Verification methods for several commonly used gas alarms
(1) The calibration environment should be maintained at a temperature of (0-40) ℃ and a relative humidity of ≤ 85%, with good ventilation and no electromagnetic interference that affects the normal operation of the instrument.
(2) Before calibrating the alarm, it is necessary to obtain the alarm manual and understand basic information such as the working principle and range of the instrument; Secondly, make accurate judgments on whether the alarm is working properly. After introducing standard gas, the alarm did not respond. It is necessary to check if there are any debris (rust, dust, etc.) blocking the probe. If there are any, compressed air can be used to blow them away; Is the selection of standard gas type correct, is there a fault in the circuit, or is the probe sensor out of function.
(3) Selection of standard gas flow rate: Use a flow controller to control the flow rate of standard gas according to the different sampling methods of the tested instrument. When calibrating a diffusion type instrument, the flow rate should be in accordance with the requirements of the instrument manual, and the calibration diffusion cover that matches the instrument should be used. If there are no clear requirements in the instrument manual, the flow rate is generally controlled within the range of around 500mL/min; When calibrating a suction instrument, its flow rate should be equal to the flow rate of the suction pump, and it is also necessary to ensure that the bypass flow meter in the flow controller has flow venting. Pay attention to the airtightness of the pipe every time it is used to prevent false display of values due to pipeline leakage. For standard gases of different concentrations, the flow rate must be stable and uniform during the calibration of ventilation, in order to obtain accurate and reliable calibration values.
(4) Selection of pressure reducing valves and pipelines: Based on the tested instrument and the standard gas used, use pressure reducing valves that are compatible with standard gas and standard gas cylinders; Pipeline materials that do not affect gas concentration, such as polytetrafluoroethylene pipes for combustible gases, and stainless steel pipes that do not affect normal calibration for gases with high adsorption and corrosion such as chlorine and hydrogen sulfide.
(5) Verification of indication error: The calibration should be carried out after the instrument is powered on and preheated to stabilize. Because some sensors require a certain amount of preheating time to stabilize after connecting to the power supply, during which the display value may fluctuate slightly. This is only a transitional state, not a detector failure. Therefore, ensuring sufficient preheating stability is also an important measure to ensure the authenticity and reliability of basic errors; At the same time, when verifying the indication error, the instrument should be calibrated at full range first to achieve the goal of saving standard gas.
(6) Verification of response time: Generally, the purpose can be achieved by following the requirements of the verification regulations, while emphasizing the stability and uniform speed of each gas input.
(7) Verification of alarm error: Each instrument has its corresponding alarm point, which is already set at the factory. Therefore, it should be calibrated according to the alarm point set in the instrument manual, and a standard gas with a concentration of about 1.5 times the instrument's alarm (lower limit) setting value should be introduced. The concentration of this standard gas cannot be too small,
It should not be too large, otherwise it is not conducive to the reading or directly affects the reading.
(8) Repeatability verification: Since repeatability is done after the verification of indication error, it is not possible to simply use the data of indication error. Instead, it needs to be redone to obtain the numerical value. Under normal working conditions, calibrate the zero point by injecting zero gas, and then inject standard gas for calibration.
(9) Due to the combustible, harmful and toxic nature of the gas, it can cause harm to the human body when the concentration reaches a certain range, such as carbon monoxide concentration reaching 1.6 × At 10-9 hours, it can cause headaches and vomiting in 20 minutes, and cause death in 2 hours. Therefore, during calibration, attention should be paid not only to the impact of residual gases on the calibration, but also to the impact of the emitted gases on the human body. Necessary equipment should be added for ventilation and ventilation to ensure indoor air cleanliness.
