User Guide

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.

Note The NC contact is available with electromechanical relays only.

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.

OFF

Setpoint

Setpoint –

Hysteresis