JP2704849B2 - Displacement detector and displacement signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for electrically detecting displacement such as the position of a float in an area type flowmeter and a device for generating an analog displacement signal for recording and controlling a measured value. Things.

[0002]

2. Description of the Related Art In the field of industry, it is common to convert a displacement into an electric quantity to perform recording on a recorder, automatic control, remote measurement, and the like. However, even if the same displacement signal is generated, a difficult problem may occur depending on the application. For example, an area type flow meter measures a vertical flow by holding a tapered pipe with a scale and floating the float with the flow.It is possible to know the flow directly while visually observing the state of the flow. Widely used as a meter. In this regard, various means for generating a flow rate signal are used depending on the situation.

[0003] A method of detecting light by blocking the float is well known, and a method in which a single light receiving element is used to follow the float by a servo mechanism and a number of light receiving elements are arranged to detect the position of the float. There are things. This method has a high accuracy but has a drawback that it can be applied only to a transparent fluid. Therefore, a gas flow meter is good, but in the case of a liquid flow meter, which has the highest demand, there is a problem that the moving body becomes unreliable even if the scale is slightly attached to the tapered pipe.

It is known that a differential transformer is used for an opaque fluid. The differential transformer is provided with a rod connected to a float and provided outside a flowmeter. Is to be combined with However, this method has a problem that the structure is complicated and the error is large at a small flow rate due to the reaction force of the differential transformer.

[0005] For this reason, various sensors have been proposed and put into practical use. For example, JP-A-62-954
Japanese Patent Publication No. 25 discloses that a pair of an exciting coil and a detecting coil are arranged along a tapered tube using a ferromagnetic material for a float. However, this method has a problem in that it is difficult to arrange a large number of coils in close contact with each other, so that the measurement accuracy is limited, and there is a problem that the apparatus becomes large, such as providing a ferromagnetic outer cylinder on the outside.

In Japanese Patent Application Laid-Open No. 3-188324, an exciting coil and a detecting coil are wound around a tapered tube, and an electric conductor or a device incorporating the same is used as a float. A method for detecting a change is disclosed. This method has good detection sensitivity, but has a somewhat large temperature error and needs to be compensated for. Therefore, a simpler detector is desired.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, the present inventors have proposed a method of arranging a plurality of magnetoresistive elements in parallel with a tapered tube and detecting the positions of the magnets in a float. Invented earlier (JP-A-6-180242)
No.). The magnetoresistive element can detect a lower magnetic field with higher sensitivity than a Hall element, which is a similar magnetic detecting element. Furthermore, even if the elements themselves are small and arranged closely, they do not cause a problem in operation due to mutual interference, and thus are very suitable for such usage. Also, the problem of temperature error is essentially small in such a method of arranging a plurality of elements side by side and digitally detecting them, but the internal configuration of the magnetoresistive element itself is a bridge connection of the same kind of element, As a result, the temperature coefficient can be ignored.

On the other hand, a magnetoresistive element does not have the ability to determine the polarity of a magnetic pole in principle. Therefore, in the diagram showing the positional relationship between the magnet piece and the magnetoresistive element in FIG.
(A) It is good if the direction of magnetization of the magnet piece is perpendicular to the direction in which the magnetoresistive elements 1 are arranged, that is, the direction of displacement of the magnet piece, as shown in FIG. When the direction and the magnetization direction are the same, detection is simultaneously performed by two separated magnetic resistance elements which are similarly sensitive to both the N pole and the S pole, or the detection position itself is spread and ambiguous. When a magnet is sealed in the float in the area type flow meter, the float freely rotates around the axis, and therefore, FIG.
It is necessary to make the magnetic pole come in the direction as shown above, and some measures are necessary.

In the above-mentioned invention, a special magnetoresistive element is used to solve this problem. That is, the element is made of a hard magnetic material, and the direction of magnetization is stored by magnetic hysteresis. This was solved by devising the arrangement direction and using it. The present invention, on the other hand, uses a general magnetoresistive element to develop a displacement detection device that can be used even when the direction of the magnetic pole of the magnet piece is parallel to the direction of displacement as shown in FIG. Aim. Such general magnetoresistive elements are produced by a plurality of manufacturers in various forms and characteristics, and a displacement detection device having various forms and characteristics can be manufactured. Another object of the present invention is to develop a displacement signal generator particularly suitable for generating an analog displacement symbol using the above-described magnetoresistive element.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In a displacement detecting device for detecting the movement of a magnet piece magnetized in the direction of displacement, a displacement range of the magnet piece to be measured is determined. A plurality of magnetoresistive elements are arranged side by side,
A magnet whose length has at least a displacement range to be measured and is magnetized in a direction perpendicular to the length direction is provided with one magnetic pole facing the row of the magnetoresistive elements, and any one of the magnetoresistive elements detects the magnet. A displacement detection device for detecting a position of the magnet piece based on whether a magnetic field is equal to or more than a predetermined value. Here, the magnet piece is enclosed in the float of the area type flow meter, or is connected to the float, and the magnet piece further enlarges the displacement of the diaphragm of the differential pressure type flow meter. It is also characterized in that it is attached to.

A plurality of magneto-resistive elements are arranged over the range of displacement of the magnet piece, and when the magneto-resistive element detects a magnetic field of a certain value or more by the magnet piece, a constant voltage is output from the magneto-resistive element. And a resistor circuit that divides an output voltage from each comparator circuit by a voltage dividing ratio sequentially changed in an order in which the magnetoresistive elements are arranged. A displacement signal generator characterized in that one end of each diode is connected to the output side of the resistor in a forward direction with respect to the output voltage from the resistor circuit, and the other end of each diode is connected to output. is there.

[0012]

FIG. 1 shows the configuration of an example in which the displacement detecting device of the present invention is applied to an area flow meter. In the figure, reference numeral 1 denotes a magnetoresistive element, only a part of which is shown in the figure, but usually several tens are arranged at regular intervals over a displacement range to be measured. Reference numeral 4 denotes a taper tube of the flow meter, and reference numeral 3 denotes a float in which the magnet piece 2 is sealed. Further, there is provided a magnet whose length has at least a displacement range to be measured, that is, a measurement movement range of the float, and is magnetized in a direction perpendicular to the length direction. In this example, the plate-like magnet 5 is provided in parallel with the tapered tube 4, but is magnetized in the thickness direction of the plate, and is placed so that one pole faces the row of the magnetoresistive elements 1.

The magnet piece 4 in the float is magnetized in the vertical direction, that is, in the moving direction of the float, in terms of structure. The operation can be performed with either polarity of the plate-shaped magnet 5. However, when visually checking the scale of the area type flow meter, measurement is often performed at the upper end position of the float, but to match this, turn the magnetic pole of the same polarity as the upper end of the magnet piece in the float to the magnetoresistive element side Good.

FIG. 3 is a graph for explaining an operation state when the above arrangement is performed. The horizontal axis indicates the position, and the vertical axis indicates the magnetic field. When the magnet piece 2 is at the position shown in the graph, the magnetic field at a position parallel to the movement range of the magnet piece is represented by a curve 1
It looks like 1. On the other hand, since the magnetic detection of the magnetoresistive element does not discriminate the polarity, if the sensitivities of the N pole and the S pole are on the straight lines of 13A and 13B, the detection is performed at both. Therefore, when a magnet that generates a uniform magnetic field over the moving range of the magnet piece is placed with the N pole facing one of the magnets, the magnetic field shifts in a parallel-transformed form as shown by a curve 12.
Therefore, detection is performed only at the line 13A on the N pole side.

The position of the magnet may be provided on the side opposite to the magnetoresistive element 1 across the tapered tube 4 as shown in FIG. 1 so that its magnetic pole faces the tapered tube. By shifting or rotating around the vertical axis, the strength of the magnetic field by the magnet 5 in the portion of the magnetoresistive element can be adjusted. Of course, the strength of the magnet 5 in the portion of the magnetoresistive element 1 can be reduced by shifting the magnet 5 away from the tapered tube. Further, by changing the distance between the magnetoresistive element 1 and the tapered tube 4, the detection sensitivity of the magnetic field and the ratio of the strength of the magnetic field by the magnet 5 can also be changed.

As the magnetoresistive element used in the present invention, an element using a thin film of a generally used ferromagnetic metal such as permalloy can be used. The element has, for example, four elements 7 connected to a bridge as shown in FIG.
When the direction of the magnetic field crosses the zigzag current path, the change in resistance becomes maximum. Therefore, it has the maximum sensitivity in directions separated from each other by 90 degrees. The magnetoresistive element has a width of 3 mm, a length of 5 mm, and a thickness of 2 mm excluding, for example, a lead wire portion.
Since they are in the form of a flat plate such as mm, they may be arranged in close contact, and even if they are arranged in close contact in this way, there is no problem of mutual interference.

The mounting method may be such that a lead wire is inserted into a printed circuit board provided with a wiring pattern and soldered. In this case, if the magnetoresistive elements are closely arranged in the width direction in which the lead wires are arranged, the wiring pitch of the printed circuit board can be secured. In order to further increase the resolution of the measurement, two rows can be shifted by a half pitch as shown in FIG. 5 (a) front view and (b) side view. By thus arranging the rows in two rows, it is possible to improve the resolution while securing the wiring pitch to the lead wires of the printed circuit board.

The magnet used in the present invention needs to be magnetized uniformly over the entire length. The material is not particularly limited, and a ferrite magnet or the like can be used. As described above, by using a single magnet over the entire measurement range, the magnetic field can be detected with uniform sensitivity for all the magnetoresistance elements. By incorporating a small magnet called a bias magnet as a special product in the magnetoresistive element, the magnetoresistive element originally has poor linearity, and the operating position on the magnetic hysteresis curve is shifted to output in proportion to the magnetism. There is something that can be obtained. Such a device also has a function of determining the polarity of the magnetic pole depending on the method of use although it is different from the above-mentioned purpose of use.
However, when the magnetoresistive elements are closely arranged, there is a problem of mutual interference between the built-in magnets, and there is also a problem of variation of the built-in magnets of the individual elements. I have.

In the above description, the case where the displacement detecting device of the present invention is applied to an area type flowmeter in which a magnet piece is sealed in a float has been described as an example. The present invention can also be applied to a system in which the position of the end of the rod is read in a transparent cylinder provided in the above. In this case, if a non-magnetic material is used for the tapered tube, a method of enclosing the magnet piece inside the float as described above may be used, but the magnet piece is attached to the tip of the rod and the displacement of the magnet piece is detected by the apparatus of the present invention. do it. Further, it is of course that the present invention can be applied to detection of the movement of the magnet piece magnetized in the displacement direction other than the area type flow meter in principle. For example, a differential pressure type flow meter as shown in FIG. That is, in FIG. 6, the pressure guiding pipes 3 are respectively provided from the upstream side and the downstream side of the orifice 31 provided in the pipe 30.
2 and 33 communicate with the inside of the pressure chamber 34 and the diaphragm 35 provided therein. As a result, the diaphragm 35 is displaced in accordance with the differential pressure generated by the flow in the pipe, and the flow is detected as the movement of the lever 36 due to the displacement. The movement of the lever can be enlarged by further extending the length of the tip 37 of the lever, or by providing a gear mechanism or a link mechanism (not shown). Then, a magnet piece may be attached to the mechanism section in which the displacement of these diaphragms is enlarged, and the displacement may be detected by the above-described method.

If the outputs from the individual magnetoresistive elements arranged as described above are amplified and displayed at a certain level or higher, for example, in the case of a flow meter, the float is located at any position of the magnetoresistive element. You can know if there is. It can be used as it is as a digital signal,
For industrial instruments, for example, full scale is from 4 mA DC to 2 DC.
An analog signal such as a current output of 0 mA is often required. The present invention further provides a displacement signal generator suitable for obtaining such an analog output.

FIG. 7 is a diagram showing the circuit.
H denotes a magnetoresistive element, in which a power supply input terminal is omitted, and the number of elements is omitted, which is smaller than usual. The outputs of the respective magneto-resistive elements are output from comparator circuits 21A-2A.
In 1H, when the magnetoresistive element detects a magnetic field of a certain magnitude or more, the comparator circuit outputs a constant voltage that is determined by the power supply voltage of the comparator circuit.

Reference numerals 22A to 22H and 23A to 23H denote resistor circuits in which the voltage dividing ratios of 22A and 23A, 22B and 23B are sequentially changed in the order in which the magnetoresistive elements are arranged. For example, 22A and 23A are 8/10, 22
Change B and 23B to 7/10,
22H and 23H are 1/10.

Further, with respect to the output voltage from each of these resistor circuits, a diode 2 is provided with a forward polarity.
4A to 24H are connected. For example, if a positive output voltage is output from the comparator when magnetism is detected, the connection is made with a polarity such that it becomes forward with respect to the positive voltage as shown in FIG. On the other hand, the terminals at the other end of each diode are connected together and connected to the output 2 of this circuit.
5 is assumed.

In this manner, even when a plurality of adjacent magneto-resistive elements detect a magnetic field of a certain value or more, the resistor circuits 22A to 22H and 23A to 23H
, Only the output voltage of the one having the highest voltage division ratio passes through the diodes 24A to 24H and appears at the output 25. Therefore, for example, it is possible to always accurately detect a fixed position of the upper end of the float 3 of the area type flow meter, which is very convenient. As described above, an analog voltage corresponding to the position of the magnet piece can be obtained.
Needless to say, it can be converted to a DC output such as 0 mA. This displacement signal generator can be used not only for the displacement detector of the present invention but also for a displacement detector using a magnetoresistive element as shown in FIG.

[0025]

[Embodiment] The movement distance of the float in the measurement range is 60.
The displacement detection device of the present invention was applied to a mm-area flowmeter. 10mm length inside the float as shown in Figure 1
2mm along the tapered tube
As shown in FIG. 5, a total of 40 magnetoresistive elements having a thickness of 3 mm, a width of 5 mm, and a length of 5 mm were arranged in two rows in a total of 40 rows. As shown in FIG. 4, the magnetoresistive element has four elements connected to a bridge, and further includes a comparator circuit using an operational amplifier IC in the same package. The displacement signal generator shown in FIG.
All the magnetoresistive elements and some resistors (22A, 22B, etc.) were mounted on a single printed circuit board.
There is no need to attach 1A or the like separately from the magnetoresistive element, and mounting becomes very easy.

The dimensions are 6 mm thick, 14 mm wide, 60 mm
A long ferrite magnet plate was magnetized in the thickness direction, and one magnetic pole was provided facing the tapered tube on the side opposite to the row of magnetoresistive elements with the tapered tube interposed therebetween as shown in FIG. Further, a circuit was provided for converting the voltage output of the displacement signal generator into a current output having a full scale of 4 mA to 20 mA DC. As a result, a good linearity was obtained in the relationship between the position of the float and the output current, and a flow rate measuring device having excellent characteristics with little temperature error was obtained.

[0027]

According to the displacement detecting device of the present invention, the position of a magnet piece magnetized in the direction of displacement, which is difficult with conventional magnetic detecting means, such as a magnet built in the float of an area flow meter, is used as a magnetoresistive element. Can be detected more accurately. The magnetoresistive elements used in the present invention have no mutual interference even if they are closely arranged, can perform position measurement with sufficient accuracy and resolution, and have almost no temperature error.

According to the displacement signal generator of the present invention, detection signals from a plurality of magneto-resistive elements can be discriminated to obtain an analog signal corresponding to the position. Furthermore, even if there is a signal that detects the position of the magnet piece from a plurality of magnetoresistive elements at the same time, a change in the position can be accurately measured without causing an error in the measurement position. In addition, a magnetoresistive element having a built-in comparator circuit can be used, so that the number of components can be reduced and mounting can be facilitated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of an area type flowmeter to which a displacement detection device according to the present invention is applied.

FIGS. 2A and 2B are diagrams for explaining a positional relationship between a magnetoresistive element and a magnet piece, wherein FIG. 2A shows a case where a direction of a magnetic pole of a magnet piece is perpendicular to a moving direction, and FIG.

FIG. 3 is a graph showing an operation state of the displacement detection device of the present invention.

FIG. 4 is a diagram showing an example of an arrangement of elements of a magnetoresistive element.

5A and 5B are diagrams illustrating an example of a method of arranging magnetoresistive elements in the displacement detection device according to the present invention, wherein FIG. 5A is a front view, and FIG.

FIG. 6 is a diagram illustrating a mechanism of a differential pressure type flow meter.

FIG. 7 is a diagram showing a circuit configuration of a displacement signal generator according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic resistance element 2 Magnet piece 3 Float 4 Tapered tube 5 Magnet 7 Element 20A-20H Magnetic resistance element 21A-21H Comparator circuit 22A-22H, 23A-23H Resistor 24A-24H Diode 25 Output 30 Piping 31 Orifice 32, 33 Conductor Pressure tube 34 Pressure chamber 35 Diaphragm 36 Lever

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-26900 (JP, A) JP-A-6-18203 (JP, A) JP-A-59-40212 (JP, A) 199079 (JP, U) Japanese Utility Model Showa 53-79558 (JP, U) Japanese Utility Model Utility Model Showa 63-177715 (JP, U) Japanese Patent Publication No. 7-92395 (JP, B2)

Claims (5)

(57) [Claims] In a displacement detecting device for detecting the movement of a magnet piece magnetized in a displacement direction, a plurality of magnetoresistive elements are arranged side by side over a displacement range to be measured of the magnet piece, and the length is at least. A magnet having a displacement range to be measured and magnetized in a direction perpendicular to the length direction is provided with one magnetic pole facing the row of the magnetoresistive elements, and a magnetic field detected by any of the magnetoresistive elements is equal to or more than a certain value. A displacement detecting device for detecting a position of the magnet piece depending on whether or not the displacement of the magnet piece is small. 2. The displacement detecting device according to claim 1, wherein the magnet piece is sealed in a float of the area type flow meter. 3. The displacement detecting device according to claim 1, wherein the magnet piece is connected to a float of the area type flow meter. 4. The displacement detecting device according to claim 1, wherein the magnet piece is attached to a mechanism section of the differential pressure type flow meter which enlarges the displacement of the diaphragm. 5. A method in which a plurality of magneto-resistive elements are arranged over a displacement range of a magnet piece to be measured, and when the magneto-resistive element detects a magnetic field of a certain value or more by the magnet piece, a constant voltage is output from the magneto-resistive element. A comparator circuit to be output is provided for each magnetoresistive element, and a resistor circuit is provided to divide the output voltage from each comparator circuit by a voltage dividing ratio sequentially changed in the order in which the magnetoresistive elements are arranged. Displacement signal generator characterized in that one end of each diode is connected to the output side of the circuit with a forward polarity with respect to the output voltage from the resistor circuit, and the other end of each diode is connected to output. .