Emerson Rosemount 935, Reference Manual, Page: 18 / 76

If this occurs, it is due to blockage, very low signal, partial obscuration, or full beam
block. In this situation, detection is no longer possible. The detector's proper operation
can be restored (auto reset) during operation if the condition causing the problem is
removed or resolved. This mode occurs after a delay of 60 seconds from the moment
of the fault. This delay is important to eliminate momentary obscuration due to
passing through the beam.
• Fault 2 (1 mA output) - critical
In this case, the detector is disabled due to electrical/software operational failure,
central device (memory or processor) fault, or low voltage. This fault causes the
detector to cease operation.
If there is a fault in the 0-20 mA loop, the output is 0 mA.
3.1.4 Zero calibration mode (1 mA output)
This mode zeroes the base level from which the detector reads gas.
Only do this when:
• No gases are present.
• There is a clear path between the source and the detector.
• Weather conditions are clear.
Use a field communicator or host software on your personal computer (PC) to zero
calibrate after installation, re-alignment, and window cleaning. While the device is
connected to the field communicator, you can also use the magnetic mode selector for
zero calibration.
Related information
Zero calibrate
3.2 Visual indicators
One three color LED indicator is located in the back side of the detector/source and can be
seen through the back cover window.
See Figure 2-2
The detector statuses are listed in Table 3-1 .
Table 3-1: Detector LED indications
Detector status LED color LED mode
Fault Yellow 4 Hz - flashing
Alignment / Standby Yellow 1 Hz - flashing
Zero calibration Yellow Constant
Normal Green 1 Hz - flashing
Warning Red 2 Hz - flashing
Alarm Red Constant
Operating modes Reference Manual
May 2022 00809-0100-4035
18 Emerson.com/Rosemount