open loop & closed loop

[gfigo]

Hello,all!Who can tell me what are open loop and closed loop?and the difference between them,Thanks in advanced!

 

[flatulent]

This involves feedback systems. Open loop is the gain and phase around the loop when the feedback is disconnected. Closed loop is the output/input transfer function with the feedback connected.

An example for an amplifier in closed loop is that the gain is more constant as a function of frequency.

 

[paulux]

The loop concept comes from control system. An open-loop control system utilizes actuating device to control the process directly without using feedback.
A closed-loop control system uses a measurement of the output and feedback of this signal to compare it with the desired input.

 

[gfigo]

Your answers are very helpful for me , thanx! but there's a new question:How can I distinguish negative feedback from positive feedback?

 

[eda_freak]

Hi gfigo,

feedback can be of two types. positive and negative..
in positive feedback the resultant output causes the input to be added in constructive manner. you can say positive feedback systems are self sustaining..
example is a simple oscillator which is critically fedback. in negative feedback systems the output adds to input in destructive manner. these systems tend to get into a steady-state easily example is any damped system.

 

[electronics_kumar]

adding tincture to wounds ie curing mechanism comes under feedback system...
Indeed prevention is better than cure but for preventing of any untoward incident is not at all possible...so we are going for curing mechanism...
If we are having very good curing mechanism(feedback),the we can include /increase dynamism in our system...

Added after 3 minutes:

i heard that closed loop concept starts from the world war....

 

[gfigo]

Thank you，guys! Your answers are very clear and interesting. but can you tell me whicn world war it is?haha.

 

[sabu]

in feed back systems the system can know wt is happening at the o/p.so it can control it actual i/p, there by the o/p can track the input in a controlledmanner.
regards sabu