Biogas Operating Manual
BMUK0001 / Issue 1
Geotechnical Instruments (UK) Ltd
Page 13
5. User
Calibration
5.1 Introduction
The Geotechnical Instruments range of Gas Analysers are calibrated during manufacture and when
returned for service. However, to improve accuracy between services a user calibration can be
performed. Only the three main gases CH
4,
CO
2
and O
2
may be user calibrated.
This section sets out the correct procedures to achieve an accuracy user calibration.
If this calibration is completed incorrectly it may decrease the accuracy of the Gas Analyser.
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 gas present.
Span: The point at which the Gas Analyser is calibrated when a known quantity of the target gas is
present.
5.2 Calibration
Gases
User calibration of a Gas Analyser will improve the data accuracy in the range of the calibration gases
used. This may cause less accurate readings of concentrations outside this calibrated range. Users
should select the correct calibration gas for the expected gas levels on their particular application.
•
To improve calibration at lower levels requires the use of gas mixtures 1 and 2.
•
To improve higher levels use gas mixture 3
.
Calibration gas
CH
4
CO
2
O
2
Mixture 1
5%
5%
6%
Mixture 2
5%
10%
0%
Mixture 3
60%
40%
0%
These are for general use but other gas concentrations can be used.
Only use gases with a known certified concentration.
Note:
The above gases and most other gas concentrations can be supplied by Geotechnical
Instruments (UK) Ltd.
Warning
For each gas used the appropriate material safety data sheet must be
read and understood before proceeding. Calibration gases can be
dangerous.
