The calibration of an air generator is a crucial step in ensuring that its output gas quality meets the requirements of analytical instruments, which directly affects the reliability of data in fields such as environmental monitoring and industrial process control. The following is a detailed description of the calibration process:
1、 Preparation before calibration
-Equipment status check
-Confirm that the power supply, compressor, filter, and pipeline connections of the air generator are normal and there are no leaks or blockages. Check if the filter element needs to be replaced to avoid pollutants affecting the quality of zero gas.
-Preheat the equipment to a stable state, usually running for 15-30 minutes to ensure that the internal temperature and pressure reach the working range.
-Environmental condition control
-The calibration environment should meet the requirements of temperature (15 ℃~35 ℃) and humidity (≤ 85% RH), and avoid strong electromagnetic interference or vibration.
-Use an independent power supply to prevent voltage fluctuations caused by sharing circuits with other high-power devices.
-Preparation of standard materials and tools
-Select certified standard gases (such as zero point gas of 0ppm CO/NOx, etc.) or high-purity nitrogen as calibration standards.
-Equipped with high-precision gas analyzer, standard flow meter (accuracy ± 1%), stopwatch, temperature and humidity meter and other auxiliary equipment.
2、 Core calibration steps
-Zero point calibration
-Connect the output terminal of the air generator to the gas analyzer and introduce standard zero point gas. Gradually adjust the flow rate to the rated range of the equipment and observe whether the analyzer reading is close to 0ppm. If the deviation exceeds the allowable range (usually ± 2%), the output parameters need to be adjusted by the controller until they stabilize.
-Repeat the test at least 3 times to ensure data consistency, record the concentration values and adjustment measures for each calibration.
-Flow calibration
-Soap film flowmeter method: Connect the soap film flowmeter to the outlet of the generator, measure the time it takes for the soap film to move a fixed distance, calculate the actual flow rate, and compare it with the set value. The allowable error is ± 5%, and if it exceeds the tolerance, the flow control valve or pump speed needs to be calibrated.
-Standard flowmeter comparison method: Parallel connect the standard flowmeter and the device to be calibrated, synchronously read the flow readings of both, and the relative error should be ≤± 1%. This method is suitable for dynamic calibration, especially for precision instruments such as microbial samplers.
-Pressure and temperature compensation calibration
-Install pressure sensors to monitor the internal pressure of the generator, compare the measured value with the theoretical value, and adjust the pressure reducing valve or relief device.
-For temperature sensitive devices, it is necessary to verify output stability at different ambient temperatures and enable temperature compensation algorithms if necessary.
3、 Special scenario calibration
-Ozone generator calibration
-Using UV spectrophotometry, connect the superior transmission standard (traced by the primary standard) in series with the device to be calibrated, and alternately introduce zero gas and ozone samples. Calculate concentration deviation through Lambert Beer law and adjust UV lamp power or feedback loop parameters.
-Attention must be paid to the uniformity of zero gas sources to avoid cross interference caused by different zero gas residues.
-Calibration of Microbial Sampler Capture Efficiency
-Particle counting method: Compare the changes in particle counting before and after sampling in a clean environment to evaluate the capture efficiency of the filter membrane.
-Colony counting method: Collect known concentrations of microbial aerosols, calculate colony forming units (CFU) after cultivation, and verify the efficiency of the sampler.
4、 Data Processing and Reporting
-Error analysis
-Flow error=(actual flow value - nominal flow value)/nominal flow value x 100%.
-Concentration error=(measured value - standard value)/standard value x 100%.
-All errors must be controlled within the allowable range of industry standards (such as HJ 654).
-Document Record
-Record the calibration date, environmental parameters, equipment serial number, standard substance batch number, and adjustment details in detail, generate a PDF report and archive it. It is recommended to keep the original data for at least 3 years for traceability review.
Through the above process, the measurement credibility of the air generator can be systematically guaranteed, supporting the comparability and legal effectiveness of environmental monitoring data. In practical operation, it is necessary to refine the parameters based on the equipment manual and update the calibration plan with reference to the latest national standards.