EVCO c-pro mega RACK - Manual (Page 72)

C-PRO MEGA RACK & C-PRO GIGA RACK APPLICATION MANUAL
Page 72
The PC78 Sideband step overlap parameter allows improvements in the behaviour of this type of
regulation, which requires broad proportional bands in order to be stable, thus modifying the
subdivision of the regulation band between steps:
The insertion of steps occurs at PC78% of the proportional band, while release occurs at 100 –
PC78% of the band; if for example PC78 = 60%, steps are inserted between 60% and the maximum
value (100%) of the proportional band PB, and in the same way released between 40% and the
minimum value (0%) of the same band PB.
It is obvious that by using step division, as indicated in the figure, the activity interval of each
individual step is greater with respect to standard geometric division, with the obvious advantage
that the proportional band may be reduced, in favour of greater regulation accuracy, and/or the
activation of the steps occurs with reduced frequency, or reduced compressor start-ups, to the
benefit of the mechanical lifespan of the same.
6.3.2 Neutral zone regulation
This type of regulation envisages the definition of a neutral zone, within which no activation or
deactivation decision will be taken, i.e. startup operations will not be requested for any of the
devices.
The parameters defining this regulation are as follows:
⋅
Neutral zone (NZ)
⋅
Out of zone differential (Diff)
⋅
Side band suction SetPoint (SP)
Outwith said neutral zone, device on or off requests for the various steps provided by the
compressors will follow this logic:
⋅
Switch on : When the suction pressure exceeds the setPoint + Neutral Zone threshold
⋅
Switch off : when the pressure drops below the setPoint
In this type of regulation, the neutral zone is displaced to the right of the setPoint.
As may be deduced from the figure, regulation envisages setting times, within which, depending on
100 - PC78 %
SP SP + BP
Steps
Max Steps
Suction
PC78 %
Insertion
Release
SP SP + ZN SP + ZN + Diff SP - Diff
NZ_TOnMin
NZ_TOnMax NZ_TOffMax
NZ_TOffMin Neutral zone
Switching on Switching off
Suction pressure