the service life of the valve and the relay. A longer Min Pulse increases the service life
of the hardware, but it also makes the regulation less accurate.
• Run Time is the approximate time it takes for the capacity slide to move from mini-
mum position to maximum position and vice versa at constant signal. Please note that
Run Time for the capacity slide may be reduced by variable slide end stop etc where
this is relevant.
• Reg. output is the inner loop regulator output in percent between 0 and 100%.
3.1.6 Vi slide regulation
If there is automatic Vi slide control, it works the same way as the inner loop with the one
exception that Unisab III calculates the position set point according to the actual suction and
discharge pressure. The parameters are available in the picture Control values/Capacity/Vi
slide pos./Control.
3.1.7 Regulator settings
If I is selected, the regulator works approximately like the former “three-point I” regulator. Ir-
respective of whether PID or I is selected, it is recommended to begin with the factory values
and then, if necessary, adjust the values to the conditions of the actual plant.
Outer loop
If PID is selected, it is not recommended to adjust the P band further down than 10°C and
T.int. further down than 30 seconds. Higher values may very well occur. T.diff. is usually al-
ways 0.
The neutral zone can be set for 0.4°C or higher if it is not required that the suction pressure is
kept as narrow as possible around the set point. If the neutral zone is too high, the regulator
may fluctuate too much.
If I is selected, the outer loop is working more moderately than when PID is selected. A P
band of less than 10°C may therefore be used. Requirements for the neutral zone are the
same as when PID is selected. As already mentioned, T.int. and T.diff. are not accessible
when PID = No.
Inner loop
As regards the inner loop it is not recommended to use any other values than the default val-
ues for Neutral zone (Nz = 0.0) and Proportional band (P band = 200%).
The parameter Min Pulse determines the pulse duration up or down every time the solenoid
valve is activated. If the value is high, a correspondingly large capacity change is required be-
fore the regulator reacts with an up or down signal. This is a kind of neutral zone. Default val-
ue is 0.5 seconds and should not be higher than 2 seconds.
Compressor control and surveillance
Engineering manual - Unisab III 1.10
001930 en 2014.09
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