Sunday, February 6, 2011

CrazyEngineers Forum

CrazyEngineers Forum

Cascade Control Loops

Posted: 06 Feb 2011 06:30 AM PST

Cascade Control Loops


-The general concept of cascade control is to place one feedback loop inside another. In effect, one takes the process being controlled and finds some intermediate variable within the process to use as the set point for the main loop.


-Cascade control exhibits its real value when a very slow process is being controlled. In such circumstances, errors can exist for a very long time, and when disturbances enter the process there may be a significant wait before any corrective action is initiated. Also, once corrective action is taken one may have to wait a long time for results. Cascade control allows the operator to find intermediate controlled variables and to take corrective action on disturbances more promptly. In general, cascade control offers significant advantages and is one of the most underutilized feedback control techniques.


-An important question you may confront when implementing cascade control is how to select the most advantageous secondary controlled variable. Quite often, the designer has a large number of choices. The overall strategy or goal should be to get as much of the process lag into the outer loop as possible while, at the same time, getting as many of the disturbances as possible to enter the inner loop.


-The next two figures illustrate two different cascade control arrangements for a furnace that is used to increase the temperature of a fluid that is passing through it. In both cases, the primary controlled variable is the same, but in each case a different intermediate controlled variable has been selected. The question then is which type of cascade control is best.












-To determine the best cascade control arrangement, you must identify the most likely disturbances to the system. It is helpful to make a list of these in order of increasing importance. Once this has been done, the designer can review the various cascade control options available and determine which one best meets the overall strategy outlined earlier: to make the inner loop as fast as possible while at the same time receiving the bulk of the important disturbances.


-If both controllers of a cascade control system are three-mode controllers, there are a total of six tuning adjustments. It is doubtful that such a system could ever be tuned effectively. Therefore, you should select with care the modes to be included in both the primary and secondary controllers of a cascade arrangement.


-For the secondary (inner or slave) controller, it is standard practice to include the proportional mode. There is little need to include the reset mode to eliminate offset because the set point for the inner controller will be reset continuously by the outer or master controller. For the outer loop, the controller should contain the proportional mode. If the loop is sufficiently important to merit cascade control then you should probably include reset to eliminate offset in the outer loop. You should undertake rate or derivative control in either loop only if it has a very large amount of lag.

-The tuning of cascade controllers is the same as the tuning of all feedback controllers, but the loop must be tuned from the inside out. The master controller should be put on manual (i.e., the loop broken), and then the inner loop can be tuned. Once the inner loop is properly tuned, the outer loop can be tuned. This allows the outer loop to "see" the tuned inner loop functioning as part of the total process or as the "all else" that is being controlled by the master controller. If you follow this general inside-first principle when tuning cascade controllers, you should encounter no special problems.

A Good Quote...

Posted: 06 Feb 2011 02:50 AM PST

Believe those who are seeking the truth. Doubt those who find it...

What does this quote mean???

boost converter

Posted: 06 Feb 2011 02:05 AM PST

I draw a boost converter in MATLAB.........while i simulate it,I did not get answer............
I gave supply as 0.7V.............And also I dont know how to fix a range for inductance,capacitance..............help me......

Recycling Nuclear Fuels: Need of the Hour

Posted: 05 Feb 2011 11:40 PM PST

The current power scenario should be a matter of great concern to the future and present engineers. The consumer demands are increasing day by day and the rate of increase in the generating capacity is yet to match the pace of the consumers. Consequentially, we have villages with 14 to 16 hours of load shedding [...]

More...

Why Do You Ask For Ready Made Projects & Reports?

Posted: 05 Feb 2011 11:28 PM PST

I wonder why lot of engineering students ask for ready-made projects, project reports, PPTs, cricuits? We get many messages every day that are on the same lines like "I've to submit the project in next 3 days so I need everything, ready-made urgently".

If the deadline is so close, what were you doing for so many days? Also, asking for ready made stuff - do you think is right?

Hyosung’s Power Transformer: Highest Quality Since 40 Years

Posted: 05 Feb 2011 10:10 PM PST

Powertransformers are the backbone of any power system. Hyosung has been manufacturing power transformers with a very good quality for about 40 years. Let us have a look into the manufacturing details of their transformers. They manufacture both core type and shell type transformers. Core transformer Winding: The coils manufactured can bear lightning and switching [...]

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Have You Heard About The Google Bomb?

Posted: 05 Feb 2011 09:20 PM PST

Surprised after reading a bomb named after the most popular search engine in the world? Well Google hasn't started production of explosives but Google bomb is name of a practice (or you can say a malpractice!) to make alterations in the results which you see after you type a search string on Google search engine. [...]

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Viva Question: How Do Registers Work?

Posted: 05 Feb 2011 09:07 PM PST

I had a viva last week and I was asked this question.
To put it descriptively, the professor asked me we all know that 8085 is a 8-bit microprocessor and 8086 is a 16-bit microprocessor.
When we say that a register in 8085 stores 8 bit data, what actually happens inside the register?
And what changes were made to the hardware of 8085 to convert it to a 16-bit microprocessor?

Could someone explain the answer to both the above questions?

Suggest Places Every Engineer Should Visit In Lifetime

Posted: 05 Feb 2011 08:51 PM PST

There are enough lists of places one should visit in lifetime. I thought of compiling a list of places every engineer should visit.

Let me start with places I think every engineer must visit -

1. The Burj Khalifa in Dubai. - World's Tallest Building and excellent piece of extreme engineering.

2. Channel Tunnel: Between France & Great Britain. Need I say anything else about it? It's just AWESOME. I've not visited it yet, but plan to.

Suggest more!

Story of A1tolet

Posted: 05 Feb 2011 06:49 PM PST

After a request from a cean to share story of a1tolet.com

So here it is

I ,still remember the days of my training, when we were forced to change our PG 3rd time because of some problems like robbery cases, so one day me and my friends were roaming in the street of Mohali .We were so much tired after walking for around 25 km in search of pg that can satisfy our needs ,it was around 4.00 PM when we were taking tea in the road side dhaba,suddenly the idea struckinto my mind of developing some online solution for this problem .At that time my friends said that there are already so many websites available like pgspace.com,bharatrentals.com for this,so i thought why we are roaming here and there ,instead we should search on internet, immediately i stand up and return back to my pg and turn on lapppy .I searched a lot on internet ,there were so many website available ,but to my goodness none of them was able to satisfy my needs ,some of them were paid and some of them provides old data .

So i thought i will develop this website and will make it a little bit unique from all by providing some features that are provided by none of the websites ,then from the very next day i started working on this website.

One day i was working on this website during my free time ,suddenly my company project manager come to me .He noticed this and asked me about it and I told him the whole concept and he was impressed and was ready to sponsor this project then it took 2 months for me to complete this project and on last week of November ,it was launched


In My next post ,i will tell you about software development life cycle
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