The Design of a Chemical Virtual Instrument Based on LabVIEW for
Contents
1. FIGURE 7 a Panel of sub VI for redisplaying and b program of sub VI for redisplaying on the panel The mechanical natures of both icons are set as Latch When Pressed and both default values are false To avoid mistakes in reading a data file the format of the storage file should be unified 3 2 2 Sub VI for fitting curve automatically In a general way the testing system of the chemical VI is able to acquire plentiful data at tremendous speed but the whole data is discrete During data processing we sometimes need to fit discrete data to a curve obtain its equation and get intersection points of some curves for example we need to get the intersection points of some curves in drawing the bi nary metal diagram and determining molar mass with freez ing point depression and we need the curve equation in mea suring the surface tension of a solution There is no function to obtain an equation directly so we have to program it by ourselves via calling correlated functions in LabVIEW The program for curve fitting and obtaining equations automatically is shown in Figure 8 The testing data is auto matically fitted respectively in given fitting models and the mean square errors MSEs of fitting effects are sent to an array then according to the least MSE computer confirms the best fitting model or fitting order The fitting models are linear fitting exponential fitting and general polynomial fit ting which are found in2. reaction rate molar mass can be obtained by mea suring the change of the two parameters However owing to the special features of chemistry these physical parameters cannot be obtained directly from the experimental values of temperature and pressure In general these experimental val ues must be processed at a deeper level according to the prin ciples or laws of chemistry such as converting by formula plotting finding equations that obey specified laws In many situations the value of temperature and pressure can indi cate to the researcher whether the reaction is in process Ob viously a normal instrument has difficulties in achieving that effect Moreover when using a standard instrument the re searcher has to process data by hand This not only wastes time but also easily causes human measurement error In this paper LabVIEW 7 0 Express based VI for determining temperatures and pressures is developed by using temper ature and pressure sensors a signal conditioning circuit a DAQ card or standard chemical instrument This VI is able to complete the measurement of a system s temperature and pressure automatically and obtain results duly The results are satisfactory 2 THE CONFIGURATION OF THE VI SYSTEM The configuration chart for the VI system is in Figure 1 The signals of chemical reaction are analog signals con verted by sensors such as temperature temperature differ ence pressure pressure difference The an
3. Temperature Difference 0 000 0 soo N 1 000 S 1 500 difference a 2 000 2 500 3 000 F 3 500 4 000 4 500 1500 2000 2500 Number of acquired data 1000 Curve setting MW I 3000 Developed by CWNU CC amp CE Temperature difference 10 faa po w Temperature Select port com x Interval S 152 ai 100 i Save data 252 10 je ICarsor zea 4 0ce splena Operater Time l 2005 7 28 10 32 Wang Wenbin eas i 1 1 sed ah be 3500 4000 main panel Figure 6 Front panel for determining molar mass with freezing point depression information about the experiment It is possible to select the method of acquisition DAQ card or serial port via select icon The exit icon is used to exit from the VI testing sys tem safely Figure 5 b is the block program of the VI while a loop is used to ensure that the program will check con tinuously Some sub VIs that were previously made and ran well can be called up by selecting the event This programing method is convenient for extension and modification 3 2 Design of program for public sub VI There are different tasks and data processing methods in dif ferent chemical testing systems but the basic procedures data acquisition data filtering curve fitting real time dis playing calculating and generating the report of results are the same Therefore one program can be made as a shared s
4. Hindawi Publishing Corporation Journal of Automated Methods and Management in Chemistry Volume 2007 Article ID 68143 7 pages doi 10 1155 2007 68143 Research Article The Design of a Chemical Virtual Instrument Based on LabVIEW for Determining Temperatures and Pressures Wen Bin Wang Jang Yuan Li and Qi Jun Wu Department of Chemistry College of Chemistry and Chemical Engineering China West Normal University Nanchong 637002 Sichuan China Received 16 December 2006 Accepted 22 February 2007 A LabVIEW based self constructed chemical virtual instrument VI has been developed for determining temperatures and pres sures It can be put together easily and quickly by selecting hardware modules such as the PCI DAQ card or serial port method different kinds of sensors signal conditioning circuits or finished chemical instruments and software modules such as data ac quisition saving proceeding The VI system provides individual and extremely flexible solutions for automatic measurements in physical chemistry research Copyright 2007 Wen Bin Wang et al This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited 1 INTRODUCTION Measuring instruments have gone through several stages in their development analog meter discrete component parts DCP instruments digital instru
5. International lt e International Journal of Analytical ISIE ey A a Advances in Physical Chemistry Hindawi Submit your manuscripts at http www hindawi com Journal of Spectroscopy Journal of l Theoretical Chemistry International Journal of Inorganic Chemistry Pa a Fa J E Journal of Hindawi Publishing Corporation http www hindawi com Volume 2014 International Journal of medrol als aalciay Chromatography Research International Journal of Quantum S Hindawi Publishing Corporation http www hindawi com Journal of T a Analytical Methods g in a Bioinorganic Chemistry and Applications
6. alog signals are Temperature The Temp erature difference chemistry reaction Standard chemical Serial port instruments with Journal of Automated Methods and Management in Chemistry 5 u 3 3 aw Q O jaa gt 2 FIGURE 2 Signal conditioning circuit of temperature converted into digital signals in the DAQ card or by stan dard chemical instruments and are sent to a computer Finally the digital signals are processed on the LabVIEW platform 2 1 PCI DAQ card method The PCI DAQ card method was the earliest method used in the construction of the VI The method utilizes a DAQ card to convert analog signals to digital signals so that a computer can process the various analog signals It provided a way of constructing the VI by using the computer s bus input de vices output devices software and so on It is still popular in the world of measurement and control on account of its wide use and applicability for use in various laboratories and teaching sectors The analog signals from normal sensors are very weak so they must be preprocessed before entering the DAQ card by methods such as impedance conversion amplification The signal condition circuit of a temperature sensor made by the author is shown in Figure 2 A DC bridge is made up of a temperature sensor Pt100 and three impedances and sends converted DC signals caused by the change of temperature signals to the instrument ampl
7. customer meetings and train ing REFERENCES 1 J H Liu Z R Shen and F T Guo Modern Test Technology and System Integration Publishing House of Electronics Industry Beijing China 2005 2 Q Z Zhou Z H Qian and P P Liu VI and Program Design of LabVIEW 7 Express Buaapress Beijing China 2004 3 J Y Li W B Wang Y W Li Z R Liu and D C Cai LabVIEW 7 express based virtual instrument for drawing binary phase diagrams Computer and Applied Chemistry vol 22 no 8 pp 623 626 2005 4 M Y Cao X Wang and N L Sun Instrumentation amplifier AD620 and its application Electrical Measurement amp Instru mentation vol 37 no 418 pp 49 52 2000 5 H T Xiong Three methods for driving data acquisition card in LabVIEW Electrical Measurement e Instrumentation vol 38 no 428 pp 35 37 2001 6 J Y Li W B Wang and Y W Li LabVIEW 7 express based virtual instrument for measuring the surface tensions of so lution Computer and Applied Chemistry vol 22 no 11 pp 1055 1058 2005 7 LabVIEW 7 Express User Manual National Instrument 2003 8 L P Yang H T Li and Y Zhao Advanced Program Design of LabVIEW Tsinghua University Press Beijing China 2003 International Journal of nedi Chemistry International Journal of Carbohydrate Chemistry The Scientific World Journal Organic Chemistry
8. functions Mathematics Fitting and the comparing array elements are achieved depending on Array Max amp Min function When making a curve fitting in case structure the corresponding fitting result displays in stantly The program sets a sub VI of writing equation again which has a function for converting the best coefficients to strings and write expressions f x and y f x which have different functions in different conditions for example we must use the form f x in the function Eval y f x VI or Integration VI If we use the form y f x 8 the program cannot run However we have to give the form y f x when we write the equation Now we can solve the problem by connecting the right output terminals in different circum stances Due to the limitations of this paper s length other com mon modules such as data acquisition real time dynamic display elimination of excess data and curve fitting for the construction of chemical VIs are not discussed 3 2 3 Property setting for sub VI node After developing and debugging the sub VI we can create a property node and call it up as a module when we need Every sub VI has a connector pane and every connector pane has several terminals The programmer simply connects the con trols or indicators with terminals but need not worry about the internal structure of the sub VI In a sense input and output terminals correspond to formal parameter and actual parameter in C lang
9. he second way simply displays its front panel when called 4 APPLIED EXAMPLES The author carried out corresponding test experiments in turn with data acquisition real time display data process ing generating the report of result which can all be com pleted automatically giving satisfactory results 3 6 The data processing module of the system set on a different mis sion can fulfill the corresponding testing assignment For ex ample we add a data processing module of heat of combus tion in the system and can apply it to measuring the material combustion heat The results are shown as Table 1 Their rel ative measurement errors are all less than 4 a satisfactory result 5 CONCLUSION The author designed VIs for measuring temperature and pressure based on LabVIEW These instruments were com posed of four representative physical chemistry experiments drawing a binary metal diagram determining molar mass with freezing point depression determining the constant of the reactive rate in the decomposition of peroxide and mea suring the surface tension of a solution by the pressure of froth These experiments can determine the temperature temperature difference pressure and pressure difference of the system respectively In these experiments we can take the measurements by the PCI DAQ method or standard chemi cal instruments serial port method A manipulator can com bine the sensors signal condition circuit or standa
10. he serial port VISA Read and VISA Close and so forth then programe for data acquisition display saving and so forth 3 DESIGN OF PROGRAM FOR VIRTUAL INSTRUMENT 3 1 Design for control panel The control panel of the virtual instrument is an interface between user and computer Besides friendly interface and easy control the corresponding test function can be started up by a simple manipulation It should also be able to finish user s task successfully Software is a key section of the VI Given different softwares the VI can have different functions The author designs the program by the module method for convenience in development and call Figure 5 a shows the VI control panel where four physical chemistry experi ments are displayed The program is designed by selecting different events and a corresponding VI panel will open and enter the chemical testing system as long as we click the corresponding icon for instance by clicking the molecular weight icon the panel will show as in Figure 6 The program provides a helping function in that the user can get help by lighting the help icon or keeping the cursor on a few sec onds when some helping textual material will display to de scribe the function of the modules and give the user some Journal of Automated Methods and Management in Chemistry metal diagram with DAQ method VI b Figure 5 a Operation panel of the VI and b program for operation panel Real time
11. ifier AD620 for amplifica tion The bridge power source comes from 1 5 mA constant current produced by the operational amplifier AD620 is a monolithic instrumentation amplifier based on a modifica tion of the classic three op amp approach Monolithic con struction and laser wafer trimming allow the tight matching and tracking of circuit components thus ensuring the high level of performance inherent in this circuit 4 The LM399 in Figure 2 is a precision temperature stabilized monolithic offering high quality reference voltage to the fifth pin of AD620 The amplified signals are sent to a second order fil ter circuit via the sixth pin of AD620 and then are sent to a channel of a multifunction DAQ card PCI 2005 to convert analog signals to digital signals PCI 2005 is made by Beijing Art Corp and it has 16 bits 16SE 8DI 10 V input range connects to computer with PCI bus and the driver can oper ate it by calling LabVIEW s function 5 Figure 3 shows the program of the PCI 2005 driver realization and dual channel DAQs which is used to determine the constant of the reac tive rate by the decomposition of peroxide In order to realize the PCI DAQ driver we use call library function CLF node in LabVIEW implement A D converters for corresponding temperature and pressure at the same time save text file in a text model The other sensors signal condition circuits are similar to the temperature circuit the only difference lyi
12. lems for designing chemical VI to measure temperature temperature difference pressure and pressure difference When the user needs to test the temper ature and pressure which are beyond this system then he can compose a new measuring system to meet the require ments of the new testing by transferring the function de signed modules and combining them thus avoiding a waste of manpower and material resources This means that devel opers can design customized measuring instruments accord ing to their own requirements Exploiting VIs based on Lab VIEW has many advantages such as a user friendly working panel ease of manipulation complex data processing draw ing and printing the result at the click of the mouse More over using the application builder tools that belong to Lab VIEW itself to create standalone applications and installers or shared libraries DLLs for VIs the user can run and ex tend independently from the LabVIEW development envi ronment Altogether this system has very great practical ap plication value Wen Bin Wang et al ACKNOWLEDGMENTS The authors are financially supported by the Key Research Application of China West Normal University with the Project number 200201 and National Higher Education In novation with the Project number 2005 198 in Sichuan province The authors specially thank National Instruments for offering many possibilities to get support for application of software technical support
13. ments intelligent instru ments and have now reached the stage of the virtual instru ment VI 1 VI is the result of the close combination of modern electronics transducers instrumentation and com puter techniques The hardware of the VI exploits the capac ity of the transducer signal condition circuit and computer resources and so forth Under given hardware conditions the software is the VI s key component Given different soft wares the VI can transform into different instruments We might say the software is the instrument 2 LabVIEW is a graphical programming language developed by National In struments and it has great power and utility It is possible for amateur programmers to design programs of high qual ity by using LabVIEW and it suits the thinking methods of scientists and engineers so that it can be honored with the name of engineering language Nowadays it has wide appli cation in the fields of aerospace communications automo bile engineering biomedicine and so forth However to our knowledge 3 it has not yet been reported on frequently in the field of chemistry Temperature and pressure are two very important pa rameters in many fields of research including chemistry Especially in chemical thermodynamics and the chemical industry we can acquire vital information and guide pro duction by measuring temperatures and pressures Some important physical chemistry parameters such as enthalpy entropy
14. ng in amplifying times and reference voltage 2 2 Serial port method Serial port communication is a common method of com munication between computers or between computers and peripheral devices This method has the advantage of gen eralized use but the speed of data transfer is rather lower so it suits a measurement system that does not demand a high data transfer speed There are very few testing systems in chemistry experiments requiring high frequency signals so using the serial port method to acquire data is not only making the best of laboratory resources but also using tradi tional instruments to upgrade intelligent instruments Wen Bin Wang et al r data acquisition value change f a E E I 1024 ToT ee ely temperature i Ar Te x 7 T T b i EH pt a EE y 2 793751 x Pea g 11198 91 Sesen ee hi a N ast E FEE 297038 3 a Cee eee O eq Tem Temperature difference Temperature difference DBU A bSGL Figure 4 DAQ program of serial communication According to communicating protocol we can acquire the experiential data by using correlation functions in LabVIEW 3 6 Figure 4 shows a DAQ program of serial communication using the digital temperature measuring in strument for determining molar mass with freezing point de pression According to the communicating protocol by which data is sent invoke the VISA node in LabVIEW to obtain ini tialization of t
15. rd chem ical instruments and corresponding data processing mod ules according to the actual condition in the laboratory and the concrete requirements of the experiment thus the sys tem of chemical testing VIs can be constructed easily and quickly For example with the combination of VIs for draw ing a binary metal diagram if we take the measurements by the PCI DAQ method we should select Pt100 tempera ture sensor temperature signal condition circuit DAQ card in hardware select data acquisition VI data redisplaying VI abnormal point removed VI find out turning points VI find out eutectic point VI draw phase diagram VI in software If we take the measurements with standard instruments we should substitute a digital temperature measuring instru ment with serial ports in place of the hardware Nothing needs to be changed except the data acquisition VI in soft ware It is similar to other experimental testing systems The VI can be used in extensive applications because of its flex ibility It can be used in numerous experimental systems such as determining temperature and temperature difference of fusible heat burning heat determining the pressure and pressure difference of pure liquid saturated steam pressure the disposed pressure of solid This system solves the problem of communication be tween the sensors or between standard instruments and the computer which are unfamiliar for most chemical work ers and the common prob
16. uage respectively Select an appropriate terminal pattern for the sub VI by right clicking the connec tor pane There are 36 kinds of patterns to select or edit by increasing or decreasing terminals 7 For example the sub VI for fitting curve has three input and two output terminals which are connected to an array of fitting coefficient control digital precision control model of fitting control and an ex pression of equation indicator for f x y f x respec tively When LabVIEW calls a sub VI ordinarily the sub VI runs without displaying its front panel But some sub VIs need to display their front panels when called and to close their front panels after being called such as the sub VI for re displaying data There are two ways to set its properties The first way is to select VI properties select window appearance Journal of Automated Methods and Management in Chemistry Figure 8 Program for curve fitting and obtaining equation automatically 6 TABLE 1 Measurement results Sample Ignition E Sample may aea AT K Qv kJ mol Benzene 0 447 4 0 0152 1 182 3238 7 Cyclohexane 0 384 7 0 0117 1 151 3950 6 Cyclohexene 0 432 2 0 0132 1 202 3612 5 from the category pull down menu click the customize icon and set its dialog box The second way is to right click the sub VI icon and select sub VI node setup from the shortcut menu The first way requires every instance of the sub VI to display its front panel when called but t
17. ub VI for different chemical VIs to use During the design program based on LabVIEW the sub VI is a key element to modularize and layer the modular program and it corre sponds to function or subprogram in text based program ing languages User can call each VI as a sub VI 7 and the number of sub VIs is limitless Moreover a sub VI can be the subroutine itself By using a sub VI during the development of a program we can save code reduce developing time and raise efficiency It is also easy to debug and manage 3 2 1 Sub VI for redisplaying data To check or compare with acquired data expediently the au thor designed a data redisplaying icon on every subpanel Figure 7 a is a picture of a data redisplaying sub VI panel Clicking the redisplay icon a dialog box will allow user to select a file to read User can redisplay acquired data sev eral times until he clicks the exit icon Values of the x y axes are shown in the region of the cursor The curve setting icon is used to set the curve s type color and thickness and enlarge some segment of the curve The print icon is used to print the curve on the panel Figure 7 b is a program for a data redisplaying sub VI There are two case structures in the whole loop the uppercase structure is used to read an acquired data file and send the data to waveform graph for display and the lowercase structure is used to print the curve Wen Bin Wang et al 4 a h 5
Download Pdf Manuals
Related Search