Ametek Land 4500 MKIII, User Manual

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Opacity and Dust Monitor
User Guide
Model 4500 MkIII
B - 18
B4.12 AFU Modbus Interface
Modbus communications, based on the RS485 hardware standard, provide
direct access to the Model 4500 MkIII system data. Details of the Modbus
protocol are available from the Modbus website
www.modbus.org
. The Model
4500 MkIII implements Functions: 3 (Read Holding Register), 6 (Pre-
set Single Register) and 10 (Pre-set Multiple Registers). Modbus Register
numbers are given in Section 9.
Each AFU has three Modbus output ports called the Data Output Port, the
Master Port, and the Control Port.
The Data Output Port is a Modbus slave. It can be connected to a Data
Acquisition System for continuous monitoring of Opacity or Dust Density
measurements. It can also be used to receive commands, such as Calibration
Check, from a Plant DCS. The Data Port uses RS 485 communications
The Master Port is normally connected to the 4500 MkIII Transceiver,
however if additional AFUs are needed, the Master Port of the second AFU
is connected to the Data Output Port of the first AFU, and so on, up to a
maximum of four AFUs connected to one Transceiver.
The Control Port is a Modbus slave. It can be used to monitor the operation
of the 4500 MkIII, and to change the settings, without interrupting normal
operation. RS485 and RS232 connections are provided for this port. They
should not be used simultaneously. The Control Port can also be used as a
second Data Output port.
RS485 networks connected to the Data Output and Control ports must have
one termination resistor at each end and one bias network somewhere on the
bus. The Model 4500 MkIII AFU can provide a termination resistor and a bias
network. As supplied, the termination resistor is switched on, and the bias
network is switched off. To change the switch settings, See section A4.4.
AFUs are shipped with the Data Output and Control Ports set as follows:
Baud rate: 19200
Parity:
Even
Data bits: 8
Stop bits: 1
The Baud rate and Parity are controlled by switch settings as described in
section A4.4.
The Slave Address for both slave ports is set in the Transceiver, and its
default value is 7.
The Slave Address can be changed using the Transceiver Control panel as