4. RS 485 ( ModBus )
Current Transducer supports MODBUS (RS485) RTU
protocol( 2-wire )Connection should be made using twisted
pair shielded cable. All "A" and "B" connections are daisy
chained together. The screens should also be connected to
the “Gnd” terminal. To avoid the possibility of loop currents,
an Earth connection should be made at one point on the
network. Loop (ring) topology does not require any
termination load. Line topology may or may not require
terminating loads depending on the type and length of cable
used. The impedance of the termination load should match
the impedance of the cable and be at both ends of the line.
The cable should be terminated at each end with a 120 ohm
(1/4 Watt min.) resistor.
RS 485 network supports maximum length of 1.2km.
Including the Master, a maximum of 32 instruments can be
connected in RS485 network. The permissible address
range for Current Transducer is between 1 and 247 for 32
instruments. Broadcast Mode (address 0) is not allowed.
The maximum latency time of current transducer is 200ms
i.e. this is the amount of time that can pass before the first
response character is output.
After sending any query through software ( of the Master) , it
must allow 200 ms of time to elapse before assuming that
the Current Transducer is not going to respond. If slave does
not respond within 200 ms, Master can ignore the previous
query and can issue fresh query to the slave.
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