VI. EXPLANATION OF PID CONTROL SCREENS
PID Control:
The PID Control program can be accessed via Confi guration screen 1. It uses the fi rst three
menu options: “PID Contorl”, “Flow Input” and “PO1 Output”. The Confi guration sceens can accessed from
the operation mode, scroll down and enter “100” as the password when prompted.
Control
Mode:
Select desired control type.
OFF:
When “OFF” is selected, the PID Control program will be deactivated.
Flow Pacing:
This control type will provide a process output (PO1) proportional to the AI1
proportional input signal (and multiplied by the Dosage setting). This control method does not factor
the eletrode readings in any way.
Set Point:
This control type will provide a process output (PO1) that is adjusted as needed to
maintain the “Set Point” value.
Compound (Compound Loop):
This control type will provide a process output (PO1) that is adjusted
as needed to maintain the “Set Point” value and also factors in changes registered through the
proportional input signal (and multiplied by the Dosage setting). This control method type will not
appear as an option unless the needed input signals are detected.
Channel:
Select the channel (i.e. measurement) that the PID control will use in its calculations (e.g. pH,
ORP or Conductivity).
Set Point:
Set the target measurement value that the PID control will use to adjust chemical feed.
Dead Band:
This is a dead band around the Set Point. As long as the reading is within (+ or -) this
amount from Set Point, the program will consider the Set Point met. This is used to avoid excessive,
continual adjustments.
Integral:
A factor used in the calculation of needed adjustments to the process output. This value ranges
from 0 – 100%. Essentially, the program makes a calculation of how much the output needs to be
adjusted in order to reach Set Point and this factor. Increasing the Integral will increase the rate of each
individual adjustment (and vice versa).
Lag Time:
This is the time that elapses between a change in chemical feed rate and the change in
measurement observed by the monitor. The PID Control program will wait-out this amount of time
between each adjustment to PO1. Instruments should be installed to minimize lag time in order to
optimize control (ideally limit this time to less than 5 minutes).
Max Lag Time:
A maximum Lag Time, which can be used in Compound Loop Control only. When in
use, this sets limits the maximum lag time that can be calculated by the variable lag time formula.
Lag Time Mode:
Select “Fixed” or “Variable”. If “Fixed” is selected, only the “Lag Time” will be used.
If “Variable” is selected, the lag time used will vary as the fl ow varies, but will be limited to the Max Lag
Time.
Flow Variable K:
Enter desired fl ow level. If “Variable” is selected, the lag time will be calculated as
follows: Flow at Variable Lag divided by the current fl ow rate and then multiplied by the Lag Time.
NOTE: In applications where
fl
ows vary greatly, lag times may also change signi
fi
cantly. In these
instances, the use of variable lag times will improve control timing.
NOTE: If “Fixed” is selected as “Lag Time Method”, the settings of “Max Lag Time” and “Flow at Variable
K” are ignored.
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