Hitachi RAS-25WX8 Manuel De Maintenance page 112

(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
the set value, the microcomputer decreases the rotation speed of the compressor and reduces the
load.
(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
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
Fig. 6-4 shows the rotation speed control. When the voltage at pin
set value, the microcomputer decreases the rotation speed of the compressor and reduces the load.
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Power P.W.B.
Voltage at microcomputer pin
61
Rotation speed of compressor
and supplied to microcomputer pin
5
Amplification : high DC current : low
Amplification : low DC current: high
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Reset output
Reset
Main P.W.B.
Fig. 6-2
Commanded rotation speed
Actual rotation speed
Deceleration Acceleration Deceleration Acceleration
Fig. 6-3
. The microcomputer compares this
60
60
Judgement value according to the rotation speed
(internal judgement value)
Rotation speed
Fig. 6-4
– 111 –
of the microcomputer exceeds
61
of the microcomputer exceeds the