Hanna Instruments HI 8000 Series - Manual (Page 59)

59
6.2.1 PID TUNING PROCEDURE
Due to the fact that the pH and EC controls function with minimal error at the
control output value, the PID controller must be tuned separately for each pro-
cess (pH and EC).
To access the PID parameters use panel S 57 (SET PID PARAMETERS). The
displayed PID parameters are as follows:
pH
Factory amplification setting for pH control (controller gain).
pHTi
Integral constant for pH control.
pHTd
Derivative constant for pH control.
ECk
Factory amplification setting for EC control (controller gain).
ECTi
Integral constant for EC control.
ECTd
Derivative constant for EC control.
1. CONDITIONS THAT IMPOSE THE TUNING OF THE PID CONTROLLER
- Each time when a new installation is turned on.
- Each time when mechanical modifications are made within the irrigation
installation (pump, pipes, electro valves, etc.).
- If the water source from which the irrigation is made is changed.
- If the substance for neutralization is changed (or its concentration).
- When the controller is replaced.
2. NECESSARY STEPS FOR TUNING THE PID CONTROLLER
Tuning the PID controller necessitates successive tests with different values of the
approval parameters. The following method needs increase of the K amplifica-
tion factor up to the steady level of the system’s oscillation. Below is presented a
user-friendly procedure for this tuning.
During the PID tuning (for pH as well as for EC) we are going to have big
variations of the outlet value (the pH and EC of the irrigation water) compared to
the prescribed value. This is the reason why during the tuning the water that exits
the pump has to be directed to a collecting channel designed for residual water
and not to irrigation (for the protection of the crops).
In the above case we are going to set only one sector.