OTT HydroMet SUTRON XLINK 100, Руководство по эксплуатации и техническому обслуживанию

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19 Modbus
Modbus is a communications protocol commonly used in industrial applications. Please see the W
IKIPEDIA
ENTRY
for more details.

The station can be configured as a Modbus server or as a limited Modbus client.

In Modbus client mode, the station collects data from Modbus sensors.

In Modbus server mode, the station provides sensor data to a Modbus client.
19.1.1 The Station as a Modbus Server
The station is able to function as a Modbus server. In this role, the station will respond to requests from a
Modbus client, typically providing data that the station has collected from sensors.
The example below illustrates performance as a Modbus server:

The station is setup as a Modbus server on RS-485. This involves setting Modbus RS485 Server
Enable to ON.

Measurement M1 is configured to collect data from an SDI-12 sensor. This means that the station
collects data from the SDI-12 sensor on a scheduled basis.

Periodically, the Modbus client will get the most recent data that was collected by the station
from the SDI-12 sensor. This effectively makes the station a bridge between the Modbus client
and the SDI-12 sensor.

The Modbus client gets th at sensor data by reading the station’s input registers 1 and 2,
combining the result into a 32bit floating point value. Registers 1 and 2 reflect the last reading
from measurement M1. Similarly, registers 2 and 3 relate to M2. Please see the section
19.4.1.2
I
NPUT
R
EGISTERS
for details on other registers.
Please note that if the station is setup as a Modbus server, it will no longer perform any other function
on that port.
This means that if the station is a Modbus server on RS-232, the RS-232 port cannot be used for command
line communications. Similarly, if the station is a Modbus server on RS-485, then the station cannot collect
sensor data over RS-485.
In server mode, extended Modbus commands allow the downloading of the station log, reading and
writing station setup, accessing status information, and more.
Please note that using Modbus server will increase power consumption of the station. When it is a
Modbus server, the station is always ready to accept incoming data. RS-232 and RS-485 do not have
control lines that can be used to wake the station up, resulting in an power consumption increase of about
8mA @ 12V. Modbus over cell requires that the cell modem be on and listening all the time, which
increases power consumption too.