39
5. Serial interfaces
5.1 RS485 interface with BMS protocol
The RS485 interface which is galvanically isolated from the device electronics
and current output serves as a physical transmission medium for the BMS
protocol. If several A-ISOMETER®s or other bus-capable devices are inter-
connected in a network via the BMS bus, the BMS bus must be terminated at
both ends with a 120
Ω
resistor.
An RS485 network that is not terminated, is likely to get instable and may
result in malfunctions. Only the first and the last device in one line may be
terminated. Devices in between must not be terminated with 120
Ω
. Hence,
stub feeders in the network must not be terminated. The length of the stub
feeders is restricted to 1 meter.
A
B
A
B
A
B
1st device
... device
last device
120
W
0.4 W
120
W
0.4 W
Stub feeder
maximum 1 m
Maximum length of the RS485 bus: 1200 m
Summary of Contents for A-ISOMETER AGH575S-6
Page 6: ...Table of Contents 6 TGH1384en 06 2005...
Page 16: ...Function 16 TGH1384en 06 2005...
Page 20: ...Installation and connection 20 TGH1384en 06 2005...
Page 25: ...Operation and setting 25 TGH1384en 06 2005...
Page 59: ......
