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Refrigerant Level Control
this pre-positioning feature). After the chiller has been
running 3 minutes, if the level is greater than or equal
to the Refrigerant Level Setpoint, it begins controlling
to the Setpoint. However, if it is less than the Refrig-
erant Level Setpoint, a linearly increasing ramp limit,
called the Refrigerant Level Target, is applied to the
Refrigerant Level Setpoint. This ramp limit allows
the level to go from the present level to the Refrigrant
Level Setpoint over a period of time programmed as
the Ramp-Up Time setpoint (3 to 15 minutes; default
8). During this ramp-up period, the Refrigerant Level
Target is used to control the refrigerant level in the
condenser and the Refrigerant Level Setpoint message
on the Condenser Screen is replaced by "REFRIGER-
ANT LEVEL TARGET = XX%". While the ramp is in
effect, "RAMP UP TIME REMAINING = XX MIN"
is displayed. After the ramp period has elapsed, the
refrigerant level is controlled by the Refrigerant Level
Setpoint for the remainder of chiller run. If the Valve
Preset Time is set to 0 seconds and the Ramp-Up Time
Setpoint is set to 15 minutes, the control will operate
the same as previous Flash Memory Card versions, as
described above.
If equipped with Flash Memory Card C.MLM.01.05C.xxx
and earlier or "P" compressors with C.MLM.04.01B
and ear li er, a ramp function as described above, is also
executed anytime the Vane Motor Switch (VMS) transi-
tions from closed to open while the chiller is running.
When the VMS opens, if the re frig er ant lev el is less
than the Level Setpoint, a setpoint ramp is ini ti at ed as
previously described. If the re frig er ant level is great er
than the Level Setpoint when the VMS opens, the level
is con trolled to the Level Setpoint. Since this feature
can produce unstable operation under cer tain conditions,
it has been eliminated in Flash Mem o ry Card version
C.MLM.01.06.xxx and later or C.MLM.04.02.xxx.
If the Liquid Level Sensor output ever increases to
great er than 4.4VDC, indicating a level greater than
100%, "WARNING - REFRIGERANT LEVEL OUT
OF RANGE" is displayed and the Orifi ce Actuator
is driv en open until the level has decreased to a level
with in range. When within range, the warning mes sage
is au to mat i cal ly cleared and normal control is resumed.
This feature can cause unstable operation under light
load conditions. Therefore, both the warning message
and the associated open signal have been eliminated in
Flash Memory Card version C.MLM.01.06.xxx and later
or C.MLM.04.02.xxx.
92
The Program applies an open or close signal, as re quired,
from the Microboard to the actuator to main tain the level
to the Level Setpoint. The duration of the signal de ter -
mines the magnitude of change to the Or i fi ce po si tion.
The duration of the signal and whether it is an open or
close signal depends upon the Proportion Error and the
Rate of Change of the actual level com pared to the Lev el
Setpoint in a recurring period of time called a Lev el Con-
trol Period. At the end of each Lev el Con trol Pe ri od, the
Proportion error and Rate of Change are com pared to
Programmable Setpoints Pro por tion Limit Close, Pro-
portion Lim it Open and Rate Limit Close and Rate
Lim it Open. The re sult of this com par i son de ter mines
the signal that will be applied to the Ac tu a tor at the end
of the Level Con trol Period as fol lows:
The entire chiller run time is divided into Level Con trol
Periods. They occur consecutively and con tin u ous ly. The
fi rst one begins upon entering SYSTEM RUN and when
it ends the next one begins, etc. This repeats until the
chill er is shutdown. The duration of these periods are
pro grammed as the Level Control Pe ri od Setpoint This
period has different ranges, depending on Flash Memory
Card version as follows: 3.5 to 30.0 seconds (version
C.MLM.01.06.xxx and later or C.MLM.04.02.xxx);
1.0 to 5.0 seconds (all earlier versions). The Default
value varies depending upon the Flash Memory Card
version and compressor application as follows: versions
C.MLM.01.06.xxx and earlier (3.5 seconds); version
C.MLM.01.07.xxx and later (10.0 seconds "P" com-
pressors; 3.5 seconds all other compressors). At the
completion of each Level Con trol Pe ri od, the ac tu al level is
com pared to the Lev el Setpoint. The re sult is the Pro por tion
Error (+ 3% is considered zero). The Pro por tion Error is
compared to Setpoints Pro por tion Limit Open (if level
is above setpoint) and Pro por tion Limit Close (if level
is below setpoint). Both of these Setpoints are pro gram -
ma ble over the range of 10% to 50%. If the Pro por tion
Error ex ceeds the Limit Setpoint, the Pro por tion Error
infl uence in the response will be large. If the Pro por tion
Error is less than the Limit Setpoint, the Proportion er ror
in fl u ence in the re sponse is de ter mined by how close the
Proportion Error is to the Limit Setpoint; close yields
larger infl uence, further yields smaller in fl u ence. To
es tab lish the re sponse to the rate of change, the amount
of change in the Level within the Lev el Control Period
(+1% is con sid ered zero) is com pared to the Rate Limit
Close (if level less than setpoint) and Rate Limit Open
(if level greater than setpoint) Setpoints. Both are pro-
gram ma ble over the range of 10% to 50%. (5% to 50%
with Flash Memory Card version C.MLM.01.06.xxx
and later or C.MLM.04.02.xxx). If the result ex ceeds the
Setpoint, the rate in fl u ence in the response will be large; if
FORM 160.54-M1(503)
YORK INTERNATIONAL
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