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Aeroqual AQM60 User Guide
4.
Calibration
4.1. Calibration Frequency
The frequency of calibration depends on a range of operational factors including importance of the dataset,
cost and stability of the instrument under the prevailing conditions. A discussion of these factors is given
below. For further reference you may view:
a) The US EPA Quality Assurance Handbook at:
http://www.epa.gov/ttnamti1/qalist.html
b) The Good Practice Guide for Air Quality Monitoring and Data Management,
2009” Ministry for the
Environment, New Zealand at
http://www.mfe.govt.nz/publications/air/good-practice-guide-air-quality-
Calibration frequency is a key consideration for a calibration and maintenance programme. There are three
types of standard method calibration requirements for gaseous contaminants:
1.
Initial calibration:
Where zero air and calibration gas atmospheres are supplied and any necessary
adjustments are made.
2.
Operational precision checks:
Where the zero and span responses of the instrument are checked
for drift on a regular basis. The recommended frequency is daily,
but in any case it is recommended
that precision checks be undertaken at least weekly
to adjust or correct for zero and span drift.
3.
Operational recalibration:
Where zero and span gases are supplied, as for an initial calibration. It
should be done when the instrument drift exceeds the instrument performance requirements, or after
six months
since the last calibration. Multi-point checks should be carried out every six months.
It is recommended that instrument be calibrated (or recalibrated):
Upon initial installation
Following relocation
After any repairs or service that might affect its calibration
Following an interruption in operation of more than a few days
Upon any indication of instrument malfunction or change in calibration
At some routine interval (see below).
The routine periodic calibrations should be balanced against a number of considerations, including the:
Inherent stability of the instrument under prevailing conditions of humidity, temperature, pressure,
mains voltage stability and the like
Costs and time involved in carrying out calibrations
Amount of ambient data lost during calibrations
Data quality goals
Risk of collecting invalid data due to a problem with the analyser not discovered until the calibration
is performed.
Note: Routine maintenance and calibrations should be scheduled in such a way that any associated
data loss is evenly distributed throughout the year, avoiding critical monitoring times. Tracking the
results of the calibrations on a spread sheet can help determine the frequency of calibrations and
also draws attention to trends in the drift.
Summary of Contents for AQM60
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