5.2 Control
Introduction
There are various modes for controlling air temperature for the preservation of foodstuffs in cold rooms
and showcases. The following figure shows the position of the intake probe (air on) Sr and the outlet
probe (air off) Sm. The virtual probe Sv is a weighted average of these two, based on parameter /4,
according to the following formula:
Code Description Def Min Max UOM User
User
terminal
/4
Virtual probe composition
0 = Air off probe Sm
100 = Air on probe Sr
0 0 100 % S NO
For example, if /4=50, Sv=(Sm+Sr)/2 represents an estimated value of the air temperature around the
refrigerated food.
Note: HACCP: parameter /4 can be set to change the temperature used for control and for display.
This operation may be prohibited by HACCP procedures or require record keeping and authorisation.
Example: vertical showcase
Fig.5.e
Ref. Description
Sm Outlet probe (air off)
Sr Intake probe (air on)
Ref. Description
Sv Virtual probe
During the day, most of the load in a refrigerated showcase is due to warm air that enters from the
outside and mixes with the cold air inside. Control based on the intake probe, due to high temperature
outside the showcase and the mixing of the air, may not manage to reach the set point. Displaying the
intake temperature would show a temperature that is too high. Setting a set point that is too low for the
intake probe Sr may cause the food to freeze. On the other hand, displaying the outlet temperature
would show a temperature that is too low. Consequently, the display of the control probe, set point or
virtual probe can be configured using parameters /t1 and /t2.
ON/OFF control on the outlet (air off) probe is defined by:
l set point;
l differential
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