Hanna Instruments HI 8001, Instruction Manual

Page: 63 / 88

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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 slowly or very speed.
Write down the final value obtained with ECk
0
(for the amplification factor).
For this ECk
0
value, measure the oscillation period (expressed in seconds).
Based on the following relations, determine the 3 factors of PID tuning:
ECk = 0,75*ECk
0
ECTi = 0,6*T
0
ECTd = 0,1*T
0
Using the above settings we are going to have a Proportional, Integrative and
Derivative control for EC.
If you want to obtain other type of control please proceed at next settings.
For P controller:
ECk = 0,5*ECk
0
ECTi = 99.9
ECTd = 0
For PI controller: ECk = 0,4*ECk
0
ECTi = 0,8*T
0
ECTd = 0
These values are going to be set later in panel S 57 (SET PID PARAMS). With
these values for the tuning parameters, the PID controller for EC is considered
tuned.
6.2.2 PARTICULAR CASES FOR PID TUNING PROCEDURE
1. AMPLIFICATION CONSTANT (pHK OR ECK) TOO LARGE
- The output of the controller oscillates between repletion and blockage
depending on the error of the process.
- The valves will be opened all the time or blocked (closed) depending on
the variation of the process.
2. AMPLIFICATION CONSTANT (pHK OR ECK) TOO SMALL
- The output of the controller varies insignificantly and doesn’t compensate
adequately for the variations in the system.
- The opening and the closing periods vary slightly from one control cycle to
another creating a chaotically evolving process (cannot achieve stability).
3. INTEGRATIVE CONSTANT (pHTI OR ECTI) TOO LARGE
- Integral effect is limited.