JP2004151074A - Multi-point object detecting device for vibratory level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-point object detecting device for a vibratory level sensor, which can reduce the number of parts, thereby enabling the improvement of reliability. <P>SOLUTION: Each sensor unit having a different oscillation frequency is provided at a plurality of locations of a tank. Coils of an electromagnet of each sensor unit are connected in series or in parallel. Impedance variations at these oscillation frequencies are detected. Based on these variations, the presence of an object at each location is collectively detected in a single control circuit unit. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multipoint object detection device of a vibration type level sensor, and in particular, a sensor unit including a detection pipe, a diaphragm provided with a magnet in the detection pipe, and an electromagnet opposed to the diaphragm with a slight gap therebetween. The present invention relates to a multi-point object detecting device of a vibration type level sensor that generates vibration by the electromagnet and detects the presence or absence of an object.
[0002]
[Prior art]
FIG. 8 is a schematic block diagram of a conventional vibration type level sensor, which is described in JP-A-11-351944. In FIG. 8A, the detection pipe portion 1 has a fixed end at a base 11 and a free end closed at a tip end by a closing portion 12 to constitute a folded cantilever. An elongated rectangular vibrating reed 2 is provided inside the detection pipe portion 1. That is, one end of the vibrating reed 2 is fixed to the closing portion 12 of the detection pipe portion 1, and the other end is provided with the permanent magnet 3 and is free.
[0003]
Further, the electromagnet 4 is attached to the inner wall of the detection pipe 1 so as to be in close contact with the axial direction of the resonator element 2. When the electromagnet 4 is driven by the alternating current, the vibrating reed 2, the closing portion 12, and the detection pipe portion 1 are folded back with the base portion 11 as a fixed end due to the magnetic field generated by the electromagnet 4 and the repelling action of the magnetic field of the permanent magnet 3. Generates vibration of the cantilever.
[0004]
A strain detecting element 5 is provided on an inner wall of the detection pipe unit 1 on the base 11 side. The strain detecting element 5 detects a vibration amplitude state on the base 11 side of the detection pipe 1, converts the vibration amplitude state into an electric signal, and supplies the electric signal to the amplifier circuit 6. The amplifier circuit 6 amplifies the input signal and inputs the amplified signal to the electromagnet 4 again.
[0005]
Assuming that the relationship between the polarity of the current applied to the electromagnet 4 and the magnetic field generated in the electromagnet 4 is as shown in FIG. 8B, the pole of the electromagnet 4 facing the permanent magnet 3 becomes the N pole, and is attached to the vibrating bar 2. Attraction force is generated between the permanent magnet 3 and the S pole, and repulsive force is generated between the permanent magnet 3 and the N pole. The free end of the vibrating reed 2 is forced upward in FIG. Will be displaced in response to this.
[0006]
Conversely, when the polarity of the current applied to the electromagnet 4 is reversed, as shown in FIG. 8C, the polarity of the electromagnet 4 on the side facing the permanent magnet 3 is reversed to become the S pole, and the permanent magnet The free end of the vibrating reed 2 receives a downward force to repel the S pole of No. 3 and attract the N pole, and the vibration mode changes. Therefore, by switching the polarity of the current applied to the electromagnet 4 in accordance with the natural vibration frequency of the vibrating system of the folded cantilever, vibration can be generated and continued.
[0007]
[Problems to be solved by the invention]
In the example shown in FIG. 8, the vibration of the vibration system is detected by the detection element 5, converted into an electric signal, amplified by the amplification circuit 6, input to the electromagnet 4 again, and output the detection signal from the detection circuit 7. . A piezoelectric element or an acceleration pickup is used as the vibration detecting element 5. However, the piezoelectric element is easily broken, and is easily affected by environmental characteristics and temperature characteristics caused by sticking to the detecting pipe with an adhesive. There is a problem of low.
[0008]
In addition, for example, there is a method using a vibration-type detection device disclosed in Japanese Patent No. 2636871. In this vibration type level detecting device, a vibrating body is provided with a piezoelectric element for excitation and a piezoelectric element for receiving, and the vibration of the vibrating body is excited by the piezoelectric element for excitation, and the vibration of the vibrating body is detected by the piezoelectric element for receiving. Then, the output from the receiving piezoelectric element is input to the band-pass filter to pass a vibration frequency fa when the vibrating body does not contact the detection target, and a vibration frequency when the vibrator contacts the detection target. fb. The output of the band-pass filter is supplied to a voltage comparison circuit and compared with a reference voltage. When the vibrating body does not contact the detection target, the detection target is detected because the voltage is higher than the reference voltage.
[0009]
However, in the above-described conventional example, there are problems that the number of components of the detection circuit increases, the cost increases, the structure becomes complicated, and the number of assembly steps increases. Increasing the number of parts also leads to lower reliability.
[0010]
FIG. 9 is an explanatory diagram of a level sensor when the conventional sensor unit shown in FIG. 8 is provided at a plurality of positions of a tank. When a sensor section 43 is provided in the tank 41 and a sensor section 44 is provided in the tank 42 to detect the presence or absence of an object at each position, a power supply line 47 for supplying power to each of the sensor sections 43 and 44 and each of the sensor sections 43 , 44 to the control unit 45 for discharging and supplying the object, a signal line 46 is required for each sensor unit, and each line requires two lines on the plus side and the minus side. In the example of FIG. A total of eight wires are required, four for 44.
[0011]
In addition, a large number of connecting parts such as a terminal block for connecting these wires to the sensor unit and the control device are required.
[0012]
In addition, a control circuit for each sensor requires an additional circuit such as an amplification circuit, a detection circuit, and a power supply circuit that accompanies it.It can be used when the temperature around the tank is high or when the temperature exceeds the temperature range of parts. Or no means such as cooling is required. In addition, electronic components are often vulnerable to vibration, etc., especially when sensors are provided near vibrators or shock generators provided to prevent clogging of objects, measures such as reinforcement are necessary. .
[0013]
Therefore, the main object of the present invention is to reduce the cost of the level sensor by detecting the presence or absence of an object at a plurality of sensor positions by a single control circuit unit, and at the same time to minimize the wiring between the sensor unit and the control device. In addition to reducing the number and length of wiring materials and reducing the cost of wiring materials, an electronic circuit inside the sensor is eliminated, and an object detection device for a vibration type level sensor with excellent environmental performance such as heat resistance and vibration resistance is provided. To provide.
[0014]
[Means for Solving the Problems]
The present invention has a sensor unit including a detection pipe, a diaphragm provided in the detection pipe, and a magnet provided with a magnet, and an electromagnet opposed to the diaphragm with a slight gap therebetween, and generates vibration by the electromagnet. A vibrating level sensor for detecting the presence or absence of powder, wherein the sensor units having different vibration frequencies are provided at a plurality of positions of a tank, and coils of electromagnets of the sensor unit are connected in series or in parallel, and these vibrations are detected. An impedance change in frequency is detected, and the presence or absence of an object at each position can be collectively detected by a single control circuit unit from the change.
[0015]
Further, each sensor unit and the control circuit unit are connected by a single loop-shaped line.
[0016]
[Embodiment]
First, before describing an embodiment of the present invention, the principle of the present invention will be described with reference to FIG. In FIG. 1, a sensor section A includes a detection pipe 11, a diaphragm 12, a magnet 13, and an electromagnet 14. When a current signal of the vibration frequency of the diaphragm 12 and the detection pipe 11 is applied to the electromagnet 14, the action of the alternating magnetic field between the magnetic poles of the magnet 13 and the electromagnet 14 maximizes the vibration of the sensor section A, and is generated by the magnet 13 and the electromagnet 14. The back electromotive force also becomes maximum, and the phase of the current flowing from the control signal to the signal line 15 changes. The results of measuring this change are shown in FIGS.
[0017]
2 to 5 will be described with reference to FIG. For example, when the vibration frequency of the sensor unit 23 attached to the tank 21 is 331 Hz and the vibration frequency of the sensor unit 24 attached to the tank 22 is 382 Hz, FIG. 2 shows the detection pipe 11 of the sensor unit 23 and the detection pipe of the sensor unit 24. 11 shows a free vibration state without being covered by an object. FIG. 3 shows a state in which the detection pipe 11 of the sensor unit 23 is covered with an object, and a state in which the detection pipe 11 of the sensor unit 24 is not covered with an object. FIG. 4 shows a state in which the detection pipe 11 of the sensor unit 23 is not covered with an object, and a state in which the detection pipe 11 of the sensor unit 24 is covered with an object. FIG. 5 shows a state where both the detection pipe 11 of the sensor unit 23 and the detection pipe 11 of the sensor unit 24 are covered with an object.
[0018]
When there is no object, a change occurs in the current phase at the vibration frequency of the sensor unit. However, when there is an object, the phase of the signal current due to the back electromotive force changes because the detection pipe 11 and the diaphragm 12 do not vibrate. do not do. From the presence or absence or the magnitude of the change in the current phase at the vibration frequency of each of the sensor units 23 and 24, it is detected whether each sensor is buried in the object.
[0019]
In order to change the vibration frequency of each of the sensor units 23 and 24, there is a method of changing the thickness, material, or shape of the diaphragm 12, for example.
[0020]
FIG. 7 is a block diagram of the control circuit unit 25 of the vibration type level sensor according to the embodiment of the present invention. 7, the control circuit unit 25 includes a frequency control unit 33, a frequency generation unit 32, a drive circuit 37, a current detection unit 36, and a phase comparison unit 38. The frequency control unit 33 controls the frequency generation unit 32 and outputs a signal. A sweep of a frequency range covering the vibration frequencies of all the sensor units connected to the line 15 is performed. The drive circuit 37 converts the signal of the microcomputer 31 into a current signal to be applied to the signal line 15 (in this example, 320 Hz to 400 Hz). The current detector 36 detects the phase of the current flowing through the signal line 15. The phase comparing section 38 compares the driving phase generated by the frequency generating section 32 with the current phase flowing through the signal line 15 detected by the current detecting section 36, and detects a phase difference between the two phases.
[0021]
The signal processing unit 34 determines whether or not the phase difference at a certain frequency is within a preset range of the phase difference. From the phase characteristics at the vibration frequency of each sensor unit, the vibration state of each sensor unit and each sensor It is determined whether the object is buried in the object, and the detection signal output unit 35 outputs a control / warning signal 39.
[0022]
In addition, the frequency sweep may be performed by a method in which the vibration frequencies of all the sensor units are collectively performed, or the vibration frequency of a specific sensor unit may be mainly swept, and the sweep of the vibration frequency of the other sensor units may be intermittently performed. There is a way.
[0023]
The embodiments disclosed this time are to be considered in all respects as illustrative 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.
[0024]
【The invention's effect】
As described above, according to the present invention, it is possible to detect a change in impedance at the vibration frequency of each sensor unit, and to detect the presence or absence of an object based on the change in impedance.
[0025]
Therefore, only a driving coil (electromagnet) and a permanent magnet are provided as the sensor unit, and the presence or absence of an object can be determined without using a piezoelectric element or an acceleration pickup in the receiving sensor unit as in the related art, thereby simplifying the structure. It is possible to achieve cost reduction and cost reduction, and the reliability of the device can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the principle of the present invention.
FIG. 2 shows a free vibration state in which neither sensor 23 nor 24 detects anything.
FIG. 3 shows a state where a sensor 23 detects an object and a sensor 24 does not detect anything.
FIG. 4 shows a state in which nothing is detected by a sensor 23 and a sensor 24 is detecting an object.
FIG. 5 shows a state where both sensors 23 and 24 are detecting an object.
FIG. 6 is a diagram for explaining FIGS. 2 to 5; FIG. 7 is a block diagram of a first embodiment based on the above-described principle;
FIG. 8 is a schematic block diagram of a conventional vibration type level sensor.
FIG. 9 is an explanatory diagram of a conventional vibration type level sensor.
[Explanation of symbols]
A sensor unit, 11 detection pipe, 12 diaphragm, 13 permanent magnet, 14 drive coil, 21, 22 tank, 23, 24 sensor unit, 25 control circuit unit, 26 signal lines, 31 microcomputer, 32 frequency generation unit, 33 Frequency control section, 34 signal processing section, 35 detection signal output section, 36 current detection section, 37 drive circuit, 38 phase comparison section, 39 control / alarm signal

Claims (2)

It has a sensor section consisting of a detection pipe and a diaphragm provided with a magnet and a magnet provided with a magnet, and an electromagnet opposed to the diaphragm with a slight gap therebetween. A multi-point object detection device of a vibration type level sensor for detecting, wherein the sensor units having different vibration frequencies are provided at a plurality of positions of a tank, the coils of the electromagnets of the respective sensor units are connected in series or in parallel, A multipoint object detection device for a vibration-type level sensor, which detects a change in impedance at the vibration frequency of the object and detects from the change the presence or absence of an object at each position by a single control circuit unit. . 2. The multipoint object detection device for a vibration type level sensor according to claim 1, wherein each of the sensor units and the control circuit unit are connected by a single loop-shaped line. 3.

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