Lazer Optik Teknolojisi İle Yeni Bir Sıvı Seviye Sensörü

Abstract

Sensörler teknolojik gelişmelere paralel olarak her geçen gün daha ufak boyutlara ulaşmakta ve hassasiyetleri artmaktadır.Bu çalısmanın yola çıkış noktası olarak motorların yağlanması, motorun ömrüne doğrudan etki eden kritik bir faktör olması nedeniyle, sıvı seviyesini dinamik olarak ölçebilen bir sensöre ihtiyaç duyulmuştur. Günümüzde kullanılmakta olan sıvı seviye sensörleri temelde iki tiptir: sıvının miktarını statik halde sıcaklık/direnç değişimi ile ölçebilen sensörler ve sıvının seviyesini belli bir mesafeye kadar dinamik, daha sonra statik ölçebilen ultrasonik sistemler. Bu sistemlerin başta hassasiyet olmak üzere kendi içinde birçok eksiği bulunmaktadır. Bu amaçla, doktora tezi kapsamında Hella firmasıyla yeni sensör geliştirilmesi konusunda çeşitli çalışmalar yapılmıştır. Elde edilen sonuçlara paralel olarak, sıvı seviyesi ölçümünü çok hassas gerçekleştirecek ve mevcut problemlerden arındıracak bir yöntemin varlığı ve konuya adapte edilebilirliği literatür taramalarında dikkati çekmiştir. Çesitli alanlarda mikro kürecikler yardımı ile çok hassas ölçümler yapmakta kullanılan Whispering Gallery Mode (WGM) yönteminin varlığı keşfedilmiştir. Southern Methodist Üniversitesi Makine Mühendisliği fakültesi Mikro Sensorler Laboratuarı ile iş birligi yapılarak WGM yöntemine ve uygulamalarına dair incelemeler yapılmış, ardından yöntemin sıvı seviyesi ölçümünde kullanılabilirliği üzerine deneyler gerçekleştirilmiştir. Bu çalışmanın sonucunda, çok havacılıktan savunma sanayine, otomotivden imalata, otomasyondan denizcilik sektörüne, tıptan enerji üretime kadar mühendisliğin mevcut olduğu her alanda sanayinin hizmetine sunulabilecek yüksek hassasiyetle sıvı seviyesi farklılıklarını algılayabilen yeni bir sensör geliştirilmiştir.

The discovery of new materials and the technological developments in electronics have changed the whole industry and the world. Today sensors are being used nearly in every application of aeration, space, naval, automotive, civil, mechanical, industrial, electronics and computer engineering as well as advanced medicine, medical sciences and many other areas, and led to innovations and advances to every process when used. The study has started with the need of highly sensitive, compact liquid level measurement sensor which can be used even in flammable medium. To provide the demand, the positive and negative features and aspects of the current sensors, the literature and similar studies have been investigated. At first, a valid ultrasonic liquid level sensor has been analyzed to meet the requirements by improving its characteristics. For improving and solving the problems of the current sensor, finite element analysis has been performed until reaching a new model, which can be used to build the initial production prototypes. Although consideration of the results has shown that to meet all of the targets, a new and highly sensitive liquid levels sensor has to be developed, which should be the next step of the study. When looking through the techniques of the liquid level detection, it has been seen that there is a wide variety of detection methods. Some of them are: sensors working mechanically with Archimedes’ principle, floating level sensors, magnetic liquid level indicators, liquid level sensors using ultrasound and lambda waves to measure the flight time of the waves, Nuclear level switches using low level radiations emitted by radioactive sources, and various optical detection methods. In some of the optic applications, optic sensors are located at top or bottom level according to liquid existence and some of the fiber optic based systems measure the liquid level by the change of the refractive index. Other than these, when investigating some other common sensors, capacitive pressure measurement systems based on principle that measures the pressure change between the capasitor plates, strain gage systems which measure the pressure by shape changes, load cell type systems and piezoelectric pressure measuring systems has been evaluated. These systems usually have sensitivity problems. As an example, ultrasonic liquid level systems in automotive applications have ±1mm liquid height sensitivity values, while most of the precise pressure measurement sensors are sensitive to measure 50-100 kpa. The theory of this study was found many years ago when it was seen that sound waves in whispering tone bounce along the circular gallery of St Paul s Cathedral with very little loss, and this phenomenon was named as Whispering Gallery Mode (WGM). Today WGM theory has been introduced into modern electronics, and as a result, it has become an advanced theory including optical physics and electronics. In modern WGM applications, when laser light comes into the microsphere in its contact point with the tapered film, the light undergoes total internal reflections in the sphere. After repeated total internal reflections at the curved boundary, the electromagnetic field can close on itself and a resonance occurs on the light signal going to the photodiode. More importantly these resonances change when there is a change on the refractive index or geometry. The resonance frequencies shift with the changes of the microsphere size and/or the optical properties of the surrounding medium. One of the biggest advantages of the WGM theory is that very small values such as 10-5N can be detected by using this method. For evaluating the possibility of developing a higly sensitive novel liquid level sensor using WGM phenomenon Southern Methodist University Microsensors lab. has been visited. After many meetings and discussions, it has been considered that a new kind of highly sensitive liquid level sensor can be developed by using the WGM phenomenon, in the Micro sensors lab. facilities of Southern Methodist University, where the experiments of the novel sensor have been performed. The novel sensor shows that the dependence of WGM shifts to liquid levels can be assumed as perfectly linear all the measurement range without being affected by the amount of liquid in the container. A Pa change in liquid pressure, results as high as 3,12 pm WGM shifts, which have been observed during the liquid level experiments. When the axis have been switched, it can be estimated that the values are ranging between 0,033-0,053 mm of water level per pm WGM shift of the Laser Spectrum, again with a perfect linear correlation. It has also been calculated that the total uncertainty of the experiments is assumed to be around ±1,12%, which might be improved with the usage of equipment with higher accuracy. Also another advantage relies on the WGM phenomenon, in which this novel sensor can be worked in any environment without being affected by the availability of flammable liquids and gasses etc. As a result of this study, a novel high-tech laser-optic technology based liquid level measurement sensor has been designed which can be used in automotive, aerospace & aviation industries, medicine, defense, civil engineering, and many other fields.