Hanna Instruments HI 8000 Series - Manual (Page 11)

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AGES). For each individual sector’s pH average see panel C 24 (SECTOR
AVERAGES). All pH averages can be deleted manually or at specified time of
day using panel S 61 (ERASE STATISTICS).
3.5 PID CONTROL
A simplified schematic of the control (pH and EC):
EC and pH control is performed using an automatic regulated system with PID
controller (Proportional, Integral and Derivative). The role of this controller is to
maintain a set pH and EC value within a mixing tank prior and during distribu-
tion (see diagram). The control of pH and EC is made separately.
The components are as follows:
- The mixing tank where the influent and additives are combined
- The neutral (additive) solution tank containing an acid, base or fertilizer
- The valve for introducing the additive solution into the mixing tank con-
trolled by the PID controller
- PID Controller
- The input (influent) water source
- The pump for pumping water from the tank to the irrigation sectors
The Fertigation Controller automatically provides a command output signal to a
control element such as a pump or valve based on a sensor input signal. The
function of the Fertigation Controller is to proportionally control the pH and EC
of the process at a specified set point. The above output signal commands the