Walchem WebMaster ONE Instruction Manual page 58

4-20 mA Inputs 1 - 8
This section will only appear if there is an analog input card installed in the controller.
Use the pull-downs to select the function of the analog input channel. The functions available are
described below.
Make sure that you correctly match the programmed sensor type with the actual sensor type
connected to that input!
Not Used should be selected if nothing will be connected to the input channel.
Level should be selected if a liquid level transmitter will be connected to the input channel. The
input can be logged, or alarms sent if the level is outside programmed values.
Flow Meter should be selected if a flow transmitter is connected to the input channel. The
controller can log the flow rate, total flow volume, and alarm if the flow rate or total is outside
programmed values. Relays can also be controlled to activate for a given time after a given volume
of solution has passed through the flow meter.
Generic should be selected if the transmitter connected to the input is anything else but the types
described above. You will be able to span the input, give it a custom name and units of measure,
set alarm points, and use it to control relays.
Relay (1 – 8) Control Mode
Use the pull-downs to select the control mode for each relay. The various choices are described
below. Once the control modes have been selected, click the Submit Changes button. This will
change the Relay Input Assignment section that comes next, making the possible choices for the
input assignment match the control mode.
Not Used should be selected if the relay is not being used.
On/Off Set Point should be selected if the relay needs to respond to a sensor input or analog input
signal. The relay will activate and deactivate if the input value goes outside of programmed limits.
In the relay menu, you will specify the set point value, dead band value, control direction, etc.
Time Proportional should be selected if the relay will be activated for a larger percentage of a
programmable time period as the process value gets further away from the set point value.
Cycles of Concentration should be selected to activate the relay based on a set point that is the
ratio of two conductivity sensor input readings. This option is only available if at least two sensors
are defined as conductivity sensors.
Intermittent (Fixed Blowdown Time) should be selected for boiler control where the
conductivity is checked at a fixed time interval, and if found to be above the set point, the relay is
activated for a fixed time.
Intermittent (Proportional Blowdown Time) should be selected for boiler control where the
conductivity is checked at a fixed time interval, and if found to be above the set point, the relay is
activated for a time that varies with the conductivity's deviation from the set point.
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