Reverse engineering CCW PID instruction Micro800 Micro810 Micro820 Micro830 Micro850

[drbitboy]

Cf. https://github.com/drbitboy/CCW_Micro8xx_PID_reverse_engineering

 

[drbitboy]

Summary

The [PID] instruction in CCW for Micro8xx PIC uses the Dependent Gains form of a PID algorithm. However, the [PID] instruction does not work as advertised. Specifically, the tuning parameter members of the PID_GAINS object used by [PID] are not all consistent the with the canonical/conventional meanings of their names. If pidgains is a tag in CCW of data type PID_GAINS, then its members have the following meanings:

• pidgains.Kc - Controller gain, units of dCV/dError
• pidgains.Ti - Integral time, units of seconds (s)
• pidgains.Td - Factor for calculating a first-order filter time constant, units of seconds-squared (s**2)
• pidgains.FC - Derivative time, units of seconds (s)
  the product (pidgains.Td * pidgains.FC) is the CV output filter time constant

Note specifically that

• the .FC member of PID_GAINS is not the filter constant that the CCW documentation claims it to be;
• the .Td member of PID_GAINS is not the derivative time that the CCW documentation claims it to be.

Refer to the link in Post #1 for more detail.