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MAN-0076 Rev 05 Millennium II
December 07, 2012
Net Safety Monitoring Inc
Table 6: Current output and meaning (cont’d)
Reg. Value
Current Output
(mA)
Status LED
Meaning
Red
Green
15
2.5
Fast Flash
Sensor Element Failure
16
20.0
Solid
The concentration value is greater than the
allowed range; the sensor is displaying its
maximum concentration value.
17
2.5
Fast Flash
FAULT DETECTED: Sensor baseline has
drifted into a “Negative Gas Concentration”
region (Zero Drift) and requires re-calibration.
18
4-20
Fast Flash
Sensor is nearing end of life. Replace at next
calibration.
20
2.5
Fast Flash
FAULT DETECTED: A critical memory fault
has occurred.
21
2.5
Fast Flash
FAULT DETECTED: A fault has occurred in
the sensor’s onboard power supply.
Note: A slow flash is defined as the Status LED being ‘ON’ for 50 milli-seconds and ‘OFF’ for 1 second, while a fast
flash is the LED being ‘ON’ for 250 milli-seconds and ‘OFF’ for 250 milli-seconds and a very fast flash is the LED
‘ON’ for 50 milli-seconds and ‘OFF’ for 50 milli-seconds.
5.4 RS-485 Modbus RTU
RS-485 Modbus RTU protocol is used. Tables 7 and 8 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 Figure 19. The Instrument Engineer is responsible for
calculating line length and adhering to MODBUS protocols.
Figure 19: Two (2)-Wire Modbus configuration