ABB SensyMaster FMT230 Commissioning Instruction page 21

SENSYMASTER FMT230, FMT250 THERMAL MASS FLOWMETER | CI/FMT230/250-EN REV. A
Modbus response time
The typical response time of the device is normally less than
100 ms (minimum response time). The response time is
calculated from the end of the request telegram from the
master to the beginning of the response telegram from the
slave.
The response time can be increased via the parameter
"modbusResponseDelayTime".
The length of the response telegram is dependent upon the
number of bytes read and the baud rate configured.
Cable specification
The maximum permissible length is dependent on the baud
rate, the cable (diameter, capacity and surge impedance), the
number of loads in the device chain, and the network
configuration (2-core or 4-core).
— At a baud rate of 9600 and with a conductor cross section
2
of at least 0.14 mm (AWG 26), the maximum length is
1000 m (3280 ft).
— When using a 4-core cable as a 2-wire wiring system, the
maximum length must be halved.
— The spur lines must be short, a maximum of 20 m (66 ft).
— When using a distributor with "n" connections, each branch
must have a maximum length of 40 m (131 ft) divided by "n".
The maximum cable length depends on the type of cable used.
The following standard values apply:
— Up to 6 m (20 ft):
cable with standard shielding or twisted-pair cable.
— Up to 300 m (984 ft):
double twisted-pair cable with overall foil shielding and
integrated earth cable.
— Up to 1200 m (3937 ft):
double twisted-pair cable with individual foil shielding and
integrated earth cables. Example: Belden 9729 or equivalent
cable.
A category 5 cable can be used for Modbus RS485 up to a
maximum length of 600 m (1968 ft). For the symmetrical pairs
in RS485 systems, a surge impedance of more than 100 Ω is
preferred, especially at a baud rate of 19200 and above.
Change from two to one column
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