Design And Implementation Of A Low Cost Daq.pdf

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Procedia Engineering 32 (2012) 614 – 620

I-SEEC2011

Design and Implementation of a Low Cost DAQ System for Thermoelectric Property Measurements T. Sumphaoa , C. Thanachayanontb, T. Seetawana* a

Thermoelectrics Research Center Faculty of Science and Technology Sakhon Nakhon Rajabhat University 680 Nittayo Rd., Sakhon Nakhon, 47000 Thailand b National Metal and Materials Technology Center,144 Thailand Science Park,Phaholyothin Rd.,Klong 1,Klong Luang,Pathumthani,12120,Thailand Elsevier use only: Received 30 September 2011; Revised 10 November 2011; Accepted 25 November 2011.

Abstract The research proposed the design and implementation USB data acquisition system (DAQ) for measurement Seebeck coefficient. This system consists of microcontroller PIC18F4550 and high- resolution analog to digital converter (A/D) MCP3553, voltage reference LM4140 and the “Microchip USB Device Firmware Framework”. The PC software develops in Delphi visual programming. The system was used to measure bulk Ca3Co4O9 thermoelectric material and the performance was satisfied.

© 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of I-SEEC2011 Open access under CC BY-NC-ND license. Keywords: Thermoelectrics measureme; Thermoelectrics properties; USB DAQ; PIC18F4550;MCP3553

1. Introduction Data acquisition (DAQ) is the process by which physical phenomena from the real world are transformed into electrical signals that are measured and converted into a digital format for processing, analysis, and storage by a computer [1], normally consist of three element; acquisition hardware and input storage. The advancement in electronic and Integrated Circuits (IC) technology has spawned a new platform in the DAQ system, microcontroller based DAQ is vary popular previous and still being used because of it low-cost. Investigation on thermoelectricity of solid are needed accuracy precision DAQ instrument. Commercially instrument is high cost and maintenance so we propose this system for low-

* Corresponding author. Tel.: +664-297-0295; fax: +664-297-0295. E-mail address: [email protected].

1877-7058 © 2012 Published by Elsevier Ltd. Open access under CC BY-NC-ND license. doi:10.1016/j.proeng.2012.01.1317

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cost and easy measuring. In this work the system is tested by bulk thermoelectric Ca3Co4O9 material and the result is compared with literature data. 2. System overview The system contains three main part, Part (I) sample setup , part (II) DAQ board, part (III) computer PC as shown in Fig. 1 The voltage obtained form both thermocouple Chromel-Chromel materials and the Alumel-Alumel materials wires are used to calculated Seebeck coefficient [2] by equation,

Ss

U1 ( SChromel  S Alumel )  SChromel U 2  U1

(3)

where U 1 , U 2 , S s , SChromel , S Alumel are voltage of Chromel, voltage of Alumel, Seebeck coefficient of the sample, Seebeck coefficient of Chromel and Alumel material [3], respectively.

Top Heater Sample

USB PC Computer

Sample setup

DAQ board Fig. 1. System overview

Fig. 2. A/D Circuits

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Fig. 3. Microcontroller circuits

4. DAQ Circuits The MCP3553 is a low power integrating device which provides the user with high accuracy,low noise, SPI interface and economical ,the Delta-sigma integrating 22 bit A/D converter which can make 60 conversions per second [4]. It is used to convert the voltage of thermocouple into digital values. PIC18F4550 is USB microcontroller from Microchip Company. It has SPI serial interface and example software for USB emulation. LM4140 provides high precision low noise voltage reference. Fig. 2 shows analog to digital converter circuits diagram and Fig. 3 shows USB microcontroller circuits diagram. 5. Software “Microchip USB Device Firmware Framework” and PC driver “mpusb.dll” Two type of software needed in this system, one for the microcontroller and another for PC. Microcontroller used “Microchip USB Device Firmware Framework” supported by Microchip Company, it is a set of modular firmware(C language) interfaces that handle most of the work for implementing USB communications, also provides dynamic link library “mpusbapi.dll” to access USB device by any programming languages. User can adding or modifying program in the “ProcessIO” subroutine of modular firmware. The “UserInit” subroutine used for initialize “TIMERCOUNTER1” working in interrupt Mode and the other initializations parameter. Fig. 4 shows Listing of “User.c”. The operation, line 26 for checking conversion and then if the conversion is complete the six byte of data has sent to transmit buffer (line 44).

T. Sumphao et al. / Procedia Engineering 32 (2012) 614 – 620

Fig. 4. program listing “ProcessIO” subroutine





Fig. 5. PC Flow chart

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PC software develops in Delphi visual programming to collects data form DAQ board by pooling every 100 mS. with multi-threaded applications.It contains a few componet, “Memo” and three “Button” To communication with MPUSBAPI.DLL interface “UsbAPI.Pas” is needed.In Line 7-10 loop read 20 time for A/D(1) and then it was average by Line 16 and recorded to “Memo2”.

Fig.6. Program listing Procedure “mainloopClick” and “TTstrd.Execute”



Fig. 7. Program listing Procedure “read3551Click”

T. Sumphao et al. / Procedia Engineering 32 (2012) 614 – 620

The procedure “TMainForm.read3551Click” contains Line 35-42 for checking communication, Line 44-49 receive and convert nibble byte to integer data, Line 50-62 checking and convert negative number An example screen shot for software can be seen in Fig.8.The operation is started by pressing “Run” button then the 20 sequence data of the left “Memo” are average to one data of the right “Memo”.

Fig. 8. GUI PC software

6. Results Bulk thermoelectric Ca3Co4O9 are cut in dimension in 5×5×15 mm3 and mount on sample holder. The experiment started by recording voltage of the two thermocouple probes and heat up top heater of the sample until differential temperature was around 5 K. . -1.2

Thermocouple Voltage U1,U2(mV)

-1.1 -1.0 -0.9

U2

-0.8

U1

-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0

5

10

15

20

25

30

35

Time(sec) Fig. 9. Thermocouple voltage

40

45

50

55

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Fig. 10. Seebeck coefficient of Ca3Co4O9 at room temperature

Characteristic of voltage U1 and U2 are presented in Fig. 9. These characteristics show measured voltages as a function of heating time for two different temperatures . In Fig.10 shows The Seebeck coefficient is calculated by equation (1). For calibration of the designed and realized system, the voltage before start-up heater is adjusted to zero. 7. Conclusion A DAQ system for measurement Seebeck coefficient was implemented using cost-effective resource. Commercially integrate circuit(IC) MCP3353 P18F4550 LM4140 was employed for the hardware. For the software “Microchip device Framework” was used for USB Device emulation. The two A/D work on continuous conversion mode and use the same time conversion. The two A/D work on continuous conversion mode and simultaneously made conversions. Average value reading of 20 times is reliable data. Offset voltage error was eliminated before the evaluated the Seebeck coefficient result of 140.20ȝV/K was obtained; the coefficient is corresponding well with literature data of 120 ȝV/K [5] at 300 K. Reference [1] John Park, Steve Mackay. Practical Data Acquisition for Instrumentation and Control Systems. British: Newnes An imprint of Elsevier; 2003, p.1. [2] D. Platzek, G. Karpinski, C.Stiewe, P. Ziolkowski, C. Drasar and E. Muller, Potential-Seebeck- Microprob (PSM): Measuring the Spatial Resolution of the Seebeck Coefficient and Electric Potential, International Conference on Thermoelectric; 2005. [3] Robin E. Bentley, Theory and practice of thermoelectric Handbook of Temperature Measurement. Vol. 3, Singapore: Springer; 1998, p.31. [4] Craig L. King, Designed with the MCP3551 Delta-Sigma ADC, Application Note AN1007 DS01007A Microchip Technology Inc. 2005. [5] Wang Y, Sui Y, Cheng J, Wang X, Su W. Comparison of the high temperature thermoelectric properties for Ag-doped and Ag-added Ca3Co4O9. J. Alloys Compd. 2009;477:817–821.