Re: PID question


Costas Vlachos wrote:
John Popelish wrote:

The one that reads current cannot be involved in the analog
current regulation, without slowing it down, though it is
fine to use it for monitoring the average current for other
purposes. You will have to use the analog signal it
digitizes as the feedback for the analog PID current regulator.

John, I think there is a misunderstanding here. The OP *doesn't have*
and analogue PID current regulator! He wants to do it in s/w with the
PIC. The only analogue regulator in his setup is for the voltage. He has
*one* DAC to provide the voltage set point to the analogue voltage
regulator, and reads the current through an ADC. He wants to use that
ADC's reading to limit the current digitally by modifying the voltage
set point of the analogue voltage regulator using a PID algorithm in
s/w. I hope this is now clearer.

--
Regards,
Costas
Yes, thank you! I wasn't sure if I was describing this clearly. This
is exactly what I'm doing. No analog current limiter here. On your
next post where you say that "you must allocate several samples to your
desired response time", do you mean that I should be taking an average
of several samples before feeding it into the PID loop? I am doing
this, and yes it probably would be very unstable otherwise. I will
post results when I get something more finalized, which could take
awhile.

.

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