Dielectric properties of polycarbonate coated natural fabric Grewia tilifolia

2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

Dielectric Properties of Polycarbonate Coated Natural Fabric Grewia tilifolia CH.V.V.Ramana, Williem Clarke

J. Jayaramudu, Rotimi Sadiku

Department of Electrical & Electronics Engineering Science, University of Johannesburg, PO Box 524, Auckland Park Campus, Johannesburg – 2006, South Africa e-mail: [email protected]

Department of Polymer Technology, Tshwane University of Technology, CSIR Campus, Building 14D, Private Bag e-mail: [email protected]

for field carrying conductors [1-5]. The emergence of natural fibers there has also been a growing interest in electrically conductive polymer composites. The electrically conductive composite materials are widely being used in the areas of electrostatic discharge dissipation, electro-magnetic interference shielding and various other electronic applications. Natural fibers are quite cheap compared to synthetic ones. So natural fibers have received a lot of interest for use with thermoplastics, especially for high volume and low cost applications. It may be mentioned here that natural fibers have an inherent polar and hydrophilic nature but thermoplastics have non-polar characteristic properties. These drawbacks are less important when the material is environmentally friendly [6-8]. Polycarbonates are a particular group of thermoplastic polymers. They are easily worked, moulded, and thermoformed; as such, these plastics are very widely used in the modern chemical industry. Their interesting features (temperature resistance, impact resistance and optical properties) position them between commodity plastics and engineering plastics [9]. Dielectric properties, which are the key parameter that governs the flow in the fiber bed, together with the fluid viscosity. Fabrics permeability is especially important in low pressure injection techniques like vacuum infusion where void formation and injection time can be increased dramatically when the permeability decreases. The uses of composites as dielectric are becoming more popular; therefore the dielectric properties of natural fiber reinforced polymer composites are very important. The dielectric properties such as volume resistivity, dielectric constant and dielectric loss of some natural fibers and composites have been studied [10-11]. In the present paper the authors already published characterization, electrical and dielectric properties of Grewia tilifolia and tensile properties of polycarbonate-coated natural fabric Grewia tilifolia [1214]. The purpose of this study is thus to find out the dielectric properties of polycarbonate-coated natural fabric Grewia tilifolia composites and its use in electrical applications.

Abstract - Natural fibers are emerging as low cost, lightweight and apparently environmentally superior alternatives to glass fibers in composites. With the increasing importance of environmental interactions, several innovations of the environmental performance are introduced in automotive industry. One aspect of innovation is an environmental material selection including renewable raw materials. The uses of cellulosic fibers have ranged from the construction industry to the automotive industry. The main attraction of bio-fiber reinforced composites lie in their low density and high strength. Polymer composites of a polycarbonate coated with natural fabric Grewia tilifolia were studied by means of dielectric properties in the frequency range 100 Hz to 1 MHz and temperature interval from 40°C to 160°C. It was found that the dielectric properties are lower for the treated (for both treated and treated with coupling agent) then that of the untreated (for both untreated and untreated with coupling agent) one. The present natural fabric composite has systematic and persistent research there will be good scope and better future for polymer reinforced composite for suitable electrical applications. Keywords: Natural fiber composite, Natural fabric Grewia tilifolia, polycarbonate, dielectric properties, frequency and temperature.

I.

S.S.Ray X025, Lynwood Ridge 0040, Pretoria, South Africa DST/CSIR Nanotechnology Innovation Centre, National Centre for Nano-Structured Materials, CSIR, Pretoria –0001, South Africa

INTRODUCTION

Since the 1990s, natural fiber composites are emerging as realistic alternatives to glass-reinforced composites in many applications. The most interesting aspect about natural fibers is their positive environmental impact. As they come from a natural resource they are completely biodegradable and nonabrasive material and can be easily eliminated after the degradation of the polymer. It provides excellent insulation against heat and noise. The most desirable combination of characteristics such as ease of fabrication, low cost, light weight, and excellent insulation properties have made plastics one of the most desirable materials for electrical applications. The use of plastics in electrical applications was limited to nonload bearing general-purpose applications. Fiber-reinforced plastic materials not only act as effective insulators, but also provide mechanical support

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2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

II. EXPERIMENTAL

III.

A. Materials

RESULTS AND DISCUSSION

The graphical results of dielectric properties (Dielectric constant & Dielectric loss) of polycarbonate-coated natural fabric Grewia tilifolia samples (Untreated, Untreated with coupling agent, Treated and Treated with coupling agent) are presented in Figures from 2 to 4 respectively . The dielectric properties were determined at a frequency range 100 Hz to 1 MHz at variable temperature range of 40°C to 160°C. The graphs are drawn between frequency verses dielectric properties (dielectric constant and dielectric loss) and temperature verses dielectric properties (dielectric constant and dielectric loss). Here we choosen frequency in log values.

The fabric samples were treated with 5% aqueous NaOH solution at room temperature for half an hour to remove the hemicellose and other greasy materials. The fabrics were sprayed with saline coupling agent −1% triethoxymethylsilane in acetone and dried. The fabrics were then coated with 10% polycarbonate solution prepared with dichloromethane as the solvent using a thin layer chromatographic spreader. The average thickness of the coating was found to be 0.15 mm. The coating on the fabric was allowed to dry at room temperature. The above procedure was followed for both untreated and alkali-treated fabrics [14].

A. Dielectric constant

B. Dielectric properties of fiber composites

The dielectric constant of a material depends upon the polarizability of the molecules. The polarizability of nonpolar molecules arises from electronic polarization (in which the application of applied electric field causes a displacement of the electrons relative to the nucleus) and atomic polarization (in which the application of applied electric field causes a displacement of the atomic nuclei relative to one another). In the case of polar molecules a third factor also comes into play which is orientation polarization (in which the application of applied electric field causes an orientation of dipoles). The dielectric constants for polycarbonate coated natural fabric Grewia tilifolia samples for untreated, untreated with coupling agent, treated and treated with coupling agent with respective frequency and temperature are shown in figures 2 to 4 respectively. The decrease in dielectric constant with frequency is due to decrease in orientation polarization at high frequencies. At low frequencies, complete orientation of the molecule is possible while at medium frequencies there is only little time for orientation. Orientation of the molecules is not possible at all at very high frequencies. From figure 2 (a) shows the influence of chemical modifications on polycarbonate coated fabric natural Grewia tilifolia composite on dielectric constant values with respective frequency.

The experimental set-up for the measurement of dielectric properties of polycarbonate coated natural fabric Grewia tilifolia is shown in Figure 1. A commercial digital LCR meter (HIOKI 3532-50 LCR Hi Tester, Koizumi, Japan) was used to measure the dielectric properties (capacitance and dissipation factor (D) [15]. The polycarbonate coated fabric samples were measured as a function of frequency in the range from 100 Hz to 1 MHz, temperature in the range from 40°C to 160°C. The capacitance, resistance and dissipation factor were measured with the sample in the cell.

Figure 1: Experimental set-up for the determination of dielectric properties of polycarbonate coated natural fabric Grewia tilifolia.

The dielectric constant (ε) of the samples are calculated using the formula (1) ε = [CP×d] / [ε0×A] ---- (1) where CP = Parallel capacitance d = Thickness of the sample ε0 = 8.854 × 10-12 F/m A = Area of the Sample

Figure 2: (a) Frequency dependence of dielectric constant at room temperature for polycarbonate coated natural fabric Grewia tilifolia. (b) Frequency dependence of dielectric loss at room temperature for polycarbonate coated natural fabric Grewia tilifolia.

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2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

viscoelastic nature of the polymer creates responses in the material to both mechanical and electric stimuli [16]. The Dielectric loss for polycarbonate coated natural fabric Grewia tilifolia samples for untreated, untreated with coupling agent, treated and treated with coupling agent with respective frequency and temperature are shown in figures 2 (b) and 4 respectively. The figure 2 (b) shows the influence of chemical modifications on polycarbonate coated fabric natural Grewia tilifolia composite on dielectric loss values with respective frequency. Here we can see that dielectric loss decreases with increase in frequency due to decrease in orientation polarization. Another observation is that chemical modification of fibers results in lowering of dielectric loss. This is due to the decrease of orientation polarization of composites containing treated fibers. Chemical treatment results in reduction in interaction between cellulosic fibers and water molecules.

Here also we can see that dielectric constant decreases with increase in frequency due to decrease in orientation polarization. Another observation is that chemical modification of fibers results in lowering of dielectric constant. This is due to the decrease of orientation polarization of composites containing treated fibers. Chemical treatment results in reduction in interaction between cellulosic fibers and water molecules. The resultant decrease of hydrophilicity of the fibres leads to lowering of orientation polarization and subsequently dielectric constant. On analyzing the figures further we can see that dielectric constant of composites containing alkali treated fibers decreases with concentration of alkali. The removal of hemicellulose and lignin, the treatment with NaOH solution promotes the activation of hydroxyl groups of cellulose unit by breaking the hydrogen bond. Alkali treatment results in unlocking of the hydrogen bonds making them more reactive. In the untreated state the cellulosic –OH groups are relatively unreactive as they form strong hydrogen bonds. In addition to this, alkali treatment can lead to fibrillation i.e. breaking down of fibers into smaller ones. All these factors provide a large surface area and give a better mechanical interlocking between the fiber and matrix and thus reduce water absorption. This results in lowering the overall polarity and hydrophilicity of the system. This results in reduction of orientation polarization and consequently dielectric constant of the composites.

The figure 4 shows the influence of chemical modifications on polycarbonate coated fabric natural Grewia tilifolia composite on dielectric loss values with respective temperature. For lower frequencies, the dielectric loss values reached high for some temperature values in untreated and the dielectric loss reached high value for some temperature values in untreated with coupling agent for higher frequencies. Where as in treated, the dissipation factor decreases when temperature increases for lower frequencies and in treated with coupling agent, the dielectric loss nearly constant for entire temperature at higher frequency. The high value of dielectric loss of the composite material due to the presence of water and impurities present in the Grewia tilifolia fiber. The lower value of dielectric loss of the composite material due to the removal of hemicellulose and lignin present in the Grewia tilifolia.

The figure 3 shows the influence of chemical modifications on polycarbonate coated fabric natural Grewia tilifolia composite on dielectric constant values with respective temperature. For lower frequencies, the dielectric constant values reached high when temperature increased in untreated and the dielectric constant reached high value when temperature increased in untreated with coupling agent for higher frequencies. Where as in treated, the dielectric constant decreases when temperature increases for lower frequencies and in treated with coupling agent, the dielectric constant nearly constant for entire temperature at higher frequency. The high value of dielectric constant of the composite material due to the presence of water and impurities present in the Grewia tilifolia fiber. The lower value of dielectric constant of the composite material due to the removal of hemicellulose and lignin present in the Grewia tilifolia. B. Dielectric loss Dielectric loss due to movement or rotation of the atoms or molecules in an alternating electric field. A loss of energy that eventually produces a rise in temperature of a dielectric placed in an alternating electrical field. Dielectric materials have many important functions in the microelectronics industry. Dielectric losses depend on frequency and the dielectric material. New packaging technology requires substrates with low permittivity, interconnections made of high-conductivity metals, high wiring density, and embedded passive circuit elements. The

Figure 3: Temperature dependence of dielectric constant at different frequencies for polycarbonate coated natural fabric Grewia tilifolia.

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2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

REFERENCES [1]. Joseph, S.; Sreekala, M. S.; Oommen, Z.; Koshy, P.; Thomas, S. Compos Sci Technol 2002, 62, 1857. [2]. Li T.; Matuana, L. M. J Appl Polym Sci 2003, 88, 278. [3]. Lundquist, L.; Marque, B.; Hagstrand, P.-O.; Leterrier, Y.; Manson, J. A. E.; Compos Sci Technol 2003, 63, 137. [4]. Eichhorn, S. J.; Baillaie, C. A.; Zafeiropoulos, N.; Mwaikambo, L. Y.; Ansell, M. P.; Dufresne, A.; Kentwistle, P. J.; Herrera- Ffranco, P. J.; Escamilla, G. C.; Groom, J.; Hughes, M.; Hull, C.; Rials, T. G.; Wild, P. M. J Mater Sci 2001, 36, 2107. [5]. Bledzki, A. K.; Gassan, J. Prog Polym Sci 1999, 24, 221. [6]. Anand, R.S., Daniel, F.C., Rodney, E. J. and Roger, M.R., “Renewable Agricultural Fibers as Reinforcing Fillers in Plastics:Mechanical properties of Kenaf Fibers-Polypropylene Composites”, Ind. Eng.Chem. Res., 34: 1889-1896, (1995). [7]. Valadez-Gonzalez, A., Cervantes-Uc, J.M., Olayo, R. and HerreraFranco, P. J., “Chemical modification of Henequen fibers with an organosilane coupling agent”, Composites:part B, 30: 321-331, (1999). [8]. Mohanthy, A.K., Misra, M. and Hinrichsen, G., “Biofibers, Biodegradable Polymers and Biocomposites:An overview”, Macromol. Mater. Eng., 276/277:1-24, (2000). [9]. www.wikipedia.com. This site for polycarbonate. [10]. Paul, A., Joseph, K. and Sabu, T., Compos. Sci. Technol., 67(1997). [11]. Reid, J.D., Lawrence, W.H. and Buck, R.P., J. Appl.Polym Sci., 30: 1771(1986). [12]. J. Jayaramudu, B.R.Guduri and A. Varadarajulu, “Characterization of new natural cellulosic fabric Grewia tilifolia”, Carbohydrate Polymers Journal, 79, 847-851, (2010). [13]. J. Jayaramudu, CH.V.V.Ramana and A. Varadarajulu, “Electrical and Dielectric properties of New natural cellulosic fabric Grewia tilifolia”, Sensors & Transducers Journal, Vol. 113, Issue 2, pp. 167176, February (2010). [14]. J. Jayaramudu, B.R.Guduri and A. Varadarajulu, “Tensile properties of Polycarbonate-coated natural fabric Grewia tilifolia”, Journal of Reinforced Plastics and Composites, Vol. 29, No., 1006-1008, 7/2010. [15]. LCR Meter (HIOKI 3532-50 LCR Hi Tester, Koizumi, Japan) [16]. Chand N, Jain D, Compos part A 36: 594-602, (2005).

Figure 4: Temperature dependence of dielectric loss at different frequencies for polycarbonate coated natural fabric Grewia tilifolia

IV. CONCLUSIONS The dielectric properties were determined at a frequency range 100 Hz to 1 MHz at variable temperature range of 40°C to 160°C. The graphs are drawn between frequency verses dielectric properties (dielectric constant and dielectric loss) and temperature verses dielectric properties (dielectric constant and dielectric loss). The dielectric constant lowering due to decrease of orientation polarization. The dielectric loss was seen to be decreases with increase frequency which indicates that the electrical charges can be retained over a longer period of time. These cost effective composites will therefore good scope and better future for polymer reinforced composite for suitable electrical applications. Natural fiber composites have higher fiber content for equivalent performance, reducing more polluting base polymer content. ACKNOWLEDGMENT CH.VVR and JJR wish to acknowledge the University of Johannesburg and the Tshwane University of Technology, Pretoria for their supports.

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2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

Capacitance Measurement with Integrated Instruments M. Ashok Kumar and B. Rama Murthy

CH. V. V. Ramana and Willem Clarke

Integrated Instruments Lab, Dept of Instrumentation, Sri Krishnadevaraya University, Anantapur – 515 055, Andhra Pradesh, India Email: [email protected]

Department of Electrical & Electronics Engineering Science, University of Johannesburg, PO Box 524, Auckland Park Campus, Johannesburg -2006, Republic of South Africa Email: [email protected]

conditions, such as test frequency, test signal level, DC bias, temperature and other physical and electrical environments (humidity, magnetic fields, light, atmosphere, vibration and time) change the capacitance values. Capacitors are used in radio and TV systems, for example, to tune in signals, in cameras to store the charge that fires the photoflash, on pump and refrigeration motors to increase starting torque, in electric power systems to increase operating efficiency, and so on. Standard commercial impedance analyzers are commonly used for capacitance measurements; in practice their expensiveness and frequency suitableness create some difficulties. In order to overcome these difficulties we aimed to develop a practical and useful instrument by employing integrated instruments, which are commonly available in labs. The present work presents capacitance measurement using an implemented integrated instrumentation system. The integrated instrumentation system integrates instruments with concurrent programming, graphical user interface (GUI), real-time system, objects oriented program and object – oriented technology. This takes full advantage of advanced features of current measuring instruments that operate remotely via interface bus in order to characterize accurately a wide set of passive and active electronic components. These instruments are widely encountered in electronic industry as well as in applied research. The flow of data through the interface bus is completely monitored using developed integrated software. In addition to this, and in order to make the system full featured, a set of graphical based routines under Matlab environment have been implemented. The advent of present study has opened up the new possibilities in the area of instrumentation with high standard integrated instruments. The technique utilizes integrated instruments using the MATLAB as a tool for determination of capacitance. MATLAB program interfaces the instruments through serial port and collects data, the applied and measured voltage at particular frequency, the results are analyzed to get corresponding Capacitance of any capacitance under test. The development system minimized use of compensation, calibration and linearization

Abstract-Capacitance measurement with integrated instruments (function generator & Digital multimeter) has been designed and developed. The unknown capacitance is measured by measuring the voltage across capacitor in RC network. The Digital Synthesis Arbitrary Function Generator/Counter (Protek 9305), and Dual Display Multimeter (Escort 3146A) are used as part of instrumentation. The function generator and digital multimeter instruments are available in all the labs, by integrating these devices a powerful yet cost effective instrumentation can be evolved. This paper describes such an instrument for capacitance measurement. MATLAB program interfaces the instruments through serial port and collects data, the applied and measured voltage at particular frequency, the results are analyzed to get corresponding Capacitance of the any capacitor under test. The present system will be of great use in industrial environments as well as for engineers in the industries and researchers in organizations. Keywords-Capacitance, function generator, multimeter, frequency and MATLAB software.

I.

dual

display

INTRODUCTION

In electronics, communications, computers and power systems, the capacitors are the most common electrical component had been used extensively. For any circuit design, the value of capacitance needs to measure to ensure that the value is exactly equal to the actual value [1]. A capacitor is a circuit component designed to store electrical charge. Capacitance is the electrical property of capacitors: it is a measure of how much charge a capacitor can hold. Capacitor is a passive device, and one, which stores its energy in the form of an electrostatic field producing a potential difference (Static Voltage) across its plates. In its basic form a capacitor consists of two or more parallel conductive (metal) plates that do not touch or are connected but are electrically separated either by air or by some form of insulating material such as paper, mica or ceramic called the Dielectric. Capacitance mainly depends on several

978-1-4577-2149-6/11/$26.00 © 2011 IEEE

K. Venu Madhav Department of Business Information Technology, University of Johannesburg, Auckland Park Bunting Road Campus, Johannesburg, South Africa Email: [email protected]

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2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

techniques in the field of instrumentation and measurement technology. II. PRINCIPLE

Function Generator This is a precise test instrument used to output function signal and FM, AM, FSK, PSK, burst, frequency sweep signals. It is also capable of measuring frequency and counting. The features of Protek 9305 are: Using Direct Digital Synthesis (DDS) Technology, 0.1 mHz to 5 MHz Frequency Range for Main Waveforms, 1mV Output Amplitude for small signal, high resolution of pulse duty rate up to 1/1000, high resolution and accuracy of digital FM, continuous phase adjustment function in Burst Mode, arbitrary setting of start and stop for frequency sweep output, 0.1° resolution of phase adjustment, arbitrary setting of AM Modulation in 1 % to 120 %, more than 30 kinds of output waveform, frequency measurement and counting functions available [2].

The output of the function generator (1Vrms with frequency) is controlled using MATLAB and connected to a RC network in which R is constant and C is unknown. The voltage drop across capacitor is measured using digital multimeter logged in PC through serial port using MATLAB also the applied voltage at particular frequency; the results are analyzed to get corresponding capacitance of any capacitance under test. The output voltage of any unknown sample is calculated using the equations (1) (1) (2)

Multimeter The Escort 3146A Dual Display Multimeter is 5½-digit multimeter with high resolution designed for bench-top, field service and system applications with a high performance/price ratio. The specifications are: a dual, vacuum fluorescent display that allows two properties of input sin a to be displayed at the same time, remote operation via RS-232 interface, up to 120000 counts for different measuring rate, 1µV sensitivity in Vdc measurement, true RMS Vac with 20Hz to 100KHz bandwidth, (Vac + Vdc) RMS and (Aac + Adc) RMS calculated, selectable 2-wire and 4-wire resistance measurements, wide dc and ac current measurement ranges 12mA to 12A, frequency measurements greater than 1 MHz with 0.01Hz best resolution [3].

III. INSTRUMENTATION A. Hardware design The block diagram and the photographs of the experimental setup of capacitance measurement with integrated instruments are shown in Figures 1 and 2 respectively. The integrated system consists of the following functional units

IV. WORKING The instruments (function generator and multimeter) are integrated with personal computer through RS 232 standard interface using MATLAB as a tool to measure capacitance. Resistor (R) and Capacitor (Cx) are connected in series. MATLAB program identifies and initializes the instruments PROTEK and ESCORT through serial port before starting the measurement; the software needs inputs from user (resistor and frequency values) and START command. Protek instrument gets commands from personal computer to generate 1Vrms voltage and frequency 1 KHz. The Escort multimeter gives measured AC voltage across Capacitor under test for standard frequency. RS-232 port of Escort Multimeter works in full duplex mode, which makes the meter more reliable and efficient in data transfer. In the present study we designed MATLAB Graphical User Interface (GUI), which collects the information from function generator (applied voltage and frequency) and from multimeter (voltage across capacitor under test Cx) is shown in Figure 3.

Figure 1: Block diagram of capacitance measurement with integrated instruments.

(1) Digital synthesis arbitrary generator/counter (Protek 9305) (2) Dual display multimeter (Escort 3146A)

function

Figure 2: Photographs of the experimental setup of capacitance measurement with integrated instruments.

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Figure 3: MATLAB GUI for capacitance measurement with integrated instruments.

The user needs to give a standard resistor value and frequency for the measurement. GUI collects data from the integrated instruments (function generator & multimeter), stores and computes capacitance using equations (1) and (2) for any capacitor. V. SOFTWARE

Figure 4: Flowchart for data acquisition program written in MATLAB.

VI. CALIBRATION ¾

The MATLAB [4] high-performance language for technical computing integrates computation, visualization, and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation. Use (MATLAB) External Interfaces to connect MATLAB to programs, devices and data. Application developers use external interfaces to integrate MATLAB functionality with their applications. External interfaces also facilitate data collection, such as from peripheral devices like a function generator or a digital multimeter. The (MATLAB) serial port interface provides direct access to peripheral devices that you connect to your computer's serial port, such as modems, printers, test and measurement and scientific instruments. The complete software is developed in MATLAB. The software includes initialization of serial ports one for each instrument. MATLAB sends commands to Protek function generator (initialize the voltage and frequency) and Escort multimeter (measure the AC voltage across capacitor).

¾ ¾ ¾ ¾ ¾

First select instruments (digital storage oscilloscope (DSO), function generator and multimeter) for error calculation. The function generator is connected directly to digital storage oscilloscope for error corrections. The errors for different ranges are noted and adjusted in software. The multimeter is in parallel with DSO and function generator, to verify the voltage measurement errors. The errors for different ranges are noted and adjusted in software. Choose (resistor and capacitor) values for RC network such a way that it gives exactly half of the input voltage across capacitor to minimize error throughout the frequency range. VII. RESULTS AND DISCUSSION

After making the appropriate adjustments both in hardware and software and also following the calibration procedure, the capacitance measurement with integrated instruments is tested. The results of the system are tabulated in Table 1. The results obtained are compared with the commercial LCR meters [5-7]. The results are in good agreement when compared with other LCR meters.

The flow chart for data acquisition program written in MATLAB is shown in Figure 4.

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2011 International Conference on Recent Advancements in Electrical, Electronics and Control Engineering

S.N o

Capacitanc e (sample)

1

10 pF

2

100 pF

3

1nF

4

10nF

5

100nF

6 7 8

Capacitance Measurement Aplab 4912

YF 150

10.5 pF 104.0 pF 0.91n F 8.9nF

10.4 pF 104.5 pF 0.97nF 10.4nF

LCR HiTEST ER 10.28 pF

REFERENCES

Present System

0.98 nF

10.01 pF 102.87 pF 1.09nF

10.6nF

11nF

103.5 pF

90.3n 102.8n 101.4nF F F 0.95 1μF .95 μF 0.97 μF μF 9.54 10.04 10 μF 9.81 μF μF μF 92.4 101.4 100 μF 97.65 μF μF μF Table 1: Capacitance measurement

[1] [2] [3] [4] [5] [6] [7]

97.52 nF 0.98 μF 9.85 μF 97.71 μF

VIII. CONCLUSION The hardware and software features of a capacitance measurement with integrated instruments are described. The necessary software is developed using MATLAB. The system is quite successful for the measurement of capacitance. The present paper is an attempt for integrated instruments using the MATLAB as a tool for the determination of capacitance. Strong software is provided, to make the system user friendly, and to carry out data analysis. The present system will be of great use in industrial environments as well as for engineers in the industries and researchers in organizations.

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Noremy bin sollahudin, “Multirange capacitance meter” B.E (industrial electronics) dissertation, University of Technical Malaysia, Melaka, May 2008. Digital synthesis arbitrary function generator / counter (Protek 9305) data manual. Dual display multimeter (Escort 3146A) data manual. www.mathworks.com this site for MATLAB. APLAB 4912 LCR instrument, Applied Electronics Ltd., APLAB house, Thane, India. YF-150 Capacitance meter. LCR Meter (HIOKI 3532-50 LCR Hi Tester, Koizumi, Japan)

ISSN: 2277- 7962 International Journal of Computer Application and Engineering Technology Volume 1-Issue2, April, 2012 .pp.41-48 www.ijcaet.net

MICROCONTROLLER BASED CAPACITANCE METER M.ASHOK KUMAR, B.RAMA MURTHY Department of Instrumentation, Sri Krishnadevaraya University, Anantapur – 515 055, Andhra Pradesh, INDIA.

CH.V.V.RAMANA, V.SIVA KUMAR, M.K.MOODLEY Department of Physics, School of Chemistry and Physics, Westville Campus, University of KwaZulu Natal, Durban 4000, South Africa.

K.VENU MADHAV Department of Business Information Technology, University of Johannesburg, Auckland Park Bunting Road Campus, Johannesburg, South Africa. *E-mail: [email protected] ABSTRACT: A microcontroller based capacitance meter using 89C52 microcontroller for the measurement of capacitance has been design and developed. It is based on the principle of charging and discharging of the capacitor. Atmel’s AT89C52 microcontroller is used in the present study. Further, an LCD module is interfaced with the microcontroller in 4-bit mode, which reduces the hardware complexity. Software is developed in C using Kiel’s C-cross compiler. The instrument system covers a range 1pF to 1000µF. The paper deals with the hardware and software details. This instrument has auto range selection and auto calibration facility i.e., auto reset facility. This instrument is provided with 400-value storage capacity. The system is quite successful in the measurement of capacitance with an accuracy of ±1 % and capacitance of whole construction is around 10 pF. The power consumption is less than 1W. Keywords: Capacitance measurement, Charging and Discharging, C using Keil’s C-cross compiler and 89C52 microcontroller.

1. INTRODUCTION A capacitor is a device that stores an electrical charge or energy on its plates. These plates (a positive and a negative plate) are placed very close together with an insulator (dielectric) in between to prevent the plates from touching each other. A capacitor can carry a voltage equal to the battery or input voltage. Usually a capacitor has more than two plates depending on the capacitance or dielectric type. The capacitance value of a capacitor can be measured by utilizing one of its basic properties. The process is a bit complicated when compared to measuring of a resistance value because the capacitor is a reactive. Capacitance measurement with standardized and easy to read output has been for many years the primary goal of numerous research and development efforts. As such are considered the solutions with frequency output [1-4]. Their typical disadvantages are (1) relatively slow sensor readout speed (only a few conversions per second); (2) dependence of the readout time on the value of the measurands [4]. Another trend is the direct conversion of capacitance into digital code, in which the measured capacitance makes part of the analog-to-digital converter [5-7]. In general people use to measure the capacitance value by comparing its value with the known value of another capacitor using complicated LCR Bridge. There are different bridge techniques [8-13] for measuring the capacitance, but the Schering bridge technique may, perhaps, be considered to be one of the most sensitive technique for this measurement. The measurement errors due to the stray capacitances with this bridge technique may be minimized by using the Wagner-earth technique with screened bridge components and lead wires. One disadvantage of this technique may be the requirement for several repetitions of bridge balance and Wagner-earth balance for each observation. Moreover, there are other techniques proposed by various investigators to minimize the error due to the effect of stray capacitances. A modified approach of the balancing technique of the AC Wheatstone bridge network has been reported by Takagishi [14], whereas Morioli et al. [15] and Holmberg [16] have proposed self-balancing techniques to achieve highly

ISSN: 2277-7962 accurate measurements. Kolle et.al. [17] Suggested a synchronous modulation and demodulation technique for the precision measurement of the capacitance of a capacitive transducer. Yang et. Al. [18] suggested an electrical capacitance tomography (ECT) technique for measurement of the change of capacitance of a multi-electrode capacitive transducer. Various other attempts have been made to measure small capacitance of a transducer very accurately such as Capacitance to DC voltage converter technique [19], Charge transfer technique [20-21] and circuit theory based technique [22] etc. In the present study, we adopted the basic principle of charging and discharging of the capacitor an arrangement. Nowadays, the popularity of microcontroller is increasing, due to the fact that they are being used in all types of instruments and in embedded environments. In the present study, the technique utilizes charging and discharging for determination of capacitance using the microcontroller as a tool, while most of the conventional techniques measure the capacitance using bridge methods. 2. PRINCIPLE

The capacitor C is charged through resistor R and during the process the voltage increases exponentially. Once the voltage reaches the maximum capacity a comparator drives its output high, which indicates that, the capacitor is fully charged [23]. This signal is taken into the microcontroller which is the amount of time taken for charging depends on the capacitor, by substituting the values in the following formula the value of the capacitor can be determined. C = Where C = R = δt =

(1.442 * δt) / R ------

(1)

Capacitance of the Capacitor Resistance used for charging Difference in time between charging and discharging capacitor

3. EXPERIMENTAL 3.1. Hardware Design The block diagram and the photograph of the microcontroller based capacitance meter are shown in Figures 1 and 2 respectively. The block diagram consists of the following functional units (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

Constant current source Discharge section Charging section Range selection Comparator Counting unit AT89C52 Microcontroller Memory unit LCD unit Serial communication unit Personal computer

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ISSN: 2277-7962 3.2. Constant Current Source

In the present study, the constant current source is designed using transistors (Q2N 2907) [24]. The pulse from pin P1.3 of microcontroller at the base of transistor Q8 switches on the transistor, thereby triggering Q4 and providing the source at Q5. When Q4 conducts the voltage at the collector of Q4 triggers the base of Q5 thereby providing the constant current to charge the unknown capacitor Cx. The ranges are dynamically selected and so there is no need to switch manually. This selection is a bit tricky and comes handy when it comes to range selection. 3.3. Discharge Section

The value of the capacitor depends on the time taken to charge the capacitor to a particular voltage on the other hand it is also important that we discharge the capacitor completely prior to the process of charging. So the capacitor discharges before counting the clock pulses of the microcontrollers. To do this task a pulse is applied from microcontrollers to the base of NPN transistor Q2N2222 that is placed adjacent to the capacitor under test this provides a low resistance path and will draw any voltage available across the capacitor, which acts as a voltage source in the circuit [25]. As the Q2N2222 has the fast switching times like turn-on time is 35ns, from 10% to 90%, rise time is 25ns and fall time is 60ns. This is best suited for the applications, which include very low switchover time. 3.4. Charging Section

The constant current source is to pump the constant current to the circuit following it, for providing consistent current over a period of time even if there are any voltage variations in the circuit proceeding to it. This current is fed to the capacitor under test, the process of charging and discharging is done repeatedly for precision measurement. 3.5. Range Selection

The section of the switches as to which should be on and for how long, is based on the inputs received from the microcontroller. Capacitors with lower values of capacitance will charge very fast when the current supplied to them is high, on the other hand, Capacitors with high values of capacitance will charge very slow, so three different combinations of resistors in the constant current driving circuit are provided to get three different multiplying factors for charging the capacitor under test. 3.6. Comparator

The comparator designed using LM311[26]. It is designed to operate over a wider range of supply voltages from standard ± 15V op amp Supplies down to the single 5V supply used for IC logic. The output is compatible with RTL, DTL and TTL as well as MOS circuits. In the present study it is designed with single power supply of +5V. 3.7. Counting Unit

The counting unit for the time difference is charging and discharging done by interfacing the analog unit with Microcontroller, which has very low error percentage the timer is set to mode 1 which is a sixteen bit counter which counts the internal clocks. If the timer sets overflow flag then through software

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ISSN: 2277-7962 increment counter, which is internal to the code, after the counting is complete, the counter is added to the timer. The formula used to detect the count is: Count = TL0 + TH0 * 256 + overflow*65536;

where count is a variable to store the complete number of clocks which the controller counts TL0 & TH0 are the hardware 8 bit registers, which are inside the microcontroller Overflow is the software registers which are used to count number of times the timer over flows. 3.8. Microcontroller (AT89s52)

The AT89s52 is a low power, high performance CMOS 8-bit microcontroller with 4Kbytes of flash programmable memory [27]. The device is manufactured using Atmel’s high-density non-volatile memory technology. The on-chip flash allows the program memory to be reprogrammed in-system or by a conventional non-volatile memory programmer. 3.9. Memory unit

In the present study memory unit IC AM27C512, it is 64KB CMOS EEPROM [28]. It operates from a single +5 V supply, has a static standby mode, and features fast single address location programming. AMD’s CMOS process technology23 provides high speed, low power, and high noise immunity. Typical power consumption is only 80 mW in active mode and 100 µW in standby mode. 3.10. Liquid

Crystal Display Module

In the present study the LCD display LM1620024 used for displaying measured Capacitance of a capacitor [29-30]. The display module is a dot matrix liquid crystal display that display alphanumeric, characters and special symbols. 

 

P1.0 for Enable (EN) P1.1 for Read Write (RW) P1.2 for Register Select (RS) & P0.0 - P0.7 for data (AD0:AD7)

The control lines and data lines of the LCD (LM16200) are connected to the port 1 and the data lines to port 0. 3.11. Serial Communication (RS-232)

Microcontroller transfers the data in two ways as parallel and serial. RS232 is the most widely used serial I/O interfacing standard. Its input and output voltage levels are not TTL compatible the connection between a PC and microcontroller requires a minimum of three pins. TXD, RXD, and ground as shown in figure 2. Notice in that figure that the RXD and TXD pins are interchanged [31-32]. The 89s52 have two pins that are used specifically for transferring receiving data serially. These two pins are called TXD and RXD and are part of the port3 group (P3.0 and P3.1). Pin11 of the 89s52 (P3.1) is assigned to TXD and pin 10 (P3.0) is designated as RXD. And used for the present study for the analysis made with Personal Computer. With XTAL=11.0592MHz and TH1=9600, TH1 = FDh. When timer 1 is used to set the baud rate it must e programmed in mode2, that is 8-bit auto reload.

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ISSN: 2277-7962 Table 1 Capacitance values S.No

1 2 3 4 5 6 7 8 9 10 11 12

Marked Values 4.7 pF 33 pF 100 pF 1 nF 10 nF 100 nF 1 µF 10 µF 22 µF 47 µF 100 µF 330 µF

Commercial instrument value (APLAB)[33] 4.606 pF 32.347 pF 102 pF 0.98 nF 10.2 nF 98 nF 1.02 µF 9.975 µF 21.59 µF 47.94 µF 102 µF 336.9 µF

LCR HiTESTER[34]

Designed instrument value

% Error

4.635 pF 32.89 pF 101.5 pF 0.99 nF 9.78 nF 98.5 nF 1.025 µF 9.987 µF 21.68 µF 47.32 µF 101.27 µF 333.54 µF

4.653 pF 32.67 pF 101 pF 1.01 nF 9.9 nF 99 nF 1.015 µF 10.12 µF 21.785 µF 46.53 µF 101 µF 333.3 µF

0.047 0.33 1 0.01 0.1 1 0.01 0.1 0.22 0.47 1 0.8

Figure 1: Block diagram of a microcontroller based capacitance meter.

Figure 2: Photograph of the microcontroller based capacitance meter.

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ISSN: 2277-7962

Figure 3: Flow chart for microcontroller based capacitance meter.

3.12. Personal Computer

Normally PC has one COM port with RS232-type connectors and is designated as COM1. We can connect the 89s52 serial ports to the COM1. A program to identify the incoming data can be written in any language. The data can be of two type’s one online data that is calculating at present or offline that is stored in the memory location in the hardware itself. 3.13. Operation of the Circuit

The capacitor under test is placed at Cx. The program is written in such a way that as soon as the system is started that is as soon as the unit is switched ON it first discharges the capacitor by switching high to low and then low to high in short duration there by giving a pulse to the discharge section. This triggers Q3 transistor to provide low resistance path to any charge, which is accumulated in Cx. Then a pulse to the base resistor of Q8 transistor triggers constant current source to start its function, thereby providing constant current source till the voltage in capacitor reaches its maximum value. This voltage is continuously fed to inverting input of an op-amp, which acts as a comparator. This comparator LM311 transfers its level from high to low and once the input voltage crosses the voltage at non-inverting input, which is a reference voltage. In microcontroller the program is written in such a way that the time difference between the output pulse from microcontroller (pin 1.6) to discharge section and the input pulse from comparator (pin 1.7) is counted. This process is repeated to get more precise value of count, which in turn gives more precise value of capacitor under test. The counted time is directly proportional to the capacitance and it is calculated by using the formula C = 1.442 t / R

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ISSN: 2277-7962 Depending on the value it can be shown directly as nano, pico or microfarads on LCD display module and it can also be stored in memory. There is also serial port from which the user can exchange information from the unit to personal computer for further processing. 4. SOFTWARE The necessary software is developed in Assembly / C using Keil’s C-cross compiler. The Capacitance of unknown Capacitor can be measured by inserting in to the terminals of the meter; the value of the capacitor can be displayed on the LCD. Different ranges of capacitors are measured and tabulated with marked values and values obtained from the measuring unit. The flow chart of the program is presented in Figure 3. 5. RESULTS AND DISCUSSION The performance of a low cost microcontroller-based capacitance meter for the measurement of capacitance is investigated by comparing its response with result by other standard instruments. The instrument is tested with some capacitance values for every range and the results are presented in Table I. The samples are selected to cover the wide range. The results of the present study are in good agreement with the standard instrument values. 6. CONCLUSIONS The hardware and software features of a low cost microcontroller based capacitance meter for the measurement of capacitance is described. The necessary software is developed in C using Keil’s C-cross compiler. The system is quite successful for the measurement of capacitance with an accuracy of ± 1%. The readings are observed for the time duration of 10 minutes; there is no change in the reading. The measurement of capacitance in a wide range is a special feature of the present study. Strong software support is provided, to make the system user friendly, and to carry out data analysis for quality control department. The full system, then, can be hooked up to the main computer or a Local Area Network, to achieve total integration, from measurement to analysis, to inventory control. The cost of the total system is not much more than about 25%-35% the cost of a single PC. The system was particularly designed for an industrial environment, in a less developed country like India. 7. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9]

Van der Goes F.M.L. and Meijer G.C.M., A Novel Low-Cost Capacitive-Sensor Interface, IEEE Trans. on Instrum. Meas., vol. 45, No. 2, pp. 536-540, April (1996). Francois K., A high-resolution capacitance-to-frequency converter, IEEE J. Solid-State Circuits, Vol. SC-20, No. 3, pp. 666-670, June (1985). Huang S.M., Stott A.L., Green R.G. and Beck M.S., Electronic Transducers for Industrial measurements of low value capacitances, J. Phys. E: Sci. Instrum., Vol. 21,pp. 242-250, (1988). Smartec, Universal transducer interfaces (UTI), Data sheets and user manuals, http://www.smartec.nl/interface_uti.htm. Reventer F., Gasulla M. and Pallas-Areny R., A low cost microcontroller interface for lowvalue capacitive sensors, Proc. IEEE IMTC, Italy, Como, pp. 1771- 1775, May (2004). Matsumoto H., Shimizu H. and Watenabe K., Switched-capacitor charge-balancing analogto- digital converter and its application to capacitance measurement, IEEE Trans. on Instrum. Meas., Vol. IM-36, No. 4, pp. 873-877, Dec. (1987). George B. and Jaagdeesh Kumar V., Switched capacitor triple slope capacitance to digital converter, IEE Proc. Circuits, Devices and Systems, Vol. 153, Issue 2, pp. 148- 152, April (2006). E.W. Golding, F.C. Widdis, Electrical Measurement and Measuring Instruments, LBS/ Pitman. B. Haque, Alternating Current Bridge Methods, Pitman, New York, 1971.

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ISSN: 2277-7962 [10] D.V.S. Murthy, Transducers and Instrumentation, PH (I), New Delhi, 1995. [11] A.F.P. Vanputten, Thermal feedback drives sensor simultaneously with constant supply voltage and current, IEEE Trans. Instrum. Meas. IM-39 (1) (1990) 48–51. [12] J.P. Bentley, Principles of Measurement Systems, 3rd Edition, Longman, Singapore, 1995. [13] Schering Bridge for Dielectrics, Type 4030-B, made by H. Tinsley and Co. Ltd., London. [14] E. Takagishi, On the balance of an A.C. Wheatstone bridge, IEEE Trans. Instrum. Meas. IM-29 (2) (1980) 131–141. [15] D. Marioli, E. Sardini, A. Taroni, High accuracy measurement techniques for capacitance transducers, Meas. Sci.Technol. 4 (1993) 337–343. [16] P. Holmberg, Automatic balancing of linear A.C. Bridge circuits for capacitive sensor elements, IEEE Trans. Instrum.Meas. IM-44 (3) (1995) 803–805. [17] C. Kolle, P.O. Leary, Low cost high precision measurement system for capacitive sensors, Meas. Sci. Technol. 9 (1998) 510–517. [18] W.Q. Yang, T.A. York, New A.C. based capacitance tomography system, IEE Sci. Meas. Technol. 146 (1) (1999) 47– 53. [19] N. Hagiwara, M. Yanase, T. Saegusa, A self balancing type capacitance to D.C. voltage converter for measuring small capacitance, IEEE Trans. Instrum. Meas. IM-36 (2) (1978) 385–389. [20] S.M. Herang, R.G. Green, A. Plaskowsk, M.S. Beck, A high frequency stray immune capacitance transducer based on the charge transfer principle, IEEE Trans. Instrum. Meas. IM-37 (6) (1988) 368–373. [21] A. Carlosena, R. Cabeza, L. Serrano, A new method of low capacitance probing, IEEE Trans. Instrum. Meas. IM-42 (3) (1993) 775–778. [22] A. Baccigalupi, P. Daponte, D. Grimaldi, On a circuit theory approach to evaluate the stray capacitances of two coupled inductors, IEEE Trans. Instrum. Meas. IM-43 (5) (1994) 774–776. [23] Radio and Electronic Components: Volume Four ‘Variable Capacitors and Trimmers’ by G. W. A. Dummer (1957). [24] Constant current source - en.wikipedia.org/wiki/Current_source. [25] Www.semiconductors.philips.com -- 2N2222, 2N2222A NPN switching transistor,may 21 (1997). [26] National semiconductor Corporation Design engineer Product Information - Data books www.national.com/design. [27] Advanced Micro Devices, Microcontroller hand book (1988) [28] EEPROMS, Atmel Data Manual 2004 edition. [29] Lampex LCD manual, 2004 edition. [30] LCD module with an 8051 microcontroller, Iguana labs www.iguanalabs.com. [31] RS232 serial communication www.maxim-ic.com. [32] Max232 interface circuits www.maxim-ic.com. [33] Applied Electronics Ltd., APLAB house, plot no.a-5, Wagle estate, Thane. India. [34] LCR Meter (HIOKI 3532-50 LCR Hi Tester, Koizumi, Japan)

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