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Analysis of Four Major Influencing Factors of NDIR Gas Sensors and Introduction of Infrared CO2 Sensors

Published:2019-07-30

In the process of using the gas sensor, when the sensor encounters the reading error, many customers think of the sensor’s fault, but they don't know that external environment will also affect the detection accuracy. This article will take NDIR sensor as an example to introduce the four major influencing factors of the sensor.

1. Gas concentration

There is no doubt that the gas sensor is sensitive to the concentration of the gas being measured. The greater the gas concentration, the greater the amount of change in the sensor output signal. The signal of gas sensor of the non-dispersive infrared (NDIR) detection principle is the voltage output. When the measured gas is not present, the peak value of the output voltage is the largest. When the measured gas concentration increases, the peak value of the output voltage becomes smaller. But this change is not linear with gas concentration, but follows Beer-Lambert law. When the concentration is low, the sensitivity is high, and when the concentration is high, the sensitivity of the signal becomes low. The sensitivity of a certain concentration point is expressed by a mathematical formula: dV/dC, in which V is the peak value of the signal and C is the gas concentration.

2. Temperature and humidity

Most gas sensors are sensitive to ambient temperature. The reason is that no matter chemical reactions, electronic components, or inorganic and organic materials, performance parameters vary with temperature. This results in change of current and voltage at the sensor output. The NDIR sensor has a wide temperature range and can reach military grades from -55 ° C to over 100 ° C. NDIR sensor signals vary with various temperature factors, including: source spectrum, detector, filter temperature coefficient, op amp temperature coefficient, resistance and capacitance temperature coefficient. When these factors work together, the temperature compensation of the NDIR sensor becomes very complicated. This is one of the reasons why the price of NDIR sensors is high.

There are several ways to eliminate the temperature of the NDIR gas sensor, and the cost is relatively high. The first is the formula method, the second is the table look-up method, and the third is the constant temperature method.

3. Gas pressure

The gas sensor of the non-dispersive infrared (NDIR) detection principle can have a wide pressure range from 0 to 2 atmospheres without problems. The pressure range depends on the pressure tolerance of the source and detector. If the light source is a glass bulb, the glass bulb is pressure resistant. The infrared detector is sealed with a metal casing and an infrared filter. Therefore, the detector also has a pressure resistance problem.

4. Gas flow

Gas is a fluid. The reason why the gas flows is because of the pressure difference. The larger the pressure difference, the larger the flow rate. Non-dispersive infrared (NDIR) gas sensors have a flow range from 200 ML/MIN to 2 L/MIN. The greater the flow, the faster the response. Large flow is good for NDIR sensor, without harm, the premise is to clean out dust and water. For eliminating the effects of gas flow, non-dispersive infrared (NDIR) gas sensors do not restrict. NDIR needs to respond quickly, and the airflow into the sensor should be as fast as possible.

5. Conclusion

For gas sensors, when the measured gas or environment changes, no matter it is gas concentration, ambient temperature and humidity, gas pressure or gas flow, the monitoring state will change, which will make the sensor's accuracy change.

Manufacturer and products recommendations of NDIR CO2 sensors

Company name: Wuhan Cubic Optoelectronics Co., Ltd

Product recommendation: NDIR CO2 sensor module CM1107

The infrared CO2 sensor module CM1107 is a CO2 sensor based on the principle of non-infrared detection of independent intellectual property. It adopts dual beam design and has the characteristics of high measurement accuracy, low power consumption and good stability. The sensor can be used in a wide variety of applications, especially in the areas of food transportation, storage, hatching and agriculture. It also has the following characteristics:

①Dual beam design, high precision and better stability;

②Auto-calibration, temperature correction in full measurement range.