Combustible gas detection alarm in recent years has been widely used in petrochemical, safety and environmental protection, chemical industry and other industries, particularly for use in the petrochemical industry more widely. Ensure that combustible gas alarm system equipment in good condition and stable operation, is essential for safe production of these industries, but really it is not easy to do. A large amount of maintenance combustible gas alarm system and its common not report false positives and other problems are often plagued instrument maintenance personnel, so the combustible gas alarm for regular testing is particularly important. As a first-line test personnel, I believe combustible gas alarm verification should note the following questions.

    First, the test of environmental conditions. Because it is an electronic instrument, which mainly comes from the error in the verification test environment:

    1. Required ventilation. For open-flammable gas diffusion escape, if the lack of good ventilation, it is easy to make certain parts of the combustible gas content in the air close to or reach the lower explosive limit concentration, resulting in inaccurate test results.

    2. No interference measured ingredients. Should combustible gas alarm verification process to take anti-electromagnetic interference. Electromagnetic environment factors combustible gas alarm mainly in the following three aspects: the human body static electricity, power and other input and output lines, and a narrow air burst of electromagnetic interference.

    3. Ambient temperature. In the verification process, the temperature variation will be detected after a significant change in activity of the molecule, so that the temperature increases at increased risk. Temperature no combustible gas alarm itself a direct impact, but in the following 0 ℃, standard inert gas enhanced standard gas molecules active not active when the temperature is low, the instrument display will have a great error, I believe that the temperature below 0 ℃, not suitable for test work.

    Second, the test flow control. In the verification process, the more flammable gas alarm sensor of the catalytic combustion, flows directly affect the size of the accuracy of test results. Alarm within a certain range in order to maintain the flow of high sensitivity, high or low will have a relatively large impact on the sensitivity. When the flow is less than the original sensor to measure demand will reach the surface of the true concentration, lack of new gas replenish the combustible gas, combustion can not continue, so the sensitivity is low. After the gas flow is increased, a corresponding increase in the thermal effect, the sensitivity is gradually increased when the gas flow continues to increase, the air flow and causes an excessive increase of the cooling element, but reduces the sensitivity of the measurement when the flow is greater than the requirements in accuracy, General Instrument in the design, manufacturers have chosen the best gas flow through trial and error. JJG693-2011 "combustible gas detection alarm verification procedures," also referred to flow control in accordance with technical specifications, but in the actual testing in a wide range of combustible gas alarm, it is difficult to ensure a reliable technical specifications can be found, so follow years test experience, I think is a range of flow control, as long as no pressure to probe the amount of traffic that is on the line. Most are in the normal test can be controlled at 500ml/min, individual alarm requires about 350ml/min, of course, while maintaining a stable flow of uniform, can not suddenly down suddenly on, or likely to cause fluctuations in the value of the test is shown. The amount of traffic, it is easy to damage the sensor. When the gas flow is small, the test must use inhaled alarm bypass the meter, or likely to cause inaccurate test results.

    Third, when the master controller and field detector test showing the value does not match. Generally combustible gas alarm detector from the main controller and connected using point-wire detectors distributed across multiple outlets, the master controller monitors the network centralized control of multiple, independent of the detector gas concentration display, when the environment When the gas concentration detector reaches or exceeds the preset alarm value, the master controller that alarm to alert staff on duty to take safety measures to protect the safety and production. I often found during field test master controller and a far cry from the scene showing the value of the detector, resulting in quality control personnel do not know how to determine if the equipment is qualified, I believe that this situation should be found to adjust zero and span potentiometers master controller probe The output should be associated with the gas concentration, if it should fail to adjust. The host controller can display live detectors respectively, that can be adjusted separately. If you only adjust the value on the master value ignoring the detector, then the main controller useless, not have any monitoring role.

    Fourth Test with calibration cover. Diffusion test procedures specified in the instrument calibration should be dedicated hood, each manufacturer has its own dedicated calibration hood, but in actual test in certification staff will be replaced ziplock and homemade calibration cover, I think when you try to use the original test or Dedicated better, because the calibration of the air cover and intake method (bottom and side air intake) still has some influence on the response time of the instrument and the indication error of these two indicators. Of course, regardless of when the combustible gas alarm test what kind of calibration hood must adhere to the principle that non-calibrated cover tight, no overflow positive pressure, it will affect the test results. Also prohibited too loose, causing outside air to enter, making the actual value of the standard gas is small, the impact test results.