CPC MultiFlex PAK, Руководство пользователя

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22 • MultiFlex I/O Board Operator’s Guide 026-1712 Rev 3 03-JAN-2008
analog output, called "Fan Sequencer," which
then can be used as an input to a third-party
device that translates this voltage to a series of
relay activations.
The control method for Fan Sequencer is
similar to the method used for Staged Fans (see
Section 6.2.1.1. ), except each fan stage is repre-
sented by an analog voltage on the Fan
Sequencer input. When the TD is above setpoint,
the PAK starts from all fans OFF (0V) and
begins activating fan stages by increasing the
voltage in a series of steps (with each step corre-
sponding to a fan stage). The user must program
two setpoints: the voltage that will activate the
first fan stage, and the step voltage amount that
will be added to the current voltage every time a
new stage is to be activated.
When the TD falls below the setpoint, the
Fan Sequencer output steps down the voltage in
the reverse order of its increase, until the voltage
reaches 0V (all fans OFF).
Example: a sequencing device is set up to
control four stages of fans, with the first
sequence to be activated at an input voltage of
2.0VDC, and the remaining three to be activated
with a step voltage of 1.5VDC. The Fan
Sequencer voltage at each fan stage are:
As the PAK brings on fan stages to lower the
TD, it will start with 2V, then step up to 3.5V, 5V,
and finally 6.5V to bring on fan stages. When the
TD setpoint is satisfied, the PAK will sequence
backwards from 6.5V to 5V, then 3.5V, 2V, and
finally 0V to turn off all stages.
6.2.2. Minimum Pressure Set Point
To prevent overcooling, the MultiFlex PAK
features a minimum pressure set point. If the
value of the discharge/condensing pressure falls
below this set point, regardless of the TD strat-
egy, fans will be staged OFF one at a time,
observing the Fan OFF Delay after each deacti-
vation.
6.2.3. Discharge Pressure Max
The Discharge Pressure Maximum feature
adds a second "line of defense" to TD control. If
the value of the discharge/condensing pressure
rises above the Disch Pres Max set point, fans
will be cycled ON one stage at a time (observing
the Fan ON delay after each activation), regard-
less of the number of fans called for by TD con-
trol.
6.2.4. Condenser Spray
If a condenser spray output is configured, the
PAK can be programmed to activate a water
spray to keep the discharge pressure from climb-
ing above a user-defined pressure set point.
The spray is activated when the discharge
pressure rises above the condenser spray set
point, and shuts off when the pressure falls
below the Return To Normal set point (which is
the cut-off pressure for the condenser spray) lon-
ger than the Condenser Spray OFF time.
To prevent unnecessary activation of the
spray when the ambient conditions make evapo-
rative cooling less effective, the PAK can be pro-
grammed with an ambient temperate lock out,
which prevents the spray from activating if the
ambient temperature is below a user-defined
ambient lockout set point.
6.2.5. Interlock
Interlock is an optional feature that cycles
OFF all condenser fans if:
• No compressors are operating, AND
Fan Seq
Voltage
Active Fan Stages
0V No fans ON
2.0V Fan Stage 1 ON
3.5V Fan Stages 1&2 ON
5.0V Fan Stages 1,2,&3 ON
6.5V All Fan Stages ON
Table 6-2 - Example of Fan Sequencer Voltage and Fan Stage
Mapping