Hitachi RAS-25CNH2 Service Manual page 59

Detection
resister
R24
35
R2
36
+
C515
–
Voltage at micro computer pin
Rotation speed of compressor
2
. Voltage amp. circuit
The voltage amp. circuit amplifies the DC current level detected by the detection resistor after being
G
converted to a voltage and supplies it to the micro computer. Receiving this, the micro computer converts
it to a digital signal and compares it with the internal data to judge whether or not overload control is
required.
< During overload control >
The filter consisting of R2 and C515 removes high harmonic components from the voltage generated from
G
the DC current flowing to the detection resistor, and supplies it to OP1 pin 5 OP1 forms a non-inverting
voltage amp. circuit together with the peripheral elements.
The micro computer stores the set values which vary sccording to the rotation speed. When the DC current
G
level exceeds the set value, the micro computer enters the overload control state.
The set Value is determined by the amplification of the voltage amp. circuit.
G
{
Amplification : high [ DC current : low
G
Amplification : low [ DC current: high
G
DC current
R1
0V
38
Is R3
0V
D002
0V
60
Deceleration
(260-360V)
0V
OPI
6
– 7
5
+
R4
43
+
–
0V
Fig. 8-6
Acceleration Deceleration
Fig. 8-7
– 62 –
R508
R507
39
59
Vd
R5
0V
60 Id
5V
61
Is
0V
Commanded rotation speed
Actual rotation speed
Acceleration
8J-HIC
Micro
computer
HIC