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This menu only appears if Time Proportional control mode is selected.
The proportional band menu sets the deviation from set point at which the control output will be on for the entire
sampling period.
The volume added at the worst case deviation can be calculated by multiplying the pump flow rate by the sample
period time (for example, 1 gal per minute flow rate x 2 min sample period = 2 gal of chemical added). Then
calculate the effect on the concentration of this addition (for example, if a 2 gal addition will raise the pH by 0.5
then the proportional band should be set to 0.5).
If the proportional band is set too low, then the controller could overshoot the set point. If it is set too high, then
the controller may never be able to reach the set point.
Figures below show an example of Time Proportional Mode with the following program parameters:
Control Mode
Time Prop Hi
Sample
Period
10
minutes
High Set Point
7.00 pH
Proportional Band
1.00 pH
Proportional
Band
In the example figures, the set point is 7.00 and the Proportional Band is 1.00. Note that when the pH goes above
the set point, the control relay is ON for a short period of time. As the pH increases, the control relay is ON for a
longer period of time. When the acid starts to affect the bath concentration and the pH is reduced, the control
relay is ON for a shorter period of time. When the pH drops below the set point of 7.00, the control relay is OFF
all the time.
Sample Period
This menu only appears if Time Proportional control mode is selected.
It allows setting the sampling period from 0 to 30:00 minutes. This is the time that will elapse between checking
the sensor input reading for deviation from set point. The Proportional Band setting and how far the current
reading is from the set point will determine the amount of time that the relay remains on.
The sample period should be set to approximately 1½ times the amount of time that it takes for the sensor to react
to an addition of chemical. This can be determined by making a manual addition of chemical using the HOA
menu and timing how long it takes for the controller to react.
Setting the sample period too low will result in a second addition being made before the first is detected and you
will overshoot the set point. Setting too high will delay the next addition to the point that the set point may never
be reached.
Time Limit
This menu only appears if the output mode has been selected as a Low Set Point, or a High Set Point.
Use the arrow keys to set the time limit (min:sec) for the output to be active, then press
ENTER
. If it is set for
"0:00", no limit will be imposed, and the output could stay on forever.
pH
ON TIME %
100%
0%
SETPOINT
PROPORTIONAL BAND
Figure 12a Time Proportional Mode Setup
SAMPLE
PERIOD
CTRL
OUTPUT
ON
OFF
pH
7.0
PROPORTIONAL
BAND
Figure 12b Time Proportional Mode
Timing Illustration
300
350
pH
ON TIME %
100%
0%
SETPOINT
PROPORTIONAL BAND
Figure 12a Time Proportional Mode Setup
SAMPLE
PERIOD
CTRL
OUTPUT
ON
OFF
pH
7.0
PROPORTIONAL
BAND
Figure 12b Time Proportional Mode
Timing Illustration
7.00
8.00
