Methods for Calibrating Gas Detectors
1. Pre mixed calibration gas
The method of pre mixing calibration gas is the preferred and most popular method for gas sensor calibration. Pre mixed calibration gases are preferred by people for small and lightweight gas cylinders. These small and portable gas cylinders can be divided into two categories: low-pressure and high-pressure gas equipment.
In order to calibrate the gas and allow high-pressure gas to flow out of the high-pressure cylinder, a pressure regulator is required. It consists of a pressure controller, a pressure gauge, and a flow meter. During the calibration process, in order to obtain appropriate readings, adjust the flow rate of the flowmeter to achieve stable calibration values.
2. Penetration equipment
The permeation device is a sealed container containing a gas-liquid equilibrium chemical substance. Gas molecules permeate through the edges or top cover of the permeation container. The permeation rate of gas molecules depends on the permeability and temperature of the substance. The permeability is stable over a long period of time. Caliber measuring device and flow controller.
However, the permeation tube continuously delivers chemical substances at a constant rate, and the permeability of the stored and very low vapor pressure gas chemical substances is too low to be of any use. In gas detection, it is typical to calibrate sensors with a small range using permeation equipment.
3. Cross calibration
By using the cross calibration method, each sensor can be affected by interference from other gases. For example, to calibrate 100% LEL ethane gas, 50% LEL methane gas is usually used instead of the actual ethane gas. This is because ethane is liquid at room temperature and has a low vapor pressure.
Therefore, it is difficult to use an accurate mixture and maintain 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 maintained at a high level to complete methane as a substitute for calibrating other gases.
Catalytic sensors are wired outputs, so the use of response factors conforms to the full-scale range. For example, when calibrating pentane with methane and using methane as the calibration gas, the obtained readings are multiplied by the corresponding cross response factors of the sensor for different gases to replace the readings of other gases.
Use 50% LEL methane calibration gas to calibrate 100% LEL pentane. Although methane gas was used for calibration, the instrument reads the concentration of pentane gas after calibration.
Many low range harmful gases can also be detected using cross gas calibration. However, using cross calibration methods can also lead to some issues. The response factor of each sensor may have deviations, therefore, periodic verification of the detector is performed using the actual target gas.
