Hitachi RAC-25YH4, Service Manual, Page: 78 / 121

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(1). IS OVL
The voltage amp. circuit amplifies the DC current level detected by the detection transformer CT1.
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 generate
from the DC current flowing to the detection resistor, and supplies it to IC4 pin (5). IC4 forms a non-
inverting voltage amp. circuit together with the peripheral elements.
The microcomputer stores the set values which vary according 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
→
DC current : low
Amplification : low
→
DC current: high
Fig. 6-4
Fig. 6-2
Power
Main P.W.B.
Reset
Reset output
(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 (5) and supplied to microcomputer pin (60) . The microcomputer
compares this input with the set value, and if the input exceeds the set value, it enters overload
control status.
Fig. 6-3 shows the rotation speed control. When the voltage at pin (60) of the microcomputer exceeds
the set value, the microcomputer decreases the rotation speed of the compressor and reduces the
load.
Fig. 6-3
RAS_25_35_AW_055-086 2003.12.31, 10:59 AM 76