OMBIO5KN4.1
BIOGAS 5000 gas analyser
Page
54
Copyright Geotech
9.0 Calibration
9.1
Calibration introduction
The BIOGAS 5000 gas analyser is carefully calibrated at manufacture and when returned
for service. However, it is sometimes desirable to be able to carry out a calibration
process between services.
This section outlines the correct procedures to enable the site engineer to field calibrate
the gas analyser.
Note: This does not replace the factory service and calibration. If this calibration is
completed incorrectly it may decrease the accuracy of the gas analyser.
CH
4,
CO
2
and O
2
can be measured by BIOGAS 5000 gas analyser as standard; these
channels can be user calibrated. The analysers have other gas channel options that are
specified at manufacture; these too can be calibrated. This section will describe in detail
how to calibrate the three standard gas channels plus the CO channel.
The BIOGAS 5000 instrument can have a H
2
compensated CO channel. This option
requires that H
2
is used in the calibration process and is also set out within this section.
For the other gas channel options contact Geotech for advice.
Two important terms that are used within this section are ‘Zero’ and ‘Span’.
Zero:
The point at which the gas analyser is calibrated when there is none of the
target gases present.
Span:
The point at which the gas analyser is calibrated when a known quantity of the
target gas is present.
9.2
Frequency of calibration – best practice
The BIOGAS 5000 gas analysers can be checked against a known concentration of gas, to
give confidence that the analyser is operating as expected at the time and conditions in
which it is being used.
It is recommended that the instrument is regularly serviced and calibrated by Geotech in
accordance with the due date on the instrument.
When defining the frequency of user calibration, the following are factors to be
considered:
The frequency of use of the analyser. (daily?/monthly?)
The level of confidence and accuracy required for readings to be taken.
Historical user calibration data.
Site specific requirements or conditions.
Historical understanding of expected readings on site.
Zeroing of the gas analyser should be undertaken at the start of each day’s monitoring.
Use historical data to drive your frequency of calibration.
If there is no historical data a good starting point for a daily monitoring round is
performing a calibration once every week or every other week.
The results of the calibrations will need to be recorded to monitor over time whether the
frequency of calibration needs to be increased or decreased relative to the confidence
required.
The confidence required will be driven by the site specific / user requirements.
When undertaking the monitoring with an understanding of the history of the gas levels
