLC which will compute level pressure and volume Finally this data will be monitored on a PC using a SCADA software 3 1 Sensor Firstly the depth sensor used was the one provided by the University corresponding to the model Pi9911 4mWG C10 from Applied Measurements LTD Fig 3 1 Depth sensor 15 This sensor gives an output ranging 4 20 mA with a range of 4 metres Water Gauge mWG and a cable length of 10 metres It assures a high integrity waterproof assembly which is rated to 200 metres depth It has an accuracy greater than 0 25 of the pressure range It has three wires and a static pressure input coming out from the cable The sensor connections are as follows e Red Positive Supply e Blue Negative Supply e Green Earth 22 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme The setup would probably be similar to the diagram below so the sensor has a constant power supply that is normally 24vdc When the sensor changes output the current in milliamps varies between 4 and 20 4
80. t Common Mode Rejection Ratio Supply Voltage Rejection Ratio Transient Response Rise Time Overshoot Bandwidth Note 6 Slew Rate Supply Current Power Consumption LM741A LM741 TA 25 G RL gt 2 kQ Vs 20V Vo 15V Vs 15V Vo 10V Tamin Ta S TAMAX R gt 2 kQ Vs 20V Vo 15V Vs 15V Vo 10V Vs 5V Vo 2V Ve E20V R gt 10 kQ R gt 2 kO Ve 15V R gt 10 kQ R gt 2 kO T 250 10 25 35 25 25 0 DH Tamin Ta Tamax Rs lt 10 kQ Voy 12V 70 70 Rs 500 Voy 12V 95 Tamin TAS Tama Vs 20V to Vs 5V Rs lt 5002 Rs lt 10 kQ V mV V mV lt lt lt lt A A 3 V mV V mV V mV 3 o B B o o B Q UJ Ta 25 C Unity Gain 0 25 0 8 us 6 0 Ta 25 C O Note 2 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur Operating Ratings indicate conditions for which the device is functional but do not guarantee specific performance limits www national com LDZIN LM741 Electrical Characteristics note 5 Continued Note 3 For operation at elevated temperatures these devices must be derated based on thermal resistance and T max listed under Absolute Maximum Ratings Tj TA OjA Pp Thermal Resistance Cerdip J DIP N HO8 H SO 8 M Da Junction to Ambient 100 C W 100 C W 170 C W 195 C W Dec Junction to Ca
81. t can achieve 32767 e N7 2 MIN minimum value that the input can achieve 3277 e N7 1 SPAN the difference between the maximum and minimum possible inputs e F8 0 MULTIPLIER scaling factor e F8 1 H height in metres m e F8 2 P pressure in Pascals Pa e F8 3 V volume in cubic metres m 3 3 Human Machine Interface HMI RSView32 is a Windows based software program for creating and running data acquisition monitoring and control applications Designed for use in Microsoft amp Windows Server 2003 Windows XP and Windows 2000 environments RSView32 contains the tools you need for creating all aspects of a human machine interface including real time animated graphic displays trends and alarm summaries RSView32 integrates easily with Rockwell Software Microsoft and other third party products to maximize the power of ActiveX8 VBA OLE ODBC and OPCO technologies 22 There are two packages e HSView32 Works contains both development and runtime software Use this software to develop and run RSView32 applications e RSView32 Runtime contains only runtime software Use this software to run applications developed in RSView32 Works Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 3 3 1 Control Philosophy Depending upon the application and the requirements of the control specification there are different techniques that can be applie
82. t sensor 3 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme It is a very popular method which actually uses the pressure difference transmitter It sends an electrical or pneumatic signal proportional to the difference of the two liquids one due to the object liquid level and the other due to a reference pressure for example atmospheric pressure 4 2 2 3 Hydrostatic They are used in applications where continuous monitoring of liquid level is necessary There are no mobile parts and they are not affected by turbulences foam gases vapours or fluid characteristics variations like dielectrical constant or conductivity There are two models pendulum and lateral 3 Fig 2 3 Hydrostatic sensors 3 With a very similar principle of the conduit sensor it senses the pressure in the bottom of the vessel and as it has another pressure input at the end of the cable which is measuring atmospheric pressure it sends a signal proportional to the pressure difference 4 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 2 4 Ultrasonic They give excellent precision and quality and there is no physical contact between the sensor and the measured media lt allows its use in critical applications like tanks of little diameter or with gases vapours or powders although they are sensitive to fo
83. ta 20 Therefore by using 1 10 Vdc instead of 4 20 mA as input one bit more is used resulting in an improvement in the resolution In order to convert this input value to a physical one scaling is necessary Scaling consists on enlarging or diminishing the value until the desired range Firstly the scaling will be done for the current analog input from the sensor provided by the University As seen above max and min values will be 3 277 and 16 384 corresponding to 4 and 20 mA respectively Max 2 16 384 16 384 20 mA 3 271 4 mA 819 2 1 mA SPAN 16 mA 13 107 To get the multiplying factor 3 2 m 10 4 13 107 2 44144350347 10 From the true value which enters the PLC the minimum value 3 277 is subtracted and the result is multiplied by this factor in order to get the physical value of level For example if 12 000 is the value which enters the PLC 31 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 12 000 3 277 2 44144350347 10 2 13 m Secondly the scaling for the voltage input will be done Max 2 32 767 32 767 10 Vdc 3 277 1 Vdc SPAN 9 Vdc 29 490 To get the multiplying factor 3 2 m 29 490 1 08511359783 1074 3 2 2 Ladder logic programming RSLogix 500 software is a 32 bit Windows ladder logic programming package for the SLC 500 and MicroLogix amp processors RSLogix 500 is comp
84. tem Name Javier Garc a Fern ndez Supervisor Reg Holme Another mechanical device to measure pressure is the Bourdon tube due to its inventor consisting on a metallic bended hollow tube like a hook finishing on an indicating needle When the tube is open to atmosphere it has no deviation and the needle is calibrated to zero When it is pressurized the tube lengthens and the needle moves proportionally to the applied pressure Other types of Bourbon tubes have different shapes like spiral helicoidal or twisted 2 Fig 2 11 Bourdon tube 11 The diaphragm sensor consists on a capsule divided by a membrane one side is open to targeted pressure and the other side is connected to a reference pressure 12 Diaphragm PExt PExt Pref T Diaph ragm Pref Fig 2 12 Diaphragm sensor 12 Therefore with this kind of devices it is possible to obtain the gauge pressure The bellows sensor is similar to the diaphragm but in a single piece flexible axially which allows a big displacement They have a great service life which means they bear millions of flexion cycles without deformation 9 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 2 4 2 Pneumatic pressure meters The pneumatic transmitter instruments are based on the nozzle plug system They consist on a pneumatic tube augmented to a constant pressure P with a nozzle in the end which can be
85. tentiometers Manufactured from 403 Stainless Steel these two halves are held together using a locking ring and are sealed by means of an O ring arrangement This in conjunction with an IP68 sealed polyurethane cable outlet completes a high integrity waterproof assembly which is rated to 200 metres depth Both sensor and electronics are protected against the effects of surges created by lightning strikes offering distinct advantages over competitive products The Pi991 offers rugged construction excellent long term stability and performance To further support our claim of long term reliability we offer the product as standard with a 3 Year Warranty Transducer Specialists UN V APPLIED MEASUREMENTS LIMITED AY 3 MERCURY HOUSE CALLEVA PARK ALDERMASTON BERKSHIRE RG7 8PN UK Tel 44 0118 981 7339 Fax 44 0118 981 9121 email infowWapepmeas co uk Internet www appmeas co uk SPECIFICATION Pi99 Depth Sensor Process Measurement Instrumentation 0 15 05 1 2 5 10 20 50 100 200 Burst Pressure O Pressure Range AM 12 30 Load Driving Capacity Im Ohmsat Max Supply Voltage 4 core screened polyurethane sheathed cable with PO Lessel Temperature Range Operating 40to 80 S C Cempemated to OE E OnZee 005 z96AppliedPresure C EnvironmentalProtectio IP 8to20mWG TI Wi A ot ilu cable Sram _ Construction 40
86. to understand what a PLC is since further study and programming of PLCs and will be included in the next chapters 2 5 2 Introduction to SCADA SCADA is an acronym for Supervisory Control and Data Acquisition SCADA get together all the processes in charge of doing the specific functions which have to be done in a general system from the equipment that form a given installation Then the data is sent to a central computer to be managed and controlled 14 HMI environment Human Machine Interface is the SCADA interface and must be able of managing the use of the different sources in real time taking into account the constraints of the different processes which form the system and which force each process to take place within a given interval of time This tool has to be friendly to the user which is usually a forgotten part in the automation process Summing up a SCADA system is a joint of devices and programs aimed to control and supervise secure and efficiently an industrial process in real time from an operator post lts goal is to ease the operation of the control system and must provide the operator real time centralized information remote control and historical information of the system variables With this a better vision of the system is provided and allows easier problem detection and solving With the obtained data some statistical studies and curves of variables trends may be done Glyndwr University Project Title Level sen
87. ts and packing materials meet the provisions of the Customer Products Stewardship Specification CSP 9 111C2 and the Banned Substances and Materials of Interest Specification CSP 9 111S2 and contain no Banned Substances as defined in CSP 9 111S2 d National Semiconductor National Semiconductor Americas Customer Support Center Email new feedback O nsc com Tel 1 800 272 9959 Europe Customer Support Center Fax 49 0 180 530 85 86 Email europe support 9 nsc com Deutsch Tel 49 0 69 9508 6208 National Semiconductor Japan Customer Support Center Fax 81 3 5639 7507 Email jpn feedback O nsc com Tel 81 3 5639 7560 National Semiconductor Asia Pacific Customer Support Center Email ap support 9 nsc com English Tel 444 0 870 24 0 2171 www national com Francais Tel 33 0 1 41 91 8790 Jeyidury euonelado LEIT
88. ty shows that in order to amplify correctly low voltages the negative supply of the amplifier is required or it saturates Therefore another source was required making three voltages sources in total one of 3 3 V to feed the sensor and the other two of 18V to feed the amplifier So finally the sensor assembly is Fig 4 8 Final sensor assembly The tip of the hose which is stuck to an iron bar with insulating tape can be seen on the right of the photo On the image below it is showed how the hose is fit in the water pipe from the top Fig 4 9 Fitting the sensor hose into the pipe 58 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 4 1 3 The current to voltage circuit converter It has already been mentioned that this part was not implemented in the project Anyway it has been simulated with PROTEUS to demonstrate whether it could worked or not and the results were positive Fig 4 10 Converting OV to 4mA Fig 4 11 Converting 10V to 20mA 59 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 4 2 Testing the ladder logic programming It has already been showed how to wire the PLC and how to test whether it has communication with the PC by using RSLinx In order to test the ladder the first step is to check it using the RSLogix command buttons Verify file and Verify pro
89. ty to be used with products like conductive viscous or aggressive liquids apart from granulated materials or powders hey are available for critical temperature conditions and for heavy applications like mining among others 3 Fig 2 5 Capacitive sensor 3 The principle of operation is based on the measurement of the variation of the capacitance of the dielectric media between the metallic sensor and the deposit or between two sensors in case the deposit is not metallic 4 Advantages are that it can operate under extreme temperature and pressure it works with all types of materials and it is typically inexpensive Disadvantages are that there are intrusive measurements there are errors due to build up and varying dielectric strength and it is sensitive to certain applications 2 2 6 Radioactive level sensor Radioactive devices can also be used for both discrete and continuous level measurements They are used when there is no possibility of installing something inside the vessel like in high temperature processes or very corrosive materials The radioactive source and the receiver are placed in each side of the vessel when the material is between them the radiation received changes proportionally 4 10 Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme 3 a 4 T CCC C GG J Fig 2 6 Radioactive sensor 4 2 2 7 Selecting the best method
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91. y Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme Now considering the movement of the fluid two types of pressure will be defined e Static pressure is uniform in all directions so measurements are independent of direction e Dynamic pressure is the pressure exerted by the flow which applies additional pressure in the perpendicular plane of it In this project a static gauge pressure will be measured 2 3 4 Variation with depth It is possible to prove that pressure in a static fluid does not change in horizontal planes by doing the balance of forces However it does in a vertical plane due to the gravity field Pressure increases with depth because the deeper you go the more fluid and thus the more weight This extra weight in a lower layer is balanced with a pressure increase 1 B e e 2 b eg DI e D e e e lt e gm 5 E mm e e Fig 2 7 Variation with depth 1 I In order to obtain the relation between pressure p and depth z an equilibrium fluid of height dy and surface S is considered 8 aL Glyndwr University Project Title Level sensing system Name Javier Garc a Fern ndez Supervisor Reg Holme ptdpis y Fig 2 8 Fundamental law of hydrostatics demonstration 8 Oda po Where e yand dy height and differential of height are

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