JP4073335B2 - Vibration type level sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vibration type level sensor, and more particularly to a vibration type level sensor that detects a change in the level of fine powder, liquid, and viscous material.
[0002]
[Prior art]
FIG. 17 is a schematic block diagram of a conventional vibration type level sensor described in Patent Document 1. In FIG.
[0003]
In FIG. 17, the detection pipe portion 10 has a base portion 11 as a fixed end and a distal end portion closed by a closing portion 12 to be a free end. An elongated rectangular diaphragm 2 is provided inside the detection pipe unit 10. One end of the diaphragm 2 is fixed to the closed portion 12 of the detection pipe portion 10, and the other end is provided with a magnet 3 to be a free end. Therefore, the detection pipe portion 10, the closing portion 12, and the diaphragm 2 constitute a folded cantilever where the detection pipe portion 10 is folded back at the closing portion 12 and the folded portion is the diaphragm 2.
[0004]
Further, the electromagnet 7 is attached so as to be in close contact with the inner wall of the detection pipe portion 10 so as to face the axial direction of the diaphragm 2. When the electromagnet 7 is driven by an alternating current, the diaphragm 11, the closing portion 12, and the detection pipe portion 10 serve as a fixed end due to the magnetic field generated by the electromagnet 7 and the attractive repulsive action of the magnetic field of the magnet 3. Generates vibration of folded cantilever beams.
[0005]
A strain detection element 13 is provided on the inner wall of the detection pipe portion 10 on the base 11 side. The strain detection element 13 detects the amplitude vibration state on the base 11 side of the detection pipe portion 10, converts it into an electric signal, and gives it to the amplifier circuit 14. The amplifier circuit 14 amplifies the input signal and inputs it again to the electromagnet 7.
[0006]
If the relationship between the polarity of the current applied to the electromagnet 7 and the magnetic field generated in the electromagnet 7 is the relationship shown in FIG. 17B, the pole facing the magnet 3 of the electromagnet 7 becomes the N pole and is attached to the diaphragm 2. An attractive force is generated between the magnet 3 and the south pole of the magnet 3, a repulsive force is generated between the magnet 3 and the north pole of the magnet 3, and the free end of the diaphragm 2 has an upward force in FIG. Will be displaced.
[0007]
Conversely, when the polarity of the current applied to the electromagnet 7 is reversed, as shown in FIG.
The polarity of the side of the electromagnet 7 facing the magnet 3 is reversed to the S pole, repels the S pole of the magnet 3 of the diaphragm 2 and attracts the N pole. In response, the vibration state changes. Therefore, vibration can be generated and continued by switching the polarity of the current applied to the electromagnet 7 in accordance with the natural vibration frequency of the folded cantilever vibration system.
[0008]
As another example of a conventional vibration type level sensor, a sensor using a tuning fork type vibrator is widely known (see, for example, Patent Document 2).
[0009]
This vibration type level sensor includes a mechanical vibration system composed of a tuning fork having two vibration rods that are attached to a membrane stretched at an edge at a distance from each other and projecting into a container, and a vertical movement of the vibration rods. Excitation device for exciting vibration in the opposite direction across the axial direction, excitation transducer having a piezoelectric element that can be excited by an alternating voltage, and piezoelectric element for converting mechanical vibration system vibration into an electrical output signal And an evaluation circuit for starting the display process depending on the output signal of the reception converter.
[0010]
The vibration type level sensor according to the present configuration ensures high detection sensitivity and reliability because the natural resonance frequency of the mechanical vibration system changes greatly even with slight changes in the load or density of the object to be detected. be able to.
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-351944 (FIG. 1)
[0012]
[Patent Document 2]
Japanese Examined Patent Publication No. 2-60245 (page 4-5, FIG. 1)
[0013]
[Problems to be solved by the invention]
In the conventional vibration type level sensor shown in FIG. 17, it is not necessary to support the vibrating body with a flexible and thin film like silicon, for example, by using the folded cantilever vibration mode. It can be firmly fixed to the side wall, sufficient strength can be secured, and corrosion resistance can be improved.
[0014]
In addition, since the diaphragm 2 is sealed in the detection pipe unit 10, the object to be detected does not come into direct contact with the diaphragm 2, and thus the diaphragm 2 is not affected by aging such as wear or damage, and performs a stable operation. be able to.
[0015]
Furthermore, the detection pipe unit 10 can be configured as one simple configuration by arranging the diaphragm 2, the electromagnet 7 and the magnet 3 in a line inside, and the object to be detected becomes the detection unit. It does not accumulate, has excellent adhesion resistance, and can suppress malfunction.
[0016]
On the other hand, in a conventional tuning fork type vibration type level sensor, high detection sensitivity can be expected in that the object to be detected is in direct contact with the detection unit, while powder is deposited between two vibration bars of the tuning fork. As a result, there is a drawback that malfunction occurs. In addition, the vibration characteristics of the tuning fork are lost due to wear due to contact between the detection unit and the object to be detected, deformation due to impact, and the like.
[0017]
Therefore, the conventional vibration type level sensor shown in FIG. 17 is widely used as being particularly suitable for powder detection.
[0018]
However, if this vibration type level sensor is applied to the detection of a liquid such as water or a viscous body, even if the liquid contacts the detection pipe unit 10, the internal vibration plate 2 does not directly contact the object to be detected. For this reason, the vibration is not attenuated and stopped, and sufficient detection sensitivity cannot be obtained.
[0019]
SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a vibration type level sensor that has high detection sensitivity and is not affected by wear due to contact with an object to be detected or deformation due to impact.
[0020]
[Means for Solving the Problems]
According to an aspect of the present invention, a vibration type level sensor that detects the presence or absence of an object to be detected includes a main body portion of the vibration type level sensor and a detection portion fixed to the main body portion. The detection portion includes a folded member having one end fixed to the main body portion and the other end being a free end and having a shape folded at the folded portion, and a magnet attached to the other end of the folded member. A support plate is configured between the one end and the folded portion, and a diaphragm is configured between the other end of the folded member and the folded portion. The main body portion is based on an electromagnet arranged so as to face the magnet at a predetermined interval, a detection circuit for detecting a current phase at the vibration frequency of the coil of the electromagnet, and a change in the detected phase. And a determination unit for determining the presence or absence of an object to be detected.
[0021]
Preferably, the detection circuit includes an alternating current applying means for applying an alternating current having a sweep frequency within a predetermined range centered on the resonance frequency of the detection portion to the coil of the electromagnet at every predetermined measurement period, and an alternating current applying means. Phase detecting means for detecting a change in phase that occurs depending on whether or not the object to be detected contacts the diaphragm when an alternating current is applied. The determination unit includes a determination unit that determines the presence or absence of an object to be detected based on a change in phase detected by the phase detection unit.
[0022]
More preferably, the detection circuit includes a temperature measurement unit that measures the temperature based on the detection output of the phase detection unit in the first half period in the predetermined measurement cycle, and a temperature measurement unit that is in the second half period in the predetermined measurement cycle. Frequency change means for changing the frequency to be swept based on the measurement result is further provided.
[0023]
Preferably, the phase detection means detects a phase fluctuation due to a beat frequency component generated in the coil of the electromagnet by mixing the vibration frequency of the detection portion and the sweep frequency of the alternating current.
[0024]
More preferably, the phase detection means includes a filter for extracting a beat frequency component.
[0025]
Preferably, the temperature measuring unit measures the temperature based on a change in the phase angle of the current caused by a change in the resistance value due to the temperature of the coil.
[0026]
According to another aspect of the present invention, the vibration level sensor detects the presence or absence of an object to be detected, and includes a main body portion of the vibration level sensor and a detection portion fixed to the main body portion. The detection portion includes a folded member having one end fixed to the main body portion and the other end being a free end and having a shape folded at the folded portion, and a magnet attached to the other end of the folded member. A support plate is configured between the one end and the folded portion, and a diaphragm is configured between the other end of the folded member and the folded portion. The main body part is an electromagnet arranged so as to face the magnet at a certain interval, a voltage is applied to the coil of the electromagnet for a predetermined period, a magnetic field is generated in the electromagnet, and the vibration plate is And a voltage applying means for displacing the magnetic field of the electromagnet after a predetermined period of time and shifting the detection portion to the reverberation vibration state, and the object to be detected on the diaphragm in the reverberation vibration state Attenuation period detection means for detecting a change in the attenuation period until the vibration is attenuated, which is generated depending on whether or not the contact is made, and a change in the attenuation period detected by the attenuation period detection means. Determination means for determining presence or absence.
[0027]
Preferably, the main body portion electrically couples / separates the coil and the voltage applying means in accordance with a pulse voltage indicating the first voltage state in a predetermined period and indicating the second voltage state after the predetermined period. And a switch circuit.
[0028]
Preferably, in the reverberation vibration state, the decay period detection means includes: a voltage comparison means that compares an electromotive voltage proportional to the vibration frequency of the detection portion generated in the electromagnet with a comparison voltage; and the voltage comparison means, wherein the electromotive voltage is a comparison voltage. Counting means for counting the number of times described above, and a comparison unit that compares the count value of the counting means with a set value and outputs a comparison result signal. The discriminating unit discriminates the presence / absence of the detection object in the comparison unit based on a change in the comparison result signal generated depending on whether or not the detection object contacts the diaphragm.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.
[0030]
[Embodiment 1]
1 is a perspective view (FIG. 1 (a)), a side view (FIG. 1 (b)), and a top view (FIG. 1 (c)) showing a structure of a vibration type level sensor according to Embodiment 1 of the present invention. ).
[0031]
With reference to FIGS. 1A to 1C, the vibration type level sensor includes a detection portion including a support plate 1 and a vibration plate 2, a screw portion 4, and a plug 5.
[0032]
One end of the support plate 1 is fixed by the screw portion 4 and the other end is folded back to be a free end, and the detection unit forms a folded cantilever. The folded portion of the support plate 1 constitutes the diaphragm 2, and a magnet 3 is bonded to the free end thereof.
[0033]
The threaded portion 4 is further coupled to one surface of the plug 5. From the other surface of the plug 5, two lead wires 6 for driving a current to an electromagnet inside the screw portion 4 (not shown) are drawn out.
[0034]
The vibration type level sensor of the present embodiment is different from the conventional vibration type level sensor shown in FIG. 17 in that it does not have a detection pipe portion. As a result, the diaphragm 2 as a detection unit is exposed and the object to be detected comes into direct contact.
[0035]
Further, as is clear from FIG. 1C, both the support plate 1 and the diaphragm 2 are formed of thin plates. In this configuration, the vibration amplitude is larger than that of a conventional vibration type level sensor configured by a pipe, and high detection sensitivity can be expected.
[0036]
2 is a cross-sectional view of the vibration type level sensor of FIG.
Referring to FIG. 2, an electromagnet 7 is disposed inside the screw portion 4 so as to face the magnet 3 with a slight gap in the axial direction of the diaphragm 2. The electromagnet 7 generates a magnetic field corresponding to the drive current supplied from the lead wire 6. The vibration plate 2 and the support plate 1 generate a vibration mode of the folded cantilever beam with one end of the support plate 1 as a fixed end by an attractive repulsive action of the magnetic field of the magnet 3 and the magnetic field generated by the electromagnet 7.
[0037]
FIG. 3 is a diagram showing a vibration mode in the vibration type level sensor of FIG.
Referring to FIG. 3, FIGS. 3 (a) and 3 (b) are diagrams showing the attractive repulsive action between the magnetic field generated in the electromagnet 7 and the magnetic field of the magnet 3, and FIG. It is a figure which shows the vibration mode of the support plate 1 and diaphragm 2 which generate | occur | produce by the effect | action of.
[0038]
First, it is assumed that the relationship between the polarity of the current applied to the electromagnet 7 and the magnetic field generated in the electromagnet 7 is the relationship shown in FIG. At this time, the pole of the electromagnet 7 facing the magnet 3 is an N pole, an attractive force is generated between the magnet 3 and the S pole, and a repulsive force is generated between the magnet 3 and the N pole. Therefore, the free end of the diaphragm 2 is displaced by receiving a force upward as shown in FIG. The vibrations of the diaphragm 2 and the support plate 1 at this time are in the state shown in FIGS. 3 (c) (iv) to (ii).
[0039]
Next, when the polarity of the current applied to the electromagnet 7 is reversed, the pole facing the magnet 3 of the electromagnet 7 becomes the S pole as shown in FIG. For this reason, a repulsive force is generated between the magnet 3 and the south pole, and an attractive force is generated between the magnet 3 and the north pole. Therefore, the free end of the diaphragm 2 is displaced by receiving a force downward as shown in FIG. Therefore, the vibrations of the support plate 1 and the diaphragm 2 change from the state shown in FIGS. 3C and ii to the state shown in FIG. 3C via FIGS. 3C and iv.
[0040]
Therefore, vibration can be generated and continued by switching the polarity of the current applied to the electromagnet 7 in accordance with the natural vibration frequency of the folded cantilever vibration system.
[0041]
FIG. 4 is a diagram for explaining the principle of the vibration type level sensor of FIG.
As shown in FIG. 4A, when the rod-shaped electromagnet 7 and the magnet 3 are opposed to each other with a slight gap and the direction of the current flowing through the electromagnet 7 is switched, the polarity of the electromagnet 7 is switched and opposed. It is a well-known fact that repulsion occurs when the polarity of the magnet 3 is the same as that of the magnet 3, and suction occurs when the polarity is different.
[0042]
When this principle is applied to the diaphragm 2 shown in FIG. 4B, the polarization of the magnet 3 at the tip of the diaphragm 2 is in the thickness direction (in FIG. 4B, the upper side is the N pole and the lower side is the S pole). By doing so, it is possible to apply a force to the magnet 3 in the vertical direction by an electric current.
[0043]
Since the magnet 3 is at the free end of the diaphragm 2, if the switching period of the direction of the current flowing through the electromagnet 7 and the period at which the diaphragm 2 resonates are matched, the diaphragm 2 will vibrate to the maximum extent. become.
[0044]
In the conventional vibration type level sensor, as shown in FIG. 17, the electromagnet 7 as the drive unit and the detection element 5 as the reception unit are configured with different parts. The driving unit and the receiving unit are configured by a common electromagnet 7.
[0045]
FIG. 5 is a diagram showing the principle of the vibration type level sensor of FIG.
With reference to FIG. 5, for example, when a power source such as a battery 32 is connected to the motor 31, a current flows and the motor 31 rotates. At this time, it is assumed that the current value a is obtained from the ammeter 33 for the current flowing through the motor 31.
[0046]
Next, when the rotation shaft of the motor 31 is grasped by hand and the rotation is stopped, the current flowing through the motor 31 increases to the current value b. This is because, when the motor 31 is rotating, a reverse current (electric power) is generated due to the power generation action caused by the rotation of the motor 31, and the current is suppressed. When the rotation of the motor 31 is stopped, this reverse direction occurs. This is because the current (power) is lost and the suppression effect is lost.
[0047]
The vibration type level sensor according to the present embodiment is not the motor 31 as shown in FIG. 5, but as shown in FIG. 4B, when the current is passed through the electromagnet 7 and the magnet 3 is vibrated, the vibration level sensor vibrates. Due to the power generation action of the magnet 3, a reverse current is generated in the electromagnet 7, and the current flowing for driving is suppressed in the same manner as the description of the motor 31 in FIG. 5.
[0048]
Here, when the detection unit is covered with an object to be detected and does not vibrate, the power generation action of the magnet 3 fixed to the diaphragm 2 is lost, and the drive current flows without being suppressed.
[0049]
Therefore, by detecting the drive current, the magnitude of vibration can be determined, and the presence / absence of an object to be detected can be detected.
[0050]
By the way, in the vibration type level sensor, the vibration is generated by making the frequency of the drive current coincide with the resonance frequency of the diaphragm 2, but the frequency width of the vibration of the diaphragm 2 is the center of 80 Hz (representative value). Since the frequency is in a very narrow range of ± 0.1 Hz, it is difficult to always keep the frequency of the drive current in this range.
[0051]
Therefore, in the present embodiment, as shown in FIG. 6, the frequency is repeatedly changed (swept) within a certain range above and below the center frequency. Thus, by sweeping the frequency, the possibility that the resonance state cannot be detected can be eliminated.
[0052]
Further, since the vibration frequency of the diaphragm 2 changes with respect to the temperature at a rate of about −0.1 Hz / ° C., the sweep frequency is also subjected to temperature control (correction) at this rate. That is, the sweep frequency is corrected so as to decrease as the temperature increases.
[0053]
The frequency sweep range is, for example, 30 Hz from the lower 20 Hz to the upper 10 Hz of the reference value. Here, the reference value is not the resonance frequency of the diaphragm 2 but the frequency with respect to the peak of the interference voltage, which will be described later.
[0054]
The frequency sweep rate is 16.67 Hz / second, and 30 Hz is swept in 1.8 seconds. The slower the sweep speed, the more closely the change in vibration can be observed, but this value is set in consideration of the measurement time.
[0055]
FIG. 7 is a waveform diagram for explaining the interference voltage (beat).
It is known that when two frequencies are mixed, new frequency components of the sum and difference of the frequencies are generated. For example, when the frequencies of 80 Hz and 85 Hz are mixed, frequency components of 165 Hz and 5 Hz are generated.
[0056]
In the present embodiment, as described with reference to FIG. 6, the frequency range of 30 Hz above and below the resonance frequency of the diaphragm is swept at a speed of 16.67 Hz / second.
[0057]
As shown in (1) of FIG. 7, immediately after the start of the sweep, the sweep frequency and the resonance frequency are separated, so that no vibration occurs and no back electromotive current is generated.
[0058]
Next, as shown in (2), when the sweep frequency approaches the resonance frequency, the vibration of the diaphragm starts to increase. When the frequencies coincide with each other, the maximum is obtained and the back electromotive current is also maximized.
[0059]
Subsequently, as shown in (3), after that, the sweep frequency continues to change at a constant speed. The vibration amplitude of the diaphragm is gradually attenuated while maintaining the vibration frequency at the maximum resonance frequency in (2).
[0060]
Here, in the vibration attenuation period (3), it is important that the vibration frequency does not change. By mixing the sweep frequency of the drive current whose frequency changes and the vibration frequency of the counter electromotive current whose frequency does not change, Beat frequency is generated. Of the generated beat frequency, only the frequency component (variable) of the difference is extracted by a filter, and the presence / absence of an object to be detected is determined based on the size.
[0061]
If the detection unit is covered with the object to be detected and the diaphragm does not vibrate, no back electromotive current is generated and no beat frequency is generated. An embodiment of a vibration type level sensor using this principle will be described in detail.
[0062]
FIG. 8 is a block diagram of the vibration type level sensor of FIG.
In FIG. 8, a microcomputer 40 includes a pulse generation circuit 41 that generates a pulse voltage having a sweep frequency. The generated pulse voltage is supplied from the drive circuit 51 to the electromagnet 7 via the current detection circuit 52.
[0063]
The current detection circuit 52 detects the pulse current flowing through the electromagnet 7 and supplies it to the phase comparison circuit 53.
[0064]
The phase comparison circuit 53 detects the phase difference between the pulse current from the current detection circuit 52 and the pulse voltage supplied from the pulse generation circuit 41.
[0065]
When the object to be detected is not in contact with the diaphragm 2, the diaphragm 2 vibrates, and the beat component described above is generated in the drive current. Therefore, fluctuation occurs in the output of the phase comparison circuit 53.
[0066]
On the other hand, when the object to be detected is in contact with the diaphragm 2, the diaphragm 2 does not vibrate, and thus the phase fluctuation does not occur.
[0067]
The output of the phase comparison circuit 53 is given to the smoothing circuit 54 and taken in as a capture signal of the microcomputer 40.
[0068]
Since the output of the phase comparison circuit 53 is a kind of PWM (pulse width modulation) signal, the smoothing circuit 54 converts the analog voltage into a manageable analog voltage. The analog voltage converted by the smoothing circuit 54 is supplied to a BPF (band pass filter) 55 and to an A / D converter 42 in the microcomputer 40 to be converted into a digital signal. This digital signal is used as an input for temperature measurement.
[0069]
The BPF 55 detects a fluctuation (beat) only in the vicinity of 5 Hz. The detection signal is given to the A / D converter 43 built in the microcomputer 40 via the amplifier circuit 56. The digital signal converted by the A / D converter 43 is read into the microcomputer 40 as a detection signal.
[0070]
A relay circuit 65 and an operation indicator lamp 66 are connected to the microcomputer 40. The microcomputer 40 computes the read detection signal to obtain its peak value, and compares the peak value with a predetermined set value. Furthermore, the microcomputer 40 outputs a signal indicating the presence / absence of an object to be detected to the relay circuit 65 and the operation indicator lamp 66 based on the comparison result.
[0071]
Further, since the microcomputer 40 shows a temperature value that is normally not possible when the electromagnet 7 is disconnected, this can be regarded as an error and an alarm can be issued by means such as the buzzer 57.
[0072]
In this embodiment, the fluctuation is detected by the phase comparison circuit 53. However, the present invention is not limited to this, and other means for detecting the phase difference may be used.
[0073]
FIG. 9 is a diagram showing a measurement sequence of the vibration type level sensor of FIG. 8, and FIG. 10 is a diagram showing details of a detection period of an object to be detected in the measurement sequence of FIG.
[0074]
As shown in FIG. 9A, the microcomputer 40 performs level measurement, for example, with a fixed period of about 4 seconds. Of one measurement cycle of about 4 seconds, for example, the front half of about 2.2 seconds is set as the temperature measurement cycle, and the back half of about 1.8 seconds is set as the measurement cycle. In the first half of the temperature measurement period, the microcomputer 40 measures the temperature value based on the digital output of the A / D converter 42. The microcomputer 40 controls the sweep frequency during the detection period based on the measured temperature value.
[0075]
During the temperature measurement period, as shown in FIG. 9B, the sweep frequency is fixed at 500 Hz. In the detection period of FIG. 10A, 0.54 seconds after the start of detection is affected by the disturbance of the drive current due to switching from 500 Hz to the sweep frequency as seen in FIG. During the period, the output of the A / D converter 43 is turned on to read the voltage.
[0076]
When there is no liquid, a fluctuation component due to a beat voltage or the like is generated as shown in FIG. On the other hand, when it is covered with liquid and does not vibrate, no voltage due to fluctuation is generated as shown by the thick line in FIG. This amplitude value is the vibration value.
[0077]
FIG. 11 is a diagram showing details of temperature measurement of the vibration type level sensor shown in FIG.
As shown in FIG. 11B, the electromagnet 7 includes a coil, and it can be considered that an inductance XL and a resistance R are equivalently connected in series.
[0078]
When an alternating voltage (pulse) voltage is applied to this circuit, a current delayed by a phase determined by the inductance XL and the resistance R flows. When the coil temperature changes, the resistance value changes, but the inductance XL is not subject to fluctuation due to temperature. Therefore, as shown in FIG. 11A, the phase angle of the flowing current changes due to the resistance value change due to the temperature change.
[0079]
Here, the reason why the drive frequency is kept constant at 500 Hz is to avoid the influence of mechanical vibration and to eliminate errors due to frequency fluctuations.
[0080]
The phase of the current flowing through the electromagnet 7 is compared with a reference phase supplied to the drive circuit 51 in the phase comparison circuit 53 of FIG. 8, and becomes a DC voltage corresponding to the phase difference in the smoothing circuit 54. 42.
[0081]
Therefore, the resolution of the temperature is determined by the resolution of the A / D converter 42. In the circuit shown in FIG. 8, the temperature data changes by one count for a change of about 3.3 ° C.
[0082]
In addition, since the direct current | flow change part is removed by BPF55 with respect to vibration data, the voltage change by a temperature change has no influence.
[0083]
Here, the vibration frequency of the diaphragm 2 varies to some extent in manufacturing, and the vibration frequency varies depending on the shape of the diaphragm 2. It needs to be stored in the computer 40. This operation is called tuning.
[0084]
A reference (sweep) frequency range at the time of measurement is calculated from the temperature data and frequency data stored at the time of tuning and the temperature data at the time of measurement based on the following equation. Thereby, the best sweep frequency can be determined and measurement can be performed.
[0085]
Fs = (Ts−Tt) · k + Ft
Tt: Temperature data during tuning, Ts: Temperature data during measurement
Ft: Frequency data during tuning, Fs: Reference frequency during measurement
k: Proportional coefficient
FIG. 12 is a diagram illustrating a state in which the vibration type level sensor of FIG. 1 detects water.
[0086]
FIG. 12A shows frequency-phase characteristics, and FIG. 12B shows frequency-gain characteristics.
[0087]
Referring to FIGS. 12A and 12B, when water that is an object to be detected is not in contact with diaphragm 2 (in the air), and when water is in contact with diaphragm 2 Then, obviously, the latter has a smaller change in phase and gain. Therefore, no error occurs in the determination of the presence or absence of the object to be detected.
[0088]
As described above, according to the first embodiment of the present invention, the detection sensitivity of the detection unit of the vibration type level sensor is improved by exposing the diaphragm and directly contacting the detected object. It is possible to detect the level of the liquid and the viscous body with high accuracy.
[0089]
Note that the detection portion is not a tuning fork but a folded cantilever structure using a support plate and a diaphragm, so that the mechanical strength can be increased and a stable operation is guaranteed.
[0090]
[Example of change]
13 is a perspective view (FIG. 13 (a)), a side view (FIG. 13 (b)), and a top view (FIG. 13 (c)) showing a vibration type level sensor according to a modification of the first embodiment of the present invention. )).
[0091]
Referring to FIGS. 13A to 13C, the vibration type level sensor includes a detection unit including a support plate 1, a vibration plate 2, and a magnet 3 bonded to a free end of the vibration plate 2, and a detection. It comprises a screw part 4 that supports the part and a plug 5.
[0092]
The basic configuration of the vibration type level sensor of this modification is the same as that of the vibration type level sensor of the first embodiment shown in FIG. 1, but the structure of the folded cantilever of the detection unit is different. Therefore, description is not repeated about a common part.
[0093]
In the first embodiment shown in FIG. 1, the detection unit has a structure in which the diaphragm 2 is supported by the support plates 1 positioned on both sides. However, in the modification of FIG. The structure is supported by two support plates 1.
[0094]
14 is a cross-sectional view of the vibration type level sensor of FIG.
Referring to FIG. 14, the electromagnet 7 is arranged inside the screw portion 4 with a slight gap facing the magnet 3 in the axial direction of the diaphragm 2. A lead wire 6 for driving current is connected to the electromagnet 7.
[0095]
As described above, the vibration type level sensor according to the present modification example differs from the vibration type level sensor of the first embodiment only in the shape of the detection unit. Also in this case, the vibration mode of the folded cantilever and the operational effect of the vibration type level sensor are the same as those in the first embodiment.
[0096]
Thus, if the detection unit is in direct contact with the object to be detected and the vibration mode of the folded cantilever structure, the shape is not necessarily limited to the shape of FIG. Various shapes can be applied including examples.
[0097]
[Embodiment 2]
FIG. 15 is a block diagram of a vibration type level sensor according to the second embodiment of the present invention.
[0098]
Referring to FIG. 15, microcomputer 40 includes a basic pulse generation circuit 46 that generates a one-shot pulse voltage. The generated pulse voltage is supplied to the contact control unit 60. The contact controller 60 inputs a control signal corresponding to the pulse voltage to the switch circuit 59.
[0099]
The switch circuit 59 is disposed between the electromagnet 7 and the power supply unit 61, and selectively couples the electromagnet 7 with the power supply unit 61 or the amplification circuit 62 in accordance with a control signal from the contact control unit 60. . When receiving a control signal based on the generated pulse voltage, the switch circuit 59 electrically couples the electromagnet 7 and the power supply unit 61. On the other hand, when the pulse voltage disappears, the switch circuit 59 switches the coupling with the power supply unit 61 so far to the coupling state with the amplifier circuit 62.
[0100]
The amplification circuit 62 receives an electromotive voltage proportional to the vibration frequency of the diaphragm 2 when electrically coupled to the electromagnet 7. This electromotive voltage is amplified by the amplifier circuit 62 and supplied to the voltage comparison circuit 63.
[0101]
The voltage comparison circuit 63 compares a constant comparison voltage set inside with the amplified electromotive voltage, and outputs a signal indicating the comparison result to the counting circuit 64. As the comparison result signal, for example, a pulse signal that is H (logic high) when the electromotive voltage is equal to or higher than the comparison voltage and L (logic low) when the voltage is equal to or lower than the comparison voltage is generated.
[0102]
The pulse signal is then input to the counting circuit 64. The counting circuit 64 counts the number of times the pulse signal becomes H level and outputs the count value to the comparison unit 45 in the microcomputer 40.
[0103]
When the count value from the counting circuit 64 and the set value stored in advance in the microcomputer 40 are input, the comparison unit 45 compares these two values and outputs a comparison result signal to the relay circuit 65 and Transfer to the operation indicator 66.
[0104]
Next, the detection operation of the vibration type level sensor of the present embodiment having the above circuit configuration will be described.
[0105]
First, when the pulse generated by the basic pulse generation circuit 46 is input to the switch circuit 59 as a control signal via the contact control unit 60, the electromagnet 7 and the power supply unit 61 are electrically coupled. As a result, a magnetic field whose polarity is determined by the direction of the drive current is generated in the electromagnet 7.
[0106]
Here, the magnet 3 bonded to the free end of the diaphragm 2 is opposed to the electromagnet 7, and the magnet 3 is moved in the vertical direction by the attraction and repulsion action between the magnetic field generated by the electromagnet 7 and the magnetic field of the magnet 3. It will be displaced in either direction. This displacement is kept fixed during the period when the pulse voltage is at the H level and the power supply unit 61 and the electromagnet 7 are coupled.
[0107]
Next, when the pulse disappears in the basic pulse generation circuit 46 and the pulse voltage falls to the L level, the switch circuit 59 performs the switching operation by the control signal from the contact control unit 60, and the electromagnet 7 and the amplification circuit 62. Are electrically coupled.
[0108]
In the electromagnet 7, the generation of the magnetic field is stopped when the drive current from the power supply unit 61 is interrupted. As a result, the magnet 3 is no longer attracted to and repelled from the electromagnet 7, and the diaphragm 2 tries to return to its original state from the fixed state. Thereafter, as shown in FIG. 15, the detection unit including the diaphragm 2 is in a reverberation vibration mode that vibrates while the amplitude is attenuated in the vertical direction of the electromagnet.
[0109]
On the other hand, in the electromagnet 7, an electromotive voltage proportional to the vibration frequency is generated when the magnet 3 bonded to the diaphragm 2 vibrates. This electromotive voltage is transmitted to the amplifier circuit 62.
[0110]
Furthermore, when the electromotive voltage amplified by the amplifier circuit 62 (corresponding to the potential at point A in FIG. 15) is input to the voltage comparison circuit 63, it is compared with the comparison voltage. As a comparison result, a pulse signal indicating the H level is output when the voltage level is equal to or higher than the comparison voltage (corresponding to the potential at point B in FIG. 15).
[0111]
FIG. 16 is a waveform diagram showing potentials at points A and B in FIG. FIG. 16A shows a potential waveform when the object to be detected is not in contact with the diaphragm 2, and FIG. 16B shows a potential waveform when the object to be detected is in contact with the diaphragm 2. FIG. is there.
[0112]
Referring to FIGS. 16 (a) and 16 (b), the waveform at point A shows a reverberation vibration mode in which the amplitude is attenuated, but the waveform until the amplitude converges to 0 level is seen. The period (hereinafter also referred to as the attenuation period) is clearly longer in FIG. 16A where the object to be detected is not in contact with the diaphragm 2. Therefore, also in the waveform at the point B indicating the comparison result signal with the comparison voltage, FIG. 16A shows a result that the number of generation of pulses is larger than that in FIG. 16B.
[0113]
The counting circuit 64 counts the number of occurrences of pulses from the waveform at the point B and outputs the count value to the comparison unit 45. From the waveforms of FIGS. Counted as times.
[0114]
The comparison unit 45 compares these count values with the set value 44. Here, for example, if the set value is three times, in the case of FIG. 16B, a comparison result signal indicating that the count value is equal to or less than the set value is output. The relay circuit 65 and the operation indicator lamp 66 display that the detected object has been detected using the comparison result signal as a control signal.
[0115]
On the other hand, in the case of FIG. 16A, when a comparison result signal indicating that the count value is equal to or greater than the set value is output, the operation indicator light 66 and the relay circuit 65 indicate that the detected object is not detected. Recognize and do not perform the above display operation.
[0116]
The above description of the detection operation has been made with one pulse generated by the basic pulse generation circuit 46, but the same applies to a plurality of pulses.
[0117]
As described above, according to the second embodiment of the present invention, the damping period is measured in the reverberation vibration mode of the diaphragm generated when the diaphragm is displaced by the magnetic field generated in the electromagnet and then the magnetic field is removed. By doing so, it is possible to detect the presence or absence of an object to be detected.
[0118]
The detection method of the present embodiment is a vibration type level sensor according to the present invention in which the vibration plate of the detection unit is made of a thin plate with respect to the conventional detection pipe portion shown in FIG. This is the first implementation possible.
[0119]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0120]
【The invention's effect】
As described above, according to an aspect of the present invention, the detection sensitivity of the detection unit of the vibration type level sensor can be improved by exposing the diaphragm and directly contacting the detected object. In addition, it is possible to accurately detect the level of the liquid and the viscous body.
[0121]
Furthermore, the detection unit having a folded cantilever structure including a support plate and a diaphragm can increase the mechanical strength that is a problem with a tuning fork, and ensures stable operation.
[Brief description of the drawings]
FIG. 1 is a perspective view (FIG. 1 (a)), a side view (FIG. 1 (b)), and a top view (FIG. 1 (c)) showing a structure of a vibration type level sensor according to a first embodiment of the present invention. ).
FIG. 2 is a cross-sectional view of the vibration type level sensor of FIG.
FIG. 3 is a diagram showing a vibration mode in the vibration type level sensor of FIG. 1;
4 is a view for explaining the principle of the vibration type level sensor of FIG. 1; FIG.
FIG. 5 is a diagram illustrating the principle of the vibration type level sensor of FIG. 1;
FIG. 6 is a graph showing the relationship between frequency sweep and temperature correction.
FIG. 7 is a waveform diagram for explaining an interference voltage (beat).
FIG. 8 is a block diagram of the vibration type level sensor of FIG. 1;
FIG. 9 is a diagram showing a measurement sequence of the vibration type level sensor of FIG.
10 is a diagram showing details of a detection period of an object to be detected in the measurement sequence of FIG.
FIG. 11 is a diagram showing details of temperature measurement of the vibration type level sensor shown in FIG. 8;
12 is a diagram showing a state in which the vibration type level sensor of FIG. 1 is detecting water.
13 is a perspective view (FIG. 13A), a side view (FIG. 13B), and a top view (FIG. 13C) showing a vibration type level sensor according to a modification of the first embodiment of the present invention. )).
14 is a cross-sectional view of the vibration type level sensor of FIG.
FIG. 15 is a block diagram of a vibration type level sensor according to a second embodiment of the present invention.
16 is a waveform diagram showing potentials at points A and B in FIG.
FIG. 17 is a schematic block diagram of a conventional vibration type level sensor described in Patent Document 1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support plate, 2 Diaphragm, 3 Magnet, 4 Screw part, 5 Plug, 6 Lead wire, 7 Electromagnet, 10 Detection pipe part, 11 Base part, 12 Closure part, 31 Motor, 32 Battery, 33 Ammeter, 40 Microcomputer , 41 Pulse generation circuit, 42, 43 A / D converter, 44 set value, 45 comparison unit, 46 basic pulse generation circuit, 51 drive circuit, 52 current detection circuit, 53 phase comparison circuit, 54 smoothing circuit, 55 BPF, 56 Amplification circuit, 57 buzzer, 59 switch circuit, 60 contact control unit, 61 power supply unit, 62 amplification circuit, 63 voltage comparison circuit, 64 measurement circuit, 65 relay circuit, 66 operation indicator lamp.

Claims (8)

A vibration type level sensor that detects the presence or absence of an object to be detected,
A main body portion of the vibration type level sensor;
A detection portion fixed to the main body portion,
The detection portion is
One end is fixed to the main body portion and the other end is a free end, and a folded member having a shape folded at the folded portion;
A magnet attached to the other end of the folded member,
Between the one end of the folded member and the folded portion constitutes a support plate, and between the other end of the folded member and the folded portion constitutes a diaphragm,
The body portion is
An electromagnet arranged to face the magnet at a predetermined interval;
A detection circuit for detecting a phase of a current at a vibration frequency of the coil of the electromagnet;
Based on a change of the detected phase, it saw including a determination unit for determining presence or absence of the object to be detected,
The detection circuit includes :
An alternating current applying means for applying an alternating current whose frequency is swept within a predetermined range including a resonance frequency of the detection portion to a coil of the electromagnet for each predetermined measurement period ;
Phase detection means for detecting a change in phase that occurs depending on whether the object to be detected contacts the diaphragm when an alternating current is applied by the alternating current application means ;
The determination unit
A vibration type level sensor including a determination unit that determines the presence or absence of the detection object based on a change in phase detected by the phase detection unit . The detection circuit includes:
Temperature measuring means for measuring the temperature based on the detection output of the phase detecting means in the first half of the predetermined measurement cycle;
In the period of the second half in the predetermined measurement period, based on a measurement result of the temperature measurement means further comprises a frequency changing means for changing the frequency of the sweep, the vibration type level sensor according to claim 1. 3. The vibration type level sensor according to claim 2 , wherein the phase detection unit detects a phase fluctuation due to a beat frequency component generated in the coil of the electromagnet by mixing the vibration frequency of the detection portion and the sweep frequency of the alternating current. . 4. The vibration type level sensor according to claim 3 , wherein the phase detection means includes a filter for extracting the beat frequency component. The vibration type level sensor according to claim 2 , wherein the temperature measuring unit measures the temperature based on a change in a phase angle of a current caused by a change in a resistance value due to a temperature of the coil. A vibration type level sensor that detects the presence or absence of an object to be detected,
A main body portion of the vibration type level sensor;
A detection portion fixed to the main body portion,
The detection portion is
One end is fixed to the main body portion and the other end is a free end, and a folded member having a shape folded at the folded portion;
A magnet attached to the other end of the folded member,
Between the one end of the folded member and the folded portion constitutes a support plate, and between the other end of the folded member and the folded portion constitutes a diaphragm,
The body portion is
An electromagnet arranged to face the magnet at a predetermined interval;
A voltage is applied to the coil of the electromagnet for a predetermined period to generate a magnetic field in the electromagnet, the diaphragm is displaced by the magnetic field of the electromagnet and the attractive repulsive action of the magnet, and after the predetermined period has elapsed, the electromagnet Voltage application means for extinguishing the magnetic field and moving the detection portion to the reverberation vibration state,
In the reverberation vibration state, an attenuation period detection unit that detects a change in an attenuation period until the vibration is attenuated, which occurs depending on whether the object to be detected contacts the diaphragm,
A vibration type level sensor comprising: a discriminating unit that discriminates the presence or absence of the object to be detected based on a change in the decay period detected by the decay period detection unit. The main body portion electrically couples the coil and the voltage applying means in accordance with a pulse voltage indicating a first voltage state in the predetermined period and indicating a second voltage state after the predetermined period. The vibration type level sensor according to claim 6 , further comprising a switch circuit for separating. The decay period detecting means is
In the reverberation vibration state, voltage comparison means for comparing an electromotive voltage proportional to the vibration frequency of the detection portion generated in the electromagnet with a comparison voltage;
In the voltage comparison means, counting means for counting the number of times that the electromotive voltage is equal to or higher than the comparison voltage;
A comparison unit that compares the count value of the counting means with a set value and outputs a comparison result signal;
The discriminating unit discriminates the presence or absence of the detected object based on a change in the comparison result signal generated according to whether or not the detected object comes into contact with the diaphragm in the comparing unit. Item 7. The vibration type level sensor according to item 6 .

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