Computer Interface of F18 High Precision AC

PERFIK-2014 Abd Rahman Bin Tamuri

Computer Interface of F18 High Precision AC Thermometry Bridge Abd Rahman Tamuri1*, Hafidzah Othman2 and Nurulaini Ali2 1

Physics Department, Faculty of Science, UTM JB, 81310, Johor Bharu, Johor,

2

Resistance Thermometry Laboratory, Thermophysical Section, National Metrology Laboratory, SIRIM Bhd. Sepang Tel: +075534064; Fax: +065566162; E-mail: [email protected]

Abstract. The F18 high precision AC thermometry bridge is used to measure resistance from the ratio of resistance of Standard Platinum Resistance Thermometer (SPRT), and standard resistor, in the range 0 to 1.299,999,9. Any standard resistor in the range 0 to 100 Ohms could be used, making the F18 suitable for most Platinum thermometer types. The F18 performance has been optimized for work with lower resistance, making it an indispensable tool for measuring the higher temperature PRTs. The accuracy which can be achieved in resistance ratio measurement is limited by the accuracy of the precision PRT ratios which, for the F18 is ± 0.1 parts per million (ppm) ratio. The F18 was supplied with an IEEE-488.1 interface. This paper will discuss about the technique of computer interface of F18 via National Instrument USBGPIB-HS and Microsoft Office Excel VBA software. By using this technique, the data from F18 was directly collected and was stored to the computer. As the result, the F18 could measure resistance ratio ( ⁄ ) in the range of up to 9 decimal points and the accuracy of the precision SPRT ratios was increased to ± 0.04 ppm. . Keywords: F18 Thermometry Bridge, computer interface, Excel VBA. PACS: 0084.37.+q

Introduction The International Temperature Scale of 1990 (ITS-90) is based on a series of fixed points. At temperature above 0° C, the freezing point of Indium (In), Tin (Sn), Zinc (Zn), Aluminum (Al), Silver (Ag), Gold (Au) and Copper (Cu) are the defining fixed points of the ITS-90 [1]. Most of the fixed points are the freezing points of specified pure metals. Pure metals melt and freeze at a unique temperatures through a process involving the absorption or liberation of the latent heat of fusion. Primary fixed points play an important role, from the definition of the temperature scale and its dissemination. Under controlled conditions these freezing points are highly reproducible. A metal freezing point is the phase equilibrium between the liquid phase and solid phase of the pure metal at pressure of one standard atmospheric pressure (101, 325 Pa). For measurement purpose, usually an AC Thermometry Bridge is utilized to read the reading from the fixed point cell [2-3]. In this paper, an AC High Precision Bridge, F18 with General Purpose Interface Bus (GPIB) was utilized. A computer interfacing software based on Visual Basic Application (VBA) was developed in order to record and to display the data is reported. Experimental Setup In order to obtain the Zinc freezing plateau, the fixed point of sealed cell were used. The cell containing a pure 99.999% Zinc was placed in the furnace Fluke, Heart Scientific, 9114. This furnace could maintain temperature range from 100 °C to 680 °C. The freezing point of Zinc is 419.527 °C and in order to realize the Zinc freezing point, the temperature of furnace was set to 423.5 °C which is about 5 °C higher than Zinc’s freezing point. After the Zinc has completely melted, the furnace was set at a stable temperature of 1 °C to 1.5 °C higher than the freezing point overnight. The furnace temperature was slowly reduced. A SPRT was inserted into the cell. The Zinc’s temperature will decreases to less than freezing point before recalescense. After recalescence the thermometer was removed from the furnace immediately and a cold fused silica tube was inserted into the fixed point cell for one minute. After that, the SPRT to be calibrated is introduced into the cell while the furnace was kept at a stable temperature of 1 °C below the freezing point. The technique provides a very stable, long freezing plateau that typically last for more than ten hours. The changes in temperature in the first half of the plateau are usually within ± 0.2 mK.


For measurement purpose, a High Precision AC Thermometry Bridge F18 was utilized to record the reading from the fixed point cell. This F18 was supplied with General Purpose Interface Bus (GPIB). The F18 also uses a reference of 100 Ω resistor that was maintained in water bath at a constant 23 °C temperature. The influences of the standard of reference resistor are not included in this paper. All the measurement are reported with self-heating correction by using the current of 1 mA and the √ mA and recorded for 100 reading at each sensing current. In the experiment, the four wire of a Chino, Standard Platinum Resistant Thermometer (SPRT) R800 was connected to the bridge F18. All the components involved in the experiment were calibrated by National Metrology Laboratory, SIRIM Bhd. Figure 1 shows the experimental setup of the Zinc’s freezing plateau realization process.

Chino R800 GPIB-HS National Instrument

Personal Computer

Standard Platinum Resistor Thermometer

F18 Thermometry Bridge Visual Basic Application Software

Fluke 9114 Heart Scientific, Freeze Point Furnace

Figure 1: The experiment setup of Zinc Freezing Plateau Realization Process

Software Configuration A personal computer (PC) is connected to F18 Bridge via USB-GPIB. The Interface software based on Microsoft Visual Basic for Applications (VBA) was developed and install into the PC. This software was designed to record data in Excel and text file. Before this software can be used, the two VBA-GPIB modules need to be installed to the VBA.

Initialization of software and USB-GPIB-HS

Set the configuration of Measurement Type Data Reading and Data Storage Data display FIGURE 2: Algorithms of the measurement Figure 2 shows the algorithms of the developed software. The first step of operation is the initialization of GPIB software interface followed by the setting of measurement types. All the data will be recorded in text file and shows in the display panel. Figure 3 shows the example of interface of F18 software based on VBA. The user could plot a graph directly by using Excel program without turning off the software. This software provides a window that consists of setup configuration, graph plot, display unit and exit button.


Figure 3: The interface of developed VBA software. In order to configure the software, the user can just tick the carrier current required ether 1 mA, 2 mA or √ mA. The user could set the time interval of reading as well as the number of reading. Before this software can be used, the user only require to click one button, “Initialize button”. After initialization of the software, the National Instrument GPIB-HS is now ready to communicate and collect data. To ensure the system record the correct data, the users are advice to stamp date and time when data is collected. Furthermore, the user could save their own files by entering the filename. The display unit is one of the features of the developed software, where the user could monitor the temperature ratio up to 9 decimal points through the display unit and graph. All the data collected are automatically recorded on the active sheet of Microsoft Excel as show in Figure 4.

Figure 4: The layout of data collection during experiment


Results and Discussion This developed VBA software was designed to collect and display the string of codes given by USBGPIB. The string code given by GPIB consists of 13 characters. For recording and displaying purposes, all this string data need to be converted to double type variable. This VBA software could store the data in Microsoft Excel as well as in text file as shown in Figure 5. This software is capable to record and store up to 9 decimal points and ready to be manipulated by computer system.

Figure 5: Example of data collection using VBA F18 Reader Figure 6 show the generated graph from this developed VBA software. This graph is corresponding to the ratio of / with time. The lower part of the graph is representing the temperature ratio due the carrier current of 1 mA and the upper part is representing the ratio of correction factor with √ mA. The standard deviation of distribution for the first part and second part are 4.8015 × 10 and 2.0073 × 10 respectively. In this experiment, the time interval for each data was set 5 second and 100 of data was recorded. By using this developed software, the accuracy measurement of AC Thermometry Bridge, F18 was increased from ±0.1 ppm to ±0.04 ppm.

Zinc Freezing Point Cell (Sealed) 0.677066500 0.677066000

Ratio, RT/Rs

0.677065500 0.677065000 0.677064500 0.677064000 0.677063500 0.677063000 0.677062500 0.677062000 15:50:24

16:04:48

16:19:12

16:33:36

16:48:00

17:02:24

17:16:48

17:31:12

17:45:36

Time Figure 6: The data collected from sealed Zinc Freezing Point at 419.525 °C.


Conclusion As conclusion, this software brings some improvements being user friendly, more efficient and consume less time of measurement. By using computer interfacing technique via National Instrument USB-GPIB and developed VBA software, data from High Precision Thermometry Bridge F18 is directly collected, stored and displayed in the computer. The data is directly written in Microsoft Excel making easy for user to manipulate the data for future analysis. As the result, the capability of Thermometry Bridge, F18 was increased where it could measure resistance ratio ( ⁄ ) in the range of up to 9 decimal points and the accuracy of the precision SPRT ratios was increased to ± 0.04 ppm.

Acknowledgments The authors would like to thank the Universiti Teknologi Malaysia and Government of Malaysia for their financial supported and Industrial Training Scheme as well as the National Metrology Laboratory, SIRIM Bhd. for supporting this project by allowing the of their facilities.

References 1. H. Preston-Thomas, 1990, The International Temperature Scale of 1990 (ITS-90), Metrologia, Vol.37: 3-10 2. C. Yaokulbodee, U. Norranim, & E. Puttiwong, 2008, Realization of Zinc Fixed Point Cell in NIMT, Acto Metrologia Sinica, Vol.29, No. 4A. 3. T. Podgornik, V. Batagelj, G. Winkler, H. Hartl, & J Drnovsek, 2011, Evaluation of a Modified ADC-Based Thermometry Bridge, International Journal of Thermophysics, Vol. 32, Issue 11-12, pp 2409-2419. 4. Thermometry Bridge, F18 Operator’s Handbook, 5. R. Lukaszewski, P. Bobinski & W. Winiecki, Java-Based Distributed IEEE-488 Measuring System,