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INM MTL 130-0126 Rev 13
15
NOTE
Hysteresis is the difference between the levels at which an alarm triggers and resets. For
example, an instrument with a 100% range with an alarm set to mode = HIGH, level = 5%
and hysteresis = 1% will trigger the alarm as the reading exceeds 5%, and reset it once
the level has fallen to 4%.
The maximum hysteresis that can be set is 10% of the span of the particular channel. It
is important not to set the hysteresis to a level greater than the alarm point otherwise the
alarm will never reset.
Alarms only operate when the range they apply to is selected. E.g. If Range 3 (90 to100%
Hydrogen in Air) was selected only alarms 3 and 4 would be active; alarms 1 and 2 would be
automatically set to the ‘OFF’ mode until the appropriate range was selected. This is not the
case for alarms 1 and 2 if they are programmed as ‘Fault’ and ‘Range Selected’ indicators.
NOTE
The analogue output is set to 2mA when the instrument is initialising, in calibration mode
or a fault code is being displayed.
4.6 Fault codes
Fault code
Meaning
1
Indicates fault while instrument is in the CO
2
in air range
2
Indicates fault while instrument is in the H
2
in CO
2
range
4
Indicates fault while instrument is in the H
2
in air range
8
Temperature channel A/D reading out of range low
16
Temperature channel A/D reading out of range high
32
CO
2
offset too low ( < 4% H
2
based on H
2
in CO
2
range)
64
CO
2
offset too high ( > 4% H
2
based on H
2
in CO
2
range)
128
Air offset too low ( < 10% H
2
based on H
2
in air range)
256
Air offset too high ( > 10% H
2
based on H
2
in CO
2
range)
512
CO
2
scale too low (CO
2
reading < 60% based on CO
2
in air range)
1024
CO
2
scale too high (CO
2
reading > 140% CO
2
based on CO
2
in air range)
2048
H
2
in air scale too low (H
2
reading < 60% H
2
based on H
2
in air range)
4096
H
2
in air scale too high (H
2
reading > 140% H
2
based on H
2
in air range)
8192
H
2
in CO
2
scale too low (H
2
reading < 60% H
2
based on H
2
in air range)
16384
H
2
in CO
2
scale too high (H
2
reading > 140% H
2
based on H
2
in air range)
32768
Measure channel A/D reading < (-)4090 counts
65536
Measure channel A/D reading > 4090 counts
NOTE
If a fault occurs a code is reported on the screen. Multiple faults are shown as their sum. For
example a high air offset combined with a fault in the hydrogen in air range would be reported
as fault code 260 (256+4). In all cases alarm relay 1, if configured as a fault alarm, will switch.