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As shown below, when the measured pH exceeds the set-
point threshold, the relay(s) is (are) energized, until the pH
measure falls below setpoint value minus hysteresis .
Such a behavior is suitable to control an acid dosing pump .
A relay enabled as a low setpoint, is energized when the pH
value is below the setpoint and is de-energized when the
pH value is above the sum of setpoint and the hysteresis .
This operational mode may be used to control an alkaline
dosing pump .
P.I.D. CONTROL MODE
PID control is designed to eliminate the cycling associated
with ON/OFF control in a rapid and steady way by means
of the combination of the Proportional, Integral and Deriva-
tive control methods .
With the proportional function, the duration of the activated
control is proportional to the error value (Duty Cycle Control
Mode); as the measurement approaches setpoint, the ON
(relay energized) period diminishes .
