Hysteresis....

sirch2

Joined Jan 21, 2013
1,037
Sorry but I disagree, hysteresis is deliberately built into most control systems. Consider a heating system controlled by a thermostat, without hysteresis when the room temperature was close to the thermostat set point it would be constantly tripping on and off which would wear out the mechanical parts.

So hysteresis is built into the thermostat, it switches on at slightly lower than the set point and switches off at slightly higher, this means that there is a gap between it switching off after heating and switching on as the room cools.

In electronics a schmitt trigger is an example of somewhere where you want hysteresis.
 

GopherT

Joined Nov 23, 2012
8,009
Hi All,
What is the use of hysteresis? please explain....
Probably the most common use of hysteresis is, as previous poster said, when you want to activate a control (logic, comparitor, op amp), at one voltage from "off to on" than the voltage required for "on to off" transitions.

It helps in temp control to reduce short-cycle situations but it also reduces the impact of noisy signals on logic and comparitors.

If you have a comparitor circuit with a noisy LO signal of 0-3 volts and a HI signal of 2-5 volts. You can use hysteresis (positive feedback) to insure the lo to high transition happens at 3.5 volts and high to low transition at 1.5 volts.
 

Sensacell

Joined Jun 19, 2012
3,419
I find that hysteresis is a hard concept to convey, I usually try to use something people can relate to physically to explain it.

Snap-action toggle switches (mechanical hysteresis) are something we have all experienced, the idea that there are two different "snap points" that are not the same turning on or off is easy to grasp.
 

Thread Starter

Zsonali

Joined Apr 3, 2014
18
Thanks all..... I have something to share.....
Lets say we have a reference voltage 5 V for a comparator. Now whenever the input to the comparator exceeds 5 V, then only we will get a high at the out put. Now if anyhow, my input contains ripple, then there comes a condition when my input may go below 5V say 4.99 V, then the output is not high but low, then again when my input reaches or exceed 5 V, then my output is high. So, this is the reason why we see a glitch at the output. Now to suppress this to happen, we generally use hysteresis. Where we can change our reference, so that whenever there is a ripple in the input, circuit should not be confused with the glitches..... This is how the Schmitt trigger circuit works..... and that's why we use hysteresis.
You can write your concerns if I am wrong somewhere....

Thanks to all !!!!!! :)
 
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