Mikroişlemci kontrollu dipolmetre
Mikroprocessor controlled dipolmeter
- Tez No: 22078
- Danışmanlar: DOÇ. DR. HAKAN KUNTMAN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 93
Özet
ÖZET Kimyasal maddelerin molekül yapısının aydınlatılması buyuk olçüde dielektrik özelliklerinin belirlenmesine bağlıdır. Bu yönde atılacak ilk adım ise, dielektrik sabitinin bulunmasıdır. Bu büyüklükten yararlanarak di- pol momenti, dielektrik dağılım, dielektrik kayıp ve fre kansa bağımlılık gibi maddeye ait başka büyüklükler hak kında bilgi sahibi olmak mümkündür. Yapılan çalışmada sozkonusu sıvılar, dielektrik sabitleri 2-3 aralığında değişen polimer çözeltileridir. Bu çalışmada amaç, fiziksel kimya laboratuarlarında, çeşitli sıvıların dipol momentlerinin bulunması ve bunla rın sıcaklıkla değişimlerinin dipolmetre yardımıyla çıka rılması sırasındaki uzun ve yorucu işlemleri daha kısa surede tamamlamak ve elde edilen bilgileri bir PC yardı mıyla işleme ve değerlendirme olanağı sağlamaktır. Çalışma, donanım ve yazılım olmak Üzere başlıca iki aşamada gerçekleştirilmiştir. Donanım kısmını, kapasite ve sıcaklık olcum düzenleri ile otomasyonu sağlayan Z80 mikroişlemci sistemi, yazılım kısmını ise mikroişlemci programı oluşturmaktadır. Oluşan düzende, sıcaklık de ğişim aralığı ve adımı kullanıcı tarafından tuş takımın dan girilmektedir. Düzen, sıcaklığı artırarak sürekli kontrol etmekte ve istenen sıcaklık değerlerinde kapasi teyi ölçerek kaydetmektedir. Bu bilginin değerlendiril mesi için iki seçenek sunulmuştur. Birincisinde kayde dilen bilgiler ekrandan okunmakta, bunların değerlendi rilmesi kullanıcıya bırakılmaktadır. İkinci seçenekte ise, düzen bilgisayarla birlikte kullanılmakta, bilgiler aktarılarak değerlendirme işi orada yapılmaktadır. Bu çalışmada amaç; sadece uzun ve yorucu işlemlerin mikroişlemci sayesinde kısa surede ve zahmetsizce gerçek leştirilmesi değil, aynı zamanda elde edilen olcum sonuç larının kimya literatürü sonuçlarıyla uyum içinde olması dır. Yapılan ölçümler sonucu gereken değerlendirmeler yapılarak tatmin edici sonuçların alındığı gözlenmiştir. (v)
Özet (Çeviri)
SUMMARY MICROPROCESSOR CONTROLLED DIPOLMETER Determination of the dielectric behavior plays an important role in the investigation of the molecule structure of macromolecules [1-4]. This involves dielec tric constant measurements which gives an idea about the dipole moment, dielectric loss and frequency dependency of the material [4-9]. Polymer solutions having dielec tric constants in the range of 2-3 is concerned in the work [10]. The aim of the work is to save mental and manual labor used in physical chemistry laboratories during the measurements in order to determine the dipole moment and temperature dependency of macromolecules and give the oppurtunity to process and evaluate the information obtained by the use of a PC. The studies have been made in two stages. The hardware section consists of the dielectric constant and temperature measurement circuits as well as the Z80 microprocessor system which provides the automation of the instrument. The software section consists of the assembler program. The instrument requires the informa tion of temperature range and step to be given from the keyboard. The system then switches the heater on, makes temperature measurements continuously and displays a value proportional to the capacity of the measurement cell at temperatures desired. The evaluation of the in formation obtained is possible in two ways. The first option is to use the system separately. Results are reached to the user by the display and the user himself is to make the evaluation. The second option is to send the information to a PC and make it do all the processing and evaluation. (vi)Various methods have been described for dielectric constant measurements in a wide frequency range. The bridge method available in the O.OlHz-lOMHz range and the heterodyne beat method available in the l-100MHz range are the most common methods given in literature [11-14]. Other methods are also described upto 1000GHz for dielec tric constant measurements. In this work, the heterodyne beat method has been prefered due to the compatibility with microprocessors. In this method, the oscillations of two high frequency oscillators are brought to super position in a mixing section. By the means of the vari able oscillator, a match in the two frequencies to zero beat is provided. The capacitor value providing this leads to the information for determining the dielectric constant. Almost universally, solution dielectric constants are measured by observing the change in capacitance as solution is introduced between the plates of a capacitor. This makes the capacity increase by a factor e, called the dielectric constant. Thus, if C is the capacitance O with a vacuum, C = s.C is the capacitance with a dielec tric. The total capacitance of a capacitor generally con sists of a replaceable capacitance C, associated with the volume into which the solution is introduced, and an irreplaceable capacitance C., associated with the cables, circuitry and the empty cell. So the circuit should be able to measure capacitance values between the range C + C. and e.C + C., where e is the maximum dielectric constant value expected. The choice of the operating frequency is governed by a number of factors. The beat frequency change for a given shift in dielectric constant increases with the operating frequency. The effects of small solution con ductivities are also decreased by increasing the operat ing frequency. The upper limit is imposed by the effects of series inductance associated with the leads and cables. At 10MHz the impedance of the inductance may (vii)equal or exceed that of the capacitor. Since the impe dance ratio of the inductor to the capacitor increases as the square of the frequency, selecting low operating fre quencies cuts down this problem. At 1MHz, series induct ances may still introduce errors of 1-2%. Below 200kHz, very little trouble should be expected from this source. If still high operating frequencies is prefered either the circuit should be designed carefully to minimize series inductance, or a method allowing these effects should be considered. The measurement cell is a capacitor, between the plates of which the solution is introduced. Most designs consist of two or more concentric cylinders of conducting material. The outermost cylinder should be kept at ground potential in order to minimize the hand effect and other stray capacitance changes. The plates should be rigid and conveniently designed for filling and emptying. The cylinders may be of metal, of glass with a coating of silver or platinum. If the outer grounded electrode does not form a complete shield around the cell, the effect of a change in the bath liquid can cause errors. For this reason, actually water with its high dielectric constant is a poor bath liquid. In addition water contamination is a problem and a water bath tends to raise the humidity and to complicate the sealing of the system. Water baths are also subject to corrosion. For this reason, mineral oil or kerosen should serve better as a bath liquid. Actually, using liquid baths is not the only way for the heating operation. For some systems or problems it may be impossible to immerse the cell in a bath. In such cases, resistive heating or water jackets may solve the problem. It should be noticed that by any means of heat ing, temperature regulation should be provided. The capacity measurement section of the system con sists of six main blocks including two high frequency oscillators, a mixer, a low-pass filter, a wideband amp lifier and a Schmitt trigger. (viii)One of the high frequency oscillators is the most critical part of the system, since the results depend al most on this circuit. The low and narrow range of the capacitance values requires high operating frequencies which makes the series inductance effects innegligible. Also, providing the linear operation of oscillators in such high frequencies becomes difficult. After analyzing various configurations, an RC oscillator used with a NAND Schmitt trigger has satisfied the problem. A logic cir cuit was preferred due to its frequency output suitable for the microprocessor. Also, linearity has been provid ed in the desired range of capacitance values. Measure ments have shown that at least a 300pF offset value of capacitance need to be paralleled to the cell in order to provide the condition above. The capacitance value is expected to be in the range of 300-500pF. This oscilla tor gives an output frequency between l.l-1.6MHz. The cell consists of two concentric cylinders. The capacitance expression of such a configuration is given below. 2n.e.e.h r o C = (1) b In a h : the height of cylinders b : the radius of the outer cylinder a : the radius of the inner cylinder e : the dielectric constant of the solution introduced r between the plates 2 s : the dielectric constant of vacuum (8. 85x10" F/m) O The design of the cell has been made in order to provide a 20oc volume and 20pF capacitance. (ix)The second high frequency oscillator is a 1MHz TTL oscillator which generates the signal the first oscilla tor output is to mixed. The mixing operation provides a relatively wider frequency output range which is also more proper for the microprocessor to process. Obviously, the mixer is used to mix the output sign als of the two high frequency oscillators. The aim of this operation has been described above. The modulation of two sinusoidal signals concludes with the sum and difference of the two input frequencies. The low-pass filter has been used to pick out the differ ence frequency. This frequency is expected to change in the range of 100-600kHz. A second order OTA-C filter configuration has been used in order to obtain a wideband structure. It had been mentioned that the output signal was to be processed by the microprocessor. This requires a dc level and amplitude adjustment at the filter output. This is done by the means of a wideband amplifier. A quasi-Darlington structure has been used. This signal applied to the Schmitt trigger has a dc level of 2.5V with 0.5V amplitude. The temperature measurement section consists of three blocks including a temperature-voltage converter, an amplifier and a voltage-controlled oscillator. The temperature change is sensed by the means of a transistor and this voltage is amplified by a V__ multiplier. The BE second block provides the calibration and amplification required for the microprocessor. The final section is to obtain a convenient output for the microprocessor. The linearity of this section has been provided for a tempe rature range of 15-115°C. The Z80 microprocessor has been used for the automation of the system. This 8 bit processor requires (x)peripheral devices in order to complete the system. The system consists of a 27128 EPROM, 6116 RAM, Z80 CTC, 8255A PIO, keyboard and an LCD display. A 5V power sup ply and a 2.5MHz clock frequency is also required for the system to work. After completing the hardware and software sections, various measurements have been made in order to check the results. It has been observed that comparable and ac ceptable results have been obtained. (xi)
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