Hitachi RAM-60QH4 Manuel De Service page 98

Detection resistor
DC current
R245
＋
C220
−
〜
Voltage at point
of microcomputer
Rotation speed
of compressor
(2) Voltage amplifier circuit
• Voltage amplifier circuit voltage-amplifies DC current level detected by converting to voltage using detection resistor
and sends this to microcomputer. Microcomputer A/D-converts it and then compares with internal data to judge over-
load control.
[During overload control]
• Voltage generated from DC current flowing to detection resistor is balanced by resistor R245 and C220, then input to
pin of IC4. IC4 composes non-inverting amplifies, combined with peripheral components.
5
• As shown in Fig. 8-5, a set value varying according to rotation speed is programmed in microcomputer: When DC
current value exceeds this set value, overload control is set. Control of compressor motor is the same as that in
external judgment.
• Set value is determined by amplification rate of voltage amplifier circuit programmed by software.
Amplification rate: High → DC current: Low
Amplification rate: Low → DC current: High
6
5
Is
R247
0V
D104
R108
0V
◯
６ ０
Decelerating
( 300-330V )
−
7
＋
R249
＋
C105
−
0V
Fig. 8-3
Accelerating Decelerating
Fig. 8-4
– 110 –
R500
R253 C205
0V 0V
5V
R278 R222
R221
C221
0V
0V
Commanded rotation speed
Actual rotation speed
Accelerating
Vd
59
Microcomputer
60
Id
Is
61