Hitachi RAC-25FX8, Service Manual

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60
(1). IS OVL
Current transformer CT1 reads the input flowing current and detected to the microcomputer as a voltage
signal. 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.
Fig. 6-3 shows the rotation speed control. When the voltage at pin
of the microcomputer exceeds
the set value, the microcomputer decreases the rotation speed of the compressor and reduces the
load.
Fig. 6-4
Fig. 6-2
Power P.W.B.
Main P.W.B.
Reset
Reset output
Fig. 6-3
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(2). ID OVL
Fig. 6-2. The filter consisting of R245 and C217 removes high harmonic frequencies from the voltage
generated by the current flowing to Detection resistor; R245 and C217 average the voltage. This voltage
is then input to IC4 pin
and supplied to microcomputer pin . The microcomputer compares this
input with the set value, and if the input exceeds the set value, it enters overload control status.
The set Value is determined by the amplification of the voltage amp. circuit
Amplification : high
→
DC current : low
Amplification : low
→
DC current: high
Fig. 6-4 shows the rotation speed control. When the voltage at pin of the microcomputer exceeds the
set value, the microcomputer decreases the rotation speed of the compressor and reduces the load.
DC current
Rotation speed
Judgement value according to the rotation speed
(internal judgement value)
Voltage at microcomputer pin
Rotation speed of compressor
Deceleration Acceleration Deceleration Acceleration
Commanded rotation speed
Actual rotation speed