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Each digital input channel set up as a Feed Monitor type has a Flow Alarm Mode setting used to specify how the
pump output is handled when Flow Verify alarms are identified. Based on this setting, the Lead Lag group responds
as follows:
Disabled
The Flow Verify alarm is never activated and the Lead Lag group is not affected by
the status of the PosiFlow input.
Interlock
When a Flow Verify alarm is activated, the related output is immediately turned
off; if available, other outputs in the Lead Lag group are activated instead.
Maintain
When a Flow Verify alarm is activated, other outputs in the Lead Lag group are ac-
tivated instead if they are available; if no other outputs are available, or if addition-
al outputs are required due to Output Activation Mode settings, output(s) reporting
a Flow Verify alarm may still be activated as a last resort.
Wear Leveling Modes
After the Lead Lag group is defined, additional parameters can be configured within the settings list of the last out
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put in the group. These options optimize the behavior of the Lead Lag functionality. Several different wear leveling
options can be selected to control the order in which outputs are activated.
Disabled
The order in which the Lead and Lag outputs turn on does not change automatically. They are always energized in
the same order.
Duty Based
The order in which outputs are activated changes every time the Lead output is activated. How long each individu-
al pump has been running is not considered.
Example: When the Lead output, set for On/Off control, drops below the setpoint, R1 is activated. R1 turns off
after its deadband is satisfied. The next time the measurement goes below the setpoint, R2 is activated and R1
remains off. After all outputs in the group have been exercised for one feed cycle, the process begins again with the
first output (R1).
Time Balanced
Time balanced mode alternates outputs in a manner that equalizes the runtime of all connected pumps. This mode
takes into account how long each output in the Lead Lag group has been running (since a manual reset) and selects
the output that has the lowest on-time during each cycle. If the output remains energized longer than the specified
cycle time, the time-on for each output is recalculated and a different output may be activated to balance the usage
of each.
Example: In a two-pump Lead Lag group, time balanced wear leveling is selected with a cycle time of 2 hours.
When the Lead control mode (R1) determines the output should be activated, R2 turns on because it has the lowest
accumulated on-time. After 2 hours, if the output remains activated, the on-times are re evaluated and R2 turns off
and R1 turns on because it now has the least accumulated total on time. The cycle continues until the Lead control
mode determines the feed is complete.
Time Unbalanced
This wear leveling mode improves fault-tolerance of the group by varying the wear on each pump by activating
each pump for a different percentage of time. In this mode, a primary output is activated most of the time and sec
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ondary (auxiliary) output(s) are activated for a smaller percentage of the total output on-time. This strategy can
be useful to ensure that a backup pump is exercised sufficiently so that it will be functional when needed, but does
not wear at the same rate as the primary pump to minimize the chances of both pumps failing at the same time.
When one Lag pump is defined within the Lead Lag group, the Lead pump runs 60% of the time and the Lag pump
runs 40%. If more than two (2) pumps are defined for the group, fixed ratios are used to insure all pumps are exer
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cised periodically and wear at different rates, as shown in the chart.
