Anti-Windup and Bumpless Transfer.

[sfq]

Can anyone explain what these are please.

Thanks in advance,

[AnalogKid2DigitalMan]

I can't, but my Alta Vista search of "Anti-Windup" + "Bumpless Transfer" yielded 150 results. I would start there.

[AnalogKid2DigitalMan]

OK, I knew they were related to PID loops, and curiosity got the best of me, so here they are:

Anti-Windup:
During automatic PID control, the integral portion of the PID calculation will be readjusted if the anticipated PID output exceeds the min_out or max_out settings. By not allowing the integral term to "wind up", smooth control is achieved quickly when the PID output re-enters the proportional band after being pinned at the maximum or minimum allowable value.

Bumpless Transfer:
When switching from Automatic Mode to Manual Mode, the PID output will change quickly to the value of manual_level. It is usually desirable to regularly set the manual_level input equal to the PID output while the control is in automatic mode. When the control is switched to manual mode, the manual_level input will initially be equal to the PID output, and subsequently varied by other logic in your program.

Note: If you elect not to preset the manual_level input with the value of the PID output, you may experience a significant, instantaneous change in the output when switching from automatic control to manual control.

Here are two methods that may be used to preset the manual_level input:

Ladder Example
Structured Text Example

When switching control from Manual Mode back to Automatic Mode, the PID output will ramp back toward the setpoint value according to the current PID calculation. Note that you can prevent the possibility of a sizeable, instantaneous change in the output by specifying a value for max_change. This lets you control the rate of change of the PID output when switching from manual control back to automatic control.

[sfq]

Thanks, I tried google and found those too, but it's not enough for me :(.

And it's anti-reset windup I'm looking for, made a mistake in the header.

[AnalogKid2DigitalMan]

Anti-Reset Windup: Same as reset windup.


Reset Windup: With a simple PID controller, integral action will continue to change the controller output value (in voltage, air signal or digital computer value) after the actual output reaches a physical limit. This is called reset (integral) windup. For example, if the controller is connected to a valve which is 100% open, the valve cannot open farther. However, the controller's calculation of its output can go past 100%, asking for more and more output even though the hardware cannot go past 100%. Most controllers use an "anti-reset windup" feature that disables integral action using one of a variety of methods when the controller hits a limit.

No I'm all wound up, int it great?