Hanna Instruments HI 8000 Series - Manual (Page 61)

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10. At the end of the program consult the log table. Write down in a table the
values for the pH sensor and the time when the reading was done (see Section
4.10, LOGGING (DIARY) FUNCTIONS).
11. The obtained data is used to compose a graphic having as horizontal axis
the time and vertical axis the pH variations. The next step is to analyze the
obtained graphic.
12. Increment the amplification constant’s value gain (pHk) from panel S 57
(SET PID PARAMS). Repeat steps 9, 10, 11 and 12 until the form of the wave
corresponding to pH variation has the sinusoid shape with approximately
constant amplitude (unamortized oscillation).
NOTE: The period of time for Irrigation time (15 minute default) - panel S 37
(PRE/POST IRRIG) - can be modified (increased or decreased), if the
process is very slow or very fast.
Write down the final value obtained with pHk
0
(for the amplification factory).
For this pHk
0
obtained value, measure the period of oscillation (expressed in
seconds). In accordance with the following relations determine the 3 factors:
pHk = 0,75*pHk
0
pHTi = 0,6*T
0
pHTd = 0,1*T
0
Using the above settings we are going to have a Proportional, Integrative and
Derivative control for pH.
If you want to obtain an other type of control please proceed to the next settings.
For P controller:
pHk = 0,5*pHk
0
pHTi = 99.9
pHTd = 0
For PI controller: pHk = 0,4*pHk
0
pHTi = 0,8*T
0
pHTd = 0
These values are going to be set in panel S57 (SET PID PARAMS). With these
values the pH tuning of the PID controller is considered finished.
B. NECESSARY STEPS FOR TUNING THE PID CONTROLLER FOR EC AD-
JUSTMENT
1. Go to panel S 37 (PRE/POST IRRIG) and using the UP, DOWN arrows select
the irrigation program number 10. This program has the following default
settings :