45
ULM.0.01.000RE_10_08_20
the work start. Should that be the case, set as follows: transmission rate – 9600bps,
parity – Even, number of data bits – 8, number of stop bits – 1 or 2.
After the interface converter connection to USB, install the device driver where
necessary. Right-click “My computer” label and choose “Properties” in the context
menu. In the appeared window “System Properties”, click on “Equipment” tab,
then click “Device Manager” key (Win XP procedure). Open “COM and LPT
Ports” section in the equipment list. Find COM-port corresponding to the connect-
ed device, double click it to open “Property” window for chosen port and make
sure that the device functions properly.
The RS485 data communications line is laid with the use of “twisted pair” type ca-
ble with surge impedance of 120Ω. External cable insulation must provide adequate
mechanical and electric strength according to the customer’s process and climatic
conditions. Total line length can reach several kilometers.
Fig. 6.4 Classic RS-485 line laying method
Classic line laying method diagram complying with the general requirements of the
RS-485 standard designed for the high-speed data transmission in the industrial in-
terference environment is shown in Fig. 6.4. In case of extended line length, it is
recommended to install tracking resistors 120 Ω at the line ends between the ‘A’
and ‘B’ wires. For this purpose, level transmitter is equipped with switch connect-
ing such resistor to the line; it is designated R
A-B
on nameplate. It should be noted
that in some interface converters, this resistor is also mounted inside. When line
length exceeds 800 m or number of devices per line exceeds 32 items, it is recom-
mended to use standard repeaters for RS-485, for example, ADAM-4510.
Devices with data communications protocol different from Modbus RTU protocol
should not be connected to the data communications line of level transmitter.
The same data communications line must not include transmitters with the identical
Modbus addresses.
!
CAUTION
!
CAUTION
