The reliability of gas analyzer readings relies on regular calibration: zeroing with a zero-point gas (such as high-purity nitrogen), adjusting the span with a standard gas of known concentration, and checking for linearity at intermediate points. The standard gas must have a certificate and be traceable, and the concentration should be close to the actual measurement range. The calibration cycle is determined based on frequency of use, stability and quality system requirements. Calibration records and reports are required for audits such as CQI-9.
- Zero point calibration: high purity nitrogen and other zero point gases
- Span calibration: known concentration, traceable standard gas
- Concentration selection: close to the actual measured value
- Period: determined according to usage intensity, stability and system requirements
- Save calibration records and reports, and trace the impact of deviations beyond limits
Why calibrate
Aging of the infrared light source, air chamber contamination, detector drift, and ambient temperature changes will gradually cause the analyzer readings to deviate. The analyzer is used as the "standard" for carbon potential calibration. If it itself is inaccurate, all calibration conclusions will be invalid.
Calibration content
1. Zero point calibration Pour in zero-point gas (commonly high-purity nitrogen) that does not contain the component being measured, and adjust the reading to zero.
2. Range calibration Pour in the standard gas of known concentration and adjust the reading to the certificate value.
3. Linearity check (optional) Check the midpoint with another concentration of standard gas to confirm that the linearity is good.
4. Calculation function verification Use known gas concentration and temperature inputs to check whether the carbon potential calculated by the instrument is consistent with the theoretical value.
Standard gas selection
| Main points | Description |
|---|---|
| concentration | Close to the actual measurement range, such as CO about 20%, CO₂ low concentration range |
| Certificate | Concentration, uncertainty, expiry date |
| Traceability | Traceable to national or international standards |
| Balance Qi | Commonly used nitrogen balance |
| Validity period | Expired standard gas must not be used |
Calibration period
There is no one-size-fits-all cycle, consider:
- Manufacturer's recommendations;
- Frequency of use (portable instruments that measure multiple furnaces per day need to be more frequent);
- Historical stability (several consecutive drifts that are very small can be extended appropriately, otherwise shortened);
- Customer and quality system requirements.
Recommendation: Do a zero-point check before daily use, perform complete calibration regularly, and issue a calibration report every year or as required by a qualified unit. The service section of the Gosi Control official website provides analyzer calibration services; the FAA-B product introduction also mentions the provision of factory calibration services and reports.
Records and reporting
Each calibration record:
- Date, person, instrument number;
- The standard gas number, concentration, and validity period used;
- Readings before calibration (as found) and readings after calibration (as left);
- Whether the allowable deviation is exceeded.
If the reading is out of tolerance before calibration, it is necessary to evaluate whether the calibration conclusions made with the instrument since the last calibration have been affected, and record the processing results.
Frequently asked questions
Can I use air to make a zero point?
Air contains CO₂ on the order of about 400 ppm and is not suitable as a CO₂ zero point gas. High-purity nitrogen or zero-point gas specified by the manufacturer should be used.
What is the difference between on-site calibration and return-to-factory calibration?
On-site calibration is convenient and fast, suitable for daily use; return to the factory or third-party calibration can perform more comprehensive inspection and maintenance, and issue a formal report. A better combination of the two.
Can I prepare the standard gas myself?
Not recommended. The concentration and uncertainty of self-prepared gas cannot be guaranteed, cannot be traced, and will not be recognized during audits.