OK, I'm at a loss for words on this one. I'm looking for a word or phrase to describe the following situation...

I have an open loop control system that when I apply voltage \$A\$ I get output \$A_1\$. When I'm at state \$A_1\$ I apply voltage \$B\$ (\$B > A\$) I get output \$B_1\$. But when I apply voltage \$A\$ again I get output \$A_2\$ (\$A_2 \ne A_1\$).

I'm still not sure about hysteresis. I took some data on the system and attached a graph of what I'm seeing. The system is a camera with a liquid lens and a voltage source. The blue line represents starting at voltage step 126 and then starting to capture an image at each voltage from 127 to 143.

The red line represents setting the voltage to 144 and then capturing the same image moving from voltage step 143 to 127.

You can see that depending on which way I come from the results are different for the same voltage step.

lens sharpness example


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  • \$\begingroup\$ Do you mean hysteresis? \$\endgroup\$ – Kwin van der Veen Apr 27 at 14:51
  • \$\begingroup\$ Maybe, but there is no lag in changing from one state to the other and back again. Also doesn't hysteresis also return to the same state? I'll have to look more into it. Thanks. \$\endgroup\$ – dave Apr 27 at 15:22
  • \$\begingroup\$ In physical systems, the action time can be quite short, smaller than our ability to visualise it. A physical example of hysteresis is a mechanical light switch when we move it up to the on position, the transition can be very fast. \$\endgroup\$ – Ertxiem Apr 27 at 23:20

This phenomenon is called Hysteresis it is a special type of nonlinearity.

enter image description here

The \$E\$ axis is your input voltage. As you can see the when we are increasing \$E\$ we get different values for \$D\$.

Whenever your characteristic curve is changing you will have nonlinear effects. There are also other effects like time-variant changes in the characteristic curve.

  • \$\begingroup\$ @MachineLearner I've updated my post with an example of what I'm seeing. \$\endgroup\$ – dave Apr 28 at 22:54
  • \$\begingroup\$ @dave Yes, this is hysteresis that you're seeing. \$\endgroup\$ – Hearth Apr 28 at 23:27

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