JPH04106425A - Level detector - Google Patents

Abstract

PURPOSE:To obtain a detector using an acoustic type switch with neither mechanical type contact piece nor pressing manipulation part by receiving an oscillation output from an oscillator to generate a fixed frequency of standing wave in such a manner that a node or an antinode thereof is given at one end opening. CONSTITUTION:The entire rear side of a speaker 1 provided behind a cylinder body 4 is covered with a cylinder body 5 so that no gas passes directly between the cylinder bodies 4 and 5. A cylinder body 8 having a sponge 7 at one end thereof has an outer diameter coinciding with an inner diameter of the cylinder body 4 and is forced into the cylinder body 4 so that the sponge 7 is placed at a regular position (at a position of a node of a stationary wave) inside the cylinder body 4. Then, the speaker 1 is driven alternatively at different amplitude values using two kinds of oscillation circuits 14 and 15. In a normal operation, a standing wave is generated within the cylinder body 4 with an oscillation circuit 13 which oscillates at a small amplitude value and as an object approaches a position of one end opening A, the standing wave in the cylinder body 4 is made antiresonant (or resonant) and a bridge circuit 15 detects a high impedance (or a low impedance) to output a switching signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a level detection device for detecting the level of powder or the like.

[Prior Art] Conventionally, this type of level detection device uses a contact type, for example, a powder body that vibrates vertically at a constant frequency.

It is installed extending from the wall of the tank that stores stored items such as granules and lumps into the inside of the tank, and the stored items come into contact with the rod body and the vibration of the rod body is regulated.

The vibration of the rod body was stopped by the stored object, and it was thereby detected that the stored object had been stored to a predetermined level.

[Problems to be Solved by the Invention] However, this type of level detection device has a structure in which the vibration of one rod is suppressed from the surroundings by a heavy stored object to restrict and stop it, If the object is very light, such as feathers or cotton, there is a problem in that it cannot be detected at all even if the object reaches a predetermined level.

[Means for Solving the Invention] The present invention has been made in view of the above-mentioned points, and includes an oscillator, a cylindrical member with one end open, and a cylindrical member provided at the other end of the cylindrical member, and a a sound generating means for generating a standing wave of a constant frequency such that it becomes a node or an antinode at the one end opening in response to the oscillation output of the cylindrical member; and a switching circuit that outputs a switching signal when the object approaches the part, and the oscillator oscillates with two types of amplitude values that are alternatively selected. be.

[Function] According to the configuration of the present invention, the sound generating means such as a dynamic speaker or a ceramic speaker provided at the other end of the cylindrical member having one end open is selectively driven at two different amplitude values. Normally, one of the smaller amplitude values generates a standing wave inside the cylindrical member, and when the opening at one end is blocked by a human finger or the like, or when an object approaches the opening at one end, Detects that the standing wave in the cylindrical member becomes anti-resonant ml (or resonance state), and the drive coil etc. becomes high impedance (or low impedance), and detects high impedance (or low impedance). When this occurs, a switching signal is output. Further, when dust or the like adheres to the surface of the sound generating means, the sound generating means is selectively driven at a larger amplitude value to sift it out.

[Example] First, the basic principle of the present invention will be explained based on FIGS. 1 to 3.

(1) is a dynamic, ceramic, etc. speaker (sound generating means) having a resonance point (resonant frequency) in its acoustic characteristics, and is oscillated by a sine wave at an audible frequency by a first oscillation circuit (13) to be described later. Note that the driving frequency is set to match the resonant frequency of the speaker (1). The electrical equivalent circuit of the speaker (1) is a series circuit of a capacitor (la), a coil (lb), a resistor (IC), and a variable acoustic impedance (1d), as shown in Figure 2. When the speaker (1) is driven at the resonant frequency, the combined impedance of the capacitor (1a) and the coil (1b) becomes O (Ω), and the electrical equivalent circuit of the speaker (1) is: It becomes like the series circuit R4 in FIGS. 4 and 5. (2) is a cylindrical body (cylindrical member) with openings at both ends;
2) One end opening (A) is open, and the other end opening is completely closed by the speaker (1). Further, the length of the cylinder (2) is set to an odd multiple of the l14 wavelength of the sine wave drive signal of the speaker (1),
) is set so that a node of a standing wave is formed at one end opening (A).

With the above configuration, when the opening (A) at one end of the cylinder (2) is open, the sound waves of the audible frequency emitted from the speaker (1) are kept constant within the cylinder (2). There is a current wave (solid line waveform in Figure 1), and a resonance state is reached.

However, as shown in FIG. 3, if the opening (A) at one end of the cylinder (2) is completely blocked by an object (3) such as a finger.

The sound wave (solid line waveform in Figure 3) emitted from the speaker (1) hits the object (3) at its node and switches to an anti-resonance state (the phase is 90° with respect to the solid line waveform in Figure 3).
(switched to a shifted dotted line waveform). That is, one end opening (
The point A) becomes the antinode and changes the variable acoustic impedance (1d) of the speaker (1) to the highest impedance.

Note that since the speaker (1) is driven at the same driving frequency as the speaker's own resonance frequency (the resonance frequency of the series resonance circuit constituted by the capacitor (1a) and the coil (1b)), the speaker (1) The electrical equivalent circuit is a series circuit of a resistor (lc) and a variable acoustic impedance (ld), as shown by R4 in FIG.

Therefore, the composite impedance (sum of resistance (xcj and variable acoustic impedance (1d)) when one end opening (A) of the cylindrical body (2) is open, and the composite impedance when it is closed. (the sum of resistance (1c) and variable acoustic impedance (ld)), it is possible to detect whether or not the object (3) completely blocks the one end opening (A).

In the above explanation, the illustrated standing wave is considered as an air propagation velocity waveform, and a standing wave that becomes a node is set at one end opening (A), but a standing wave that becomes an antinode may also be set. In this case, an anti-resonant state occurs when the opening (A) at one end is open, and when it is closed by the object (3), it switches to a resonant state.

Furthermore, in recent years, it has been pursued as an ideal that the acoustic characteristics of the speaker (1) with respect to frequency be flat, that is, it should not have a resonance point, but in the present invention, since the resonance point is actively utilized, In some cases, the speaker (
It goes without saying that a desired resonance point may be newly generated by forming a weight of resin or the like on the cone paper (or its equivalent) such as 1).

Next, an example of application of the above principle to a level switch for powder, liquid, etc. will be explained with reference to FIGS. 5 to 7.

First, in FIG. 5, (4) is the cylindrical body (
The first cylindrical body corresponds to 2), and the rear thereof, that is, the entire rear side of the speaker (1) is covered by a second cylindrical body (5). Further, the spaces formed in each of the first and second cylindrical bodies (4) and (5) are blocked by the speaker (1) so that gas does not directly flow therein, and Both cylinders (4) are blocked,
The second cylindrical body (5) is provided with a pore (6) in order to prevent a pressure difference from occurring in the space inside the second cylinder (5). (7) is a spongy body such as a sponge that allows fine dust etc. to pass through naturally.
Nodal portion of standing waves in the first cylindrical body (4) caused by sound waves emitted from the speaker (]) (portion where air molecules vibrate (or move) least for propagation of sound waves) To,
It is provided to block the propagation path of sound waves from the speaker ( ).

(8) is a third cylindrical body having an outer diameter that matches the inner diameter of the first cylindrical body (4) and is open at both ends, and has an opening at one end (B).
has a ring-shaped flange (9) that protrudes inward.

The corpora cavernosa (7) is adhered and fixed to the flange (9). The other end opening (A) is provided with the first cylindrical body (4).
) is formed with an engaging portion (lO) having an opening-like cross section that fits around the periphery of the other end opening (A). (11) is the second cylindrical body (
5) is attached to the tank, (12) is the tank (11)
Objects such as liquids and powders that are stored in

The third cylindrical body (8) configured as described above is pushed in until its engaging portion (10) is fitted into the periphery of the other end opening (A) of the first cylindrical body (4). As a result, the cavernous body (7) is disposed at the normal position M (the position W of the standing wave node) in the first cylinder (4), and the first cylinder (
4) Dust entering the first cylindrical body from the other end opening (A) can be prevented from adhering to the speaker (1), and the passage of sound is not obstructed, so detection accuracy can be maintained for a long period of time. The effect is that it can be guaranteed for a long time. Also, if the corpus cavernosum (7) becomes dirty.

Maintenance is easy as it is only necessary to pull out the third cylindrical body (8) and replace it.

Next, a method of detecting a change in the composite impedance due to a change in the variable acoustic impedance of the speaker (1) in FIGS. 3 and 4 and a switching operation thereof will be described.

That is, in FIG. 7, (13) is the speaker (1)
The first oscillation circuit (dynamic circuit) whose oscillation frequency is set to the same audible frequency as the resonance point frequency (14) always outputs a signal with a larger amplitude than the first oscillation circuit (13). The second oscillator circuit (15) is a composite impedance R4 of resistors R1, R2, R3 and the speaker (1) (normally when in a resonant state, a capacitor shown in FIG. 2)
The combined impedance of 1a) and coil (lb) is 0(
Ω), and as a result, the composite impedance is the sum of the resistance (1c) and the variable acoustic impedance (1d)), and a sinusoidal oscillation output is supplied from the first oscillation circuit (13). In the bridge circuit, when one end opening (A) of the first cylindrical body (4) is open and not blocked by the object (12), 1 old・R3=R2・R4
is established, and the voltage value at the connection point between the resistor R1 and the composite impedance R4 and the voltage value at the connection point between the resistors R2 and R3 become the same and are output. (16) is a switching circuit,
A movable section (16a) and two fixed contacts (isb), (i
6c), the movable section (16a) is connected to one of the fixed contacts (16b) during measurement, and when not measuring, that is, when dust etc. adheres to the cone paper of the speaker (1) or an equivalent object. , the movable contact (16a) is connected to the other fixed contact (16c).
). (17a) and (17b) are the first
and a second half-wave rectifier circuit, the voltage values from the corresponding bridge circuits (15) are supplied to the first and second half-wave rectifier circuits, and the supplied voltage waveform is half-wave rectified and output. I will do it. (18a) and (18b) are first and second integrating circuits that integrate the rectified flows supplied from the corresponding first and second half-wave rectifier circuits (17a) and (17b) with a predetermined time constant; i9) is the first and second integrating circuit (18a)
, (18b), and outputs a high level signal when the output of the second integrating circuit (18b) is large; (20) is the comparing circuit (19); When the output of the first
This lamp indicates that the end opening (A) of the cylindrical body (4) is completely or almost completely blocked by an object (12) such as liquid or powder.

When the speaker (1) configured as described above is driven by the first oscillation circuit (13) at the same frequency as its resonance point, for example, as shown in FIG. When the opening (A) at one end of the cylindrical body (4) of No. 1 is opened and in a resonant state, the bridge circuit (15) is balanced, and from each of the first and second integrating circuits (18a) and (18b) The integral outputs of will be the same. Therefore, the output of the comparator circuit (19) becomes low level, and the lamp (20) remains unlit.

Next, one end opening (
When A) is completely or almost completely occluded by an object (12) such as a liquid or powder, the standing wave switches to an anti-resonant state (sine wave indicated by a dotted line in Figure 3). The variable acoustic impedance R4 of the speaker (1) is changed to a larger one, and the bridge circuit (13) is changed to the old R3≠R
2.H4 and is brought into a non-equilibrium state. As a result, the first
and the integrated outputs from the second integrating circuits (18a) and (18b) are different in magnitude from each other, and the lamp (20) is activated by a high level output signal from the comparator circuit (19), and the one end opening (A) is now blocked.

On the other hand, when operating this device, the movable section (16a) of the switching circuit (16) is periodically connected to the fixed contact (16C).
) and make contact with it, a large amplitude signal will be supplied to the speaker (1), which will cause the paper cone (or its equivalent) of the speaker (1) to vibrate greatly, causing Dust in the powder, substances contained in the liquid, etc. will be filtered out. Note that during this work, a lamp (20) lights up to notify other people.

In the above embodiment, only when the opening (A) at one end of the first cylindrical body (4) is closed, the resonance state (or anti-resonance state) of the standing wave becomes anti-resonance: Ii (resonance). Although it has been explained that the blockage does not have to be completely blocked, it goes without saying that it is sufficient to distinguish which state is in the circuit.

As described above, the present invention includes an oscillator, a cylindrical member provided with an opening at one end facing the surface of the object to be measured, and a cylindrical member provided at the other end of the cylindrical member to generate a signal from the oscillator. a sound generating means that receives an oscillation output and generates a standing wave of a constant frequency such that it becomes a node or an antinode at the one end opening; and when the one end opening of the cylindrical member is completely blocked by the object; or a switching circuit that outputs a switching signal when the object approaches the opening at one end.

And since the oscillator is a level detection device characterized in that it oscillates with two types of amplitude values that are alternatively selected,
Based on an unprecedentedly simple principle, an extremely effective effect can be obtained in that an acoustic switch device without a mechanical contact piece or a push-button operation part can be easily obtained. Further, even if dust or the like adheres to the surface, it can be easily removed.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle to explain the present invention, Fig. 2 is an electrical equivalent circuit of the speaker (1), Fig. 3 is an explanatory diagram of the principle operation to explain Fig. 1, and Fig. 4 is Speaker (1)
5 is an explanatory diagram of the device according to the present invention installed in a tank, and FIG. 6 is an illustration of the corpora cavernosa in FIG. 5 as a cylinder. FIG. 7, which is an explanatory diagram of the configuration for mounting inside the body (4), is an example of the circuit of the speaker (1) according to the present invention. 1...Speaker 2,4.5.8...
・・・・・・Cylinder 3.12・・・・・・・・・Object
6... Pore 7... Cavernous body 9... Flange 10...
... Fitting part 11 ... Tank 13
．． 14......Oscillation circuit 15...
...Bridge circuit 16...Switching circuit 17a, 17b...Half-wave rectifier circuit 18
a, 18b...Integrator circuit 19...
......Comparison circuit 20...Lamp Fig. 1 Fig. 3 Fig. 2 Fig. 4 Fig. 7

Claims (1)

[Claims] (1) An oscillator, a cylindrical member with an opening at one end, and a constant frequency provided at the other end of the cylindrical member to receive the oscillation output from the oscillator and generate a node or antinode at the one end opening. and a switching circuit that outputs a switching signal when one end opening of the cylindrical member is closed or when the object approaches the one end opening. , and the oscillator oscillates with two types of amplitude values that are alternatively selected.