JP3834915B2 - Gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor that measures the concentration of NOx in a sample gas, such as a constant potential electrolytic NOx gas sensor.
[0002]
[Prior art]
A gas sensor is an element that mainly detects and quantifies a specific gas component in the atmosphere, and is used not only for general analysis but also for control of industrial process systems from various devices.
When using a measuring instrument equipped with such a sensor, an operation called calibration is performed before actual measurement. In calibration, measurement is performed at two points when a zero gas that does not contain any measurement target gas and a span gas that contains a measurement target gas having a known concentration is flowed, and a calibration curve is created using these values. In general, a gas supplied from a dedicated gas cylinder is used as a calibration gas.
[0003]
[Problems to be solved by the invention]
Among these measuring instruments, when considering portable measuring instruments for on-site measurement, in order to calibrate on-site, each gas cylinder for zero gas and span gas must also be brought into the field. There were disadvantages in the size and weight of the gas supply device.
Accordingly, an object of the present invention is to create a zero gas from the atmosphere as a raw material without using a gas cylinder for zero gas, which is one of calibration gases, and to supply it to a NOx measuring device at the time of calibration.
[0004]
[Means for Solving the Problems]
In the present invention, a zero gas supply device that uses the atmosphere as a raw material and removes NOx in the atmosphere using an absorbent to obtain zero gas is used. Such a zero gas supply device is composed of a porous ceramic coated with KMnO ₄ on the air introduction side in a cylindrical container having an air introduction port at one end and a zero gas discharge port at the other end, and absorbs and oxidizes NO. And an integrated gas purifier filled with NO ₂ absorbent on its zero gas discharge side, and provided on the upstream side or downstream side of the gas purifier and from the gas purifier, NOx And a pump for creating a gas flow to the measuring device.
[0005]
Part of the nitrogen oxides in the air introduced into the container from the air inlet is partially absorbed by the NO oxidation absorbent provided on the air introduction side, and the rest is oxidized to NO ₂ . All nitrogen oxides in the air that have passed through the NO oxidation absorbent portion are NO ₂ . The NO ₂ gas is absorbed by the NO ₂ absorbent on the zero gas discharge side, and the gas discharged from the discharge port is a zero gas from which nitrogen oxides have been removed, and is supplied to the NOx measuring device and subjected to zero gas calibration.
[0006]
【Example】
FIG. 1 shows an embodiment. 1 is a purifier that uses air as a raw material and removes nitrogen oxides in the air to create zero gas. Its container 2 is a cylindrical tube made of polyvinyl chloride, one end of which is closed by a lid 4, In the center of the lid 4, a hole for the air introduction port 5 is formed. The other end side of the container 2 is a zero gas discharge port 3 whose central portion protrudes.
[0007]
The inside of the container 2 is filled with the NO oxidation absorbent 8 on the air introduction side, and the NO ₂ absorbent 10 is filled on the zero gas discharge side. Between the NO oxidation absorbent 8 and the NO ₂ absorbent 10, 0.2 g of polypropylene cotton 6b is interposed as a spacer to prevent mixing of both. Polypropylene cotton 6a and 6c are filled on the air inlet side of the NO oxidation absorbent 8 and the zero gas discharge side of the NO ₂ absorbent 10 respectively, and the NO oxidation absorbent 8 and the NO ₂ absorbent 10 are discharged from the container 2 to the outside. Prevents spills.
[0008]
As the NO oxidation absorbent 8, Purafil (manufactured by Purafil) coated with porous ceramics with KMnO ₄ can be used. As the NO ₂ absorbent 10, silica gel of a special grade reagent can be used.
Reference numeral 12 denotes a NOx measuring device such as a constant potential electrolytic gas sensor. A suction pump 14 is disposed in a flow path connecting the zero gas outlet 3 of the purifier 1 and the NOx measuring device 12. Zero gas is supplied from the purifier 1 using the suction pump 14 during calibration.
[0009]
2 (A) is, in the embodiment of FIG. 1, a result of the NO ₂ as a gas to be supplied to the purifier 1 continued flowed standard gas was 100ppm the NO ₂ concentration was diluted with the air, NO ₂ removal It shows your ability. Even if the standard gas was allowed to flow for 40 hours or more, no change was observed in the instruction of the measuring instrument.
[0010]
FIG. 2 (B) shows the result of continuously supplying a standard gas in which NO is diluted with nitrogen and the NO concentration is 100 ppm as the gas supplied to the purifier 1 in the embodiment of FIG. Is shown. In the state of flowing for about 1 hour, 100 ppb which is 1/1000 of the concentration of the supply gas was maintained, and after about 4 hours and 30 minutes, it reached 1 ppm which was 1/100 of the concentration of the supply gas.
[0011]
【The invention's effect】
In the present invention, since zero gas can be supplied using the atmosphere as a raw material at the time of zero gas calibration of the NOx measuring instrument, it is not necessary to carry a cylinder for zero gas, which is advantageous in realizing a portable gas sensor.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment.
FIGS. 2A and 2B are diagrams of measurement results showing characteristics of the example, wherein FIG. 2A is a diagram showing NO ₂ removal capability, and FIG. 2B is a diagram showing NO removal capability;
[Explanation of symbols]
1 Purifier 2 Container 3 Zero gas outlet 5 Air inlet 6a, 6b, 6c Polypropylene cotton 8 NO oxidation absorbent 10 NO ₂ absorbent

Claims (1)

In a gas sensor comprising a NOx measuring device for measuring a NOx concentration in a sample gas, and a zero gas supply device for supplying zero gas to the measuring device during zero gas calibration,
The zero gas supply device is made of porous ceramics coated with KMnO ₄ on the air introduction side in a cylindrical container having an air introduction port at one end and a zero gas discharge port at the other end, and absorbs and oxidizes NO. An integrated gas purifier filled with NO oxidation absorbent and filled with NO ₂ absorbent on its zero gas discharge side, and the NOx measurement from the gas purifier provided upstream or downstream of the gas purifier And a pump for forming a gas flow to the vessel.

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