When performing error calibration on a combustible gas detector, how many seconds should the air intake time be?
In recent years, combustible gas detectors have been widely used in various industries such as petrochemical industry, safety and environmental protection, chemical industry, etc., especially in petrochemical industry. Gas Detector Dongri Ying can ensure that the equipment of the combustible gas detector system is intact and operates stably, which is very important for the safe production of these industries, but it is not easy to achieve this. The heavy maintenance of combustible gas detector systems and common problems such as non-reporting and false alarms often trouble instrument maintenance personnel, so regular calibration of combustible gas detectors is particularly important.
Check environmental conditions
Because the combustible gas detector is an electronic instrument, the errors in its calibration mainly come from the calibration environment:
1. Good ventilation is required. For open flammable gas diffusion and escape, if there is a lack of good ventilation conditions, it is easy for the combustible gas content in the air in a certain part to approach or reach the lower explosion limit concentration, resulting in inaccurate verification results.
2. No interference with measured components. When calibrating combustible gas detectors, attention should be paid to preventing electromagnetic interference. The electromagnetic environment affects the combustible gas detector mainly in the following three aspects: human body static electricity, narrow pulse groups on power supply and other input and output lines, and airborne electromagnetic wave interference.
3. ambient temperature. During the verification process, changes in temperature before and after detection will significantly change the activity of the molecules, and an increase in temperature will increase the risk. Temperature has no direct impact on the combustible gas detector itself, but when it is below 0°C, the inertness of the standard gas increases and the molecular activity of the standard gas is not active enough. When the temperature is low, the instrument display value will have a large error. Dongfang Alarm Co., Ltd. The company believes that it is not suitable for verification work when the temperature is below 0℃.
Calibrate flow control
During the calibration process, since most combustible gas detectors are catalytic combustion sensors, the flow rate directly affects the accuracy of the calibration results. The detector can maintain high sensitivity within a certain flow range. If it is too high or too low, it will have a relatively large impact on the sensitivity. When the flow rate is less than the measurement requirement, the surface of the sensor element will not reach the true concentration. After the combustible gas is burned, new gas cannot be replenished in time, and the combustion cannot continue, so the sensitivity is very low. When the gas flow rate increases, the thermal effect increases accordingly, and the sensitivity gradually increases. When the gas flow rate continues to increase, the excessive air flow will increase the heat dissipation of the components, which in turn reduces the sensitivity. When the flow rate is greater than the measurement requirements, the accuracy decreases. When designing general instruments, manufacturers have already selected the optimal gas flow rate through repeated trials. The "Calibration Regulations for Combustible Gas Detectors" also mentions that flow control can be based on technical instructions. However, in actual verification, there are many types of combustible gas detectors, and it is difficult for us to guarantee that we can find reliable technical instructions. Therefore, based on years of verification experience, Dong Riyingneng Co., Ltd. believes that the flow rate is controlled within a range, as long as no pressure is applied to the probe, that is, the flow rate is too large. In normal calibration, most of them can be controlled at 300-500ml/min. Some detectors are required to be around 350ml/min. Of course, at the same time, the flow rate must be kept stable and uniform, and cannot rise and fall suddenly, otherwise it will easily cause the calibration indication value to fluctuate. fluctuation. Excessive flow can also easily damage the sensor. When the gas flow rate is very small, a bypass flowmeter must be used to calibrate the inhalation detector, otherwise it will easily cause inaccurate calibration results.
During calibration, the indication values of the main controller and the on-site detector do not match.
Generally speaking, the combustible gas detector is connected by the main controller and the detector in a split-line manner. The detectors are distributed at multiple outlets. The main controller centrally controls multiple monitoring outlets. The gas concentration of each detector is displayed independently. When the environment When the concentration of the detector gas reaches or exceeds the preset alarm value, the main controller will issue an alarm to remind the personnel on duty to take safety measures to ensure the safe production of the enterprise. During on-site calibration, Dongri Yingneng Co., Ltd. often finds that the indication values of the main controller and the on-site detector are very different, causing the calibration personnel to not know how to judge whether the instrument is qualified. If this situation is found, the zero point and range potentiometers of the main controller should be adjusted. , the output of the probe should be related to the gas concentration, and it should be adjusted if it is unqualified. The main controller can display the on-site detectors separately, which means they can be adjusted separately. If you only adjust the value on the detector and ignore the value on the main controller, then the main controller will be useless and will not play any monitoring role.
Calibration cover for calibration
The calibration regulations stipulate that diffusion instruments should have special calibration covers. Each manufacturer has its own special calibration cover. However, in actual calibration, the calibration staff will use ziplock bags and self-made calibration covers instead. During calibration, try to use the original ones. It's better, because the inner space of the calibration cover and the air intake method (bottom air intake and side air intake) still have a certain impact on the two indicators of the instrument's response time and indication error. Of course, no matter what kind of calibration cover is used to calibrate the combustible gas detector, one principle must be adhered to, that is, the calibration cover is strictly prohibited from being too tight and there is no overflow port to generate positive pressure, which will affect the calibration results. It is also strictly forbidden to be too loose, which will cause outside gas to enter, making the actual value of the standard gas smaller and affecting the calibration results.
