CB-100-2 35
Fig.23: Graphical representation of the general control functions
6.1 Extension module for pressure control
Graphical explanations of the control functions of the
extension module for pressure control described in the
following sections, see figure 24, page 36.
Basic function and minimum settings
If the extension module for pressure control is connec-
ted with the VARIPACK frequency inverter, this is im-
mediately detected by the VARIPACK frequency in-
verter which then enables the relevant parameters for
the extension module.
Apart from the basic settings, at least the following
parameters must be set for direct control:
• Refrigerant
• Evaporation temperature
• Evaporation temperature limiter (pump down)
• Condensing temperature
The compressor control is based on the so-called pump
down logic. For this, the digital start input (DI1) must be
permanently closed or can be used to release a control
switch. The compressor is switched on as soon as the
evaporation temperature exceeds the setpoint and
stops when the evaporation temperature falls below the
set value of the evaporation temperature limiter (pump
down).
In operation, the VARIPACK frequency inverter controls
the set evaporation temperature by regulating the com-
pressor frequency and by switching on/off the fixed fre-
quency compressor (relay FsC2, X5: 1 and 2). The reg-
ulation speed can be adjusted to the requirements by
setting the P band.
The set condensing temperature can be regulated via
the analogue output by means of the 0..10V signal. In
order to guarantee the most efficient level of operation,
it is recommended to set the minimum allowable con-
densing temperature of the compressors if the system
allows doing so. If the condensing temperature ex-
ceeds the setpoint, the rotation speed of the fans is in-
creased accordingly. By adjusting the P band to the
system inertia, the quality of the control can be optim-
ized. In addition, a minimum fan speed can be set, if
necessary.
"Evaporation temperature setpoint 2"
By a signal to the input DI3, the evaporation temperat-
ure setpoint 2 is activated.
"Condensing temperature setpoint 2"
By a signal to the input DI4, the condensing temperat-
ure setpoint 2 is activated. This value can be used, for
example, as setpoint for heat recovery.
"Condensing temperature limiter"
The condensing temperature limiter reduces the com-
pressor frequency as soon as the set condensing tem-
perature is exceeded. Thus a cut out on high-pressure
can be avoided in many cases since the load on the
condenser is reduced by lowering the frequency.
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