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2.4 Gas conditioning and filtering information
The LGD Compact Gas Sensor Modules are based on an optical measurement technique where performance
is directly linked to optical transmission through the measurement cell. Sample gas containing particles and
aerosols are likely to contaminate the optical windows of the measurement cell and degrade the optical
transmission more or less quickly. Contamination strongly depends on particle size, material, charging effects,
etc. which can vary considerably across different applications. It is therefore generally very difficult to give a
precise specification concerning the purity of the gas in order to avoid contamination on a reasonable time
scale.
Due to the multitude of applications for the LGD, gas conditioning and filtering has to be carried out by the
integrating Original Equipment Manufacturer (OEM). The following points are crucial in order to operate the
module correctly and to achieve long operating lifetime:
The sample gas has to be dust-free; we recommend the use of appropriate filters with pore size ≤ 2
µm.
The sample gas has to be moisture-free; we recommend the use of appropriate sample gas dryers
ensuring r.H. ≤ 50% or non-condensing.
The overall performance of the module, the amount of service intervals as well as the lifetime can be
positively influenced by employing appropriate filter technology. We recommend the use of commercial
solutions available from industry-specific manufacturers.
The temperature of the incoming sample gas has to be at the same temperature as the temperature
of the measurement cell. Deviations will create a decrease in accuracy
2.5 Calibration / calibration verification / offset and span
The calibration is factory set. When the sensor module is used in conditions defined for calibration (operating
temperature 20°C, pressure 1013 hPa and humidity 45% r.H.) there is no need for re-calibration. However,
an additional off-set and span can be added, for instance, in order to compensate for systematic errors in
gas delivery and calibration equipment, or when the device is operated at a different temperature.
If adjustment of calibration is desired, proceed
as follows:
The device is designed and calibrated for
measurements of a target gas in N
residual humidity content.
Before executing offset and span calibration or
verification, ensure the gas measurement is
stable.
Allow for sufficient time for the instrument to
de-gas before fixing the 0-concentration and
span calibration.
First, carry out the offset and follow with the
span correction procedure. To verify the
calibration, the procedure can be repeated.
The values for span and offset can be set in the
Customer Frontend in the menu "Settings" ->
"Sensor Parameter", changed parameter can be
saved in EEPROM with "OK" button
Axetris AG
LGD Compact Operating & Integration Instructions; Rev. D
with
2
Figure 14 Schematic representation of offset
and span adjust for calibration correction
21/46
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