Sensor Cross Sensitivity
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- Chirag Shah
- 16th December 2021
The reaction of a sensor to other gases that can interfere with how the sensor reacts is known as cross sensitivity. When a sensor is exposed to a gas that isn’t the target gas, an undesirable consequence can occur, which can be either positive, negative, or inhibitory reaction. For locating the gas leakages in installation areas, stack moisture gas detector is a popular one. Similarly, portable hydrogen gas detectors can be used in emissions monitoring systems as well as multifunction detectors for gas leakage.
A positive response indicates that sensors respond not just to the target gas but also to another gas. This response may give the user the impression that target gas is present when it isn’t, or that there is more target gas present than is the case. This may prompt the user to utilise forced ventilation, evacuate the area, or take other corrective action to eliminate the gas hazard, which isn’t always necessary. Here’s an example of a situation where you should answer positively: H2 gives a positive reaction to a CO sensor. As a result, if the CO sensor detects 200ppm of H2, the CO sensor will display about.
When sensors are exposed to a gas that generates an unfavourable reaction, they produce a diminished response to the target gas. If this occurs, the user may be exposed to the target gas without realising it, or the level of gas displayed on the instrument display may be reduced as a result of the negative effect. Here are a number of examples of negative responses: The response of a SO2 sensor to NO2 is negative. As a result, if a SO2 sensor detects 10ppm of NO2 and 10ppm of SO2, the net result could be 0ppm or even a negative number, depending on the instrument.
Inhibition is comparable to a negative reaction; however, if the sensor is exposed to the inhibitor at the same time as the target gas, the sensor may not respond to the target gas at all, or it may take hours, if not days, to recover before responding to the target gas again. H2S, for example, inhibits a Cl2 sensor. NH3 can suppress SO2 sensors, which can take many hours to recover before responding to SO2.
Dangers of cross sensitivity
A risky condition is when a multigas detector is monitoring NO2 and SO2 gases at the same time. NO2 sensors can react negatively to SO2 gas and vice versa; some SO2 sensors can also react negatively to NO2 gas. It’s feasible that the metre will show 0ppm for both gases while they’re both present.
Making good use of known Cross Sensitivity
There are many more types of gases than there types of gas sensors in the world. Using one type of sensor to detect another gas can be helpful. Detecting Phosphine fumigation gas with a CO or SO2 sensor is one example. Both the CO and SO2 sensors have a high cross-sensitivity to PH3 gas, making them appropriate for PH3 monitoring at high ppm levels. CO sensors with problematic cross sensitivity are extremely sensitive to H2, acetylene, ethanol, and alcohol. Some safety offices are responsible for both site breathing apparatus and gas detection equipment. When alcohol is used to clean the face masks, the gas detectors are more likely to detect CO. After alcohol exposure, CO sensors can take a long time to recover.
Cross Sensitivity’s Benefits
For the calibration of gas sensors, not all calibration gases are easily available. Formaldehyde is one such example. Formaldehyde calibration gas is costly to create and, unlike most other calibration gases, is not easily available in disposable gas cylinders. Some formaldehyde gas sensors, on the other hand, are cross-sensitive to CO gas and may thus be calibrated using CO gas, which is inexpensive and easily available.