Johnson Controls SABROE Unisab III Control, Engineering Manual

Page: 76 / 348

Engineering manual - UniSAB III 1.10.8
76/346
001930 en 2021.06
Compressor control and surveillance
3.1.8 Regulation of reciprocating compressors
Reciprocating compressors are capacity regulated in stages by connection/disconnection of cylinders,
typically in pairs, through solenoid valves controlled by UniSAB III.
How fast the compressor loads/unloads stages is determined by the timers Delay up and Delay down ,
which will start counting as soon as the value is outside the neutral zone. The regulator is allowed to
have a P Band of 0, which means that the stages are loaded in seconds as set.
If the P band is above 0, the delay times can be prolonged as long as the value is within the P band. The
P band is only relevant if the P band factors
Delay up and/or Delay down are set in the picture P band
factor at a value above 1. See P band factor in section 6.5 Timers .
If the value is just outside the neutral zone and the P band factor Delay up is e.g. 10, counting will be
slow: “1 sec.” becomes 10 sec. If the value is just outside the P Band, counting will be speeded up, "1
sec." becomes 1 sec.
For reciprocating compressors connected to frequency converters see also the UniSAB III sequence
manual.