CIRCUTOR DHB Series - Manual (Page 26)

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DHB-324
DHB-324
DHB-324
6. INTERFACE RS-485
DHB-3xx programmable digital meters have serial links in RS-485
standards for the communication in computer systems and with other
devices fulfilling Master function. An asynchronous communication
character protocol MODBUS has been implemented on the serial link.
The transmission protocol describes ways of information interchange
between devices through the serial link.
6.1. Connection Way of the Serial Interface
The RS-485 standard allows to a direct communication of 32 devices
on a single serial link of 1200 m long. For the connection of a higher
quantity of devices, it is necessary to apply additional intermediate-
separating systems.
The leading of the interface line out is given in the meter user’s manual.
To obtain a correct transmission, it is necessary to connect lines A and
B with their equivalent in other devices. The connection must be made
through a shielded wire. The shield must be connected to the protection
terminal in a single point. The GND line serves to the additional protection
of the interface line at long connections. One must connect it to the pro-
Fig. 10. Connection way of the RS-485 interface