Endress+Hauser EngyVolt RV12, Operating Instructions Manual

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Appendix EngyVolt RV12
42
period, (set by control software in the “master”), the “master” will abandon the
“conversation”.
11.3.2 Connecting the instruments
Screened twisted pair cable should be used. For longer cable runs or noisier environments,
use of a cable specifically designed for RS485 may be necessary to achieve optimum
performance. All “A” terminals should be connected together using one conductor of the
twisted pair cable, all “B” terminals should be connected together using the other
conductor in the pair. A line as described in (→  35) or any other line with equal
specification and a characteristic impedance of 120 Ω is recommended. The cable should
be terminated at each end with a 120 Ω, min. 0.25 W, resistor and a capacitor with 1 nF in
series with the resistor.
2
B A Gnd
B AGnd
2
B A Gnd
2
B A Gnd
1
1 nF 1 nF
120
W
120
W
A0016443
 8 Modbus connection
1 Modbus Master
2 EngyVolt Modbus Slave
There must be no more than two wires connected to each terminal, this ensures that a
“Daisy Chain or “straight line” configuration is used. A “Star” or a network with “Stubs
(Tees)” is not recommended as reflections within the cable may result in data corruption.
A0016444
 9 Correct straight line connection
A0016445
 10 Incorrect star or stubs connection
11.3.3 A and B terminals
The A and B connections to the EngyVolt devices can be identified by the signals present
on them whilst there is activity on the RS485 bus.