PPI HumiTherm Plus, User Manual

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HumiTherm Plus for PC User Manual
FACTORY COMPRESSOR
Compressor Switching Strategies
The PPI “Tempe Humidity” composite controllers offer different programmable strategies for compressor switching to
meet different design approaches by the manufacturers of Humidity Chambers. The various strategies and the
implementations are described here.
1. Compressor Off
The compressor is kept Off. This strategy is usually selected for temperature values significantly above the ambient
temperature.
2. Compressor On
The compressor is kept On regardless of the measured or set temperature value. This strategy is usually selected for
temperature values significantly below the ambient temperature.
3. SP Based Strategy
In this strategy, the chamber temperature range is split in two zones by setting the parameter 'Boundary Set-point' (BSP).
Refer Figure 5.2 below.
The zone at and above the boundary SP ( ) is referred as Heat Pre-dominant zone and that below the boundary SP ( )
is referred as Cool Pre-dominant zone. The controller automatically switches between the two zones depending upon the
Temperature SP. If the Temperature SP is below boundary SP, Cool Pre-dominant zone is active and the compressor is kept
ON. If the Temperature SP is at or above boundary SP, Heat Pre-dominant zone is active and the compressor is kept OFF. This
strategy eliminates the need for the user to manually switch the compressor ON or OFF.
If the parameter Control Zones is set to “Dual”; separate tuning can be performed in the Cool and Heat Pre-dominant zones for
accurate control in each zone. The controller maintains separate sets of Proportional Band, Integral Time & Derivative Time
constants for each zone that are automatically selected and used by the controller depending upon the active zone.
However, if the parameter Control Zones is set to “Single”; the controller uses a single set of Proportional Band, Integral Time
& Derivative Time constants for both zones.
Figure 5.2
70°C
0°C
45°C
30°C
50°C
Temp. Control SP in
Cool Pre-dominant Zone
Temp. Control SP in
Heat Pre-dominant Zone
Compressor Status
Boundary Set-point
ON
OFF