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App. - 31
Appendix 4.21 Compressor sequential operation using ring counters
This system provides pressure control using three compressors.
A pressure shortage is detected by the three pressure switches. The number of
compressors operating simultaneously depends on the degree of shortage. To equal
the number of usages of each compressor, compressors are activated according to
the set order.
System configuration of compressor control
ABC
Compressor
Pressure switch
PX1 PX2 PX3
Operating panel
MELSEC-Q
Sufficient
pressure
Start button Stop button
Pressure shortage "Major"
Pressure shortage "Medium"
Pressure shortage "Minor"
Start
PB0
Stop
PB1
Pressure switch
PX1
PX2
X0
X1
X2
X3
Input
Y70
Output
Y71
Y72
Y73
MC
A
MC
B
MC
C
Y74
Y75
Y76
Compressor A
Compressor B
Compressor C
Sufficient pressure
Pressure shortage "Minor"
Pressure shortage "Medium"
Pressure shortage "Major"
PX3
X4
MELSEC-Q