JPH0511498Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a microwave moisture meter whose measuring principle is that microwaves are attenuated by rotational resonance with water molecules. This invention relates to a microwave moisture meter that is equipped with a plurality of transmitting/receiving systems each consisting of an antenna and a receiving horn antenna, with the planes of polarization of adjacent systems rotated approximately 90 degrees.

[Prior art]

Conventionally, for example, a microwave moisture meter shown in FIG. 1 has been known. In the microwave moisture meter, a transmitting/receiving system is housed in metal casings 1 and 2 to constitute a detection head 30, and the detection head 30 is mounted on an O-shaped frame 31 as shown in FIG. It is configured to perform measurements while scanning (reciprocating) between predetermined sections L ₁ and L ₂ in the width direction of the sheet-like paper 23 flowing in the direction of arrow A.
The housing 1 includes a microwave oscillator 3 and an isolator 4.
and a transmission system 6 consisting of a transmission horn antenna 5,
The receiving system 10 includes a receiving horn antenna 7, a detector (a Schottky diode) 8, and a signal amplification/arithmetic processing section 9. The signal amplification/arithmetic processing unit 9 of the receiving system 10 has a predetermined size, for example, 155
The calibration curve obtained using the measurement brand cut into [mm] x 280 [mm] is stored, and processing is performed based on this. On the other hand, the housing 2 includes a receiving horn antenna 11 that pairs with the antenna 5 to configure a transmitting/receiving system, and a transmitting antenna 12 that pairs with the antenna 7 to configure the transmitting/receiving system. is connected to the antenna 11 by a coaxial cable 13, and transmits the microwaves received by the antenna 11). Microwave transmission/reception port 1 in each housing
4 to 17 are closed with thin membranes, for example polyethylene terephthalate membranes 18 to 21.

In the above configuration, the microwave moisture meter performs measurement while scanning the detecting head 30 in the interval L ₁ to L ₂ . At this time, generally the transmission system 6
The microwaves emitted from the paper 23 are transmitted from the antenna 5 to the paper 23 to the antenna 11 to the coaxial cable 1.
It is propagated along the route 3→antenna 12→paper 23→antenna 7 and detected by detector 8. Then, the signal amplification/arithmetic processing unit 9 amplifies the signal from the detector 8, performs predetermined processing based on the calibration curve, and outputs a water content signal g (MW).

However, with conventional microwave moisture meters,
In addition to the microwaves propagated in the path, paper 2
Since the water reflected from the surface of 3 is also detected (reflectance varies depending on the paper quality), the moisture content signal g (MW)
may not correspond accurately to the moisture content of the paper 23 due to the influence of the paper quality.

[Purpose of this invention]

The present invention has been made in view of these points, and its purpose is to provide a microwave moisture meter that is not affected by paper quality.

[Structure of the idea]

The present invention achieves the above object in a microwave moisture meter that has a plurality of transmitting/receiving systems each consisting of a pair of transmitting horn antennas and a receiving horn antenna that are arranged opposite each other with a sheet-like object to be measured in between. a first transmitting horn antenna that polarizes microwaves from a microwave oscillator into a predetermined plane of polarization via an operated switch and irradiates the object to be measured;
a first receiving horn antenna that is opposite to the first transmitting horn antenna and receives only microwaves having the same polarization plane as the first transmitting horn antenna that has passed through the object to be measured; and a coaxial cable with the first receiving horn antenna. a second antenna for irradiating the object to be measured with microwaves that have been received by the first receiving horn antenna and rotated by approximately 90 degrees with respect to the polarization plane of the first receiving horn antenna; a transmitting horn antenna, a second receiving horn antenna that is opposite to the second transmitting horn antenna and receives only microwaves having the same polarization plane as the second transmitting horn antenna that has passed through the object to be measured again; The measurement microwave received by the receiving horn antenna or the reference microwave transmitted from the microwave oscillator via the switch is used as a magic T.
an amplifier for amplifying the output signal of the detector; a first hold circuit for holding a signal corresponding to the reference microwave among the output signals of the amplifier; and an output signal of the amplifier. a second hold circuit that holds a signal corresponding to the measurement microwave, a control section that controls the holding timing of these hold circuits to be synchronized with the switching operation of the switch, and a second hold circuit that holds a signal corresponding to the measurement microwave; The microwave moisture meter is characterized by comprising a signal processing section that receives output signals from the first and second hold circuits and calculates the moisture content of the object to be measured through signal processing.

[Example of idea]

The present invention will be described below with reference to the drawings.

FIG. 3 is a configuration diagram showing an embodiment of the present invention. In FIG. 3, the same symbols as those shown in FIG. 1 are used with the same meaning, so their explanations will be omitted here. The antennas 5 and 7 have their respective apertures as shown in FIG. 4 (a diagram showing the apertures of the antennas 5 and 7 when viewed from the traveling position of the paper 23).
Rotate the plane of polarization of each antenna by 90° relative to each other.
It is configured to rotate 90 degrees. antenna 11
and 12 are also configured to rotate the plane of polarization by 90° in the same manner as above. The transmission system 41 switches the microwave from the microwave oscillator 3 to a switch 42 (control unit 4
The image is projected onto the paper 23 from the antenna 5 via the antenna 5 (operated by the operator 3). Further, the receiving system 44 detects the reference microwave obtained via the switch 42 or the measurement microwave incident on the antenna 7 with the detector 8 via the magic T 45, amplifies it with the amplifier 46, and then outputs the reference microwave. The signal E _R corresponding to the measured microwave is sent to the hold circuit 47, and the signal E _M corresponding to the measurement microwave is sent to the hold circuit 48.
(Circuit 4)
7 and 48 are controlled by the control section 43 and are synchronized with the switching operation of the switch 42).

The signal processing unit 51 includes a CPU 52, a ROM 53,
Consists of a computer consisting of 54 RAM, etc.
It processes signals from the detection head 30, operation panel 55, etc., and outputs a moisture percentage signal E _P on the vertical axis of the display section 56 (the horizontal axis of the display section 56 shows the measurement value determined in the width direction of the paper). The signal E _N corresponding to the point
is entered). When inputted to the ROM 53 are a calibration curve obtained using a measurement brand cut into predetermined dimensions and a signal from the detection head 30, sampling is performed at predetermined time intervals and the moisture content is determined based on the calibration curve. A program that outputs the calculated moisture content signal E _P is stored.

In the above configuration, as described later, the transmission system 4
1 intermittently projects microwaves onto the paper 23, and the receiving system 44 detects the microwaves (measurement microwaves) based thereon. At this time, as the microwave incident on the antenna 7, the antenna 5→paper 23→
Antenna 11 → Coaxial cable 13 → Antenna 12
→ paper 23 → propagates along the route of antenna 7,
Some light is reflected from the surface of the paper 23, but since the plane of polarization of the latter is rotated by 90 degrees with respect to the plane of polarization of the antenna 7, it does not propagate to the detector 8 and is not detected. Therefore, when the transmitting system 41 operates, the receiving system 44
The signal detected corresponds only to the microwave that has passed through the paper 23 twice.

Next, the operation based on switching of the switch 42 will be explained.

The switch 42 is operated by a control signal from the control section 43 shown in FIG. Therefore, the detection signal of the detector 8 consists of a signal E _R (directly detected via the magic T45 ₎ caused by the reference microwave shown in FIG. This is a time-series signal of the signal detected via the magic T45. The gates of the hold circuits 47 and 48 are controlled by signals S _R and S _M that are synchronized with the switching operation of the switch 42 shown in FIGS. When the measurement microwave is transmitted, the gate of the hold circuit 48 is opened. As a result, the output signals E _R and E _M of the hold circuits 47 and 48 become as shown in E and F in FIG.

On the other hand, the signal processing section 51 performs the first outgoing scan of the detection section head 30 (when the head changes from L ₁ to L ₂
The signal from the detector head 30 is sampled N times using N sample signals (N is a natural number) that equally divides the scan time per scan, and the ratio of the signals E _M and E _R is calculated. (This cancels the output fluctuation of the oscillator 3. This ratio corresponds to the measured moisture content g ₁ (MW)), calculates the moisture content MP _X based on the calibration curve stored in the ROM 53,
The moisture content signal E _P is stored in the RAM 54 and outputted to the display section 56 . Here, the detection head 30
is scanned at a constant speed, the N moisture percentages determined by the above process are determined at N measurement points (hereinafter N ₁ , N ₂ , . . . The measured values MP _x1f , MP _x2f , ... MP _x(o-1)f , MP _xof at the measurement point _No.
The signal processing unit 51 also performs the above processing during the first return scan of the detection unit head 30 (the head moves in the L ₂ →L ₁ direction), and determines the measurement points N _o , N _o-1 . . . N ₂ ，
Moisture content at N ₁ MP _xob , MP _x(o-1)b …MP _x2b ,
MP _x1b is determined and stored in the RAM 54, and the moisture content signal E _P is output to the display unit 56. Similarly, the signal processing section 51 performs the above processing for each scan of the detection head 30, and continuously outputs the moisture content signal E _P at the measurement point determined in the paper width direction to the display section 56. 56, the moisture content analysis (profile) in the paper width direction is accurately displayed.

By the way, depending on the degree to which the transmitting and receiving systems can be separated (distance and angle of view), the reflected waves may be so weak that the configuration of the present invention as described above may not be necessary. However, unless the distance between the transmitting and receiving systems (distance and viewing angle) becomes extremely large, the strength of the reflected waves remains constant, and the amount of reflected waves only differs depending on the type of paper 23. . That is, paper 2
If 3 is, for example, ordinary paperboard, the amount of reflected waves will be large, and if it is, for example, blotting paper or nonwoven fabric, the amount of reflected waves will be small.

Considering these circumstances, in order to keep the distance between the transmitting and receiving systems within an appropriate range, the moisture analyzer was installed so that the distance between the casings 2 and 3 in Figure 2 was approximately 13 mm. A moisture meter will be installed. Also,
The maximum thickness of the paper 23 is 1 mm, regardless of the type of paper.

Therefore, the paper 23 with a maximum thickness of 1 mm runs between the casings 2 and 3 with an interval of about 13 mm while vibrating up and down, and the paper 23 is irradiated with microwaves from the transmitting antenna horn. It's summery.

Note that the present invention is not limited to the above-mentioned embodiments, and the number of times the microwave passes through the object to be measured is 4 times (consisting of 4 transmitting/receiving systems) or 6 times (consisting of 6 transmitting/receiving systems). (composed of) etc.
Further, although it is not necessary to set the rotation angle of the polarization planes of adjacent transmitting/receiving systems to exactly 90°, 90° is most effective.

[Effect of idea]

As explained above, according to the microwave moisture meter of the present invention, microwaves polarized in a predetermined plane of polarization are transmitted from the first transmitting horn antenna, transmitted through the sheet-shaped object to be measured, and then transmitted to the first transmitting horn antenna. 1. The first receiving horn antenna receives only microwaves with the same polarization plane as the transmitting horn antenna, and this signal is sent to the second transmitting horn antenna via a coaxial cable. A microwave whose polarization plane has been rotated approximately 90 degrees with respect to the polarization plane of the antenna is transmitted, and after passing through the sheet-shaped object again, a second transmitting horn antenna receives only microwaves whose polarization plane is the same as that of the second transmitting horn antenna. 2 Receiving horn antenna.

As a result, in the second receiving horn antenna, the second
Only the microwaves that have passed through the sheet-shaped object to be measured from the transmitting horn antenna are detected, are transmitted from the first transmitting horn antenna, are reflected from the sheet-like object to be measured, and are incident on the second receiving horn antenna. microwaves are not received.

That is, since the second receiving horn antenna does not receive reflected waves that are affected by the paper quality, it is possible to obtain measurement values that are not affected by the paper quality.

Therefore, according to the present invention, it is possible to obtain a microwave moisture meter that is not affected by paper quality.

[Brief explanation of drawings]

Fig. 1 is a diagram showing a conventional example, Fig. 2 is a diagram showing an example of the installation of the detection head of a microwave moisture meter, Fig. 3 is a diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing an example of the installation of the detection head of a microwave moisture meter. ,
FIG. 3 is a diagram showing the relative position of the aperture of the antenna, and FIG. 5 is an operational diagram of the microwave moisture meter shown in FIG. 3. 1, 2... Housing, 5, 12... Transmitting horn antenna, 7, 11... Receiving horn antenna, 8...
Detector, 41...transmission system, 42...reception system.

Claims (1)

[Scope of utility model registration request] In a microwave moisture analyzer that has multiple transmission/reception systems consisting of a pair of transmitting horn antennas and receiving horn antennas facing each other with a sheet-shaped object to be measured in between, microwaves are transmitted via a switch operated by a control unit. a first transmitting horn antenna that polarizes microwaves from an oscillator into a predetermined plane of polarization and irradiates the object to be measured; and a first transmitting horn that is opposite to the first transmitting horn antenna and transmits through the object to be measured. a first receiving horn antenna that receives only microwaves with the same polarization plane as the antenna; and a first receiving horn that is connected to the first receiving horn antenna via a coaxial cable and receives the microwaves received by the first receiving horn antenna. Approximately relative to the polarization plane of the antenna
a second transmitting horn antenna that reirradiates the object to be measured with microwaves whose polarization plane has been rotated by 90 degrees; and a second transmitting horn antenna that is opposite to the second transmitting horn antenna and transmits the object to be measured again. and a second receiving horn antenna that receives only microwaves with the same polarization plane, and the measurement microwave received by the second receiving horn antenna or the reference microwave transmitted from the microwave oscillator via the switch. a detector that detects through the
an amplifier that amplifies the output signal of the detector; a first hold circuit that holds a signal corresponding to the reference microwave out of the output signal of the amplifier; and a first hold circuit that holds a signal corresponding to the measurement microwave out of the output signal of the amplifier. a second hold circuit that holds the signal; a control unit that controls the holding timing of these hold circuits to be synchronized with the switching operation of the switch;
Output signals from the operation panel and the first and second
A microwave moisture meter comprising: a signal processing section that receives an output signal from a hold circuit and calculates the moisture content of the object to be measured through signal processing.