Popular Ozone Tester Types and their Working Principles
Research has demonstrated that ozone's 253.7nm ultraviolet light possesses a high absorption coefficient, leading to the attenuation of ultraviolet light at this wavelength in accordance with the Lambert-Beer law. The ozone sensor functions on the principle of ultraviolet absorption, using a consistent ultraviolet light source to produce ultraviolet light. A light wave filter is implemented to sift out ultraviolet light of other wavelengths, allowing only 253.7nm ultraviolet light to pass through.
The ultraviolet light passes through the sample photoelectric sensor and is subsequently absorbed by ozone, reaching the sampling photoelectric sensor. In the case of an ozone sensor that utilizes UV absorption principle, the electrical signals from the sample photoelectric sensor and the sampling photoelectric sensor are compared, and the ozone concentration is calculated via a mathematical model based on the Lambert-Beer law.
Gas-sensitive semiconductor materials such as WO3, Sn0, In203, and other oxides are utilized in the construction of sensitive elements for a semiconductor ozone sensor. These materials generate or release heat due to oxidation-reduction reactions when exposed to ozone, causing a corresponding shift in the element's temperature and resistance. The ozone concentration is then transformed into an electrical signal to measure the concentration. Typically, as the concentration increases, the component's resistance value rises significantly and exhibits a linear correlation within a certain range.
The electrochemical ozone sensor comprises a working electrode, counter electrode, reference electrode, electrolyte, and circuit system. A consistent potential value can be upheld between the working electrode and the reference electrode. Upon ozone diffusion into the sensor, a reduction reaction takes place on the working electrode, while an oxidation reaction occurs on the counter electrode, resulting in a slight current flowing between the counter electrode and the working electrode. This current is proportional to the ozone concentration in the sensor within a specific range, which is subsequently computed by the circuit system to determine the ozone content.
Choose the Right Ozone Sensors
Before buying an ozone detector, it's important to determine the characteristics of the intended environment and the purpose of use. This information should be used to select an ozone monitoring device that balances stability, sensitivity, selectivity, and corrosion resistance.
Stability refers to the ability of the sensor's fundamental response to remain consistent throughout its entire operational period, which relies on the zero drift and interval drift. Zero drift denotes changes in the sensor's output response during the working period when ozone isn't present. Interval drift, on the other hand, refers to the output response shift of the sensor that remains continuously exposed to ozone, which is evident in a reduction of the sensor output signal throughout the working period. An ideal sensor operating under continuous conditions should exhibit an annual zero drift of less than 10%.
Sensitivity pertains to the correlation between the output alteration of the ozone sensor and the corresponding input change. It predominantly relies on the technology employed in the sensor's structure. Most gas sensor designs use principles based on biochemistry, electrochemistry, physics, and optics. The first consideration when selecting a sensitive technology is to ensure that it has adequate sensitivity to detect the valve limit (TLV-threshold limit value) or the lowest explosive limit (LEL-lower explosive limit) percentage of the target gas.
Selectivity, also referred to as cross-sensitivity, can be assessed by measuring the sensor's response to a particular concentration of interfering gas. This response is akin to the sensor's response generated by a specific concentration of ozone. This feature is crucial in monitoring multiple gases as cross-sensitivity can negatively affect the measurement's repeatability and reliability. Ideally, an ozone sensor should exhibit both high sensitivity and selectivity.
Corrosion resistance pertains to the capability of the ozone sensor to withstand exposure to a high concentration of the target gas. In the event of a significant gas leakage, the sensor probe should be able to endure ten to twenty times the expected gas volume fraction. During regular operation, the sensor drift and zero-point correction value should be minimal.
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