1. Sampling detection type oxygen probe
The sampling detection method is to introduce the measured gas into the zirconia detection chamber through the guiding tube, and then heat the zirconia to the working temperature (above 750°C) through the heating element. Zirconia is generally tubular, and the electrode is porous platinum electrode (Figure 2). The advantage is that it is not affected by the temperature of the detected gas, and the oxygen content in the gas at various temperatures can be detected by using different flow tubes. This flexibility is used in many industrial online detections. The disadvantages are slow reaction time; complex structure, which easily affects the detection accuracy; when the detected gas has more impurities, the sampling tube is easy to be blocked; the porous platinum electrode is easily corroded by sulfur, arsenic, etc. in the gas and blocked by fine dust and becomes invalid; The heater is generally heated by electric furnace wire, and its life is not long.
When the temperature of the gas to be tested is low (0℃～650℃), or the gas to be tested is relatively clean, sampling detection methods are suitable, such as oxygen measurement by a nitrogen generator, oxygen measurement in a laboratory, etc.
2. In-line detection type oxygen probe
In-line detection is to insert zirconia directly into the high temperature measured gas to directly detect the oxygen content in the gas. This detection method is suitable for the temperature of the detected gas at 700°C to 1150°C (the special structure can also be used for high temperature of 1400°C). ), it uses the high temperature of the gas to be tested to bring the zirconia to the working temperature without using a heater (see Figure 3). The key technology of the in-line oxygen probe is the high temperature sealing of the ceramic material and the electrode problem. The following lists the structure of two in-line oxygen probes.
(1) Overall zirconia tube
This form is developed from the form of the zirconia tube used in the sampling and detection method, that is, the original zirconia tube is lengthened so that the zirconia can directly extend into the high-temperature measured gas. This structure does not need to consider the high temperature sealing problem.
(2) In-line zirconia oxygen probe
Due to the need to insert zirconia directly into the detection gas, there is a high requirement on the length of the oxygen probe, and its effective length is about 500mm to 1000mm, and the length in a special environment can reach 1500mm. And the detection accuracy, working stability and service life have high requirements, so it is difficult for the in-line oxygen probe to adopt the integral zirconia tubular structure of the traditional zirconia oxygen probe, and more technically demanding zirconia and oxide The structure of the aluminum pipe connection. Sealing performance is one of the most critical technologies of this zirconia oxygen probe. At present, the most advanced connection method in the world is to permanently weld the zirconia and alumina tube together. Its sealing performance is excellent. Compared with the sampling detection method, the in-line detection has obvious advantages: the zirconia directly contacts the gas. , The detection accuracy is high, the response speed is fast, and the maintenance amount is small.
Integral
The integral structure is to make zirconia into a complete long tube, the reference gas path is in the tube, and the electrode and zirconia tube are sintered together to form a whole. Its advantages: good air tightness, low internal resistance, high and stable output signal strength, and good interchangeability of probes. Disadvantages: easy to fall off or break due to vibration, and it is not easy to repair once damaged.
Combination
The combined RHO zirconia is generally made into spherical, flake and conical shapes. Tighten tightly with alumina tube by spring
Closely fit with zirconia head, play a sealing role. The electrode and the alumina tube are all independent components, combined to form a composite body. Its main feature is: due to the improvement of probe processing accuracy, assembly accuracy and process technology, it has basically been able to achieve the advantages of the integrated type. Because the alumina tube and the sheet or spherical sensor element are elastically compressed, it solves the problem of anti-vibration, and it has the performance of resistance to sudden changes in temperature, and at the same time solves the problem of temperature resistance. The combined zirconia head, electrode, alumina tube and other components are independent and can be replaced at will, with strong regeneration ability.
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