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Connect your device to the COM and NO (Normally Open) or NC
(Normally Closed) terminals.
The ON relay state occurs when relay is energized (NO and COM
connected, NC and COM disconnected).
The OFF relay state occurs when relay is de-energized (NO and
COM disconnected, NC and COM connected).
The following graphs show relay states along with EC measured value (similar graph
can be derived for TDS control).
As shown below, a high setpoint relay is activated when the measured EC exceeds the
setpoint and is deactivated when it is below the setpoint value minus hysteresis.
Such a behavior is suitable to control a high conductivity dosing pump.
A low setpoint relay as can be seen from the following graphs is energized when the
EC value is below the setpoint and is de-energized when the EC value is above the sum
of setpoint and the hysteresis. The low setpoint relay may be used to control a low
conductivity 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
derivative
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 period diminishes.
The following graph describes the EC/TDS process controller behavior. Similar graph
may apply to the controller.
ON
OFF
Setpoint
EC
Setpoint –
Hysteresis
ON
OFF
EC
Setpoint +
Hysteresis
Setpoint
