DYACON
®
, Inc
Modbus
Modbus Summary
Modbus is a simple protocol that can be transmitted over several modes including TCP/IP, TIA-
232-A (RS-232), TIA-485-A (RS-485), TCP/IP, SMS, and many others.
Mi-Met WSD-1 uses Modbus-RTU over RS-485.
WSD-1 is a slave device and must be connected to a host device, such as a programmable logic
controller (PLC), host computer with an RS-485 adapter and Modbus software, or to the Mi-Met
weather station control module.
RS-485 is a robust, differential pair electrical protocol that is noise immune and capable of long
cable runs. With twisted pair cabling, such as CAT-5, distances over 1200 m (4,000 ft) can be
achieved. WSD-1 can be configured for 1200 bps or 2400 bps to extend the range. Relatively long
runs are achievable even without twisted pair cables.
The wide operating voltage range and low power of WSD-1 allows for power to be injected over
the same data cable without concern for excess voltage drop. (Two wires for power and two for
data.)
For example, 1200 m (4000 ft) of Cat-5 cable (24 AWG) will result in a voltage drop of less than
0.2 V at an operating current of 2 mA.
WSD-1 ships standard with 20 ft (5 m) of non-paired, outdoor-rated cable.
Modbus Utilities
The address of the sensor and other parameters are configurable. A Modbus computer utility may
be required to change these settings. A number of utilities are available including:
ModBus Constructor
www.kurysoft.com
Simply Modbus
www.simplymodbus.ca
ModbusTools
www.modbustools.com
Only ModBusConstructor and the companion ModbusReader have been tested with the Mi-Met
product. Contact
for copies of the constructor files.
A list of Modbus software can be found at:
www.modbus.org/tech.php
Mi-Met WSD-1 Manual
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