JPS637892Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a gas humidity measuring device that continuously measures the humidity of a circulating gas.

For example, when a radioactive material (for example, a rat) that has been exposed to radioactivity for testing was to be subsequently processed, it was used to be immersed in formalin, but now it is dried and processed. During this drying, dielectric heating is performed using microwave irradiation. In this case, if the radioactive material is dried more than necessary, it will catch fire, so it is necessary to constantly monitor the water content of the radioactive material so as not to dry it beyond a certain level. The humidity of this circulating air is measured remotely.

Some gas hygrometers for this purpose use a special ceramic-like semiconductor that takes advantage of the fact that its electrical resistance changes with humidity, but its operating principle is not very clear, and it changes significantly with temperature. Furthermore, due to the complex composition, there was a problem of large changes over time.

There are also methods that measure humidity by changes in capacitance by utilizing the change in dielectric constant due to moisture absorption of an organic dielectric film that reversibly absorbs and desorbs moisture, but the drawback is that the measuring device is expensive. It was hot.

The present invention was developed in view of the above points, and its purpose is to utilize the fact that microwave absorption changes depending on the dielectric constant, and to change the absorption level depending on the degree of microwave absorption. To provide a stable and inexpensive gas humidity measuring device that measures humidity.

Hereinafter, embodiments of the present invention will be described in detail. First, if the permittivity of a dielectric is ε, then
The microwave power P at the frequency absorbed by the dielectric is expressed as P∝f・ε・tanδ. δ is the dielectric loss angle, and ε・
tanδ is called the loss coefficient. The dielectric constant of general dielectrics is about 3 to 6 (CGS units), but the dielectric constant of water is extremely large, reaching 60 to 90 (CGS units). Therefore, the dielectric constant of an object containing water is
Depending on the water content, the dielectric constant has a value intermediate between that of general dielectrics and that of water. On the other hand, certain types of hydrophilic polymer membranes (e.g., cellulose, cellophane, etc.) absorb and desorb moisture in proportion to the concentration of moisture in the surrounding gas, so By measuring the rate, it is possible to measure the moisture in the gas. According to the above equation, the microwave absorption power P is proportional to the change in the dielectric constant ε, so by measuring the microwave absorption power P, the humidity can be measured.
In this case, it is clear from the above equation that the sensitivity increases if high frequency microwaves are used.

FIG. 1 is a basic block diagram of an embodiment of a gas humidity measuring device, in which 1 is a microwave oscillator (which may be used in common with the drying device described above if necessary), 2, 2', 2'' is the first to third waveguides, 3 is an attenuator for stabilizing the microwave oscillation operation, and 4 is a microwave detector.The humidity is measured between the waveguides 2 and 2'. A measurement waveguide 5 is connected to the second measurement waveguide 5.
As shown in the figure, opposing surfaces are open and each surface is covered with meshes (perforated plates may be used) 6, 6' with dimensions that prevent microwaves from passing through (cut-off dimensions), and another The opposing surfaces are blocked by side plates 7, 7', and the connecting parts with the first waveguide 2 and the connecting parts with the second waveguide 2' are each made of low-loss dielectric material (quartz, Teflon, etc.). , glass,
Partition walls 8, 8' made of ceramic or the like are provided to maintain airtightness. Reference numerals 9 and 9' denote guide tubes for circulating the gas to be measured, and the planes of the meshes 6 and 6' of the measurement waveguide 5 are perpendicular to the passing direction (although not shown, even if they are not perpendicular or oblique) so that it becomes good)
They are provided corresponding to the meshes 6, 6'. In this case, the gas flowing through the guide tubes 9, 9' passes through the meshes 6, 6', but is blocked by the partition walls 8, 8' and cannot flow into the waveguides 2, 2'. The microwave passing through the waveguide 5 is transmitted through the mesh 6,
6' and the remaining side plates 7, 7' to prevent leakage into the guide tubes 9, 9'. Mesh 6, 6' in measurement waveguide 5, partition walls 8, 8', side plate 7,
The measurement space surrounded by 7' is filled in advance with strips of a hydrophilic polymer compound (dielectric) that freely absorbs and releases water depending on the surrounding humidity. Reference numeral 10 designates a probe as an input power detection terminal provided on the microwave input side of the waveguide 2, that is, on the attenuator 3 side, and its output signal is input to the proportional amplifier 11. An output signal from another microwave detector 4 is also input to this proportional amplifier 11, and the ratio of both output signals is detected here and outputted to an output terminal 12.

In the above, when the microwave oscillator 1 is operated, the microwave from there is guided to the waveguide 2 via the waveguide 2'' and the attenuator 3, reaches the measurement waveguide 5, and is further guided into the waveguide 5. It is input to the microwave detector 4 through the tube 2'.The filling in the measurement waveguide 5 changes its moisture content according to the humidity of the gas flowing through the guide tubes 9, 9'. The filling has a dielectric constant that corresponds to the humidity of the gas, and the microwave absorption there changes depending on the humidity of the flowing gas.Figure 3 is a diagram showing the relationship between water content and microwave absorption. , the microwave input to the measurement waveguide 5 is detected by the probe 10 and the detected signal is sent to the proportional amplifier 11, while the attenuated microwave that has passed through the measurement waveguide 5 is detected by the microwave detector. 4 and sends the detection signal to the proportional amplifier 11, and detecting the ratio of both detection signals, the attenuation of the microwave can be determined.Since this attenuation ratio is proportional to the water content of the filling, the distribution The humidity of gas can be detected continuously.

As mentioned above, in order to improve the sensitivity in the above embodiments, it is sufficient to increase the frequency of the microwave, but as another method, as shown in FIG. and guide tube 9,
There is also a method of enlarging the connecting portions 9a and 9a' of the measurement waveguide 5 to enlarge the measurement space and increase the amount of filler filled therein.

Alternatively, as shown in FIG. 5, the measurement waveguide 5 is lengthened, and meshes 6 and 6' on opposite sides are provided at opposite corners to which guide tubes 9 and 9' are connected, respectively. , side plates 13, 13' are provided on the remaining portions of the surfaces on which the meshes 6, 6' are attached, and the measurement space is expanded by shifting the positions of the inlet and outlet of the circulating gas to the measurement waveguide 5. There is also a method of increasing the amount of filler to be filled.

From the above, according to the present invention, since the humidity of the circulating gas is measured by absorption of microwaves, continuous and stable measurement is possible, and the microwave oscillator is also used for drying. Therefore, it can be made inexpensive. Furthermore, since microwaves do not escape from the measurement waveguide to the outside and no circulating gas flows into the waveguide from the measurement waveguide, accuracy can be extremely high. Furthermore, the sensitivity can be easily adjusted by selecting the type and amount of filling to be filled into the measuring waveguide in addition to selecting the frequency of the microwave.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a gas humidity measuring device according to an embodiment of the present invention, FIG. 2 is a perspective view of a measurement waveguide portion of the same embodiment, and FIG. 3 is a diagram of microwave absorption characteristics.
4 and 5 are side views of portions of another example of a measurement waveguide. 1... Microwave oscillator, 2, 2', 2''... Waveguide, 3... Attenuator, 4... Microwave detector, 5... Measurement waveguide, 6, 6'... Mesh, 7, 7'... Side plate, 8, 8'... Partition wall, 9,
9'... Guide tube, 10... Probe, 11...
Proportional amplifier, 12... Output terminal, 13, 13'...
...side plate.

Claims (1)

[Claims for Utility Model Registration] A microwave oscillator, a first waveguide connected to the microwave oscillator, and a measurement waveguide connected to the first waveguide for measuring humidity. a second waveguide connected to the measurement waveguide, and a microwave detector connected to the second waveguide; The first and second waveguides are closed by two dielectrics with low loss, and each of the opposing wall surfaces has a pore that blocks microwaves in at least a portion thereof,
The inside is filled with a dielectric material that reversibly attaches and detaches moisture, and a guide tube through which gas flows is connected to cover the pores, so that the structure allows the measurement gas to pass through the measurement waveguide. A humidity measuring device for gases.