Engineering manual - UniSAB III 1.10.8
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001930 en 2021.06
Compressor control and surveillance
3.1.5 Capacity P regulation (inner loop)
The parameters for the inner loop, which is only a proportional regulation (P regulator), are set in the pic-
ture Control values/Capacity/Capacity/Control. The P regulator parameters include Actual Set point,
Neutral zone, Proportional band and P Part. Actual set point is the capacity set point generated by the
outer loop.
Additionally the following parameters can be selected:
• Min Pulse is the shortest pulse given by UniSAB III on the relay output. E.g. it takes time for a
hydraulic valve to open and close and for the hydraulic oil to move so a pulse shorter than about
half a second would have no effect and would only shorten 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 regula-
tion less accurate.
• Run Time is the approximate time it takes for the capacity slide to move from minimum position
to maximum position and vice versa at constant signal. Please note that Run Time for the ca-
pacity 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. Irrespective 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.
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