As a "safety sentinel" for frontline personnel, the accuracy of handheld hydrogen sulfide gas detectors is directly related to life safety. Hydrogen sulfide (H ₂ S), as a highly toxic, flammable, and explosive gas, is widely present in scenarios such as petrochemicals, wastewater treatment, and mining operations. Daily inspection and rapid calibration are the core links to ensure the reliability of instruments, and strict adherence to standardized operations is required.
1、 Daily inspection: a basic check to prevent problems before they occur
Daily inspection should be completed before daily use or during shift handover, with a focus on the three-dimensional development of "appearance function status":
1. Appearance and environmental inspection: Observe whether the instrument casing is damaged, whether the buttons are sensitive, and whether there is dust, oil, or liquid residue in the sensor window (which can be lightly swept with a soft bristled brush); Confirm that there is no strong electromagnetic interference in the detection environment (such as high-voltage equipment, radio transmitters) to avoid affecting signal stability.
2. Power on self-test and alarm test: Long press the power button to start the instrument and observe whether the self-test interface displays normally (such as battery level, sensor type, range parameters); Enter the alarm settings menu, trigger the sound and light alarm (usually set to the low limit alarm value of 10ppm and the high limit of 15ppm), verify that the buzzer volume is ≥ 90dB and the light flashing frequency meets the requirements.
3. Zero point and response verification: Let it stand for 3 minutes in clean air (or a known environment without H ₂ S), and check if the reading returns to zero (error ≤± 0.5ppm); If equipped with a standard gas source (such as 2ppmH ₂ S standard gas), it can be briefly introduced (flow rate 0.5L/min), and the reading can be observed for 30 seconds to see if it steadily rises and approaches the concentration of the standard gas (error ≤± 5%), quickly determining the sensor activity.
2、 Quick calibration: a key operation to ensure accurate data
When zero drift (such as reading>1ppm in clean air), response delay, or alarm abnormality is found during the inspection, rapid calibration should be carried out immediately. Steps are as follows:
1. Preparation tools: Use certified standard H ₂ S gas (recommended concentration 50% LEL or commonly used range intermediate value, such as 10ppm), pressure reducing valve, flow meter (0.5-1L/min), and calibration cover (ensure gas path sealing).
2. Zero point calibration: Place the instrument in a clean air environment, connect the flowmeter to the air inlet, and enter calibration mode after the reading stabilizes (some models long press the "CAL" button). Select "Zero point calibration" and confirm according to the prompt, wait for the screen to display "ZEROOK" (about 1-2 minutes).
3. Range calibration: Switch to the standard gas cylinder, adjust the flow meter to 0.5L/min, and introduce standard gas into the calibration cover; Wait for the instrument reading to stabilize (fluctuation ≤± 1%), input the concentration value of the standard gas (such as 10ppm), press the "SPANCAL" button to perform calibration until "SPANOK" is displayed.
4. Verification and recording: After calibration is completed, clean air is introduced again to confirm the zero point, and standard gas is repeatedly introduced to verify the reading deviation (should be ≤ ± 5% FS); Fill out the Calibration Record Form, indicating the time, operator, standard gas information, and results, and archive it for future reference.
Precautions
Daily inspections should combine "watching, listening, and testing" to avoid being mere formalities; Calibration should use concentration standard gases that match the tested scenario (such as prioritizing low concentration standard gases for confined space operations); Instruments that have not been used for a long time should be turned on and preheated for 30 minutes in advance to prevent the sensor from "sleeping"; Conduct comprehensive calibration (including third-party calibration) at least once a month to ensure compliance.