BASI
Electromagnetic flowmeter
BF
M921
Operation manual
31
5.1.8
RS485 interface
The serial port RS485 is designed for online communication between flowmeter and computer. It is suitable
for real time flowmeter monitoring. In contrast to the RS232 serial port, which is suitable for one-shot
configuration or calibration of the flowmeter. The RS485 can be connected to up to 16 flowmeters together
and the total connection length of all wires can be up to 800 meters. Positive output (A) is on terminal 11,
negative output (B) on terminal 12.
Example of three flowmeters and one computer interconnection:
All flowmeters and computer are connected parallel using twisted pair cable. At each end of the
communications line should be 470
terminations.
Interconnection of three flowmeters and computer using RS485 bus
Flowmeters are marked with numbers. These numbers are equal to flowmeter’s RS485 address.
FlowAssistant software for PC is designed for flowmeter control using RS485 or RS232 serial bus
Note 1: Communication through the serial port RS485 is a half duplex type. The flowmeter is a listener and
sends data only after a query from a computer. Each flowmeter has its own RS485 address. The range of
addresses is 0 to 255. Factory setting of RS485 address is 0. Communication speed is selectable between
4800 and 115200 Bd. For cables over 100m or a noisy power supply voltage (especially peaks generated,
usually by motors, etc.), select communication speed below 9600 Bd.
Note 2: Serial port RS485 is galvanically isolated from all the other electronic circuits.
5.1.8.1
RS485 bus properties
RS485 interface can work in three modes:
a) Normal – communication protocol ADAM compatible with flowmeter M910.
b) Modbus RTU – communication protocol Modbus, binary communication.
c) Modbus ASCII – communication protocol Modbus, ASCII communication.
To transfer the data using RS485 bus, 8N1 data format is used, i.e. each data word includes 8 bits, no parity
and one stop bit.
5.1.9
USB/RSR232
USB/RS232 interface is intended for flowmeter configuration and calibration. It’s not recommended to use
this interface during general flowmeter operation, since IP protection is void as a result necessity of the case
lid to be open. For communication during operation use of RS485 interface is recommended. Interface is
galvanically isolated from all the other parts of flowmeter. Configuration or calibration data can be changed
with remote commands, or using supplied software FlowAssistant.
5.1.9.1
USB connector
The connector is located on the top left corner of the bottom PCB. Flowmeter can be connected to computer
with supplied USB A-B cable.
BF
M921 _ 1
BF
M921 _ 2
BF
M921 _ 3
PC
470
470
