Hitachi RAS-50WX8 Service Manual page 100

Detection Resistor
N1
A
Is
B
0V
Voltage at micro computer pin
Rotation speed of compressor
Voltage amp. circuit
The Voltage amp. circuit amplifies the DC current level detected by the detection resistor after being converted to a voltage
and supplies it to the microcomputer. Receiving this, the microcomputer 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 R245 and C217 removes high harmonic components from the voltage generated from the DC
current flowing to the detecition resistor, and supplies it to IC4 pin
with the peripheral elements.
The microcomputer stores the set values which vary sccording to the rotation speed. When the DC current level exceeds
the set value, the microcomputer enters the overload control state.
The set Value is determined by the amplification of the voltage amp. circuit.
Amplification : high
Amplification : low
R24
DC Current
10
1
38 39
CT1
D104 R005
58
+
0V 0V 0V
Deceleration Acceleration Deceleration Acceleration
DC current : low
DC current : high
P2
9 1
CN14 CN13
2 5
C205
0V
37
5V
6
7
R245
+
IC4 R248
+
5
5V
R222
C218
R221
0V
Fig. 7-6
Fig. 7-7
IC4 forms a non-inverting voltage amp. Circuit together
– 140 –
Direct Current
DC320-360V
SPM2
MAIN P.W.B.
IC1
59 Vd
AX-8T11
0V
Id
60
0V
61 Is
0V
Commanded rotation speed
Actual rotation speed