KR900004737B1 - Vibrator - type level sensor - Google Patents

Abstract

The level sensor has an improved lifespan. Sensor comprises a hollow member one end of which is fixed and other end of which is blocked, and having a predetermined wall thickness. An inner vibration member is provided in the blocked end of the hollow member and is fixed to the end by a blocking member which is not a diaphragm and is thicker than the holow member wall thickness. A vibrator is included for the inner vibration member with the blocking member coupling vibration from the vibration member to the hollow member. The latter is forced into vibration, and a sensor detects a decrease of vibration.

Description

Vibration Level Detection Device

1 is a partially cutaway perspective view showing a conventional vibrating level detection device.

2 is a partially cutaway perspective view of a vibrating level detecting apparatus according to an embodiment of the present invention.

3 is a cross-sectional view showing a state in which the vibrating level detection device of the present invention is fixed to a container.

4 is a block diagram showing a block diagram according to an embodiment of the present invention.

5 is a graph showing the relationship between the length of the detection pipe and the frequency.

6 is a graph showing the relationship between the length of the detection pipe and the output of the oscillation loop.

7 is a block diagram showing another embodiment of the present invention.

8A and 8B are block diagrams showing embodiments of the present invention in the case of detecting in accordance with a frequency change.

9 is a graph showing the change of the frequency when the powder is in contact.

10 and 11 are block diagrams showing another embodiment of the present invention.

12 is a perspective view showing an embodiment in which a detection blade is formed in order to detect an object to be detected with a seemingly low specific gravity in the apparatus of the present invention.

* Explanation of symbols for main parts of the drawings

1a, 1b, 1c, 1d: detection device 2: vibrating body (raising piece)

2a: contact portion 2b: storage portion

4: thin membrane 6: cylindrical body

6a: support 8a: piezoelectric element for reception

8b: piezoelectric element for excitation 8c: piezoelectric element for detection

12: screw 13: nut

16: cylindrical frame 20: detection pipe

22: vibrating piece 24: blocking member

26a: lead wire 30: input circuit

32: amplification circuit 34: control circuit

36: output circuit 38: detection circuit

40: comparison circuit 42: relay

44: initializing circuit 50: oscillating circuit

52: vibration detection circuit 54: frequency comparison circuit

54a: first input 54b: second input

56: reference frequency oscillator circuit 58: support pipe

64: flexible pipe 70: sweep oscillation circuit

90 container 95 weight

98: detection blade L _b , L _p : length

C ₁ , C ₂ , C ₃ : Curve f _a , f _b : Frequency (frequency)

A: curve

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibratory level detection device for detecting a level change of a powder particle body or a liquid in a container.

The conventional vibrating level detection device is shown in FIG.

The vibrating body 2 is supported by the thin film plate 4, and the contact part 2a of the vibrating body 2 protrudes outside the cylindrical body 6. As shown in FIG.

An excitation piezoelectric element 8b and a receiving piezoelectric element 8a are formed in the accommodating portion 2b of the vibrating body 2 housed inside the cylindrical body 6.

The excitation piezoelectric element 8b vibrates the vibrating body 2, and this vibration is converted into an electrical signal by the receiving piezoelectric element 8a.

This electrical signal is amplified by an amplifying circuit (not shown), and is then supplied to the piezoelectric element 8b for excitation.

Therefore, the vibrating body 2 vibrates at a predetermined frequency.

When the object to be detected such as powder particles or liquid comes into contact with the contact portion 2a, the vibration of the vibrating body 2 is stopped or attenuated.

This is detected to detect whether or not the object to be detected is in contact with the contact portion 2a.

By providing such a level detection device in the container, the level of the object to be detected in the container can be known.

However, the above-mentioned conventional vibrating level detection device has the following problems.

First, since the thin membrane 4 is used, not only the life is short, but also when the object to be detected, such as powder, adheres to the membrane 4, there is a risk of incorrect operation.

Second, in spite of the fact that the objects to be detected are in contact with each other under various conditions, there are cases where the vibration is not stopped or attenuated.

In particular, in the case of ultrafine particles which give a large pressure to the contact portion 2a, such a tendency was remarkable.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and to provide a vibrating level detecting apparatus capable of detecting with high accuracy.

One embodiment of the present invention is shown in FIG.

In the cylindrical frame 16 formed by aluminum die casting, a weight 95 and an electric circuit are housed therein. A support pipe 58 having a screw 12 is fixed to the front face of the cylindrical frame 16, and a detection pipe 20, which is a cylindrical member, is fixed to the support pipe 58.

The detection pipe 20 is formed thinner than the support pipe 58.

As the material of the detection pipe 20, stainless steel (SUS 304, SUS 316, etc.), titanium, Hastelloy, Monel metal, Inconel steel (SS material, SC material, etc.) Use

The blocking member 24 is welded to the front end of the detection pipe 20.

The blocking member 24 has a step hole, and the vibration piece 22 is screwed in this step hole.

Therefore, a vibrator similar to the tuning fork is formed by the detection pipe 20 and the vibrating piece 22.

On both sides of the vibrating piece 22, an excitation piezoelectric element 8b (not shown) and a receiving piezoelectric element 8a, which are composed mainly of lead titanate titanate (PbTiO ₃ -PbZrO ₃ ), are formed.

The vibration piece 22 is vibrated by the excitation piezoelectric element 8b.

This vibration is detected by the receiving piezoelectric element 8a and converted into an electric signal. The detected electric signal is sent to the electric circuit in the cylindrical frame 16 through the lead wire 26a.

The electric circuit amplifies this signal and then applies it to the piezoelectric element 8b for excitation via the lead wire 26b.

Thus, the vibrating piece 22 vibrates with a natural frequency similar to that of the tuning fork.

The weight 95 accommodated in this embodiment is formed to be heavier than the detection pipe 20 and the vibration piece 22 to stabilize the vibration.

For example, when the vibration piece 22 is 30 g, the weight 95 is preferably set to a ratio of 200 g or more.

In addition, the support pipe 58 thicker than the detection pipe 20 may be formed instead of the weight 95.

When the powder, particle or liquid, etc., to be detected is in contact with the detection pipe 20, the vibration of the vibration piece 22 is stopped or reduced by the resistance.

In this case, the frequency of the vibration piece 22 also changes. This change in the amplitude of vibration can be detected by an electric circuit to detect that the object to be detected is in contact with the detection pipe 20.

Therefore, when this level detection apparatus is attached to the container 90, the level of the object to be detected in the container 90 can be detected.

Thus, since the vibrating piece 22 is formed in the inside of the detection pipe 20, the vibrating piece 22 is stuck to the object to be detected and does not detect erroneously.

In addition, the service life is extended because a thin membrane is not used.

3 shows various states in which the vibratory level detection device according to this embodiment of the present invention is fixed to the container 90.

The vibratory level detecting device 1a is fixed to the side wall of the container 90 by a screw 12 and a nut 13.

The detection apparatus 1b is fixed by the flange 60 screwed to the container 90.

When it is difficult to fix and fix the detection device to the side wall of the container 90, one having the long support pipe 58 like the detection device 1c may be attached and fixed at the top of the container 90.

In addition, by using the flexible pipe 64 like the detection device 1d, the transport welding in the case of transporting the detection device can be reduced.

4 shows a block diagram of the electric circuit housed in the cylindrical frame 16. As shown in FIG.

When an output from the output circuit 36 is given to the excitation piezoelectric element 8b, the excitation piezoelectric element 8b vibrates the vibrating piece 22.

The receiving piezoelectric element 8a formed on the vibrating piece 22 converts this vibration into an electrical signal.

The electric signal is amplified in the amplifying circuit 32 through the input circuit 30, and is then given to the piezoelectric element 8b for excitation via the output circuit 36.

Therefore, the vibrating piece 22 vibrates according to the natural frequency similar to the tuning fork formed by the detection pipe 20 and the vibrating piece 22.

The output of this oscillation loop is detected by the detection circuit 38.

The output of the detection circuit 38 is compared with the reference voltage in the comparison circuit 40.

When a detection target such as powder or the like comes into contact with the detection pipe 20 and the detection output is lower than the reference voltage, the comparison circuit 40 sends a detection output to operate the relay 42.

In addition, when the output of the amplifying circuit 32 becomes excessively large, the oscillation sound of the vibrating piece 22 becomes large and becomes annoying to the ear.

For this reason, in this embodiment of the present invention, the control circuit 34 is formed to limit the amplification rate of the amplifying circuit 32.

In addition, in order to prevent erroneous operation due to temperature change, a temperature compensation circuit may be formed in the amplifying circuit 32.

5 shows the change in the resonance frequency when the length L _b of the vibrating piece 22 is made constant and the length L _p of the detection pipe 20 is changed.

In FIG. 5, the natural frequency of the detector is shown by the curve C ₁ .

Curve C ₁ plots the values measured by experiment.

The curve C ₂ represents the primary vibration of the detection pipe 20, the curve C ₃ represents the secondary vibration, and at the same time plots the value by calculation.

As is apparent from the curve C ₁ of this graph, the natural frequency of the detector is almost constant regardless of the length L _p of the detection pipe 20.

In addition, this curve C ₁ approximates the natural frequency of the vibration piece 22 obtained by the calculation formula.

That is, it shows that the vibration piece 22 vibrates alone, and the forced vibration is performed with respect to the whole detector by the vibration piece 22. As shown in FIG.

In addition, the following formula was used for calculation.

In Fig. 6, the relationship between the output voltage and the length ratio L _p / L _b of the oscillation loop is shown graphically.

The output voltage decreases rapidly in the vicinity of L _p / L _b becoming one.

In the range "B" shown in the figure, the phase of the signal given to the excitation piezoelectric element 8b and the phase of the output signal from the receiving piezoelectric element 8a are the same.

Therefore, when using in the range "B", it is better to use the circuit shown in FIG.

In the range "C", the phase of the input signal and the phase of the output signal are different.

Therefore, when using in the range "C", instead of the amplifier circuit 32, it is preferable to form a phase locked oscillation loop using an amplifier circuit with a phase adjuster.

In this case, what is necessary is just to detect the contact of a to-be-detected object with the phase difference signal from the amplifier circuit with a phase adjuster.

7 shows a block diagram of an electric circuit according to another embodiment of the present invention.

Through the output circuit 36, the output of the oscillation circuit 50 is given to the excitation piezoelectric element 8b.

Therefore, the vibrating piece 22 vibrates, and the detecting piezoelectric element 8c outputs an electric signal corresponding to the vibration.

This output is amplified by the amplifier circuit 32 via the input circuit 30 and then detected by the detector circuit 38.

The detection output from the detection circuit 38 is compared with the reference voltage in the comparison circuit 40.

When a detection target such as powder or the like comes into contact with the detection pipe 20 and the detection output is lower than the reference voltage, the comparison circuit 40 sends a detection output to operate the relay 42.

Since the circuit shown in FIG. 7 can operate regardless of the phase difference of the input / output signals, it can be used in both the ranges "B" and "C".

Another embodiment of the present invention is shown in FIG. 8A.

The node of the lateral vibration of the raising piece 2 which is a vibrating body is supported by the rigid support body 6a.

In the above embodiment, the support 6a is formed integrally with the cylindrical body 6.

An excitation piezoelectric element 8b and a receiving piezoelectric element 8a are fixed to the housing portion 2b of the raising piece 2.

The excitation piezoelectric element 8b vibrates in response to a signal from the output circuit 36 and vibrates the lifting piece 2.

In addition, the excitation piezoelectric element 8b is formed in the vicinity of the node of vibration, so that the efficiency is good.

The vibration of the lifting piece 2 is converted into an electrical signal in the receiving piezoelectric element 8a and input to the input circuit 30 having a filter.

The electric signal output from the input circuit 30 having the filter is amplified by the amplifying circuit 32 and then given to the piezoelectric element 8b for excitation via the output circuit 36.

That is, in this embodiment of the present invention, the excitation piezoelectric element 8b, the receiving piezoelectric element 8a, the input circuit 30, the amplifying circuit 32, the control circuit 34, and the output The excitation means is constituted by the circuit 36.

Therefore, the lifting piece 2 vibrates at _a predetermined frequency f _a as shown in FIG.

Next, when the object to be detected comes into contact with the contact portion 2a of the lifting piece 2, as shown in FIG. 9, the vibration frequency of the lifting piece 2 changes from (f _a ) to (f _b ).

Therefore, a signal of frequency f _b is input to the first input 54a of the frequency comparison circuit 54.

In addition, the reference frequency f _a is input to the reference frequency oscillation circuit 56 to the second input 54b. This reference frequency f _a is set to be equal to the vibration frequency f _a in the free state of the lifting piece 2. The frequency comparison circuit 54 outputs an output when the difference between the frequencies inputted to the first and second inputs 54a and 54b exceeds a predetermined value W ₂ .

Therefore, when the object to be detected comes into contact with the lifting piece 2 and the vibration frequency changes, the output of the frequency comparison circuit 54 operates the contact 46 of the relay 42 so that an alarm circuit (not shown) or the like can be applied. It works.

In addition, the initializing circuit 44 does not operate the relay 42 for a predetermined time (about 3 seconds) after the power is turned on.

As described above, in this embodiment of the present invention, the frequency comparison circuit 54, the reference frequency oscillation circuit 56, the relay 42, the initializing circuit 44, and the vibration detection circuit 52 are detected. Means are constructed.

When the object to be detected comes in contact with the lifting piece 2, the vibration of the lifting piece 2 is stopped. Therefore, in this embodiment of the present invention, the vibration detecting circuit 52 is formed so that it can be detected even when the vibration is stopped.

However, when the vibration of the lifting piece 2 does not stop, this vibration detection circuit 52 is unnecessary.

In this embodiment of the present invention, since the support body 6a is made of a rigid member, even if the object to be detected remains attached to the portion of the support body 6a, the influence on the frequency of the vibrating body 2 is small. .

Thus, there is less false detection by residual deposits. Table 1 is a result of measuring the frequency f _{a at the time} of making the contact part 2a of the raising piece 2 free, and the frequency f _{b at the time} of fixing the contact part 2a.

In this case, so that the length of the contact portion (2a) measuring whether there is any effect on the difference between the frequency "W _1".

TABLE 1

Next, the case where the ultrafine particles which had many false detections in a conventional detection apparatus are in contact with each other is similar to the case where the contact portion 2a is fixed.

Table 2 shows the measurement results when the length of the storage portion 2b is changed as described above.

TABLE 2

In addition, the measurement result at the time of changing the length of the contact part 2a and the accommodating part 2b at the same time is shown in Table 3.

TABLE 3

Vibrating-type level detection device according to this embodiment, the components of the detected object is detected, the frequency level of the detected object by what is causing the change in the presence of, the larger the difference between the frequency "W _1" less is the possibility of false detection do.

Therefore, as apparent from Table 3, the vibrating body 2 is preferably short.

In another embodiment of the present invention, instead of the reference frequency oscillation circuit 56 and the comparison circuit 54, a filter having the characteristics as shown in the curve A of FIG. 9 may be used.

As described above, the vibratory level detection device detects a change in frequency caused by contact of an object to be detected.

Therefore, even when the vibration is not stopped or attenuated by the contact of the object to be detected, detection can be performed.

That is, a highly accurate vibration level detection device can be obtained regardless of the type of object to be detected.

A block diagram of an electric circuit according to another embodiment of the present invention is shown in FIG. 8B.

In this embodiment of the present invention, the detection pipe 20 and the vibration piece 22 as shown in FIG. 4 and FIG. 7 are used. It is the same as FIG. 8A about an electric circuit part. In Fig. 10, an embodiment in which the piezoelectric element 8c for detection is formed separately from the excitation piezoelectric element 8b and the receiving piezoelectric element 8a is shown. The piezoelectric element 8c for detection detects the vibration of the vibration piece 22, converts it into an electrical signal, and inputs it to the frequency comparison circuit 54. FIG. 11 shows an embodiment in the case where the sweep oscillation circuit 70 is used. The output of the sweep oscillation circuit 70 causes the vibration piece 22 to vibrate.

This vibration is converted into an electrical signal by the detecting piezoelectric element 8c and input to the frequency comparison circuit 54. In the case where the object to be detected is one having a small apparent specific gravity (for example, powdery foamed styrol), a detection blade 98 may be formed in the detection pipe 20 as shown in FIG. A small apparent specific gravity such as foamed styrol may not be detected because it does not significantly affect vibration even when it comes into contact with the detection pipe 20.

In this embodiment of the present invention, since the detection blade 98 is formed and the contact surface is widened, the object to be detected can be detected even in such a case.

According to the present invention as described above, it is possible to provide a vibrating level detecting device which has a long service life and has no fear of false detection.

Claims (8)

One end is fixed and formed inside the other end of the cylindrical member (detection pipe) 20, the other end is blocked, the other end of the cylindrical member 20, one end is the other end of the cylindrical member 20 And a fixed vibration piece (22), a means for exciting the vibration piece (22), and a means for detecting a change in the vibration frequency of the vibration piece (22). 2. The excitation means according to claim 1, wherein the excitation means amplifies the output of the excitation piezoelectric element 8b, the receiving piezoelectric element 8a, and the receiving piezoelectric element 8a formed on the vibrating piece 22. And an oscillation loop comprising the amplification means given to (8b), wherein the detection means detects a change in the oscillation frequency of the oscillation loop. The excitation means according to claim 1, wherein the excitation means excises a voltage signal having a frequency which is repeatedly changed between the excitation piezoelectric elements 8b formed on the vibration piece 22 and a predetermined frequency range as a predetermined time ratio. And a sweeping oscillation means (circuit) 70 provided to the piezoelectric element 8b to change the frequency of the output of the detection means and the measurement (detection) piezoelectric element 8c formed on the vibrating piece 22. Vibration level detection device characterized in that for detecting. The detection means according to any one of claims 1 to 3, wherein the detection means compares the vibration frequency and the reference frequency of the reference frequency oscillation circuit 56 that outputs the reference frequency with the reference frequency. And a comparison circuit (54) for outputting a detection signal when the frequency is higher than or equal to a predetermined frequency. The vibratory level detection device according to claim 4, wherein the reference frequency is selected as a frequency when the object to be detected does not contact the cylindrical member (detection pipe) (20). The vibration level detection device according to claim 4, wherein the reference frequency is selected as a frequency when the object to be detected comes into contact with the cylindrical member (detection pipe) (20). The vibration level detection device according to any one of claims 1 to 3, wherein the detection unit constitutes a filter whose output changes when the vibration frequency of the vibration piece (22) changes. The vibratory level detection device according to claim 1, wherein a weight (95) formed in the supporting portion of the cylindrical member (detection pipe) (20) is formed to be heavier than the vibration piece (22).

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