Hitachi RAS-25QH1 Technische Information Seite 175

9.2 Overload control circuit (OVL control circuit)
@ Overload control is to decrease the speed of the compressor and reduce the load when the load on
the air conditioner increases to an overload state, in order to protect the compressor, electronic
components and power breaker.
@ Overloads are judgement by comparing the DC current level and set value.
@ Fig. 9-4 shows the overload control system configuration and Fig. 9-5 is a characteristic diagram of
overload judgement values. There are two judgement methods—external judgement which compares the
externally set value with the DC current value regardiess of the rotation speed and internal judgement
which compares the set value that varies according to the rotation speed programmed in the micro
computer software with the DC current value.
AX-8H20 micro computer
© To power module
negative © terminal
DC current
externally set
value
A/D
converter
A/D
converter
Detection
resistor
Judgement OVL
according to the rotation
speed
Voltage amp.
circuit
(Internal judgement)
Rotation speed data
Selects data according
to the rotation speed and|
DC voltage.
DC voltage
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Fig. 9-4 Overload Control System Configuration
External judgement value
DC current
Judgement vaiue according to the rotation speed
(internal judgement value)
Rotation speed
Fig. 9-5
(1) Overload external judgement circuit
e@ The filter consisitng of R463A and C2 removes high harmonic components from the voltage generted by the current
flowing to Detection resistor ; R2 and C501A average the voltage. This voltage is then input to OP1 pin @ and
amplified and is supplied to micro computer pin @ . The micro computer compares this input with the internally
set value, and if the input exceeds the set value, it enters overload control status.
@. Fig. 9-7 shows the rotation speed control. When the voltage at pin @ of the micro computer exceeds
the set value , the micro computer decreases the rotation speed of the compressor and reduces the load
regardless of the rotation speed commanded by the indoor micro computer.
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