When configuring a PID, if the input is supplied by the host rather than directly from an I/O point, the controller firmware can overwrite the value of the input (making it incorrect in the equation). When this happens, the P Term and the D Term will calculate to zero.
The types of PIDs affected are:
- Velocity (Type B)
Use the Velocity Type C PID algorithm.
Opto 22 has resolved this issue.
To resolve this issue, new algorithms for ISA, Parallel, and Interacting were added to PAC Firmware R9.4c and higher.
To avoid impacting existing PID loops, the original algorithms will remain in the Algorithm list. Because they still have this defect, their names were changed to ISA (Obsolete), Parallel (Obsolete), and Interacting (Obsolete). The Velocity - Type B algorithm was also renamed, because it’s affected by the same defect. Velocity (Type C) did not change because it does not have the defect.
If you upgrade to the newest PAC software, you’ll see the new names when you edit PID loops that were configured with an obsolete algorithm. This lets you know that your PID loop was configured with the original version of the algorithm. You can continue to use the obsolete algorithms, but Opto 22 recommends you use the new algorithms or Velocity (Type C) when you configure PID loops for a new application.
You don’t need to change your PID loop configuration unless you are affected by this issue.
If you have PID loops that get their input from Host, here’s what you can do to fix them:
- For PID loops that use Velocity (Type B), reconfigure them to use Velocity (Type C), and retune them.
- For PID loops that use ISA (Obsolete), Parallel (Obsolete), or Interacting (Obsolete), you must:
- Upgrade the firmware of the I/O units (brains) that your PID loops are configured on to PAC R9.4c or higher.
- Upgrade the software you use to configure PID loops.
The lowest versions that support the new algorithms are:
Reconfigure the PID loops to use the new algorithms.Retune the PID loops.
- PAC Control R9.5a
- PAC Manager R9.5a
- EtherNet/IP Configurator R3.0n