I. Verify measurement accuracy through standard source comparison.
The most direct method is to use traceable standard substances for comparison testing.
Gas Sensors: Introduce a standard gas of known concentration (e.g., 1.0% CH₄) and observe whether the reading is within the allowable error range. According to GB 12358-2024, the indication error of a combustible gas detector should not exceed ±3% LEL. If the deviation exceeds this limit, the sensor is inaccurate.
Physical Quantity Sensors: Use a constant temperature bath, standard pressure source, or standard signal generator to input a precise physical quantity, record the output value, and calculate the deviation. For example, for intrinsically safe temperature sensors, in tests at 0℃, 50℃, and 100℃, the output should be consistent with the theoretical value; a deviation exceeding ±1% requires calibration.
✅ Practical suggestion: Preheat in a stable environment for at least 20 minutes before comparison to avoid the influence of temperature and humidity fluctuations on the results.
II. Observe Abnormal Signals During Operation
Even if the calibration cycle has not yet arrived, the following phenomena indicate that the sensor may be inaccurate:
Severe Zero Drift: In clean air, the oxygen sensor reading consistently deviates from 20.9% VOL (e.g., displaying 18.5%) and cannot be recovered through calibration.
Slow Response: The sensor fails to reach a stable value for more than 30 seconds after exposure to a standard gas, or fails to return to baseline within 3 minutes after removal.
Disorderly Data Fluctuations: The reading fluctuates frequently and is unstable even without interference.
Alarm Malfunction or False Alarms: No alarm is triggered when the concentration exceeds the limit, or alarms are frequently triggered when there is no gas, and environmental factors cannot be ruled out.
These symptoms often indicate aging of the sensing element, drift in circuit parameters, or impaired intrinsic safety performance.
III. Multi-device Cross-verification and System Linkage Inspection
At critical monitoring points, comparing multiple devices can improve reliability assessment.
Comparison of Multiple Sensors of the Same Model: In the same environment, if the readings of two or more devices deviate by more than 5%, immediate calibration and troubleshooting are necessary.
Primary/Backup System Comparison: Simultaneous measurements with fixed and portable detectors are performed. If significant data discrepancies exist, the portable detector should be checked for inaccuracies.
Control System Response Verification: When the sensor outputs an over-limit signal, confirm whether the monitoring system can receive it normally and trigger interlocking actions such as power-off and ventilation. If the signal is not recognized, it may indicate an abnormal sensor output or a transmission circuit failure.
IV. Verify Calibration Status and Intrinsic Safety Parameter Integrity: Accuracy depends not only on the sensor itself but also on the compliance of the entire intrinsically safe system.
Check Calibration Label: Check if the casing has a valid calibration label indicating the date and next calibration time. Equipment that has not been calibrated within the specified period must not be used.
Confirm Intrinsic Safety Parameter Matching: Check whether the parameters of the sensor and safety barrier meet requirements such as Uo ≤ Ui and Co ≥ Ci + Cc to prevent damage to intrinsic safety performance due to excessive circuit energy.
Review Calibration Report: Proper calibration should generate an electronic record containing environmental parameters, standard equipment information, and before-and-after data comparisons to ensure full traceability.
