AMC-DTM-Sensor Transmitter
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Decreasing alarm triggers when gas concentration stays lower than the threshold value for
period of time equal to Activation Delay. It is deactivated when concentration stays above the
threshold plus the hysteresis value for period of time equal to Minimum Run Time.
The default Hysteresis parameter is 2% of Range.
5.5.3 Zero
Buffer
Gas concentrations smaller than this value are interpreted as 0 to reduce false readings due to
noise and zero-level sensor drift. Note that the result of this is a “jump” in the concentration. For
example, if Zero Buffer is 2ppm, LCD display will “jump” from 0ppm to 2.1ppm when
concentration increases from 2ppm to 2.1ppm.
It is possible to measure and display negative values for an un-calibrated unit.
The default Zero Buffer parameter is 2% of Range.
5.5.4 Range
Range is the gas concentration used as a reference point to set the saturation point for the
4-20mA output current loop. When measured gas is of equal or higher concentration than
Range output current is driven to 20mA. It is usually set close to the highest gas concentration
the sensor can measure (saturation point).
The transmitter is capable of showing concentration values greater than the Range up to
maximum of 21mA (5% overshoot), assuming that the sensor can measure these
concentrations.
5.5.5 Engineering
Units
Advisory
: Changing Engineering Units is an intrusive action. Usually, the unit configuration
(sensor parameters) would have to be adjusted. Also, the unit would have to be re-calibrated
when engineering units are changed.
The transmitter supports the following Engineering Units:
•
ppm,
•
ppb,
•
%LEL,
and
•
%VOL.
Gas concentration values have different format for different Engineering Units:
(Note that the following does not apply to values displayed in the operator menu).
“ d” denotes decimal digit:
ppm:
dddd.dppm if Range <= 30ppm.
dddddppm if Range > 30ppm.
Max value 4999.ppb:
ddddppb
Value always rounded to 10ppb.
Max value 4999.
