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The analog input is setup to receive an externally powered 4-20 mA signal, but transmitters that require power to be
supplied can be accommodated (contact factory for details).
2.
The Analog input will need to be scaled to match the scaling of the flow transmitter’s output scaling.
This is done
under the Flow Input’s Options menu (see HydroACT menu for more information). After scaling the Flow Input, a
calibration MUST be performed for the input to begin reading accurately.
3.
Go into the PID Options menu and access the IWP setup screen discussed on page 15. Change the Minimum setting
to -100.00%. Note: It is very important to have the negative sign (-) so it shows -100.00%. Make sure the Maximum
setting is set for +100%. The IWP values must remain at -100% and +100% when flow pacing is being utilized.
4.
Go into the PID Options menu and access the Flow Setup menu. Change the Enabled setting from No to Yes. Ensure
the Flow Sensor
setting is mapped to the Flow Input and the parameter shows “Flow”.
5.
Next, set the
Nominal Flow to match the plant’s
typical flow rate. For example, the plant may typically run at 400
MGD and occasionally go up to 800 MGD and sometimes as low as 200 MGD. Since 400 MGD is the typical flow rate
the plant runs at, 400 should be entered as the Nominal Flow.
6.
The next step is to change the High and Low Output settings for upper and lower controller output range (or pump
speed) that you need at that “typical” flow rate. In our example, when the plant is flowing at the typical flow rate of
400 MGD it was determined from past experience that the lowest coagulant pump speed needed at that flow was
10% (low NTU conditions) and the highest pump speed needed would be 40% (high NTU conditions). Using this
example, the customer would enter 40% for the High Output and 10% for the Low Output. Using these settings the
controller establishes an upper and lower control range for the SCM PID output for all flow rate conditions as shown
in the below graph. These settings allow the controller to make proportional changes to the dosage as flow changes
and it will also limit the pump output to the appropriate min and max range (as defined by the blue lines in the below
graph), further reducing the potential for excessive over or under feed of coagulant should a problem occur with the
Streaming Current sensor.
7.
If at any time the Streaming Current reading is not able to reach the Setpoint value, it may be due to needing to
increase the High Output setting or decreasing the Low Output setting, or needing to increase or decrease the output
limits discussed on page 12.
