Johnson Controls SABROE Unisab III Control User Manual

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 De-
lay down, which will start counting as soon as the value is outside the neutral zone. The regu-
lator 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, count-
ing 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 se-
quence manual.
Compressor control and surveillance
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Engineering manual - Unisab III 1.10
001930 en 2014.09

Johnson Controls SABROE Unisab III Control Specifications

General

Brand	Johnson Controls
Model	SABROE Unisab III Control
Category	Control Systems
Language	English