科技英语外文翻译之英文篇

Microcontroller Based System for the
Measurement of Dielectric Constant in
Liquids
Ch.V.V.Ramana and K.Malakondaiah
Department of Instrumentation and University Science Instrumentation
Centre,Sri Krishnaevaraya University,Anantapur,India
Abstract:A microcontroller based system using 89c51microcontroller for the measurement of dielectric constant in liquids has been designed and developed.It is based on the principle that the change in frequency of an XR–2206function generator,when the liquid forms the dielectric medium of the dielectric cell,is measured with a microcontroller.Atmel’s AT89C51microcontroller 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 Ride’s C-cross compiler.The instrument system covers a wide range of dielectric constants for various liquids at various concentrations and at different temperatures.The system is quite successful in the measurement of dielectric constant in liquids with an accuracy of +0.2%.The paper deals with the hardware and software details.Keywords:Dielectric constant,XR-2206Function generator,Frequency measure-ment,C using Ride’s C-cross compiler and 89C51Microcontroller
INTRODUCTION
The dielectric constant is a property of major concern in understanding acid-base behaviour in various solvents.A “dielectric”is a substance that can sustain an electric field and acts as an insulator.Some liquids and gases can serve as good dielectric materials,having a special property of storing and dis-sipating electrical energy when subjected to electromagnetic fields.Dry air is Address correspondence to K.Malakondaiah,Department of Instrumentation and University Science Instrumentation Centre,Sri Krishnaevaraya University,Anantapur 515003,India.E-mail:ramana6@
Instrumentation Science and Technology ,35:599–608,2007
Copyright #Taylor &Francis Group,LLC
ISSN 1073-9149print /1525-6030online
DOI:
10.1080/10739140701651581
599
an excellent dielectric.Dielectric measurements are useful for detecting explosives,plastic and metal weapons,drugs,chemical agents,and biological agents.The dielectric constant 1of a liquid is defined as the ratio of the electrical capacitance of a cell when the liquid /solution forms the dielec-tric medium (C s )to the capacitance of the cell when air forms the dielectric medium (C 0)at a given temperature,which is represented by the following equation:
1¼ðC s Þ=ðC 0Þð1Þ
The dielectric cell consists of two parallel metallic plates which act as electrodes.The cell acts as a capacitor,while the liquid acts as a dielectric medium.The cell has to be first standardized to measure the dielectric constants of unknown solutions.This is accomplished by considering a pure liquid,such as benzene,as the reference liquid.The dielectric constant of an unknown liquid (1x )can be determined by measuring the capacitance of the cell in air (C 0),the capacitance of cell in the reference liquid (C r ),such as benzene,and the capacitance of the cell in the liquid whose dielectric constant has to be measured (C x ),using the relationship:
1x ¼1þ½ðC 0ÀC x Þ=ðC 0ÀC r Þ Âð1r À1Þð2Þ
where 1r is the dielectric constant of the reference liquid.The dielectric constant of a material contains detailed information about the physical and chemical composition and structure.[1]Nowadays,the popularity of microcon-trollers 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 frequency measurement for determination of capacitance using the microcontroller as a tool,while most of the conventional techniques measure the capacitance using bridge methods.
PRINCIPLE
The IC XR–2206is a function generator chip.It acts as an RC oscillator.The frequency of oscillations depends on the values of timing resistor R and timing capacitor C.The value of R is kept constant.The dielectric cell acts as a capacitor C that varies with the dielectric medium.Consequently,the frequency of the oscillator also changes.The measurement of the frequency of the oscillator enables one to measure the value of the capacitance of the cell and,thus,the dielectric constant of the medium.In the present study,with suitable interface of the oscillator circuit with a 89C51microcontroller,the frequency of the oscillator is measured.The dielectric constant of the medium is computed using Eq.(2)and is displayed on the LCD.
Ch.V.V.Ramana and K.Malakondaiah 600
EXPERIMENTAL
Instrumentation
Hardware Design
The block diagram of the microcontroller based system for the measurement of dielectric constant in liquids is shown in Fig.1.A schematic diagram which contains more details is shown in Fig.2.The designed cell is connected between pins 5and 6of THE XR-2206using A BNC connector.The dielectric cell acts as a capacitor C whose capacitance can be measured in terms of frequency.The block A of Fig.2consists of the XR-2206function generator.The output of the RC oscillator (the square wave output (pin 11)is an open collector and,hence,it needs a pull up resistor to V cc .Connecting a 10K resistor between pins 11and V cc ,makes the square wave output to be TTL compatible.In the present study,the XR-2206function generator generally operates at 1MHz frequency.But,the 8051microcontroller can measure the frequency accurately up to a few hundred kilohertz frequency.Hence,the divide counter shown in block B of Fig.2is used.The output of the RC oscillator is given to the clock input of the 74LS90IC [3]decade counter;(which acts as a divide counter (410,412,and a 4-bit binary counter)that divides the RC oscillator output by 10times.The output of the 74LS90is given to the timer 0external input,which is available on the micro-controller (port 3).The microcontroller counts the clock pulses that are given from the 74LS90over an interval of 1sec,which gives the frequency of the oscillator.Block C of Fig.2consists of an LM335[4]which is used as a sensor to measure the temperature of the solution.It also consists of
the Figure 1.Block diagram of microcontroller based system for the measurement of dielectric constant in liquids.
Microcontroller Based System 601
hardware that amplifies the signal from the temperature sensor.The output of the temperature unit is given to the analog-to-digital converter (IC 0809)which is shown in block D of Fig.2.The IC 0809is a monolithic CMOS device with an 8-bit analog-to-digital converter,8-channel multiplexer,and microprocessor compatible control logic.[5]The 8-bit A /D converter uses suc-cessive approximation,which can make 100conversions per microsecond at a clock rate 120KHz.The 0809operates 0to 5V input range with single 5V power supply.It is used to convert the analog temperature into digital values.Block E of Fig.2is an AT89C51microcontroller from the Atmel Company.[6]It is a low-power,high-performance CMOS 8-bit microcomputer with 4K bytes of flash programmable and erasable read only memory (PEROM).It has four parallel ports,two 16-bit timers /counters,six interrupt sources,and one programmable serial port,with low power
ideal Figure 2.Schematic diagram of microcontroller based system for the measurement of dielectric constant in liquids.
(continued )
Ch.V.V.Ramana and K.Malakondaiah 602
and power down modes;it has the facility of three-program memory lock.The on-chip flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer.All ports are used (port 1is used for LCD display,port 2is for ADC,port 0is used for control signals (that are RS,RW,and EN for LCD display,and SC,ALE and EOC for ADC),port 3(one line is used)is used for frequency measurement.Block F of Fig.2is a two-row 16characters LCD display from ODM;[7]it is interfaced with the microcontroller through port 1to display the measured data and results.The interfacing of the ADC with the microcontroller is shown in Fig.2(a)[continu-ation of Fig.2].
Interfacing of the Oscillator with the Microcontroller
The frequency of oscillation f 0is determined by the external timing capacitor C (across pins 5and 6)and the timing resistor R (connected to either pin 7or
8).The frequency is given by:
f 0¼1=R ÃC ð3Þ
The frequency f 0can be adjusted by varying either R or C.
In the present study,the timing resistor R is kept constant.Since the timing capacitor C is to be maintained at a minimum of 100pf,a capacitor of value 100pf is connected in parallel with the dielectric cell.
The
Figure 2.Continued.
Microcontroller Based System 603
designed cell is connected between pins5and6of the XR-2206using a BNC connector.The dielectric cell acts as a capacitor C whose capacitance can be measured in terms of frequency using the following equation:
C¼1=RÃf0ð4Þ
Software
Software is developed in C using Ride’s(Raisonance Integrated Develop-ment Environment)C-cross compiler to initialize the LCD display and measure the frequency,capacitance,dielectric constant,and temperature. After development,the codes are stored in the program memory(flash EPROM)of the AT89C51microcontroller by using the Atmel programmer and the program is executed.Theflow chart of the program is presented
Fig.3.
Calibration and Measurement
The instrument is calibrated and measured following the procedure mentioned below.
1.
Clean the dielectric cell,dry it,and keep it in a beaker containing air.2.
Connect the cell to the circuit as shown in Fig.2.3.
Switch on the system and activate the software.4.The system measures and displays the frequency,along with tempera-
ture and,in turn,the capacitance of the cell using Eq.(4).Make a note of the values.
5.Keep the reference liquid (benzene in the present study)in the cell.
6.Repeat the steps from (2)to (4).
7.Place the unknown liquid in the cell.
8.Repeat the steps from (2)to (4).
9.Then,calculate the dielectric constant of the unknown liquid using Eq.(2).
10.
Note the readings of the dielectric constant of unknown liquids along with temperature.RESULTS AND DISCUSSION
The performance of the microcontroller-based system for the measurement of dielectric constant in liquids is tested with some liquids at 308C.The samples are selected to cover a wide range.The results are presented in Table 1.The results of the present study are in good agreement with the literature values.The dielectric constant measurements for the binary liquid mixtures
(1)benzene þnitrobenzene;(2)nitrobenzene þchlorobenzene;and (3)nitrobenzene þcyclohexanone for various concentrations (mole /L)at 308C were made.The results are graphically represented in Fig.4.
Table I.Dielectric constants of pure liquids at 308C
Sample
Present work Literature Reference Toulene
2.46 2.40[9]Chlorobenzene
5.96 5.91[10]5.90[9]Cyclohexanone
17.9618.2[9]Acetone
20.3020.35[9]Methanol
32.5632.6[9]Nitrobenzene 34.8934.81
[12]34.80[11]
Ch.V.V.Ramana and K.Malakondaiah 606
CONCLUSION
The hardware and software features of a microcontroller based system for the measurement of dielectric constant in liquids are described.The necessary software is developed in C,using Ride’s C-cross compiler.The system is quite successful for the measurement of dielectric constants in liquids with an accuracy of +0.2%.The measurement of dielectric constant,over a wide range,is a special feature of the present study.
ACKNOWLEDGMENTS
The authors are thankful to M /S Mittal Enterprises,New Delhi for providing the necessary help to carry out this work.
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6.IC AT89C518-Bit Microcontroller with 4K Bytes Flash Datasheet ;Atmel Company,2000.
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8.Rajendran,A.;Neelamegam,K.An instrument for measurement of dielectric constant of liquids using 8031Microcontroller.Bull.Electrochem.2004,20(2),59–62.
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Figure 4.Concentration versus dielectric constant for three binary liquid mixtures.Microcontroller Based System 607
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Received November 17,2006
Accepted March 13,2007
Manuscript 1605Ch.V.V.Ramana and K.Malakondaiah
608。