Section 2
SEQUENCING WITH
MULTIPLE CONTROLLERS
6
6. If, after Recovery Time, the pressure is still above 108 psig (7.4 bar) then the
current trim machine will unload. This process can continue until all machines are
unloaded.
7. If the pressure falls below load pressure +2 psig (0.14 bar) or 102 psig (7.03 bar) the
first machine in the sequence will load and operate as the trim machine.
8. If after the Recovery Time the pressure is still below 102 psig (7.03 bar) then the
trim machine will go to full load and the next machine in the sequence will load and
become the trim machine.
2.6 SYSTEM SETUP AND TUNING
Table 2.1 lists settings for a system of low pressure (90-100 psig (6.2 to 6.9 bar))
machines used in a typical sequencing configuration. The Trim High & Low Setpoints are
not user settable parameters. These values are calculated from the Unload and Load
pressures. The Trim High Setpoint is 2 psi (0.14 bar) below the Unload pressure. The
Trim Low Setpoint is 2 psi (0.14 bar) above the Load pressure.
Table 2.1 Low Pressure Machine Settings (typical)
Machine Setting: Value
Unload Pressure 100 psig (6.9 bar)
Trim High Setpoint (calculated parameter) 98 psig (6.8 bar)
Trim Low Setpoint (calculated parameter) 92 psig (6.3 bar)
Load Pressure 90 psig (6.2 bar)
Lowest pressure 85 psig (5.9 bar)
Recover time (seconds) 10
Note that the unload pressure is set to 100 psi (6.9 bar) and not 110 psi (7.6 bar) as is
normal on a stand alone machine. A stand alone machine set up at 100 psi (6.9 bar) to
110 psi (7.6 bar), starts to modulate above 100 psi (6.9 bar) and the horsepower is
reduced. However, in a sequenced system a machine may be forced to full load, which
would draw more than the rated horsepower above 100 psi (6.9 bar). Therefore, the
modulation band of machines in a sequencing system should be set up to be 10 psi (0.7
bar) lower than their rated pressure.
All running machines in a sequence operate either at full load or unloaded except for one
which is operated as the trim machine. The trim machine unloads when the line pressure
rises above the Trim High setpoint.
Trim High and Trim Low setpoints signal the trim machine to unload before the fully
loaded machines and load before the unloaded machines. Otherwise, all machines
would load and unload at the same time.
LOWEST pressure parameter specifies the lowest pressure allowed before immediately
starting a machine. A machine may also be started if the line pressure drops below the
Trim Low setpoint for a determined period of time.
RECOVER time keeps multiple machines from loading, unloading or starting at the same
time. A timer is reset when a machine loads, unloads or loads after a start. Decisions to
load, unload or start another machine are deferred until the timer reaches the RECOVER
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