17 Instruction Manual
MODBUS RTU (Optional)
The β-meter uses the MODBUS RTU protocol. This protocol defines a message structure
that hosts and clients will recognize and use on the network over which they communicate.
The MODBUS RTU uses a Master-Slave Query-Response Cycle in which the signal
converter is the slave device.
Control Functions
The communications option supports the following function codes:
:
:
:
03 Read holding
registers (4xxxx)
Reads the value in a holding
register
Installation Overview
RS-485 may be multidropped up to 1200m and up to 32 units may be chained together. An
optically isolated adapter is recommended at the PC. Terminators should be used to help
improve the quality of electronic signals sent over the RS-485 serial wires. The RS-485 serial
chain should be terminated at the beginning (RS-485 adaptor) and at the last device in the
RS-485 serial chain. This is accomplished by connecting resistors (180Ω) from (A) to (B) at
the RS-485 port. A six way screw terminal is used up and down connected in the RS-485
serial chain.
BETA4 Wiring (Slaves)
External RS-485 Wiring (Master)
A
B
GND
A
B
GND
+
-
+
-
+
-
+
-
A
B
GND
A
B
GND
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