Measurement accuracy of gas detection tube

    Although the detector tube has many advantages, its accuracy is the key to determining whether it has value in use. The accuracy of the gas detection tube is gradually improved from the beginning to the semi-quantitative, with the improvement of the manufacturing technology. Today's manufacturing technology has enabled accuracy to meet general usage requirements. As a gas analysis method, the detection of the gas concentration by the test tube developed under the laboratory conditions is actually similar to the other methods, because these methods are in accordance with the analytical chemistry theory requirements, see attached Table, but the gas detection tube as a commodity, its quality technical indicators are critical to its accuracy. The detection tube for detecting different gases has different accuracy. For example, the relative standard error of the hydrogen sulfide detection tube is 10 to 5%, the sulfur dioxide, carbon monoxide, ammonia detection tube is 15 to 10%, and the hydrogen chloride detection tube is 20 to 15%. The benzene detection tube is 30 to 20%. My national standard "Gas Detection Pipe Gas Device" (GB-7230-87) specifies that the precision is not more than 10% and the accuracy is 25 to 35%.

   

From the expression, the specified gas detection tube error is relatively high, but it includes the influence of the temperature on the sampling volume during use, the error of the detection tube itself and the normal measurement volume error, because the detection tube scale is the standard temperature in the laboratory. It is calibrated at 20 °C, and the allowable temperature is generally ±20 °C. Under the condition of 760 mmHg, the effective volume changes by about 0.7% for every 2 °C change, which affects the result and produces a large error. In fact, the error is generally 15% smaller under standard conditions. (See Table 1), this measurement of ppm level has obvious advantages over chemical analysis. The volume error caused by temperature affects the accuracy of the analysis results, and also exists in traditional chemical analysis methods. In actual operation, the result can be temperature corrected if necessary. Gas analysis using mass-produced gas detection tubes should have a small precision error because of the inherent quality of the same, combined with ease of use and little introduction of external errors, and the experience is generally not more than 7%. Accuracy error mainly comes from the quality of the test tube itself. This is mainly determined by whether the measurement management and quality management of the product are standardized in the manufacturing process. Strengthening the technical management is the premise of ensuring the quality of the test tube. In addition, the chemical composition of the test tube is more complicated. It is easy to produce qualitative change, and the test tube should be used within the validity period. On the other hand, the accuracy error is derived from the conditions of use. Guanjian is a phase-collecting instrument used in combination. The metering volume should be accurate when used. Otherwise, even if the quality of the test tube is good, a large error will be caused because the gas sample passing through the test tube does not meet the specified requirements. For this, we use a medical injector as a sampling tool, using the "first metering and then inhaling" method, although it is a little troublesome, but the measurement error can be minimized.
Correction table for measurement results due to temperature at 760 mmHg:

Schedule: Comparison of different methods for analysis of hydrogen sulfide