I. Preparation before calibration
1. Confirm calibration gas:
Zero point gas: High purity nitrogen (N₂) or air without the target gas (depending on the sensor type).
- Span gas: standard gas with known concentration (such as 50ppm CO standard gas for CO detectors, 50%LEL methane standard gas for combustible gas detectors).
2. Equipment inspection:
- Ensure that the sensor is not expired (electrochemical sensor life of 1-3 years, catalytic combustion sensor life of 2-5 years).
- Clean the probe filter to avoid dust or oil clogging.
- Check the battery or power supply to ensure the calibration process is continuous.
3. Environmental control:
- Temperature: 20 to 25 ° C (High temperature may cause sensor drift).
- Humidity: < 85%RH (High humidity affects electrochemical sensor performance).
- Ventilation: Avoid strong airflow interference (calibration should be carried out in static air).
II. Common calibration steps
A. Zero Calibration
- Steps:
1. Place the detector in clean air (or pass zero gas).
2. Wait for the reading to stabilize (usually 2 to 5 minutes).
3. Go to the Calibration menu and select Zero Calibration to ensure that the current value is 0 or the background value.
4. Save the Settings.
B. Span Calibration
- Steps:
1. Connect the span gas cylinder and adjust the flow rate to the equipment requirements (usually 0.5~1 L/min).
2. Pass the standard gas, and enter the "span calibration" mode after the reading is stable.
3. Enter the standard gas concentration value (such as 50ppm H₂S).
4. Confirm that the error is within the allowable range (generally required ±3%~±5%FS), and save the data.
C. Alarm function test
- Steps:
1. Set the low/high alarm value (such as 19.5% low report and 23.5% high report).
2. Pass into the standard gas slightly above/below the alarm threshold.
3. Verify whether sound and light alarm and vibration alarm are triggered in time (response time is usually ≤15 seconds).
IV. Calibration precautions
1. Flow control:
- Use a pressure reducing valve with a flow meter to ensure a stable flow rate (excessive flow will damage the sensor diaphragm).
- Calibration flow rate of combustible gas is recommended 0.5L /min, toxic gas can be slightly lower.
2. Calibration cycle:
- Normal environment: Calibrate every 3 to 6 months.
- Harsh environment (high temperature, high humidity, high dust) : calibration every 1 to 2 months.
- Immediately recalibrate the instrument when it experiences severe shocks or frequent alarms.
Through standard calibration, the gas detector can accurately detect the concentration of oxygen, combustible gases (methane, propane), toxic gases (CO, H2S, SO2, etc.), and issue alarms in time to ensure industrial safety and personnel health.
