1. Pre-mixed gas calibration
The pre-mixed calibration gas can be compressed and stored in cylinders at a certain pressure.These bottles can be of any size, but for field calibration, people prefer small, light cylinders.These small portable cylinders can be divided into two categories: low pressure and high pressure gas equipment.
2. Cross calibration method
With the cross calibration method, each sensor is subject to interference from other gases.For example, to calibrate the LEL ethane gas, methane gas with 50%ELE is usually used instead of the actual ethane gas.And that's because ethane is liquid at room temperature and has a low vapor pressure.Therefore, it is difficult to use the mixture and keep it under 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 high pressure.Compared with ethane mixtures, methane can be used in more calibration occasions and has a long life.A 50% ethane mixture is readily available.Manufacturers of combustible gas alarms have therefore suggested using methane as a substitute for other gases.
3.Method for the calibration other gases with methane
A . Methane can be used as a substitute for other gases in two ways.One approach is to calibrate combustible gas alarms with methane and substitute the readings obtained by multiplying the response factor in the manual for the other gas readings.This is often the case with catalytic sensors.Catalytic sensors are linear outputs, so the use of response factors accords with the full scale range.When a sensor is calibrated with methane, for example, the pentane output is only half that of methane.So pentane has a response factor of 0.5.So when the sensor actually detects pentane and calibrates it with methane, multiply the reading by 0.5 to get the pentane reading.
B. The second method still USES methane as the calibration gas, but the calibration reading is double.For example, LEL pentane is calibrated using 50%LEL methane calibration gas.Although it was calibrated using methane gas, the instrument was calibrated to read pentane gas concentration.
Many low-range hazardous gas sensors can be calibrated using cross-gas.Similarly, infrared detectors that absorb any gas at the same wavelength can be cross-calibrated.The advantage of the cross-calibration method is that it allows the calibration of the sensor using a gas whose range is easily obtained and processed.However, there are some problems with cross-calibrating.One is that each sensor has a different response factor, because it is not possible to make each sensor the same when making them.In addition, response factors are not available.The response characteristics will vary with the setting of the heater voltage.Therefore, it is a good method to calibrate the sensor with actual target gas for periodic detection.
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