Hitachi NEXT Series Instruction Manual page 67

① CPCS Motor Speed Control
Based on the pressure signals detected by the pressure
sensor, the built in circuit board's CPU performs PID
operations or calculates the motor speed that will meet
the compressed air consumption rate, and then inputs
the calculated results to the inverter. The inverter will
output the instructions of the corresponding frequency to
the motor. The discharge pressure is controlled within a
targeted range due to the increasing and decreasing
speeds of the motor.
Pressure
② Two-Step Purge Control
Two-Step Purge Control is activated if the following con-
ditions below occur at the same time:
・ T he operating frequency drops to 40 (35) Hz (equiva-
lent to 60 (55) % of the air consumption).
・ T he pressure detected by the pressure sensor rises to
an upper (purge-start) pressure point.
The blowoff solenoid valve (1) will operate to start purg-
ing the compressed air (contained between the airend
and the check valve) to atmosphere. The system will
decrease the operating frequency to its lowest operating
frequency, 24 Hz, thus saving power. When the pressure
detected by the pressure sensor drops to a lower (purge-
stop) pressure point, the system increases the frequency
to 40 (35) Hz and the blowoff solenoid valve (1) reoper-
ates to stop the purging, returning the system control
back to CPCS Motor Speed Control.
（240VWN Models）
③ Motor Stop/Restart Control
Motor Stop/Restart Control will activated under one of
the following conditions:
・Air consumption decreases to about 5 %
・ P urge operating continues for 15 minutes.
The system will then automatically stop the motor. For
protection, the motor can only be stopped once every
180 operating minutes. When the pressure detected by
the pressure sensor drops to a lower (purge-stop) pres-
sure point, the system will automatically restart the
motor, returning the system control to CPCS Motor
Speed Control.
IMPORTANT
(1) Once the motor has stopped, it cannot restart for 15
seconds.
(2) The plant's system pressure may drop drastically before
the motor will restart, 15 seconds later. To avoid such
problems, install an air receiver tank of volume larger
than the prescribed one.
8. STANDARD COMPONENTS AND SUBSYSTEMS [Capacity Control System]
CPCS Motor Speed Control by Inverter and CPU
Inverter
P: proportional
I: integral
D: differential
IMPORTANT
PID stands for Proportional, Integral, and Differential.
CPCS stands for Constant Pressure Control System.
Compressed
DSP
Motor
Air
Pressure Sensor
IMPORTANT
The differential range between the upper pressure point
and the lower pressure point must be 0.05 MPa or more.
Pressure
①
Upper Pressure
Standard Pressure
Lower Pressure
Hz＞40 (35)
Operation Frequency Hz
（Q≦60 (55)%）
Q＞5%
or
T＜15 minutes
① ②
CPCS Motor Two-Step Purge
Speed Control Start/Stop Control
100
①
②
0
Constant Pressure
of the Discharge Air
② ①
Minimum
0.05MPa
Minimum
0.01MPa
Time
Hz≦40 (35)
Q≦5%
or
Air Consumption Q
T≧15 minutes
or
Purging Time T
Number of
N＞1
Motor Stopping N
(for 180 minutes)
N≦1
③
Motor Stop/Restart
Control
② ②
③ ③
Time
65