Depending on the application and pumps or valves used a shorter or
longer minimum pulse is desirable. The minimum pulse length is selected
in the next window
(Sc.2)
Pulse width is from 1 to 9 seconds.
In Adaptive Proportional mode
[Ad.P]
the relay output is controlled
through a complex algorithm that continuously monitors the difference
between actual mV and set point. The output starts to pulse and varies
the ON/OFF cycle as the mV-input approaches the set point value. The
ON/OFF cycle however is also adjusted from a ‘correction factor’, which
in turn is governed by the history of a previous dosing cycle. This makes
for a fully dynamic
dosing control, which
adapts for widely
varying conditions in
a cooling tower or
other plant installa-
tions. Dosing for an
excessive period of
time without a corre-
sponding movement
in mV is recognized
as a possible failure.
The output begins to pulse, preventing overdosing.
The pulse output exhibits a very wide duty cycle. The ON and OFF times
are both dynamic, varying from 1.5 to 30 seconds.
Up or down mode is possible with Adaptive Proportional dosing.
The time taken for the PMH-2 to register the neutralising effect of the
chemicals injected depends on the mixing and retention time of the plant
installation. The distance between the injection point of neutralising agent
and the electrode greatly affects the quantity released into the system.
Therefore which dosing mode to use largely depends on an installation
and can possibly only be determined on site after some initial running of
the plant.
FIG. 7
Adaptive Proportional Dosing.
PMH-2 Instruction manual
PAGE 23
