Rs-485 Modbus Rtu (Optional) - Emerson Net Safety Millennium II Reference Manual

Reference Manual
MAN-0076, Revision 09
The fault relay is normally energized when no fault conditions are present and is set up for non-latching.
The operation of the fault relay is not configurable.
The Millennium II transmitter provides various fault conditions to indicate that the transmitter or
connected sensor(s) are not operating as expected. These fault conditions will override any alarm
conditions because the sensor may be unable to detect a gas exposure reliably. Examples of fault
conditions can range from no detection due to memory or communication errors and sensor failure.
Other faults can provide unreliable detection due to sensor drift or sensor nearing the end of its life.
When a Millennium II transmitter is in fault mode, immediate action should be taken to determine the
source and correct the fault condition.
The fault relay output is not commonly used to imitate an automatic shutdown. The fault output
indicates a potential problem with the transmitter not an alarm condition.
6.4

RS-485 Modbus RTU (Optional)

Optional RS-485 Modbus RTU protocol is available. The tables on the following pages give the detailed
Modbus registers and the bit values for the transmitter register.
The Millennium II Transmitter utilizes 2- wire Modbus RS-485 multi serial mode. This Modbus solution
implements a 2-wire electrical interface in accordance with the EIA/TIA-485 standards. For this
MODBUS configuration, it is important that a third wire be used for connecting all the 'Common'
(COM) in the chain. Also a 120 Ohm line termination is required for the last device in the line. See
6-2. The Instrument Engineer is responsible for calculating line length and adhering to Modbus
protocols.
Figure 6-2 Two-wire Modbus configuration
Monitoring and outputs
Monitoring and outputs
June 2016
Figure
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