Hanna Instruments HI 8000 Series - Manual (Page 64)

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- The control function remains constant; however, a steady state offset is
present meaning that the set point is never completely maintained.
4. INTEGRATIVE CONSTANT (pHTI OR ECTI) TOO SMALL
- Integral effect is excessive.
- The control variable (process) enters a state of oscillation.
- A saturation effect occurs creating a “blocking effect” of the controller
outputs depending on the magnitude of the error in the process.
- The valve function will be unstable, opening and closing frequently.
5. DERIVATIVE CONSTANT (pHTD OR ECTD) TOO LARGE
- Creates unnecessary upsets in the process (spikes).
6. DERIVATIVE CONSTANT (pHTD OR ECTD) TOO SMALL
- The control variable (process) enters a state of oscillation.
- The valves remain in an opened or blocked (closed) state.
7 ALARM DESCRIPTION
There are 8 kinds of possible software alarms that may occur during the opera-
tion of the Fertigation Controller.
1. “pH SENSOR DIFF”
This alarm is triggered if the difference between the real time values of the two
primary pH sensors exceed the specified maximum allowable difference. The
maximum allowable difference (offset) between pH sensor values can be cus-
tomized using panel S 55 (SENSORS CONFIG). This particular alarm condi-
tion has a customizable threshold limit, which can be set by using panel S 40
(pH CONTROL). The threshold limit is an adjustable time response to a given
alarm condition.
2. “EC SENSOR DIFF”
This alarm is triggered if the difference between the real time values of the two
primary EC sensors exceed the specified maximum allowable difference. The
maximum allowable difference (offset) between EC sensor values can be cus-
tomized using panel S 55 (SENSORS CONFIG). This particular alarm condi-
tion has a customizable threshold limit, which can be set by using panel S 41
(COND CONTROL). The threshold limit is an adjustable time response to a
given alarm condition.
3. “pH OUT OF RANGE”
This alarm is triggered when the real time value of the primary pH sensor (pH