Saturday, January 22, 2011

CrazyEngineers Forum

CrazyEngineers Forum

On/Off Control

Posted: 22 Jan 2011 10:13 AM PST

On/Off Control


- Suppose a process operator has the task of holding the temperature, T, near the desired temperature, Td, while making sure the tank doesn't overflow or the level get too low. The question is how the operator would cope with this task over a period of time. He or she would manually adjust the hot water inlet valve (HV-1) to maintain the temperature and occasionally adjust the outlet valve (HV-2) to maintain the correct level in the tank.
- The operator would face several problems, however. Both indicators would have to be within the operator's view, and the manual valves would have to be close to the operator and easy to adjust.










- To make the operator's work easier, suppose we installed electrically operated solenoid valves in place of the manual valves, as shown in the next figure. We can also install two hand switches (HS-1 and HS-2) so the solenoid valves can be operated from a common location. The valves can assume two states, either fully open (on) or fully closed (off). This type of control is called two-position or on/off control.
- Assume for the moment that the level is holding steady and that the main concern is controlling temperature. The operator has been told to keep the temperature of the fluid in the tank at 100°F. He compares the reading of the temperature indicator with the selected set point of 100°F. The operator closes the hot water valve when the temperature of the fluid in the tank rises above the set point. Because of process dead time and lags the temperature will continue to rise before reversing and moving toward the set point. When the temperature falls below 100°F, the operator opens the hot water valve. Again, dead time and lags in the process create a delay before the temperature begins to rise. As it crosses the set point, the operator again shuts off the hot water, and the cycle repeats.












- This cycling is normal for a control system that uses on/off control. This limitation exists because it's impossible for the operator to control the process exactly with only two options.


This on/off type of control can be expressed mathematically as follows:

e = PV – SP


In the on/off control mode, the valve is open valve when the error (e) is positive (+), and the valve is closed when e is negative (–).

Motorola Defy Coming To India

Posted: 22 Jan 2011 07:20 AM PST

Motorola Defy is rumored to launch in India on January 24. The android powered rugged device is supposed to be priced around Rs. 22,000 in India. The device has android 2.1 and would soon be upgraded to Android 2.2. The phone is smaller than Nokia N8 in size, and fits perfectly in hand. It also [...]

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AKAI TRIO: Triple SIM Phone – Who Needs It?

Posted: 22 Jan 2011 06:40 AM PST

AKAI TRIO is Triple Sim Mobile has been recently introduced by AKAI Mobiles in India. Now that multi-SIM phones have been a rage in India, TRIO features 3 GSM SIM cards to suit your needs. The Japanese company wants to make a difference by offering the first ever phone to support three SIM cards. However, [...]

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Buffer Overflow attack

Posted: 22 Jan 2011 06:28 AM PST

Guys few days ago

I had participated in an online hacking competition organised by kurukshetra university

There was question asked in that level about buffer overflow attack.

After doing some search on google .I was able to crack that level, but i still don't understand actually what exactly it is and how one can avoid it?

can anyone explain me in brief what it is?

paper presentation

Posted: 22 Jan 2011 06:24 AM PST

hai friends can anybody tel me the format for paper presentation

Sponsorship for national level symposium

Posted: 22 Jan 2011 05:10 AM PST

hi!!
I am ritesh singh from karunya university,coimbatore.Our Biotechnology department is going to organize a national level technical symposium 'EVOGEN" on 18th n 19th of march.
It would include events like paper and poster presentation,debate,bioquiz,adzap and other eye catching technical events. In view of it we would require sponsors for the same. Do let m know if anyone is willing to sponsor the event through the contact address given below.
Room no-148, FDR Residence, karunya university,
karunya nagar,coimbatore 641114.
email-riteshsingh@karunya.edu.in
mob-9042096839.

Raised CAT cut-offs

Posted: 22 Jan 2011 04:54 AM PST

With the raise in CAT cut offs this year, getting admissions into IIM's has become tougher.
India's best Business Schools, Indian Institutes of Management (IIMs) have raised the cutoffs for admission into the 2011-13 Batch. IIMs on January 12, released the CAT Scores online and announced the cut-off percentiles for the admission process as well.

IIM Ranchi which had the highest cut off at 99.65 last year has raised it further to 99.66. Candidates scoring 99.66 percentile in CAT and 60 percent in higher and senior secondary levels have been short listed for GD/PI. IIM Ranchi has short listed a total of 1036 aspirants for group discussion and personal interview.

IIM-Calcutta has its cutoff at 99.59. IIM Ahmedabad announced that 540 students whose overall percentile is 99 and each sectional cutoff at 94 would be called for the personal interview. IIM Lucknow, which was one of the CAT 2010 organising institutes, has increased the weightage of CAT scores. IIM Kozhikode has also decided to give 50% weightage to CAT score, 15% to GD and social skills, personal interview 25% and writing task 10%.

The scores for the Common Admission Test (CAT) 2010 were released on Wednesday. There are eight candidates who scored 100 percentile and 19 with 99.99 percentile.

While many students found it difficult to access results online, the IIMs said that the website did not crash, despite around two lakh students checking the result on the web.

source:minglebox

Boiler Terms

Posted: 22 Jan 2011 04:04 AM PST

Shell: The shell of a boiler consists of one or more steel plates bents into a
cylindrical form and riveted or welded together. The shell ends are closed with
the end plates.

Setting: The primary function of setting is to confine heat to the boiler and form a passage for gases. It is made of brick work and may form the wall of furnace
and the combustion chamber. It also provides support in some type of
boilers(eg. Lancashire boiler).

Grate. It is the platform in the furnace upon which fuel is burnt and it is made of cast iron bars. The bars are so arranged that air may pass on to the fuel for
combustion. The area of the grate on which the fire rests in a coal or wood fired
boiler is called grate surface.

Furnace. It is a chamber formed by the space above the grate and below the
boiler shell, in which combustion takes place. It is also called fire-box.
Water space and steam space: The volume of the shell that is occupied by the
water is termed water space while the entire shell volume less the water and
tubes space is called steam space.

Mountings. The items such as stop valve, safety valves, water level gauges,
fusible plug, blow off cock, pressure gauges, water level indicator etc. are
termed as mounting and boiler can not work safely without them.

Accessories: The items such as super heaters, economizers, feed pumps etc.
are termed as accessories and they form integral part of the boiler. They increase
the efficiency of the boiler.

Water Level: The level at which water stands in the boiler is called water level.
The space above the water level is called steam space.

Foaming: Formation of steam bubbles on the surface of boiler water due to high
surface tension of the water.

Scale: A deposit of medium to extreme hardness occurring on water heating
surface.

Blowing off: The removal of the mud and other impurities of water from the
lowest part of the boiler is termed as 'blowing off'. This is accomplished with the
help of blow off cock or valve.

Lagging: Blocks of asbestos or magnesia insulation wrapped on the outside of a
boiler shell or steam piping.

Refractory: A heat insulation material, such as fire brick or plastic fire clay, used for such purposes as lining combustion chambers.

Classification of boilers

Posted: 22 Jan 2011 03:59 AM PST

Classification

1.Horizontal, Vertical or Inclined Boiler.

If the axis of the boiler is horizontal,the boiler is called horizontal, if the axis is vertical, it is called verticalboiler and if the axis is inclined it is called as inclined boiler.The parts of horizontal boiler is can be inspected and repaired easily but it occupies more space.The vertical boiler occupies less floor area.

2.Fire Tube and Water Tube

In the fire boilers, the hot gases are inside the tubes and the water surrounds the tubes.
Examples: Cochran, Lancashire and Locomotive boilers.
In the water tube boilers, the water is inside the tubes and hot gases surround them.
Examples: Babcock and Wilcox,
Stirling, Yarrow boiler etc.

3.Externally Fired and Internally Fired

The boiler is known as externally fired if the fire is outside the shell.
Examples: Babcock and Wilcox boiler,Stirling boiler etc.
In case of internally fired boilers, the furnace is located inside the shell.
Examples: Cochran, Lancashire boiler etc.

4.Forced circulation and Natural Circulation

In forced circulation type of boilers, the circulation of water is done by a
forced pump.
Examples: Velox,Lamomt,Benson Boiler etc.
In natural circulation type of boilers, circulation of water in the boiler takes
place due to natural convention currents produced by the application of
heat.
Examples: Lancashire, Babcock and Wilcox boiler etc.

5.Higher Pressure and Low Pressure Boilers
The boiler which produce steam at pressures of 80 bar and above are
called high pressure boilers.
Examples: Babcock and Wilcox, Velox,Lamomt,Benson Boiler etc.
The boilers which produce steam at pressure below 80 bar are called low
pressure boilers.
Examples: Cochran, Cornish, Lancashire and Locomotive boiler etc.

6. Stationary and Portable

• Primarily, the boilers are classified as either stationary or mobile.
• Stationary boilers are used for power plant steam, for central station utility
power plants, for plant process steam etc.
• Mobile boilers or portable boilers include locomotive type, and other small
units for temporary use at sites.

7. Single Tube and Multi Tube Boiler

The fire tube boilers are classified as single tube and multi-tube boilers,
depending upon whether the fire tube is one or more than one.
Examples: Cornish ,simple vertical boiler are the single tube boiler and rest
of the boilers are multi-tube boiler.

Aspire TimelineX 4820T – Power Packed Laptop

Posted: 22 Jan 2011 03:40 AM PST

Aspire TimelineX 4820T is the latest in Acer’s TimelineX Series. The TimelineX series features extended 8+ hours battery, HD 16:9 LCD Screen & Dolby Home Theatre V3. In addition, the laptops in this series are ultra-thin. Let’s take a look at 4820T. Building on the USP of TimlineX Series, 4820T features extreme performance, extreme battery [...]

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Sony VAIO YB Series Notebook to be introduced in India

Posted: 22 Jan 2011 01:50 AM PST

Sony has come up with yet another ravishing series of VAIO notebook. The attractive VAIO YB series laptop was launched in the pre-show event at the Consumer Electronic Show 2011.*The VAIO YB series differs very slightly in size, weight and price and good graphics performance compared to its previous launched series namely VAIO F and [...]

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Complete the statement: You know you are true CEan if...

Posted: 22 Jan 2011 01:42 AM PST

I just had this funny idea to start a thread about engineers on CE.
Add geeky, or nerdy statements to complete the following line.

You know you are true CEan if...

Best D2H Service In India

Posted: 22 Jan 2011 01:34 AM PST

Reliance, Videocon, Airtel, Dish, Tata Sky - the list is endless for the D2H service providers in India. The price war is on between all these service providers as some are offering the whole set for under Rs. 999 while others are offering free installation and free viewing for first 2 months or so. Companies like TataSky are going bullish as they have free installation for under Rs.999 (no conditions attached).

Looking forward to suggestions and opinions about the best D2H services in India. What are your recommendations based on pricing and quality of service?

Should I go for Job or Mtech?

Posted: 21 Jan 2011 10:38 PM PST

I am an electronics and telecommunication engineer. I got placed in a leading IT company and completed its training. I've been posted to my base branch and the nature of work is completely opposite to what we've been trained.They've mentioned that we would not be learning any technology or our technical knowledge would not be required but our soft skills would be developed in these two years. I feel that i should have concentrated more on my post graduation rather than joining the company. Now I feel that i should resign and continue with further studies. But I am in a dilemma as it is hard to leave a job already in hand and study for another two years. Also in order to get stability in life I'm aiming to prepare for IES and public sector units. I'm very confused what should i do?

Project Ideas

Posted: 21 Jan 2011 10:31 PM PST

Hi

Sorry for starting this thread. I feel that the project titles given in various lists of CE are based on IEEE research papers which would tough to do by oneself without having to go to some sort of place where they do and sell projects. I thought that why not we CEans jot out the ideas we have based on the projects we have seen or from the problems we have faced. I somehow feel that it would help in bringing about innovative projects. Delete this thread if it found unnecssary
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