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OPERATING INSTRUCTIONS – INTELLISYS w/ MODULATION CONTROL
SSR UP6 40, SSR UP6 50PE, SSR UP6 50PEI, HF50–PE,
EP50–PE, HP50–PE, HXP50–PE
MODULATION CONTROL
For those plants which have relatively high constant air demand
relative to the compressor capacity, the recommended control mode is
modulation.
The modulation control system retains the features of the on–line /
off–line control, but also provides for throttling of the inlet flow up to the
off–line air pressure setpoint value.
By applying line pressure to an adjustable modulator valve, the
throttling position of the inlet valve is controlled, thus allowing the
modulator to ”trim” the inlet valve position as dictated by the line
pressure.
The modulating pressure range is about 4 psig (0.3 BAR) and the
modulator normally should be set to straddle the compressor rated
pressure. Modulation begins when the line pressure reaches about 99
percent of the compressor rated pressure and continues as/if the line
pressure rises. Modulation becomes stable when the compressor
output equals the plant air demand. When the modulation is at the
factory setting, the flow will be reduced to 60 percent of the
compressor rated capacity (as indicated in Figure 1).
Capacity control of machines supplied with electro–pneumatic control
and the modulation option can be manually switched from
on–line/off–line to modulation (MOD) via the control mode switch (SS)
located adjacent to the pressure switch.
MODULATE TO
94% CAPACITY
% OF RATED LINE PRESSURE
% OF RATED FLOW
MODULATE TO
85% CAPACITY
MODULATE TO
60% CAPACITY
MODULATE TO
72% CAPACITY
KEY
A Normal settings of modulator
B Optional field settings of modulator
C IntellisysR off–line set point
FIGURE 1
ACS CONTROL (INTELLISYS w/ MODULATION OPTION ONLY)
For compressors supplied with IntellisysR control and modulation
option, ACS control will allow the compressor to automatically switch
between on–line/off–line and modulation control, depending on air
demand.
If the air demand has decreased to a level below the 60 percent
modulated output, the line pressure will increase slightly to actuate the
IntellisysR. The compressor will then shift to the off–line control
position, and operate unloaded with the compressor vented.
It is sometimes desirable to begin modulation at a higher pressure than
the standard factory setting, thereby increasing the modulated capacity
at the time the IntellisysR is actuated. Refer to Figure 1 for modulated
capacities available when this is done.
The compressor will then operate to deliver full capacity air to the plant
system. If the plant air system pressure rises to that of the IntellisysR
off–line set point, pressurized air will be sent to the inlet valve causing
it to close, and to the blowdown valve, causing it to open.
The compressor will continue to run unloaded, but since pressure
levels have reduced, it will do so with a minimum power draw.
The IntellisysR has a fixed minimum differential of 10 psi between the
off–line air pressure setting and the on–line air pressure setting. The
differential may be increased by adjusting the on–line air pressure
setting of the IntellisysR.
The automatic control selector (ACS) is designed to continuously
monitor the plant air demand and select either the on–line/off–line, or
the modulate control mode – whichever is most desirable at any time
during an operating day.
It allows the compressor to operate in its most efficient mode thereby
reducing power costs.
When the compressor operates in the on–line/off–line control mode,
the length of time the compressor remains in the ”off–line” condition is
an indication of the plant air demand. IntellisysR controller is sensing
and awaiting a sufficient line pressure decrease before signalling a shift
to the on–line mode. If the ”off–line” time period is relatively short,
thereby indicating a high demand for air, it is preferable to shift the
control system to upper range modulation.
The IntellisysR does this, and does it automatically if the compressor
unloads 3 times within a 3 minute time period.
If later, the plant demand decreases, and even under modulate control
the line pressure reaches the setting of the IntellisysR controller, and
the control shifts to the ”off–line” mode, the time in this mode will still be
monitored. A long ”off–line” time period indicates a low plant air
demand, indicating the desirability of operating in the on–line/off–line
mode.
The IntellisysR then does this, and does it automatically if the
compressor operates unloaded for more than 3 minutes.
Modulation Only
If MODULATION ONLY is turned on in the setpoint routine, the unit will
shift to Modulation control mode immediately when the unit is running.
The 3 cycles within 3 minutes time period required for ACS to change
to Modulation mode is bypassed. The unit will stay in Modulation mode
until the unit runs unloaded for 3 minutes (the unit then returns to ACS
control) or MODULATION ONLY is turned off via the set routine.
Delay Load Time
This is the amount of time the line pressure must remain below the
on–line setpoint before the compressor will load or start (if the unit was
stopped due to an auto start/stop situation). Setting the load delay time
to 0 will cause no delay. When the delay load timer becomes active, the
display will switch to package discharge pressure (if not displaying
package discharge pressure at that time) and then display the delay
load count down. Once the count down reaches 0, the unit will load or
start and the display will return to line pressure. The display select
button is inactive during the delay load count down.
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