Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1988-07-15
1989-12-26
Strecker, Gerard R.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
324 585C, G01N 2200
Patent
active
048900540
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for measuring physical or chemical properties of materials by absorption quantities of microwave energy or a shift in resonant frequency of a cavity.
DESCRIPTION OF THE PRIOR ART
The technology of measuring moisture content of paper and others, by means of microwave energy in an on-line manner in the paper-production process, has been noticed recently. It is desirable that the moisture content can be always measured and fed back, in an on-line manner, to the process of adjusting or drying raw material of pulp in order to maintain a good quality of finished paper. In addition, a paper price is determined by a paper weight per unit area on taking delivery from a factory. It is also attempted to make the paper have a moisture content as high as possible without deteriorating its quality. Therefore, measuring the moisture content accurately on-line is very important in not only paper-production processes but also in many other technical fields. As shown in Japanese Patent Publication No. 58-30354, the prior method of measuring moisture content of the object is to measure a difference in microwave energy and a shift in a resonant frequency between cases when a sheet object is inserted, and when not inserted, in a gap formed between an upper rectangular prism provided with means for emitting microwave energy and a lower rectangular prism provided with means for receiving microwave energy.
Each of the upper and lower typical rectangular prisms of cavity resonators in the prior method has an opening cross-section of about 30 cm.times.60 cm, and a depth of about 70 cm. An intermediate gap formed between an upper and a lower prism is about 1 cm. Since 3 GHz is primarily used for microwave oscillators including circuits which are commercially available, these dimensions of the cavity and this gap width have been adopted in order to suit the frequency.
There are four problems in measuring moisture content by means of the conventional rectangular prism cavity resonator when manufacturing paper.
The first problem is that the opening of the resonator cannot be smaller than 30 cm.times.60 cm. It is necessary to measure moisture content in an area as small as possible in practice. In the production of paper, especially, it is most important to adjust the moisture content contained in the width of about 10 cm from the edge of the paper to an adequate value. However it has been very difficult to make such measurement by using the conventional technique.
The second problem is that because the conventional cavity shaped like a rectangular prism has a low Q-value, the Q-value and resonant frequency of microwave energy do not vary sensitively when the object is inserted or even when its moisture content varies. Therefore the accuracy of measurement has been extremely poor.
The third problem is that if the upper and lower cavity resonators with the same dimensions are displaced relative to each other along the plane of a sheet object in the case of on-line measurement, the required measurement, then, cannot be conducted. This is because in that case, the cavity resonator does not function properly even if the dislocation is small. Therefore, this greatly reduces the stability of on-line measurement in the production of objects such as paper.
The fourth problem is the difficulty of realizing an accurate rectangular prism shape in practice because the demand of accuracy for dimensions of the cavity resonator is very severe. In case of constructing an accurate rectangular prism cavity by pasting plate members together, it is difficult to maintain parallelism at the position where the members are placed together. As a result, in practice, preventing microwave energy loss induced by the psuedomorphic cavity becomes difficult. In other words, it is difficult to make the cavity of a precise configuration having a Q-value similar to a theoretical value.
A typical prior method for the measurement of moisture content is based upon empirical determination
REFERENCES:
patent: 3079551 (1963-02-01), Walker
patent: 4581575 (1986-04-01), Osaki et al.
patent: 4600879 (1986-07-01), Scullyet
patent: 4620146 (1986-10-01), Ishikawa et al.
patent: 4673895 (1987-06-01), Tadachi et al.
patent: 4781063 (1988-11-01), Osaki et al.
Higashi Shigeyasu
Maeno Yorihiko
Dipole Electronics Co., Ltd.
Regan Maura K.
Strecker Gerard R.
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