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4
4
Transmission Wave Pattern and Noise Check
[1] M-NET Transmission
This series of air conditioning units is controlled by sending signals among centralized control, outdoor units,
and indoor units. Noise entering transmission line interferes with normal signal transmission and causes mal-
functions.
(1) Symptoms caused by noise
(2) Wave Pattern Check
Check wave patterns in transmission
line with an oscilloscope, and make
sure that the following conditions are
met:
1
No fine wave patterns (noise) are
found. Fine noises (around 1V)
may be picked up when operating
DC-DC converter or inverter. This
noise will not cause problems if
units and transmission line are
shield-earthed.
2
Voltage of transmission signals
meet the following conditions:
[With transmission]
[Without transmission]
No fine noise allowed
No fine noise
allowed
52
µ
s
52
µ
s
52
µ
s
52
µ
s
52
µ
s
V
BN
V
HL
logical
value
“0”
ogica
value
“1”
Transmission line voltage
Logical Value
VHL over 2.0V
0
BVN over 1.3V
1
Cause
Symptoms
Error
Codes
Definitions
Noise
infiltration
Alters signals and they are mistaken for other address signals
Transmission wave patterns are changed.
Wave patterns are changed and become unrecognizable and
the receiving end of the signal becomes unable to respond.
Un-communicable state lasts due to fine noise.
Signals can be sent, but response cannot be sent or received.
6600
6602
6607
6603
6607
6608
Multiple-Address Error
Transmission Processor H/W Error
Non-acknowledgeable Signals Error
Transmission Circuit Bus-Busy Error
Non-acknowledgeable Signals Error
No Response Error
1
Make sure that transmission line and power-supply
line are not cross-connected
2
Make sure that transmission line in one system is not
bundled with transmission line in another system
3
Make sure specified transmission wire is used
Place transmission wire as far away from power source line
as possible (at least 5cm).
Do not put them in the same conduit.
Do not bundle transmission lines, since they may cause
malfunctions.
Use specified transmission wire
• For systems using shield wire
Type of transmission wire - shield wire CVVS, CPEVS
Wire Diameter-over 1.25mm
2
Check Points
Remedies
Wiring Check
(3) Identifying noise source and remedying the problems
1
Treatment of Noise
Check the following when noise is picked up or when error codes in section (1) are displayed on the LED.