Gas Detector Faults; Overview; Non-Critical Faults; Critical Faults - Emerson MRLDS-250 Installation And Operation Manual

NOTE: The alarm feature includes
a 20% deadband to prevent alarm
"chatter" if the concentration
hovers near the alarm setpoint.
Once the alarm has been triggered,
it will remain latched until the concentration
drops below 80% of the alarm setpoint.
4.5.

Gas Detector Faults

4.5.1.

Overview

There are two levels of fault monitoring built into the
gas detector:
1. Non-critical
2. Critical
4.5.2.

Non-Critical Faults

Non-critical faults typically recover by allowing the
gas detector surroundings to stabilize, for example,
after a defrost cycle. The gas detector continues to
monitor its surroundings during non-critical faults,
but may report inaccurate readings.
The following occurs when a non-critical fault
condition exists.
Item Behavior During Alarm State
Green Off (indicating the gas detector is
LED offline)
Display Shows the appropriate fault code
4-20 mA output
Analog
1- 5V output
Output
2-10V output
Modbus
Modbus registers indicate the fault
Registers
Table 4-2 - MRLDS-250 Behavior During a
Non-Critical Fault
14 • MRLDS-250 Infrared Gas Detector I&O Manual
4.5.3.
Critical faults may indicate an unrecoverable
condition. Please refer to Section 7, MODBUS
Communications for more information. The following
occurs when a critical fault condition exists:
Table 4-3 - MRLDS-250 Behavior During a Critical
Fault
Changes to 2 mA
Changes to 0.5V
Changes to 1.0V


Critical Faults

Item Behavior During Alarm State
Green Off (indicating the gas detector is
LED offline)
Display Shows the appropriate fault code
4-20 mA output
Analog
1- 5V output
Output
2-10V output
Modbus
Modbus registers indicate the fault
Registers
Changes to 2 mA
Changes to 0.5V
Changes to 1.0V
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