Sunday, January 16, 2011

CrazyEngineers Forum

CrazyEngineers Forum

General Requirements of a Control System

Posted: 16 Jan 2011 01:47 PM PST

General Requirements of a Control System


The primary requirement of a control system is that it be reasonably stable. In other words, its speed of response must be fairly fast, and this response must show reasonable damping. A control system must also be able to reduce the system error to zero or to a value near zero.




SYSTEM ERROR
The system error is the difference between the value of the controlled variable set point and the value of the process variable maintained by the system. The system error is expressed in equation form by the following:

e(t) = PV(t) – SP(t)


where:-
e(t) = system error as a function of time (t)
PV(t) = the process variable as a function of time
SP(t) = is the set point as a function of time




SYSTEM RESPONSE
-The main purpose of a control loop is to maintain some dynamic process variable (pressure, flow, temperature, level, etc.) at a prescribed operating point or set point. System response is the ability of a control loop to recover from a disturbance that causes a change in the controlled process variable.
-There are two general types of good response: underdamped (cyclic response) and damped. (Figure 1) shows an underdamped or cyclic response of a system in which the process variable oscillates around the set point after a process disturbance. The wavy response line shown in the figure represents an acceptable response if the process disturbance or change in set point was large, but it would not be an acceptable response if the change from the set point was small.








- (Figure 2) shows a damped response where the control system is able to bring the process variable back to the operating point with no oscillations.










Control Loop Design Criteria
- Many criteria are employed to evaluate the process control's loop response to an input change. The most common of these include settling time, maximum error, offset error, and error area.


- When there is a process disturbance or a change in set point, the settling time is defined as the time the process control loop needs to bring the process variable back to within an allowable error. The maximum error is simply the maximum allowable deviation of the dynamic variable. Most control loops have certain inherent linear and nonlinear qualities that prevent the system from returning the process variable to the set point after a system change. This condition is generally called "offset error" . The error area is defined as the area between the response curve and the set point line as shown by the shaded area in (Figure 3).








- These four evaluation criteria are general measures of control loop behavior that are used to determine the adequacy of the loop's ability to perform some desired function.




REFERENCES , ( THOMAS HUGHES , MEASUREMENT & CONTROL BASICS )

Linear's ideal diode in a full wave bridge rectifier.

Posted: 16 Jan 2011 09:04 AM PST

I was searching for a way to design a simple synchronous rectifier with N-ch mosfets, to avoid the voltage drop of a diode bridge. I found some interesting ideas, a little expensive though.
Now I found this "ideal diode" from Linear.
Linear Technology - LTC4358 - 5A Ideal Diode

It is similar to the way a synchronous rectifier works, it has a circuit that controls a mosfet's gate.
It also seems like a simple way of making a synchronous rectifier!
But I also wonder why they don't mention that in the datasheet.

Would it be possible to use 4 of those ideal diodes as a bridge rectifier with low losses?

Circuit Diagram Help

Posted: 16 Jan 2011 05:14 AM PST

hi friends,
In the circuit diagram given in the link http://www.electronic-circuits-diagr...simages/10.gif


can you tell me what VR1 and vr2 are?is it pot?

how to connect them to the 6V supply?:confused:

More CE badges!

Posted: 16 Jan 2011 05:12 AM PST

Hi,

I have one suggestion about CE badges for blogs and websites. For now, we have the "Proud to be a Crazy Engineer" badge (and that's cool!). But what if we add yet another group of badges for specific engineering trades.

In the profile snippet to the left of forum posts, we have this sentence saying "I'm a crazy Computer Science engineer" and so on. So what if we make badges shouting out the same idea? :cool:

We can also add really cool graphics for different trades. Like binary numbers for Computer Science and Gears for Mechanical Engineers (Ah, clichés!). Well, just some innovative graphics then! :D
What say?

literature survey of a project

Posted: 16 Jan 2011 04:58 AM PST

how to write a literature survey of a project?

introduction

Posted: 16 Jan 2011 04:47 AM PST

Hi frnds...
myself Sachleen doing diploma in Electronics and comm.engg. from Punjab.I m a fun loving person..My hobbies are painting,surfing,going out and meet old frnds..i have lot of frnds.
I feel proud to be a part of ce...:D

Thoughts on CE messenger

Posted: 16 Jan 2011 04:37 AM PST

Hi guys,

One of the first things that attracted my notice in CE is the CE messenger project. I followed all the (long) threads that sprouted around this idea at various times. And I think this is something that is totally do-able, provided we stay committed this time around :).

I did my mini project based on the idea of an instant messenger. (Which is shared here at CE) This got me interested in giving a try at the CE IM.

Anyhow, I would like to be enlightened on some basic details about the messenger concept. I hope someone who has previously worked on this project could provide me some answers:
* Are we planning a messenger where we login with the CE usernames and access the chat functionality?
* Or is the idea to use any alternative ID like the CE mail ID, or the network ID
* I'm still new to CE, but I seem to notice that the Network ID is used as a means of instant communication between members. Since this is based on the Google App Engine, I think it will be pretty straightforward to implement a CE messenger based on the network id.
* If above is not the case, I suppose we'll have to implement a chat server (as mentioned in similar threads), in which case I need to do a lot more extra learning :)

Well, and that's it. I wish to continue with this idea and actually conclude it successfully :) It might take some time, but let's not give up the CE messenger forever! :cean:

paper presentation

Posted: 16 Jan 2011 01:06 AM PST

need some good topics for a tech fest on 28th jan.please suggest topics for me.(1styear btech ECE)

ilab for digital electronics experiments

Posted: 15 Jan 2011 11:40 PM PST

hi guys, i'm a finalist and i have been assigned to develop an ilab for digital electronics experiments using labview, i real need some help on what to do. thanx

Why is Capacitor's One Place It Positive and Other Negative?

Posted: 15 Jan 2011 10:57 PM PST

hi frnds..
i want to ask u that why capacitor's one plate is called positive and the other is called negative??????i mean how can we recognize that which plate is positive and the other is negative...????whereas in case of ceramic capacitor there is no polarity....

Paid to click sites

Posted: 15 Jan 2011 08:37 PM PST

I just had an idea after being paid by two of this sites. They are paying 0.01 per advertisement click and you have to click on four adverts per day. So if i was a member of 10 of this sites i would be earning 0.01x4x30x10, which is 12 dollars per month. This will enable me to pay for memberships to other sites and buy some softwares online without having to be charged from my credit card.
I have confirmed that the two sites below are genuine and therefore i need 8 more sites that people here can personally claim to be genuine.

The two that i have been a member and have been paid are

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