Research Article The Design of a Chemical Virtual Instrument Based on LabVIEW for Determining Temperatures and Pressures

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1 Automated Methods and Management n Chemstry Volume 7, Artcle ID 68143, 7 pages do:1.1155/7/68143 Research Artcle The Desgn of a Chemcal Vrtual Instrument Based on LabVIEW for Determnng Temperatures and Pressures Wen-Bn Wang, Jang-Yuan L, and Q-Jun Wu Department of Chemstry, College of Chemstry and Chemcal Engneerng, Chna West Normal Unversty, Nanchong 637, Schuan, Chna Receved 16 December 6; Accepted February 7 A LabVIEW-based self-constructed chemcal vrtual nstrument (VI) has been developed for determnng temperatures and pressures. It can be put together easly and quckly by selectng hardware modules, such as the PCI-DAQ card or seral port method, dfferent knds of sensors, sgnal-condtonng crcuts or fnshed chemcal nstruments, and software modules such as data acquston, savng, proceedng. The VI system provdes ndvdual and etremely fleble solutons for automatc measurements n physcal chemstry research. Copyrght 7 Wen-Bn Wang et al. Ths s an open access artcle dstrbuted under the Creatve Commons Attrbuton Lcense, whch permts unrestrcted use, dstrbuton, and reproducton n any medum, provded the orgnal work s properly cted. 1. INTRODUCTION Measurng nstruments have gone through several stages n ther development: analog meter, dscrete component parts (DCP) nstruments, dgtal nstruments, ntellgent nstruments, and have now reached the stage of the vrtual nstrument (VI) [1]. VI s the result of the close combnaton of modern electroncs, transducers, nstrumentaton, and computer technques. The hardware of the VI eplots the capacty of the transducer, sgnal condton crcut, and computer resources, and so forth. Under gven hardware condtons, the software s the VI s key component. Gven dfferent softwares, the VI can transform nto dfferent nstruments. We mght say the software s the nstrument []. LabVIEW s a graphcal programmng language developed by Natonal Instruments and t has great power and utlty. It s possble for amateur programmers to desgn programs of hgh qualty by usng LabVIEW, and t suts the thnkng methods of scentsts and engneers so that t can be honored wth the name of engneerng language. Nowadays, t has wde applcaton n the felds of aerospace, communcatons, automoble engneerng, bomedcne, and so forth. However, to our knowledge [3], t has not yet been reported on frequently n the feld of chemstry. Temperature and pressure are two very mportant parameters n many felds of research, ncludng chemstry. Especally n chemcal thermodynamcs and the chemcal ndustry, we can acqure vtal nformaton and gude producton by measurng temperatures and pressures. Some mportant physcal chemstry parameters, such as enthalpy, entropy, reacton rate, molar mass, can be obtaned by measurng the change of the two parameters. However, owng to the specal features of chemstry, these physcal parameters cannot be obtaned drectly from the epermental values of temperature and pressure. In general, these epermental values must be processed at a deeper level accordng to the prncples or laws of chemstry, such as convertng by formula, plottng, fndng equatons that obey specfed laws. In many stuatons, the value of temperature and pressure can ndcate to the researcher whether the reacton s n process. Obvously, a normal nstrument has dffcultes n achevng that effect. Moreover, when usng a standard nstrument, the researcher has to process data by hand. Ths not only wastes tme, but also easly causes human measurement error. In ths paper, LabVIEW 7. Epress-based VI for determnng temperatures and pressures s developed by usng temperature and pressure sensors, a sgnal-condtonng crcut, a DAQ card, or standard chemcal nstrument. Ths VI s able to complete the measurement of a system s temperature and pressure automatcally and obtan results duly. The results are satsfactory.. THE CONFIGURATION OF THE VI SYSTEM The confguraton chart for the VI system s n Fgure 1. The sgnals of chemcal reacton are analog sgnals converted by sensors, such as temperature, temperature dfference, pressure, pressure dfference. The analog sgnals are

2 Automated Methods and Management n Chemstry The system of chemstry reacton Temperature Temperature dfference Pressure Pressure dfference Sensors Sgnalcondtonng crcut Standard chemcal nstruments wth seral port DAQ card Seral port Computer LabVIEW platform Fgure 1: Confguraton for VI system. IC R 1 3.K R 3 1 Ω 15 V R 3.K R t Pt1 LM339 9V R R 7 4 A K AD6 4 5 W 1 9 V 5K C.1 μ R 5 11 K C 3. μ C μ R 6 K A LM741 7 R 7 K W 1 K 6 Out 15 V Fgure : Sgnal-condtonng crcut of temperature. converted nto dgtal sgnals n the DAQ card or by standard chemcal nstruments and are sent to a computer. Fnally, the dgtal sgnals are processed on the LabVIEW platform..1. PCI-DAQ card method The PCI-DAQ card method was the earlest method used n the constructon of the VI. The method utlzes a DAQ card to convert analog sgnals to dgtal sgnals, so that a computer can process the varous analog sgnals. It provded a way of constructng the VI by usng the computer s bus, nput devces, output devces, software, and so on. It s stll popular ntheworldofmeasurementandcontrolonaccountofts wde use and applcablty for use n varous laboratores and teachng sectors. The analog sgnals from normal sensors are very weak, so they must be preprocessed before enterng the DAQ card by methods such as mpedance converson, amplfcaton. The sgnal-condton crcut of a temperature sensor made by the author s shown n Fgure. ADCbrdgesmadeupofa temperature sensor, Pt1, and three mpedances, and sends converted DC sgnals, caused by the change of temperature sgnals, to the nstrument amplfer AD6 for amplfcaton. The brdge power source comes from 1.5 ma constant current produced by the operatonal amplfer. AD6 s a monolthc nstrumentaton amplfer based on a modfcaton of the classc three-op-amp approach. Monolthc constructon and laser wafer trmmng allow the tght matchng and trackng of crcut components, thus ensurng the hgh level of performance nherent n ths crcut [4]. The LM399, n Fgure, s a precson, temperature-stablzed monolthc offerng hgh-qualty reference voltage to the ffth pn of AD6. The amplfed sgnals are sent to a second-order flter crcut va the sth pn of AD6, and then are sent to a channel of a multfuncton DAQ card, PCI-5, to convert analog sgnals to dgtal sgnals. PCI-5 s made by Bejng Art Corp. and t has 16 bts, 16SE/8DI, ±1 V nput range, connects to computer wth PCI bus, and the drver can operate t by callng LabVIEW s functon [5]. Fgure 3 shows the program of the PCI-5 drver realzaton and dual-channel DAQs, whch s used to determne the constant of the reactve rate by the decomposton of perode. In order to realze the PCI-DAQ drver, we use call lbrary functon (CLF) node n LabVIEW, mplement A/D converters for correspondng temperature and pressure, at the same tme, save tet fle n a tet model. The other sensors sgnal-condton crcuts are smlar to the temperature crcut, the only dfference lyng n amplfyng tmes and reference voltage... Seral port method Seral port communcaton s a common method of communcaton between computers or between computers and perpheral devces. Ths method has the advantage of generalzed use, but the speed of data transfer s rather lower, so t suts a measurement system that does not demand a hgh data transfer speed. There are very few testng systems n chemstry eperments requrng hgh-frequency sgnals, so usng the seral port method to acqure data s not only makng the best of laboratory resources, but also usng tradtonal nstruments to upgrade ntellgent nstruments.

3 Wen-Bn Wang et al. 3 [] data acquston : value change 14 Read devce proad not empty I3 U3 U3 U3 I3 I I3 I3 14 y = ; y = ;.3518 y 3[...6] Lvely temperature y Data savng C Lvely pressure True E:\data Pressure data Tem. data Tme Tme 1 Fgure 3: Program of PCI-5 drver and dual-channel DAQ realzaton. VISA C Error out Sample =! False I/O 1 8 VISA seral VISA CLR 14 VISA R [U8] Epermenter 1/89 1 : 1 Tme nterval U16 1 Et SGL 55 Tme , default Temperature dfference [SGL] Data loggng Temperature Tem. dff. Tem. True Fgure 4: DAQ program of seral communcaton. Accordng to communcatng protocol, we can acqure the eperental data by usng correlaton functons n LabVIEW [3, 6]. Fgure 4 shows a DAQ program of seral communcaton usng the dgtal temperature-measurng nstrument for determnng molar mass wth freezng pont depresson. Accordng to the communcatng protocol by whch data s sent, nvoke the VISA node n LabVIEW to obtan ntalzaton of the seral port, VISA Read, and VISA Close, and so forth, then programe for data acquston, dsplay, savng, and so forth. 3. DESIGN OF PROGRAM FOR VIRTUAL INSTRUMENT 3.1. Desgn for control panel The control panel of the vrtual nstrument s an nterface between user and computer. Besdes frendly nterface and easy control, the correspondng test functon can be started up by a smple manpulaton. It should also be able to fnsh user s task successfully. Software s a key secton of the VI. Gven dfferent softwares, the VI can have dfferent functons. The author desgns the program by the module method for convenence n development and call. Fgure 5(a) shows the VI control panel where four physcal chemstry eperments are dsplayed. The program s desgned by selectng dfferent events and a correspondng VI panel wll open and enter the chemcal testng system as long as we clck the correspondng con, for nstance, by clckng the molecular weght con, the panel wll show as n Fgure 6. The program provdes a helpng functon n that the user can get help by lghtng the help con or keepng the cursor on a few seconds, when some helpng tetual materal wll dsplay to descrbe the functon of the modules and gve the user some

4 4 Automated Methods and Management n Chemstry Type [] drawng the bnary metal da. False Select method Value 1 Drawng the bnary metal dagram wth DAQ method.vi Help Select method (a) (b) Fgure 5: (a) Operaton panel of the VI and (b) program for operaton panel. Fgure 6: Front panel for determnng molar mass wth freezng pont depresson. nformaton about the eperment. It s possble to select the method of acquston, DAQ card or seral port, va select con. The et con s used to et from the VI testng system safely. Fgure 5(b) s the block program of the VI, whle a loop s used to ensure that the program wll check contnuously. Some sub VIs that were prevously made and ran well can be called up by selectng the event. Ths programng method s convenent for etenson and modfcaton. 3.. Desgn of program for publc sub-vi There are dfferent tasks and data processng methods n dfferent chemcal testng systems, but the basc procedures, data acquston, data flterng, curve fttng, real-tme dsplayng, calculatng, and generatng the report of results are the same. Therefore, one program can be made as a shared sub-vi for dfferent chemcal VIs to use. Durng the desgn program based on LabVIEW, the sub-vi s a key element to modularze and layer the modular program and t corresponds to functon or subprogram n tet-based programng languages. User can call each VI as a sub-vi [7], and the number of sub-vis s lmtless. Moreover, a sub-vi can be the subroutne tself. By usng a sub-vi durng the development of a program, we can save code, reduce developng tme, and rase effcency. It s also easy to debug and manage Sub-VI for redsplayng data To check or compare wth acqured data epedently, the author desgned a data-redsplayng con on every subpanel. Fgure7(a) s a pcture of a data-redsplayng sub-vi panel. Clckng the redsplay con, a dalog bo wll allow user to select a fle to read. User can redsplay acqured data several tmes untl he clcks the et con. Values of the -, y- aes are shown n the regon of the cursor. The curve settng con s used to set the curve s type, color, and thckness, and enlarge some segment of the curve. The prnt con s used to prnt the curve on the panel. Fgure 7(b) s a program for a data-redsplayng sub-vi. There are two case structures n the whole loop, the uppercase structure s used to read an acqured data fle and send the data to waveform graph for dsplay, and the lowercase structure s used to prnt the curve

5 Wen-Bn Wang et al. 5 True Redsplay temperature dfference 1.3 N TXT Redsplay 1 Et Prnt True Redsplay temperature dfference Wave form graph (a) (b) Fgure 7: (a) Panel of sub-vi for redsplayng and (b) program of sub-vi for redsplayng. on the panel. The mechancal natures of both cons are set as Latch When Pressed, and both default values are false. To avod mstakes n readng a data fle, the format of the storage fle should be unfed Sub-VI for fttng curve automatcally In a general way, the testng system of the chemcal VI s able to acqure plentful data at tremendous speed, but the whole data s dscrete. Durng data processng, we sometmes need to ft dscrete data to a curve, obtan ts equaton, and get ntersecton ponts of some curves, for eample, we need to get the ntersecton ponts of some curves n drawng the bnary metal dagram and determnng molar mass wth freezng pont depresson and we need the curve equaton n measurng the surface tenson of a soluton. There s no functon to obtan an equaton drectly, so we have to program t by ourselves va callng correlated functons n LabVIEW. The program for curve fttng and obtanng equatons automatcally s shown n Fgure 8. The testng data s automatcally ftted, respectvely, n gven fttng models, and the mean square errors (MSEs) of fttng effects are sent to an array, then accordng to the least MSE, computer confrms the best fttng model or fttng order. The fttng models are lnear fttng, eponental fttng, and general polynomal fttng, whch are found n functons Mathematcs Fttng, and the comparng array elements are acheved dependng on Array Ma & Mn functon. When makng a curve fttng n case structure the correspondng fttng result dsplays nstantly. The program sets a sub-vi of wrtng equaton agan, whch has a functon for convertng the best coeffcents to strngs, and wrte epressons f ()andy = f (), whch have dfferent functons n dfferent condtons, for eample we must use the form f () n the functon Eval y = f ().VI or Integraton.VI. If we use the form y = f ()[8], the program cannot run. However we have to gve the form y = f (), when we wrte the equaton. Now we can solve the problem by connectng the rght output termnals n dfferent crcumstances. Due to the lmtatons of ths paper s length, other common modules such as data acquston, real-tme dynamc dsplay, elmnaton of ecess data, and curve fttng for the constructon of chemcal VIs are not dscussed Property settng for sub-vi node After developng and debuggng the sub-vi, we can create a property node and call t up as a module when we need. Every sub-vi has a connector pane, and every connector pane has several termnals. The programmer smply connects the controls or ndcators wth termnals but need not worry about the nternal structure of the sub-vi. In a sense, nput and output termnals correspond to formal parameter and actual parameter n C language, respectvely. Select an approprate termnal pattern for the sub-vi by rght clckng the connector pane. There are 36 knds of patterns to select or edt by ncreasng or decreasng termnals [7]. For eample, the sub- VI for fttng curve has three nput and two output termnals, whch areconnectedtoanarray offttng coeffcent control, dgtal precson control, model of fttng control, and an epresson of equaton ndcator for f (), y = f (), respectvely. When LabVIEW calls a sub-vi, ordnarly the sub-vi runs wthout dsplayng ts front panel. But some sub-vis need to dsplay ther front panels when called and to close ther front panels after beng called, such as the sub-vi for redsplayng data. There are two ways to set ts propertes. The frst way s to select VI propertes, select wndow appearance

6 6 Automated Methods and Management n Chemstry [] y 1 [] 3 False N Precson I3 Wrtng equaton f () y = f () Best ft [] Ftted data I3 Raw data Fgure 8: Program for curve fttng and obtanng equaton automatcally. Sample Table 1: Measurement results. Sample qualty (g) Ignton wre (g) ΔT/K Qv/kJ mol 1 Benzene Cycloheane Cycloheene from the category pull-down menu, clck the customze con, and set ts dalog bo. The second way s to rght clck the sub-vi con and select sub-vi node setup from the shortcut menu. The frst way requres every nstance of the sub-vi to dsplay ts front panel when called, but the second way smply dsplays ts front panel when called. 4. APPLIED EXAMPLES The author carred out correspondng test eperments n turn, wth data acquston, real-tme dsplay, data processng, generatng the report of result whch can all be completed automatcally gvng satsfactory results [3, 6]. The data processng module of the system, set on a dfferent msson, can fulfll the correspondng testng assgnment. For eample, we add a data processng module of heat of combuston n the system, and can apply t to measurng the materal combuston heat. The results are shown as Table 1. Ther relatve measurement errors are all less than 4%, a satsfactory result. 5. CONCLUSION The author desgned VIs for measurng temperature and pressure based on LabVIEW. These nstruments were composed of four representatve physcal chemstry eperments: drawng a bnary metal dagram, determnng molar mass wth freezng pont depresson, determnng the constant of the reactve rate n the decomposton of perode, and measurng the surface tenson of a soluton by the pressure of froth. These eperments can determne the temperature, temperature dfference, pressure, and pressure dfference of the system, respectvely. In these eperments, we can take the measurements by the PCI-DAQ method or standard chemcal nstruments seral port method. A manpulator can combne the sensors, sgnal-condton crcut or standard chemcal nstruments and correspondng data processng modules, accordng to the actual condton n the laboratory and the concrete requrements of the eperment, thus the system of chemcal testng VIs can be constructed easly and quckly. For eample, wth the combnaton of VIs for drawng a bnary metal dagram, f we take the measurements by the PCI-DAQ method, we should select Pt1 temperature sensor, temperature sgnal-condton crcut, DAQ card n hardware, select data acquston.vi, data redsplayng.vi, abnormal pont removed.vi, fnd out turnng ponts.vi, fnd out eutectc pont.vi, draw phase dagram.vi n software. If we take the measurements wth standard nstruments, we should substtute a dgtal temperature-measurng nstrument wth seral ports n place of the hardware. Nothng needs to be changed ecept the data acquston.vi n software. It s smlar to other epermental testng systems. The VI can be used n etensve applcatons because of ts fleblty. It can be used n numerous epermental systems, such as determnng temperature and temperature dfference of fusble heat, burnng heat, determnng the pressure and pressure dfference of pure lqud saturated steam pressure, the dsposed pressure of sold. Ths system solves the problem of communcaton between the sensors or between standard nstruments and the computer, whch are unfamlar for most chemcal workers, and the common problems for desgnng chemcal VI to measure temperature, temperature dfference, pressure, and pressure dfference. When the user needs to test the temperature and pressure whch are beyond ths system, then he can compose a new measurng system to meet the requrements of the new testng by transferrng the functon desgned modules and combnng them, thus avodng a waste of manpower and materal resources. Ths means that developers can desgn customzed measurng nstruments accordng to ther own requrements. Eplotng VIs based on Lab- VIEW has many advantages, such as a user-frendly workng panel, ease of manpulaton, comple data processng, drawng and prntng the result at the clck of the mouse. Moreover, usng the applcaton bulder tools that belong to Lab- VIEW tself to create standalone applcatons and nstallers or shared lbrares (DLLs) for VIs, the user can run and etend ndependently from the LabVIEW development envronment. Altogether, ths system has very great practcal applcaton value.

7 Wen-Bn Wang et al. 7 ACKNOWLEDGMENTS The authors are fnancally supported by the Key Research Applcaton of Chna West Normal Unversty wth the Project number 1, and Natonal Hgher-Educaton Innovaton wth the Project number [5]198 n Schuan provnce. The authors specally thank Natonal Instruments for offerng many possbltes to get support for applcaton of software, techncal support, customer meetngs, and tranng. REFERENCES [1] J.H.Lu,Z.R.Shen,andF.T.Guo,Modern Test Technology and System Integraton, Publshng House of Electroncs Industry, Bejng, Chna, 5. [] Q. Z. Zhou, Z. H. Qan, and P. P. Lu, VI and Program Desgn of LabVIEW TM 7Epress, Buaapress, Bejng, Chna, 4. [3] J.-Y. L, W.-B. Wang, Y. W. L, Z. R. Lu, and D. C. Ca, LabVIEW TM 7 epress-based vrtual nstrument for drawng bnary phase dagrams, Computer and Appled Chemstry, vol., no. 8, pp , 5. [4] M. Y. Cao, X. Wang, and N. L. Sun, Instrumentaton amplfer AD6 and ts applcaton, Electrcal Measurement & Instrumentaton, vol. 37, no. 418, pp. 49 5,. [5] H. T. Xong, Three methods for drvng data acquston card n LabVIEW, Electrcal Measurement & Instrumentaton, vol. 38, no. 48, pp , 1. [6] J.-Y. L, W.-B. Wang, and Y. W. L, LabVIEW TM 7 epress-based vrtual nstrument for measurng the surface tensons of soluton, Computer and Appled Chemstry, vol., no. 11, pp , 5. [7] LabVIEW TM 7EpressUserManual, Natonal Instrument, 3. [8] L. P. Yang, H. T. L, and Y. Zhao, Advanced Program Desgn of LabVIEW, Tsnghua Unversty Press, Bejng, Chna, 3.

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