The method of premixed calibration gas is a method of gas transducer calibration. The premixed calibration gas can be compressed and stored in a cylinder at a certain pressure. The size of these bottles can be arbitrary, but in the field calibration, people like small and light cylinders, which can be divided into two categories: low pressure and high pressure gas equipment.
Many gas transducers are mainly disturbed by other gases that is why we use the cross calibration method. For example, to calibrate the ethane gas of LEL, 50% ELE methane gas is usually used to replace the actual ethane gas. This is because ethane is liquid at room temperature and has low vapor pressure. So it's very difficult to use the gas mixture and keep it at high pressure. In other words, methane has a high vapor pressure and is very stable. In addition, it can be mixed with air and kept at a high pressure. Compared with ethane mixture, methane can be used in more calibration occasions and has a long life. In addition, 50% ethane mixture is easy to get. Therefore, industrial instrument manufacturers of combustible gas alarm devices recommend using methane as a substitute for calibrating other gases.
1. There are two methods to use methane calibration as a substitute for other gases. One method is to calibrate the combustible gas alarm with methane, at the same time, multiply the obtained numerical reading by the response factor in the manual to replace the numerical reading of other gases. The method is applied in the commonly used catalytic transducers. The catalytic transducer is linear output, so the use of response factor conforms to the full scale range. For example, when the transducer is calibrated with methane, the output of pentane is only half that of methane. So the response factor of pentane is 0.5. Therefore, when the gas transducer detects pentane by calibrating methane, multiply the numerical reading by 0.5 to get the numerical reading of pentane.
2. The second method still uses methane as calibration gas, but the calibration reading is double. For example, 50% LEL methane calibration gas is used to calibrate LEL pentane. Although methane gas is used in calibration, the numerical reading of the instrument is the concentration of pentane gas after calibration.
Many low range harmful gas transducers can be calibrated with cross gas. Similarly, the infrared detector can use the cross calibration method for any gas with the same wavelength absorption. The advantage of the cross calibration method is that it allows the calibration of the transducer to use a gas, and its range is easy to obtain and process. However, there are some problems in using cross calibration method. One is that the response factor of each transducer is different, because it is impossible to make every transducer the same when manufacturing transducers. In addition, the response factor cannot be used. The response characteristics will vary with the setting of the heater voltage. Therefore, it is a good method to use the actual target gas to calibrate the transducer for periodic detection.