Instruction Manual

C-PRO NANO RACK E C-PRO MICRO RACK APPLICATION MANUAL
Page 48
6.3 Adjustment of the compressors
Checking the suction pressure of the compressors implies the management of the compressors to reach and
maintain a certain operating pressure value: according to the type of check (sideband adjustment or neutral zone
adjustment) and the use or lack thereof of the inverter for a finer adjustment, four types of adjustment are
considered.
6.3.1 Sideband adjustment
The sideband check uses the characteristics of the PI regulators (proportional and integral) or of the P regulators
(proportional) to establish when to plug in or unplug the compressors being used, in order to regularize, within
the differential range, the turning on or off of the various devices.
The parameters relative to the first circuit are the following:
1 SPC1 = Setpoint compressors (SP)
2 PC14 = Type of adjustment = 0
3 PC16 = Integral time (TI)
4 PC17 = Sideband (BP)
5 PG11 = Number of compressors
6 PG04 = Number of throttlings
The number of compressors and the number of throttlings supplies the Maximum Number of Steps with which
the proportional band is divided.
The purpose of the Proportional +Integral adjustment is to obtain a null error in this type of scheme.
The image above shows the behavior of the proportional band adjustment (SP, SP +BP). Based on the value of
the suction pressure, the adjustment adds or subtracts the number of steps that are required of the compressors.
In this adjustment, the band is entirely moved above the setpoint.
It is possible to choose whether the check will refer to the PI or only to the P adjustment, by setting the
parameter for the integral action, which is the integration time (Ti). Specifically, if this parameter is set to a
value of zero, the adjustment is only proportional, otherwise it also becomes integral. The Ti corresponds to the
time needed by the integral action to be equal to the proportional action, given the hypothesis of a constant
error: the speed of this action is proportionally linked to the value of the integration time. The default parameter
is worth 600 seconds, and so the adjustment takes advantage of the proportional + integral characteristic.
Through the PC78 Sideband steps overlapping factor, it is possible to improve the behavior of this type of
adjustment, which requires wide proportional bands in order to be stable, by modifying the subdivision of the
adjustment band of adjustment between the steps:
SP SP + BP
Steps
Max steps
Suction