Page 10
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Operation and Maintenance Manual
Rev: L13
A – 5: Control Outputs
Press the Menu button on the front of the Controller
and select Control Outputs. Depending on the
controller configuration, some control outputs may
or may not be installed.
A – 5.1: pH Control
If your controller is configured to control pH, you
will have the following options:
Control Type (Op):
Choose from On/Off or
Time Base Proportional control.
In general, if you are using a motor driven
chemical feeder then you should choose the
On/Off option. If you are using a solenoid
driven or pulsed diaphragm chemical feeder
(such as Pulsatron, most LMI models or most
Prominent Models), you should choose the
TBP option. This feature helps to hold a set
point and to minimize over-shoot by making a
standard feeder mimic the action of more
sophisticated modulating feeders.
If you choose the On/Off option and are
feeding up, then the controller will activate
the chemical feeder whenever the pH falls
below the set point and continue to feed until
the pH rises above the set point plus
hysteresis at which point it will stop.
If you choose the TBP option and are feeding
up then the controller will activate the
chemical feeder whenever the pH falls below
the set point and will feed for a percentage of
the Time Base (default one minute)
proportional to the offset from set point. For
the remainder of the Time Base the feeder will
be paused. The feeder will continue this feed
and pause cycle until the controller achieves
the set point plus hysteresis. The closer to set
point, the less time the feeder is ON.
Set Point (Op):
This value sets the desired level
to maintain the pH at. Input the desired pH set
point.
Span/Prop. Bnd (Op):
This option is only shown if
the Control Type is Time Base Proportional.
This value
sets the distance (or span) from the set point that
the output will be proportionally controlled.
Time Base (Op):
This option is only shown if the
Control Type is Time Base Proportional.
This sets the
total time that control is based on. During this
time, the feeder will turn on for a percentage of
the Time Base and turn off for the remainder.
Failsafe Timer (Op):
This value sets the time
that the relay is allowed to stay continuously on.
The most common failures of automated
chemical feed systems are depletion of the
chemical supply and/or chemical feeder
failure. Both problems result in the controller
being unable to reach set point in a reasonable
period of time. The failsafe timer sets the
maximum length of time the feeder can run.
If the feeder has been trying to achieve set
point without success for the selected time,
the controller will cut power to the feeder,
flash the Reset Fail/Safe LED on the face
panel and display a message to alert the
operator. If in TBP Pause mode, the
controller will reset the timer.
An operator must reset the failsafe through
the Reset Fail/Safe button to re-enable
normal control.
Dead Band (Mgr):
This option is only shown under
dual pH control.
This value sets the amount the
input must exceed the set point by before the feed
of the opposite direction will trigger. (The range is
from twice the feeds' hysteresis to 2.8 pH)
Warning: Disabling the failsafe timers is
highly discouraged. They are an important
safety feature to protect against dangerous
chemical overfeeds and will protect the
equipment from running continuously if it runs
out of chemical.
Warning: Increasing or decreasing the
Span/Prop. band
or
Time Base
may cause the feed
to severely overshoot or never achieve set point.
Adjust this option only when recommended to do
so by a factory representative.