JPS60187818A - Flow meter for powdery body - Google Patents

Abstract

PURPOSE:To measure the density of powdery body accurately, by applying substantially the same electric field in the powdery body conveyed through a conveyor tube. CONSTITUTION:A waveguide 7 having a rectangular section and bent in the shape of U is provided on the outer periphery of a conveyor tube 6 for conveying powder which is formed of a low-loss dielectric showing little microwave loss. A Doppler transmission-reception unit 2 is fitted to one end part of the bent waveguide 7, and a reception unit 3 to the other end part thereof. Since the conveyor tube 6 is passed through the central part 7a of the waveguide 7, the electric field of the tube 6 is strong, and the strength thereof is substantially the same. The density can be determined from a power transmitted by the unit 2 and a power received by the unit 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a powder flow meter that measures the flow rate of powder such as No. 5 charcoal in real time using microwaves.

As shown in Fig. 1, a conventional powder flow meter using microwaves has a Doppler transmitting/receiving unit placed in the middle of a metal conveying pipe 1 that conveys powder in the direction of arrow A by a predetermined distance B. 2 and a receiving unit 3 are connected via a waveguide 4.5.

In this powder flow needle, a Doppler transmitting/receiving unit 2 injects microwaves into the conveying tube 1, and the Doppler transmitting/receiving unit 2 receives the reflected microwaves reflected by the powder being conveyed in the conveying tube 1. Then, by mixing the reflected microwave and the incident microwave in a mixer, a beat of a frequency corresponding to the frequency difference between the two microwaves, that is, a Doppler frequency, is obtained, and from this, information about the transport speed of the body is obtained. I am getting .

In addition, Doppler transmitter/receiver unit 2 to II! ! Feed pipe 1
A part of the microwaves entering the inner tube 1 propagate along the II feed tube 1, and along the way, the amplitude decreases (power loss occurs) and the phase changes depending on the density of the powder. , the microwave reaches the receiving unit 3, and the phase or power of the microwave obtained by the receiving unit 3 is compared with the phase or power of the microwave transmitted by the Doppler transmitting/receiving unit 2 to obtain density information of the powder. It has gained.

Then, from this density information and the above-mentioned conveyance speed information,
Measuring the flow rate of powder.

By the way, the above-mentioned change in the phase of the microwave or loss of power is caused by the interaction with the powder being transported, but the electric field distribution of the microwave inside the transport tube 1 is caused by the fact that the transport pipe 1 In the case of a round tube, see Figure 2 ((a) is T
As shown in (Eu wave), the electric field on the central axis is strongest and becomes weaker as it approaches the periphery (the same applies to the case of till feed tube 1 furnace tube 1), and the powder is filled in the conveyor tube 1. It doesn't necessarily mean that

Therefore, even if the powder has the same density, there will be differences in the density information obtained depending on the position of the powder in the cross section in the conveying pipe 1, and errors will occur in the density information. Errors occur in flow measurement.

Furthermore, in the powder flowmeter having the configuration shown in FIG.
This is also a cause of error in the density information, as there are some that do not reach .

The present invention has been made in view of the above points, and its purpose is to prevent errors in density information due to the strength of the microwave electric field or leakage of microwaves to other sources, and thereby enable highly accurate flow rate measurement. It is an object of the present invention to provide a powder flow needle that can perform powder flow.

Examples of the present invention will be described below. Fig. 3 shows an example of this, in which 6 is a conveyor tube (low-loss dielectric tube) with a round cross section for conveying powder made of a low-loss dielectric with little microwave loss, and 7 is a cross-section. is a metal waveguide whose overall shape is rectangular and bent into a substantially U-shape. It passes through the central portion 7a. and,
A Doppler transmitter/receiver unit 2 is attached to one bent end of the waveguide 7 (the side where the powder is conveyed), and a receiver unit 3 is attached to the other @ part (the side where the powder is conveyed). It is being Reference numeral 8.9 denotes a round metal guide tube for fixedly passing the carrier tube 6 into the waveguide 7.

In the above, the distribution of the microwave electric field in the waveguide 7 is such that for TE+o waves, the electric field is strong at the center and weakest at both sides in the longitudinal direction, as shown in FIG. However, in this embodiment, since the carrier tube 6 coaxially penetrates the central portion 7a of the waveguide 7, the carrier tube 6 has a strong electric field (the electric field is located in a portion where the magnitude is almost the same). Therefore, the same electric field is applied to the powder in the transport pipe 6 regardless of its position in the cross-sectional direction within the transport pipe 6.

On the other hand, depending on the size of the waveguide, there is a cutoff frequency that prevents microwaves below a certain frequency from propagating.For example, in a rectangular waveguide with long sides a, the wavelength at that cutoff frequency, In other words, the cutoff wavelength λC is λc=2
It is a. In addition, for a round waveguide with radius r, λc=2π
r/k (k is a constant determined by the mode of the electromagnetic field used). Therefore, in the above embodiment, when the frequency of the microwave to be used is determined in advance, the outer diameter of the conveying tube 6 is set to a dimension that corresponds to the above-mentioned cutoff wavelength, or the diameter of the conveying tube 6 is determined in advance. Sometimes, by using microwaves with a wavelength longer than the cutoff wavelength determined by the outer diameter of the conveyor tube 6, microwaves can be applied to the portion of the conveyor tube 6 outside the attachment part of the guide tube 8.9. There will be no leakage, and the microwave loss there will be eliminated.

As a result of the above, almost the same electric field is applied to the powder in the conveying tube 6, and there is no leakage of microwaves to the outside R1+, so the microwaves that reach the receiving unit 3 from the Doppler transmitting/receiving unit 2 are controlled by their phase and power. changes continuously depending on the density of the powder in the conveying tube 6. Note that the phase and power of the microwave are affected by the bending part of the waveguide 7 and the carrier tube 6 itself, but these can be treated as constants, so the density signal or the final flow rate signal obtained therein can be treated as constants. By correcting, accurate flow rate can be measured.

FIG. 5 shows the structure of another embodiment, in which the waveguide 7
The attachment to the Doppler transmitting/receiving unit 2 and the receiving unit 3 at ' is the same as that shown in FIG. 3 except that the bent portions of the parts are approximately 90 degrees.

Note that at least the portion of the transport tube 6 that passes through the waveguides 7 and 7' may be formed of a low-loss dielectric material, and the rest may be made of the same metal as a normal transport tube. Further, the waveguides 7, 7' may be round, and furthermore, the conveying pipe 6 may be rectangular.

As described above, according to the present invention, it is possible to prevent the leakage of microwaves from the Doppler transmitting/receiving unit to the receiving unit and the occurrence of errors in density information due to non-uniform electric fields, and it is possible to realize flow Wit with improved accuracy. It has the characteristic that it can be done.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the structure of a conventional flowmeter, Figure 2 is a diagram showing the electric field mode in the conventional INN feed direction, fbl is a characteristic diagram showing the distribution of the electric field, and Figure 3 is a diagram showing the current electric field mode. FIG. 4 is a sectional view showing the structure of a flow rate needle according to an embodiment of the invention;
bl is a characteristic diagram showing the distribution of the electric field, and FIG. 5 is a sectional view showing the structure of a flowmeter according to another embodiment. DESCRIPTION OF SYMBOLS 1... Conveyance tube made of metal, 2... Doppler transmission/reception unit, 3... Receiving unit, 4.5... Waveguide, 6... Conveyance tube (low loss dielectric tube), 7 .7'...
Waveguide, 8.9...A guide tube made of metal. Patent applicant Nippon Steel Corporation New Japan Radio Co., Ltd. Agent Patent attorney Tsuneaki Nagao Figure 3 Figure 5

Claims (1)

[Claims] (1j, Inject a microwave in the transport direction of the transport pipe that transports the powder, and obtain the flow velocity signal of the powder using the Doppler frequency obtained from the incident microwave and the reflected microwave reflected by the powder. In addition, a density signal of the powder is obtained by the loss of acid or phase delay of the incident microwave due to the powder, and the flow rate of the powder is measured based on the density signal and the flow velocity signal. In the mass flowmeter, at least -g8 of the conveying pipe is formed of a low-loss dielectric pipe, and the low-loss dielectric pipe is coaxially placed in the center of a metal waveguide bent in a box-shaped shape. A Doppler transmitting/receiving unit is connected to one end of the waveguide, and a receiving unit is connected to the other end of the waveguide. The powder flow consists of using a needle.