[Editor’s note: This is a response to Greg McMillan’s answer to this question in the Control Talk Blog.]
I have been a great fan of your work for quite some time. I don't see a lot of replies, as if this is a non-issue in the industry, or there is nothing else to say on the subject. Here is my two cents. When talking about PID sample rate, we still should remember the Nyquist sampling theorem. Even with the great advances of late in A/D conversion precision and input channel scan rates, a PID can still be fooled into controlling an alias signal given the right circumstances. The sampling theorem thus adds another low limit on the PID execution rate.