2. Equipment preparation: prepare standard gas, flow controller, stopwatch, insulation resistance meter and other equipment and substances for verification.The standard gas shall be provided by the unit approved and issued by the administrative department of measurement and has the corresponding standard substance "Manufacturing License", and its concentration unit shall be expressed by molar ratio concentration or volume ratio concentration in the standard state, and converted into the corresponding LEL (lower explosive limit) value.

3. instrument preparation: the verified combustible gas alarm, gas cylinder for verification and supporting devices shall be placed under the above environmental conditions for more than 12 hours to ensure that the instrument is in a stable state.

4. verification items and methods

1. appearance and power-on inspection: check whether the appearance of the alarm is intact, the structure is complete, and the accessories are complete, whether each component can operate normally after power-on, and whether the display part has corresponding display.

2. Zero point calibration: use clean air to calibrate the zero point of the alarm to ensure that the indication value of the alarm is zero when there is no combustible gas.

3. indication error verification: select standard gases with different concentrations (e.g. 10%, 40%, 60% LEL), record the indication value after entering the alarm, compare with the standard value, and calculate the indication error.

4. response time verification: select a certain concentration of standard gas (e.g. 40% LEL), and record the time required from the indication value to reach 90% of the stable indication value after entering the alarm, I .e. the response time.

5. Repeatability verification: fill in standard gas several times at the same concentration, record the indication value of the alarm, and calculate its repeatability.

6. Alarm function and action value check: set alarm point, supply standard gas with corresponding concentration, check whether the alarm can send out alarm signal in time, and record its alarm indication value.

5. Verification Results Processing