To determine the accuracy of the detection data of the ozone concentration detector, it is necessary to start from four core dimensions: calibration verification, comparative testing, environmental and working condition investigation, and instrument status self inspection. Combined with the particularity of ozone detection (ozone is easily decomposed and interfered with), the reliability of the data should be verified layer by layer. The following are specific methods of judgment:
1、 Core verification method: Confirm data accuracy through calibration
Calibration is the most direct/effective method to determine the accuracy of detector data, which can be divided into two categories: laboratory calibration and on-site calibration, and must comply with national or industry standards (such as HJ504-2009 "Determination of Ozone in Environmental Air - Sodium Indigo Disulfonate Spectrometric Method" and JJG950-2018 "Ozone Analyzer Calibration Regulations").
Laboratory calibration (highest accuracy, recommended for regular execution)
Principle: Use ozone standard gas (provided by a national metrology certification agency, with known and traceable concentration) to calibrate the detector under standard conditions (temperature 20 ± 2 ℃, humidity 50 ± 5% RH, no interfering gas).
Operation steps:
Connect the detector to the standard gas generation device, introduce zero gas (clean air without ozone), calibrate the zero point after the reading stabilizes, and ensure that the zero drift is ≤ the allowable range marked by the instrument (such as ± 0.005mg/m ³).
Introduce ozone standard gases of different concentrations in sequence (such as low, medium, and high concentration points, covering the commonly used range of the detector), record the reading after it stabilizes, and calculate the reading error.
Judgment criteria: The indication error should be ≤ ± 2% to ± 5% of the instrument range (depending on the instrument accuracy level); The repeatability deviation is ≤± 1%, which means that the fluctuation range of values measured multiple times with the same concentration standard gas must meet the requirements.
Periodic recommendation: Portable detectors should be calibrated every 6-12 months; Fixed online detectors should be calibrated every 3-6 months, and the cycle should be shortened in industrial high dust/high humidity environments.
On site calibration (emergency verification, suitable for scenarios where inspection is not possible)
Method: Use a portable ozone calibrator (which has completed laboratory calibration and has higher accuracy than the instrument to be tested) as a reference, place it in the same environmental location as the instrument to be tested, collect data simultaneously, and record continuously for more than 30 minutes.
Judgment criteria: The deviation between the reading of the instrument to be tested and the reading of the calibrator should be ≤ ± 5%, and the data change trend should be consistent (such as synchronous response when the concentration increases/decreases). If the deviation exceeds the range, it indicates that the instrument under inspection may have drift or malfunction.
2、 Auxiliary verification method: Cross checking through comparative testing
If calibration cannot be performed temporarily, data reliability can be verified through multi instrument comparison and reference method comparison, which is suitable for quick on-site judgment.
Comparison of multiple instruments of the same type
Operation: Place 2-3 ozone detectors of the same model and range at the same detection point (with a spacing of ≤ 0.5 meters), ensuring consistent sampling conditions (such as the same sampling flow rate and sampling height), and monitor continuously for 1-2 hours.
Judgment criteria: The reading deviation of multiple instruments should be ≤ ± 10%. If the reading of a certain instrument deviates significantly from other instruments (deviation>15%), the data of that instrument is likely to be inaccurate.
Attention: The compared instruments must be within the valid calibration period to avoid misjudgment caused by multiple instruments simultaneously losing accuracy.
Comparison with standard testing methods
Applicable scenarios: occasions that require high accuracy of data (such as environmental monitoring, scientific research experiments).
Reference method:
Sodium indigo disulfonate spectrophotometric method: a classic laboratory method that quantifies ozone concentration through chemical color reactions, and the results can be used as a gold standard.
UV absorption standard instrument: Ozone has characteristic absorption of 254nm ultraviolet light, which conforms to Lambert Beer's law. This type of instrument has high accuracy and is suitable for on-site reference.
Judgment criteria: If the deviation between the detector data and the standard method result is ≤ ± 5%, then the data is accurate; Excessive deviation requires troubleshooting of the instrument.
3、 Troubleshooting environmental and working condition interference: excluding non instrument related factors
The chemical properties of ozone are active (easy to decompose and react with other substances), and the detection environment and working conditions will directly affect the accuracy of data. It is necessary to first eliminate such interference before determining whether the instrument is inaccurate.
Interference gas investigation
The core sensors of ozone detectors, such as electrochemical sensors and ultraviolet sensors, are susceptible to interference from oxidizing gases (such as chlorine and nitrogen dioxide) or reducing gases (such as sulfur dioxide and hydrogen sulfide), resulting in readings that are either too high or too low.
Judgment method: If there are the above-mentioned interfering gases in the detection environment, the detector can be placed in clean air to observe whether the reading returns to near zero; If there is still a significant increase, it indicates that the sensor may be contaminated.
The influence of environmental temperature, humidity, and pressure
Ozone is prone to rapid decomposition in high temperature and high humidity environments, leading to a decrease in actual concentration. If the detector does not compensate for temperature and humidity, the reading will be lower; Changes in air pressure can also affect the sampling volume, leading to concentration calculation bias.
Judgment method: Compare whether the temperature and humidity compensation function of the detector is turned on. In the same environment, the reading after turning on the compensation should be more stable; If the data fluctuates significantly after turning off compensation, it indicates that environmental factors are the main cause of data deviation.
Sampling system blockage or leakage
If the sampling pipeline and dust filter membrane of the portable detector are blocked by dust, it will cause a decrease in sampling flow rate and lower readings; If the sampling pipeline leaks, it will introduce external air, dilute the ozone concentration, and also lead to low readings.
Judgment method: Check whether the sampling pipeline is unobstructed and whether the dust filter membrane has accumulated too much dust; After blocking the sampling port, the reading of the detector should quickly drop to zero, otherwise there may be pipeline leakage.