19 – 4
Section 19 • Compressor Sequencing
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
Start Offset:
• Denes the offset from process temperature control
setpoint to start compressor. If process temperature
surpasses start offset setpoint and compressor ca-
pacity has reached max, then the sequencing algo-
rithm allows the starting and loading of compressors
to cater for increasing load requirements. The lead
compressor should bypass this setpoint(i.e. should
not wait for start time period when suction pressure
is below setpoint + start offset).
Stop Offset:
• Denes the offset from process temperature control
setpoint to stop compressor. If process temperature
surpasses stop offset setpoint and compressor ca-
pacity has reached min, then the sequencing algo-
rithm allows the stop and unloading of compressors
to cater for decreasing load requirements. The lead
compressor in sequencing should bypass this off-
set (i.e should not stop and keep running with min
load).
Figure 19-3. Compressor Sequencing Screen – Control Mode Change
Start Timer:
• If process temperature surpasses the process tem-
perature control setpoint then this timer’s value is
used to make periodic sequencing decisions.
Stop Timer:
• If process temperature drops below the process tem-
perature control setpoint then this timer’s value is
used to make periodic sequencing decisions.
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