Vibration-frequency densitometer

The following is a brief translated version of my Bachelors project.

Densitometers are instruments which are used to measure the density of the liquid they are immersed in. They can be of the following types: mass, hydrostatic, radio-isotopic and vibrational. Their function is to constantly measure density and hence they play a very important role in modern fuel equipment. The following densitometer is a vibration-frequency densitometer which measures the density with the help of the Wiedemann effect and is used on board most commercial aircrafts.

The fuel tanks of an aircraft are usually situated inside the wings, under the fuselage and in the tail assembly. The densitometer(7) is located in the lower section of these tanks. They also contain several ultrasonic probes(2,3,4), which are connected to a micro processing unit(10) along with the densitometer. The micro processing unit uses the readings from the probes and the densitometer to calculate the speed of sound and mass of the fuel. It also converts the resultant density with the help of the analog-digital converter and indicates the density of the fuel on one of the cockpit indicators(11). The accurate measurement of density inside the fuel tank depends upon the amount of water and other particles mixed with the fuel. This brings into question the purity of the fuel. Hence, the better the quality of the aviation fuel, the better the accuracy of the densitometer.

The construction of the vibration-frequency densitometer includes a sensor, which measures the change in density of the fuel and proportionally vibrates. A mechanical resonator, which can either be a single tube or the cylinder, acts as a sensor through which the fuel flows. The tube begins to vibrate as a result of the change in density and gradually reaches a resonant frequency. The whole densitometer is coated with a layer of aluminum. A wound coil along with an attached magnet in the central portion of the densitometer help form the mechanical resonant system and make sure the device remains stable and accurate for longer periods. The resultant resonant frequencies are calculated by the surrounding electronic devices.

The Wiedemann effect – This is a magnetostrictive phenomenon where a magnetic field gets divided into two perpendicular fields: spiral and tangential, which create an electric current within the rod. The potential difference of the rod due to the current is proportional to the spiral moment.

The schematic representation of the entire fuel measuring system includes the sensing element of the densitometer, which is connected to a phase detector. The detector measures the resultant vibrations and its frequencies. A generator acts as a regulating medium between the phase detector and an amplifier. The phase detector compares the signal from the sensor with the feedback signal from the generator, which passes through an integrator. The resulting signal goes through a micro processing unit, as mentioned before and then is shown on the indicator.

The use of different fuels around the world means that their densities will vary. The following two diagrams show the similarities in the signals but the difference in their frequencies. In the first signal diagram, the input fuel is TS-1, used only in Russia, which has a density of 780 grams per cubic centimeter. The second diagram shows the fuel Jet A, used in USA, India and many other countries, which has a density of 840 grams per cubic centimeter.

All in all, the densitometer is a very important part of the fuel system, but the vibration-frequency densitometer has some disadvantages. The surrounding temperature effects the densitometer’s readings and factors like contamination increase the error.

The advantages of such a densitometer are: the vibrational method of measuring the density is much more efficient than other methods, this type of densitometer reduces the error due to viscosity and it’s static error is not more than 0.2%

The University of Illinois

When I got into the U of I at Urbana Champaign, I knew that no other university would interest me. After that I got accepted into 6 other universities, but none of them could live up to the name of U of I. I had heard a lot about it for many years now, about the department, the location, the faculty, the perfect study atmosphere, about everything.
Now that I am on campus, I feel that this university has lived up to it's name and reputation. I am proud to be a part of this esteemed institution.


The University of Illinois at Urbana-Champaign began in the year 1867. The University is in the twin cities of Champaign and Urbana (total population 180,000) in east-central Illinois. Situated about 140 miles south of Chicago, 125 miles west of Indianapolis, and 180 miles northeast of St. Louis.
It boasts of :
37 campus libraries
130 buildings with wireless access
70,000 computer connections on campus
The college of engineering is ranked 5th in the USA while my department of Aerospace Engineering is ranked 7th in 2008.
Facilities - 286 main campus buildings, 2.3 square miles (1468 acres)
559 total buildings, 7.7 sqyare miles (4938 acres)

Sports
10 & 11 Number of men's and women's (NCAA) teams (respectively) with 14 major facilities including Memorial Stadium (62,000 seating), the Assembly Hall (17,200 seating), Atkins Tennis Center, Huff Hall (4,000 seating), Illinois Field (3,000 seats for baseball), Eichelberger Field (1,500 seats for softball), the Illini Track and Soccer Stadium, two 18-hole championship golf courses with driving range and the newly opened Demirjian Golf Practice Facility.

470,000 square feet of recreational space between two newly expanded campus recreation and wellness centers. Includes indoor tracks, leisure pool with slide, climbing wall, basketball and racquetball courts, indoor and outdoor 50-meter pools, and much more; other recreational facilities include an ice arena, outdoor adventures center, inline skating rink, and several play fields.

Population
6,450 Undergraduate students living in 15 Private certified housing units and 63 Greek Houses.
1,700 Single graduate students or students with families living in two University-owned apartment complexes; two residence halls are home for 720 graduate students.

1,000+ Registered student organisations, coalitions, honorary societies, and teams.

5,378 international students in 2007 from 123 countries; ranked #4 in the nation’s “top 20 Research Institutions” in number of international students.

42,326 Total students: 30,895 undergraduate and 11,431 graduate and professional students, 53% men, 47% women, 6.0% African-American, 6.0% Latino/a, 11.0% Asian-American, 0.26% Native American, and 12.7% International.

Faculty
2,971 Members; 1,402 tenured, 570 tenure track, and 1000 other faculty.
22 Nobel Prize faculty and alumni winners; many noted scholars, including one Crafoord Prize and 19 Pulitzer Prize winners; others recognized with memberships in prominent national and international societies, academies, and foundations.

Campus
The campus is one of a kind, really beautiful. Soon, I'll write about the campus in detail, the places I hangout, the amazing transport system and the sheer efficiency of everything that is done on campus.

Go Illini!!!!!

I realize that I am here now..... it's been a month..... I just stood in front of the Alma Mater(photo above).... just like I did on the first day when I got here....... I've changed the time on my blog from St.Petersburg time to Central Standard Time....

..............times have indeed changed!

When she smiles....

One attribute that defines your attitude is a smile. Silence is bliss, it speaks volumes. A smile is paradise, it pacifies, it alleviates.

Her smile is brighter than sunshine, it makes my day. Even though it’s brief, her smile takes away all my troubles. There just ain’t no sunshine when she’s gone.

"I'm a house of cards in a hurricane
A reckless ride in the pouring rain
She cuts me and the pain is all I wanna feel
She danced away just like a child
She drives me crazy, drives me wild
But I'm helpless when she smiles"
- Backstreet Boys

The Learning Curve

Over the years, I have made a number of friends. Different kinds of people, from different parts of the world, with different perspectives and different personalities. Once upon a time, I was a lousy friend. I never performed to my fullest. I let myself and my friends down on many occasions. They were just people who I played cricket with, or guys at school or kids my age who just happened to live in the same neighborhood.

Gradually, my views on this topic changed. I learned some valuable lessons, sometimes the hard way. I became more mature and responsible towards my friends. I understood that I had a duty. My relationships with most of them matured, took a new direction. I never let them down anymore, or at least tried not to. I began to realize that this wasn’t a piece of chocolate cake with icing on top, it wasn’t a walk in the park with my babysitter holding my hand, and it wasn’t something that could be taken lightly. Screwing up is easy, just like dying. It is holding on to life that is difficult. You have to strive, work hard at any relationship in order to keep your end of the bargain.

It’s been such a long time since I screwed up that I had forgotten that I CANNOT take it. I cannot handle being a poor friend; it just throws me into an abyss. Recently, I let a friend down and I didn’t realize it until she told me about what went wrong and how I had played a part in it. Once I understood my mistake, I knew what had gone wrong with me. I had taken things for granted, which is something I never do. This took me to another planet. I just had to deal with it, deal with myself. Nothing else around me made sense, nothing else mattered. It was a reverie! It is this feeling inside me that ensures the safe landing of future voyages. It helps me to be careful of turbulence. I just hope I haven’t lost my seat yet.

Rush Hour

Kestrel, the friend that I mentioned in one of my earlier posts, has finally started his blog. I'll be posting a permanent link to his blog soon. Akshata, on the other hand, has completely stopped posting. She tells me that she writes regularly, just not on her blog. Should I remove the link to her blog just because she has stopped writing?

Moving along...
Ever since I arrived in Champaign, I've been swamped. Busy with assignments, busy with classes, busy with household chores, busy with my friends. The sheer pace by which things are moving is alarming, almost unbelievable. I never knew that being a graduate student is such a demanding affair. This is where my diligence and meticulousness will come into question.

I was so into convincing people that I won't be going to Champaign, that I started believing it myself. I wish someone had adviced me before, "Ashwin, don't graduate and start your post-graduation in the same week, you might not believe it."

Sometimes, pursuit is better than possession. You sometimes realize that when you really really want something, and you finally get it, you don't feel like keeping it. Not me! I have wanted to come to UIUC for a long time. And now that I am here, I will cling on to these moments with whatever I can muster.

Still, why is it so hard for me to believe that I am here? I think I need to change the clock on the top right-hand side of my blog to Champaign time. Somebody pinch me!

The Transition

This is the longest break I have taken from blogging so far. In the past three weeks, I have thought about blogging almost everyday, but didn't have the time, didn't have access to the internet and couldn't find the words, at times. The week between 20th January and 27th January could be described as one of the most crucial I have ever had. I divided my plans into three stages.

Stage 1: Graduation
I finally graduated! I had been waiting for "Graduation Day" for a while, had worked very hard to present my project well. All my effort, all my prayers, all my energy was being utilized. This was something I just had to do, something that I couldn't screw up. If this went wrong, then I wouldn't go to USA for my masters. This was something that was always on my mind.

My thesis was ready, and so was my presentation speech. The only thing that bothered me on the morning of the 22nd of January was the question-answer session that followed my speech.

As I walked onto the podium with a nervous smile, the curator had trouble pronouncing my name. With the cane in my hand and my speech in my head, I began. I was confident and sharp, I paused when necessary and took my time. The speech went well.

I was bombarded with three questions, two of them were expected. The third, I answered out of nowhere. My asnwer came out of the back of my head as a result of the extra research and long hours at the library. I even explained parts of that answer that weren't needed. "Relief" was the first word that came to my mind, "graduate" was the second.

The curator started calling out the results and my name was last. "Ashwin Jadhav, excellent!" said the curator, (A=Excellent, B=Good, C=Satisfactory) then he added "I congratulate you all on behalf of the university and the department upon completion of your undergraduate studies. I hereby pronounce you "graduates". "Phase One complete", I said to myself.

Stage 2: The journey and the beginning

Exactly 12 hours after my graduation, I was sitting at the St.Petersburg International Airport waiting to board my flight to Chicago via Munich. My friends were all with me till the very end. After paying for my excess baggage, I saw the very last exit stamp being put on my russian visa. The flight was delayed due to excessive ice on the wings and tail. But I had to wait in Munich for a couple of hours anyway.

Munich was great! I would place it's airport in the league with Heathrow and Charles De Gaule. Everyone spoke english, I suddenly missed russian.

I slept during the 10 hour flight to Chicago. The flight landed on time and I was excited to meet one of my closest friends. I hadn't seen him for almost 16 months. Since I had to catch the bus to my university from the airport itself, we didn't exit. We enjoyed a burger and a drink accompanied with a lot of catch-up talk. We were so engrossed that I even missed a bus, but that gave me an extra hour with him.

The three hour drive to Champaign was comfortable. I suddenly felt alone. I felt the need to be alert to this new beginning.

My apartment was just how I wanted it to be. The department was just two blocks away. Most of the people I knew were very friendly, very helpful and went an extra mile for me. The next two days were dedicated to registering for classes and making sure I became a certified student of the University of Illinois at Urbana Champaign. Stage two was completed.

Stage 3: The surprise

I was in Champaign, I had graduated, I had settled down. But the one person that deserved to know all of this was kept in the dark by me. Reason: To surprise her. She had planned a lot for me, looked at apartments for me, answered hundreds of questions for me, had been my closest friend for the previous six months. I didn't want her to run around anymore.

She was scheduled to return from Philadelphia four days after my arrival in Champaign. I met her online after she landed and told her to go to the Illini Union on campus if she wanted to receive a surprise left by me. Something told me that I had given away too much, but I had to see her on that day itself.

Late that evening, she entered the Union and walked along the it's longest corridor. As she drew closer, she realized that I was standing at the end. She hugged me and said, "I knew it, I so knew it". Well, she was surprised, she didn't care how or when I got there, just seeing me there made her happy. Later we dove into the details of how much had happened so fast and how I had planned it all.


One of the most important weeks of my life, probably. Everything went well, thankfully.

I'd like to thank the following people:
Rohit for his support and help all the way.
Pragni for her support, help and commitment all the way.
Pallavi, Omkar and Pinky for their company, help and for keeping the surprise a surprise.