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.
14 • MRLDS-250 Infrared Gas Detector I&O Manual
026-1315 Rev 4
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.
Table 4-2
- MRLDS-250 Behavior During a
Non-Critical Fault
Item
Behavior During Alarm State
Green
LED
Off (indicating the gas detector is
offline)
Display
Shows the appropriate fault code
Analog
Output
4-20 mA output Changes to 2 mA
1- 5V output Changes to 0.5V
2-10V output Changes to 1.0V
Modbus
Registers
Modbus registers indicate the fault
4.5.3.
Critical Faults
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
Item
Behavior During Alarm State
Green
LED
Off (indicating the gas detector is
offline)
Display
Shows the appropriate fault code
Analog
Output
4-20 mA output Changes to 2 mA
1- 5V output Changes to 0.5V
2-10V output Changes to 1.0V
Modbus
Registers
Modbus registers indicate the fault
