Walchem W600 Series Instruction Manual page 73

Example 1: The Lead output (R1) is set for On/Off control of pH with a setpoint of 8.50, a deadband of 0.20
and a "force lower" control direction. The first Lag output (R2) has a setpoint of 9.00 and a deadband of 0.20.
The second Lag output (R3) has a setpoint of 9.50 and a deadband of 0.20. The delay time is disabled (set for
0:00 minutes). Wear leveling is disabled. When the pH goes above 8.50, R1 energizes. If the pH proceeds to
exceed 9.00, R2 energizes. And if the pH rises above 9.50, R3 energizes. When the pH decreases to below 9.30,
R3 goes off. When the pH falls to below 8.80, R2 goes off. And finally, when the pH decreases to below 8.30, R1
is turned off.
Example 2: The same three-pump configuration (R1←R2←R3) as in Example 1 except the delay time is set
for 30 minutes. When the pH goes above 8.50, R1 energizes. If 30 minutes passes before the pH exceeds 9.00
or drops below 8.30, R1 remains on and R2 is energized. If the pH then rises above 9.00, the next output in the
group, R3, is energized. If the pH continues to rise and exceeds 9.50, no additional action is possible. When the
pH decreases to below 8.80, R3 goes off. When the pH falls to below 8.30, both R1 and R2 are turned off.
This control is very similar to the operation if three (3) separate On/Off control outputs are configured all with
the pH as Input and using the setpoints listed above. However, the Lead Lag option improves on this control by
incorporating backup pump controls and optional time based activation. If the pH rises above 8.50 when pump
R1 has an active Flow Verify alarm or is in HOA Off mode, pump R2 immediately energizes. R3 energizes
when the pH goes above 9.00. Although no third pump is available to activate if the pH continues to rise above
9.50, this control system is more fault tolerant than the currently available options.
Switch Based
When using switch based activation mode, each Lag output has an Activate With Channels setting that is used
to specify one or more digital input or relay output channels that activates an additional output. Switch based
activation mode incorporates time based activation and can also be configured to trigger an additional output
(if available) after a specified delay time. This menu selection is available only when the Lead output is using
Manual control mode.
Example 1: A lift station includes a tank with a high level switch (D1) and a high-high level switch (D2). Three
pumps are configured as a Lead Lag group (R1←R2←R3). The Lead output (R1) is set for Manual control
mode with an Activate With Channels selection of D1 (high level switch), R1 will be energized if D1 closes. The
first Lag output (R2) has an Activate With Channels selection of D2 (high-high level switch). The last Lag out-
put (R3) has no Activate With Channels selected. All pumps are in HOA Auto mode. The delay time is disabled
(set for 0:00 minutes). Wear leveling is disabled. When the high level switch closes, the R1 pump is activated.
If the high-high level switch closes, the R2 pump is also activated. When D2 opens, R2 is turned off. When D1
opens, R1 is turned off. In this configuration, the R3 pump serves only as a backup in case one of the pumps is
down for maintenance (in HOA Off mode).
Example 2: The same lift station, two-level switches, three-pump configuration (R1←R2←R3) as in Example
1 except the delay time is set for 1 hour. When the high level switch closes, the R1 pump is activated. If the
high-high level switch closes, the R2 pump is also activated. If the tank level remains above the high-high level
switch for another 1 hour, the R3 pump is activated. When D2 opens, R3 is turned off. When D1 opens, both R2
and R1 are turned off. In this configuration, the R3 pump serves not only as a backup in case one of the pumps
is down for maintenance, but also provides additional capacity should it be needed.
Advanced Functionality
The examples listed above detail the control behavior if wear leveling or output activation modes are enabled.
The features are implemented independently. Wear Leveling modes are used to determine which output(s) are
activated. Output Activation modes determine how many output(s) are activated at one time. More advanced
output control strategies can be implemented when these features are used in combination.
Example: In a two-pump scenario, the Lead output (R1) is set for On/Off control of pH with a setpoint of 8.50,
deadband of 0.20 and a "force lower" control direction. The Lag output (R2) has a setpoint of 9.00 and a dead-
band of 0.20. Time unbalanced (80/20) wear leveling is selected with a cycle time of 15 minutes. When the pH
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