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An upper boundary is imposed for acid/base dosage time
when relays are energized continuously, i.e. when relay
works in ON/OFF mode or in PID mode but in the latter
case only if the relay is always ON. This parameter can be
set through setup procedure. When the maximum boundary
is reached, an alarm is generated; device stays in alarm
condition until relay is de-energized.
ON/OFF CONTROL MODE
Either for mode 1 or 2 (base or acid dosage) the user has
to define the following values through setup:
• relay setpoint (pH/mV value);
• relay hysteresis (pH/mV value).
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 pH mea-
sured value (similar graph can be derived for mV control).
As shown below, a high setpoint relay is activated when the
measured pH exceeds the setpoint and is deactivated when
it is below the setpoint value minus hysteresis.
Such a behavior is suitable to control an acid dosing pump.
A low setpoint relay as can be seen from the following
graphs 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. The low setpoint relay may
be used to control an alkaline dosing pump.
