JP7138872B2 - Magnetostrictive sensor position detection method, magnetostrictive sensor, liquid level gauge, and magnetostrictive signal arrival time identification method - Google Patents

Description

The present invention relates to a magnetostrictive sensor that detects the position of a magnet when an object whose position is to be detected has a magnet.

A magnetostrictive sensor is, as described in Patent Documents 3 and 4, an object to be measured having a magnet provided movably along a magnetostrictive line, and by applying a current pulse in the axial direction of the magnetostrictive line, the proximity of the magnet is detected. A torsional elastic wave is generated at the site of the magnetostrictive line, the torsional elastic wave is detected by a detector provided at a specific site of the magnetostrictive line, and the propagation time of the torsional elastic wave from the magnet to the detector is measured. It detects the position of the magnet in the axial direction of the line.

As an effective application of the magnetostrictive sensor, an example of detecting the position of the float of a magnet gauge liquid level gauge is known. By installing a magnetostrictive sensor in parallel near the magnet gauge type liquid level gauge, the liquid level detection resolution can be improved. It allows remote control of the surface position.

A magnet gauge type liquid level gauge has a vertical communication pipe along the tank where the liquid is stored, and a float with a built-in magnet is inserted into the communication pipe so that it can move up and down. A large number of liquid level indicators that receive and rotate are arranged in the vertical direction along the communicating pipe, and the liquid level is indicated by the rotation of these liquid level indicators (see Patent Documents 1 and 2). Since the float changes according to the fluctuation of the liquid level in the tank, the position indicated by the liquid level indicator of the magnet gauge type liquid level gauge attached to the connecting pipe directly indicates the liquid level position in the tank. As a result, the liquid surface position can be easily visually recognized from the outside of the tank.

Japanese Utility Model Laid-Open No. 55-179330 JP-A-9-138155 U.S. Pat. No. 3,898,555 JP-A-4-16722

However, the magnet fixed inside the float that moves according to the fluctuation of the liquid level has the optimum magnetic field and its strength to reliably rotate the liquid level indicator of the magnet gauge type liquid level gauge. Therefore, it is not necessarily optimal for the magnetostrictive sensor, and difficulties have arisen in the adjustment of the magnetostrictive sensor. In other words, even if the magnet's magnetic field and its strength to be detected by the magnetostrictive sensor fluctuate, careful adjustment work is required so as not to cause errors in detection.

In addition, a gap is provided between the inner diameter of the communicating pipe and the outer diameter of the float so that the float moves smoothly against fluctuations in the liquid level. Even if there is, the position of the magnet to be detected fluctuates in the direction perpendicular to the axial direction of the magnetostrictive sensor. Therefore, there is a problem that the strength of the magnetic field applied to the magnetostrictive sensor of the magnet fluctuates, the waveform of the magnetostrictive signal changes, and the accurate position of the float cannot be detected.

SUMMARY OF THE INVENTION The present invention was devised to eliminate this drawback. We propose a position detection method.

According to the present invention, a magnetostrictive signal detected by a detector includes a point indicating the arrival of the magnetostrictive signal as a specific time even if the strength of the magnetic field of the magnet fluctuates, and the specific time is detected. This is based on the knowledge that the position of the magnet (object to be measured) can be specified accurately. Therefore, a magnetostrictive sensor position detection method according to a first embodiment of the present invention includes steps of converting a torsional elastic wave into an electrical signal by a detector to obtain a magnetostrictive signal, and converting the magnetostrictive signal into a plurality of comparators having different trigger voltages. and one waveform defining a specific time related to the axial position of the magnet, regardless of the amplitude variation of the magnetostrictive signal, from among the plurality of waveform-shaped waveforms representing times. and determining the axial position of the magnet based on the time between the arrival time of the waveform and the application time of the current pulse applied to the magnetostrictive wire. Here, "the axial position of the magnet" means the position of the magnet along the length direction or the axial direction of the magnetostrictive sensor.

If the waveform of the magnetostrictive signal is shaped using a plurality of comparators with different trigger voltages, a plurality of different pulse waveforms can be obtained. From among these pulse waveforms, a logic decision is made to select one waveform that defines a particular time relative to the position of the magnet regardless of the amplitude variation of the magnetostrictive signal. For example, the fall time of this selected waveform may be determined at a specific time.

At least one of the plurality of comparators may be a Schmitt trigger comparator, and the single waveform defining the specific time may be obtained from the output waveform of the Schmitt trigger comparator. A Schmitt trigger comparator is a comparator with so-called hysteresis in which the ON voltage and the OFF voltage are different. For example, by setting the OFF voltage to a voltage that defines a specific time identified in advance, this OFF time can be detected as the specific time, that is, the accurate arrival time of the torsional elastic wave regardless of the amplitude variation of the magnetostrictive signal. This OFF voltage may be 0 V, that is, the zero point may be detected.

The ON voltage of the Schmitt trigger comparator may have a lower absolute value than the ON voltages of the other comparators, and the OFF voltage of the Schmitt trigger comparator may be a potential level previously identified to define a specific time. Since the ON voltage of the Schmitt trigger comparator has a lower absolute value than the ON voltages of the other comparators, the output waveform of the Schmitt trigger comparator contains the most waveforms. Among these, the waveform when the comparator with the lowest ON voltage (absolute value) forms the maximum peak wave, that is, the waveform that overlaps most with the output waveforms of other comparators, is selected, and the OFF point of that waveform, that is, the falling edge, is selected. A point in time can be determined as the final specified time.

A second embodiment of the present invention includes a detector provided at a specific portion of a magnetostrictive wire to convert a torsional elastic wave into an electrical signal to obtain a magnetostrictive signal, and a detector having a different trigger voltage for shaping the waveform of the magnetostrictive signal. a plurality of comparators, and one waveform defining a specific time related to the axial position of the magnet, regardless of the amplitude variation of the magnetostrictive signal, from among the plurality of waveforms shaped by the plurality of comparators and indicating a plurality of times. and a logic judgment circuit that determines the axial position of the magnet based on the time between the arrival time of the waveform and the application time of the current pulse applied to the magnetostrictive wire. offer. The action of this magnetostrictive sensor is as described above.

A third embodiment of the present invention provides a method for identifying the arrival time of a magnetostrictive signal of a magnetostrictive sensor. That is, in this method, the magnet is provided so as to be displaceable in the directions of approaching and separating from the magnetostrictive line, and when the separation distance between the magnet and the magnetostrictive line is varied while the axial position of the magnet is held constant, A step of respectively measuring a plurality of magnetostrictive signals obtained by converting torsional elastic waves into electrical signals by a detector, and identifying a specific time among the plurality of magnetostrictive signals that does not change even if the distance between the magnet and the magnetostrictive line changes. step.

The distance between the magnet and the magnetostrictive line is the distance between the magnet and the magnetostrictive line in the direction perpendicular to the axis of the magnetostrictive line. When this separation distance changes, the magnetic field intensity of the magnet with respect to the magnetostrictive line changes, so the waveform (especially amplitude) of the magnetostrictive signal also changes. Therefore, when the distance between the magnet and the magnetostriction line is varied while the axial position of the magnet is held constant, the change in the magnetostriction signal can be observed by measuring each magnetostriction signal. Among these magnetostrictive signals, there is a point indicating a specific time that does not change even if the distance between the magnet and the magnetostrictive line changes. By identifying the specific time of the magnetostrictive signal, the identified time can be used to perform stable position detection.

The identifying step may be determining a signal level at an intersection point of the plurality of magnetostrictive signals, the intersection point immediately after the peak of the maximum peak waveform. For example, by setting this signal level to the OFF voltage of the aforementioned Schmitt trigger comparator, it becomes possible to easily detect a specific time.

The specific time may be the zero point immediately after the maximum peak waveform of the magnetostrictive signal or a time in the vicinity thereof. The waveform of the magnetostrictive signal changes depending on the shape of the magnet and the direction of the magnetic field, but the specific time that does not change even if the separation distance between the magnet and the magnetostrictive line changes exists near the zero point immediately after the maximum peak waveform. There are many. By identifying that point, the specific time can be easily detected.

As described above, according to the present invention, the waveform of the magnetostrictive signal is shaped using a plurality of comparators having different trigger voltages, and from among the shaped waveforms representing a plurality of times, the A single waveform defining a specific time relative to the axial position of the magnet is selected, and the axial direction of the magnet is determined based on the time between the arrival time of the waveform and the application time of the current pulse applied to the magnetostrictive line. Since the position is determined, even if the strength of the magnetic field applied to the magnetostrictive sensor of the magnet fluctuates, the position of the magnet can be stably and accurately detected.

1 is a schematic diagram showing a tank equipped with a magnetic gauge type liquid level gauge and a float in a communicating pipe; FIG. Fig. 3 shows the relationship between the float in the communicating pipe and the liquid level indicator of the magnet gauge type liquid level gauge, wherein (a) is a sectional view showing the operation of the liquid level indicator, and (b) is a right side view. FIG. 2 is a partial view of a liquid level measuring device in which a magnetostrictive sensor is provided beside a magnet gauge type liquid level indicator. It is a figure which shows an example of the principle of operation of a magnetostrictive sensor. FIG. 4 is a diagram showing the relationship between a current pulse applied to a magnetostrictive sensor, a magnetostrictive signal, and waveform shaping; FIG. 4 is a time magnified view of the magnetostrictive signal; It is a figure which shows an example of a controller. FIG. 10 is a diagram showing another example of a controller; FIG. 4 is a diagram showing an example of a magnetostrictive signal detected when the strength of a magnetic field applied to a magnetostrictive sensor of a magnet varies; FIG. 10 is a diagram showing an example of a method of waveform shaping a magnetostrictive signal and detecting a specific time when the separation distance is 12 mm; FIG. 10 is a diagram showing another example of a method of waveform-shaping a magnetostrictive signal and detecting a specific time when the separation distance is 15 mm; FIG. 10 is a diagram showing still another example of a method of waveform-shaping a magnetostrictive signal and detecting a specific time when the separation distance is 20 mm; It is a figure which shows an example of the controller of this invention.

Before describing embodiments of the present invention, an example of a liquid level measuring device to which a magnetostrictive sensor according to the present invention is applied will be described with reference to FIGS. 1 to 3. FIG. FIG. 1 shows a state in which a conventionally used magnet gauge type liquid level gauge 5 is attached in parallel to a communicating pipe 3. A float 4 moves up and down in conjunction with the liquid surface 2, and a magnet 4m is fixed inside the float 4.

The magnet gauge type liquid level gauge 5 is arranged in parallel near the communicating pipe 3, and its operating principle is shown in Patent Document 1 and Patent Document 2. For ease of understanding, FIG. I will explain it again. The same symbols are used for the same items as in FIG.

The magnet 4m fixed inside the float 4 is composed of two axially magnetized magnets with the same polarity facing each other. , to stably hold the rotor (liquid level indicator) 6, which is a component of the magnet gauge type liquid level gauge 5. magnets may be used.

As shown in FIG. 2(a), the rotor 6 is also magnetized at its outer peripheral portion distant from the center of rotation, so the rotor 6 rotates when the float 4 approaches. If one of the side surfaces of the rotor 6 is given a color such as 6a that can be distinguished from the other side surfaces, the liquid level 2 in the tank 1 can be clearly seen by reversing the rotor 6 as shown in FIG. 2(b). I understand.

FIG. 3 shows an embodiment in which a magnet gauge type liquid level gauge and a magnetostrictive sensor are combined. The magnetostrictive sensor 7 is installed together with the magnet gauge type liquid level gauge 5 so that the rod portion 7r thereof extends in the vicinity of the communicating pipe 3 along the longitudinal direction. Details of the magnetostrictive sensor 7 and its rod portion 7r are shown in FIG. 4, which will be described later. The magnetostrictive sensor 7 detects the axial position of the magnet 4m inside the float 4 (proportional to the height of the liquid surface 2). Between them, there are gaps g1 and g2 for obtaining smooth movement of the float 4, and the distance between the outer circumference of the float 4 and the outer circumference of the rod portion 7r of the magnetostrictive sensor 7 varies from several millimeters to ten-odd millimeters. The magnetostrictive signal of the magnetostrictive sensor 7 will be affected.

One operating principle of the magnetostrictive sensor 7 is detailed in Patent Document 3, and will be briefly supplemented here with reference to FIG. If a magnetostrictive wire 8 is placed in the axial direction where the displacement is to be measured and a current pulse 9 is periodically applied to it (in FIG. , the current pulse generating circuit is well known and is not shown in FIG. 4), the circumferential direction magnetic field 9a is instantaneously generated in the entire axial direction of the magnetostrictive wire 8, and vector-synthesized with the magnetic field 10a of the axially movable magnet 10, Due to the Wiedemann effect, a torsional elastic wave (not shown) is generated in the magnetostrictive wire 8 near the magnet 10 only when a current pulse is applied.

The magnet 10 in FIG. 4 is magnetized in a direction perpendicular to the magnetostrictive lines 8, but may be magnetized parallel to the magnetostrictive lines 8. FIG. The magnet 10 is only schematically illustrated and corresponds to the magnet 4m inside the float 4 in FIG. The aforementioned torsional elastic wave becomes a transverse wave and propagates toward both ends of the magnetostrictive wire 8, and the arrival of the transverse wave can be converted into an electric signal by the detection means 12 provided at the leading end of the magnetostrictive wire 8. On the other hand, transverse waves due to torsional elastic waves propagating in the right direction of the magnet 10 in FIG.

The propagation speed of the transverse wave propagating through the magnetostrictive wire 8 is determined by the material of the magnetostrictive wire 8 and the magnetic field applied to the magnetostrictive wire 8 by the magnet 10, and is generally known to be approximately 2.8 mm/μsec. is located, for example, 2800 mm (the distance indicated by L in FIG. 4) from the beginning of the magnetostrictive line, the detection means 12 will know the arrival of the transverse wave about 1000 μsec after the current pulse is applied. .

The detection means 12 shown in FIG. 4 is composed of a ferromagnetic strip 13, a coil 15 and a bias magnet 14. The strip 13 is fixed near the leading end of the magnetostrictive wire 8 by resistance welding or other mechanical method, A bias magnetic field is applied in the longitudinal direction of the strip 13 by the bias magnet 14 . The coil 15 circulates around the strip 13, and when the torsional elastic wave arrives, strain is generated in the strip 13 in the longitudinal direction, and a voltage change is induced in the coil 15 according to the inverse Villary effect in accordance with the change in strain. The polarity of the voltage change can also be reversed, such as by reversing the polarity of bias magnet 14 or reversing the polarity of coil 15 .

Although the torsional elastic wave cannot be directly observed as shown, the torsional elastic wave is known as an electrical signal observed by the detection means 12 when it arrives. 5, a current pulse 9 is periodically applied to the magnetostrictive wire 8, and the detection means 12 observes electromagnetic noise 18 at the moment the current pulse 9 is applied. However, this can be ignored by appropriate means, and the arrival of the torsional elastic wave can be determined by detecting a specific portion of the magnetostrictive signal 19 . The magnetostrictive signal 19 may be observed directly from the voltage induced in the coil 15, or may be observed as a voltage amplified by an amplifier (not shown in FIG. 4) or the like.

That is, the position of the magnet 10 can be known by measuring the time T from the application of the current pulse 9 to the arrival of the magnetostrictive signal 19 . The magnetostrictive signal 19 exhibits a substantially sinusoidal vibration, although it varies depending on the material and shape of the magnetostrictive wire 8, the magnetic field and strength of the magnet 10 applied to the magnetostrictive wire 8, and the impedance of the detecting means 12, as described above. The arrival time of the magnetostrictive signal 19 may be the so-called zero-crossing point indicated by the black dot mark 26 in the time-enlarged view of the magnetostrictive signal 19 shown in FIG. 6 or its vicinity.

Although the magnetostrictive wire 8 using a solid wire is shown in FIG. 4, it is not limited to this and may be a magnetostrictive tube (not shown). A current pulse may be applied directly to the magnetostrictive tube. Here, as a means for converting the arrival of the transverse wave (torsional elastic wave, which is one of the mechanical elastic waves) into an electric signal, a magnetic member that converts the transverse wave into a longitudinal wave is provided near the leading end of the magnetostrictive wire, and the inverse Villary effect is obtained. (This method is described in Patent Document 3 and specifically shown in FIG. 4).

In addition to the above-mentioned method, a coil is provided around the magnetostrictive wire near the beginning of the magnetostrictive wire and the inverse Wiedemann effect is used to convert it into an electrical signal (not shown), or the arrival of the transverse wave is converted into mechanical strain such as a piezoelectric element. A method (not shown) of directly converting into an electric signal by a sensitive element can be used. The rod portion 7r of the magnetostrictive sensor 7 shown in FIG. 3 is made in the shape of a non-magnetic pipe, and the magnetostrictive wire 8 shown in FIG. 4 is accommodated therein.

Application of the magnetostrictive sensor 7 of FIG. 3 to a liquid level gauge is described in detail in Patent Document 4, for example. Since the float fluctuates according to changes in the liquid level, it is possible to know the position of the liquid level based on the operating principle described above. In the example of Patent Document 4, the magnetic field applied to the magnetostrictive sensor is relatively stable because the magnet surrounds the magnetostrictive sensor, so it is relatively easy to detect the magnetostrictive signal. is. However, if the doughnut-shaped magnet can be displaced in the radial direction of the magnetostrictive line, the same problem as the float 4 in FIG. 3 exists, so the present invention can be applied.

How to measure the required time will be described with reference to FIG. As described above, the current pulse 9 is periodically applied to the magnetostrictive wire 8, and simultaneously with the application, the electromagnetic noise 18 received by the coil 15 of FIG. As for these signals, the voltage signal of the coil 15 may be directly observed, or the output of the amplifier 27 in FIGS. 7 and 8 may be observed as necessary. 7 and 8 attached to FIG. 5, the same symbols are used for those having the same functions.

Symbol 20 in FIG. 5 indicates the zero potential of the magnetostrictive signal 19 (zero potential, in other words, indicates the observed potential in the absence of the magnetostrictive signal). A dashed line 21 is a potential lower than the zero potential 20, for example. The output is turned ON, as indicated by output 23 in FIG. The output 23 consists of three pulses associated with the electromagnetic noise 18 and three pulses associated with the magnetostrictive signal 19 (strictly speaking, these pulses have temporal widths, but for clarity the pulses have been linearized). drawn in a shape). Since the electromagnetic noise 18 is unnecessary as already mentioned, when the masking pulse 9a having an appropriate width synchronized with the current pulse 9 is ANDed with the output 23, the output of the AND element 29 in FIG. As such, only three pulses associated with the magnetostrictive signal 19 can be obtained.

FIG. 6 magnifies the time around the magnetostrictive signal 19 to explain this in an easy-to-understand manner. The output 23 of the inverting comparator 28 shown in FIG. is turned ON, and when the magnetostrictive signal 19 is higher than the potential 21, the output 24 of the AND element 29 is turned OFF. However, having obtained three pulses associated with the magnetostrictive signal 19, it is not possible to determine which of these pulses is the arrival time of the magnetostrictive signal 19.

The magnetostrictive signal 19, or the vicinity of the zero cross point 26 of the magnetostrictive signal 19 in FIG. You can think of it as the arrival time of 19. A single output 25 related to the magnetostrictive signal 19 can easily be obtained by replacing the potential 21 with a comparator trigger voltage of 22 . As can be seen from FIG. 6, if the inverting Schmidt trigger comparator 33 of FIG. 8 is used as the comparator, the magnetostrictive signal 19 is turned ON when the potential is 22 or less and turned OFF when the potential is 26 or more. Therefore, if the required time T is set from the application time of the current pulse 9 to the fall of the output 25, the position of the magnet can be easily specified.

As shown in FIG. 8, the inverting Schmidt trigger comparator 33 is a comparator with a so-called hysteresis that turns ON when the input signal or magnetostrictive signal 19 falls below 22 and turns OFF when it exceeds 26. FIG. Here, the controller 201 in FIG. 7 and the controller 202 in FIG. 8 will be explained again. A controller 201 surrounded by a dashed line in FIG. 7 includes an amplifier 27 that amplifies the magnetostrictive signal detected by the coil 15, an inverting comparator 28, an AND element 29, a current pulse driving circuit 31, and a current pulse that periodically generates. and a control circuit 30 for generating the masking pulse 9a, and a logical decision circuit 32 for obtaining the required time T.

8 includes an amplifier 27 for amplifying the magnetostrictive signal detected by the coil 15, an inverting Schmidt trigger comparator 33, a current pulse drive circuit 31, and a current pulse periodically. It consists of a control circuit 30 for generating and a logic decision circuit 32 for obtaining the required time T. In the case of the controller 202, the potential 22 is below the electromagnetic noise 18, so the AND element 29 like the controller 201 is not required.

9, the magnetostrictive signal generated in the magnetostrictive sensor 7 by the magnet 4m in the float 4 shown in FIG. 3 is observed as the output voltage of the coil 15 of the detection means 12 of FIG. This is an example of the synchroscope screen. The magnetostrictive signal 34 indicates a case where the outer circumference of the float 4 and the outer circumference of the rod portion 7r of the magnetostrictive sensor 7 are separated by 12 mm, the magnetostrictive signal 35 by 15 mm, and the magnetostrictive signal 36 by 20 mm. At this time, there is no change in the axial position of the rod portion 7r of the magnetostrictive sensor 7 of the magnet 4m, and only the separation distance described above changes. Alternatively, the separation distance may be said to be the separation distance between the magnet 4m and the rod portion 7r of the magnetostrictive sensor 7 in the axis-perpendicular direction. For reference, the zero potential 20 and the zero cross point 26 of the magnetostrictive signal are also shown in FIG.

In this way, when the separation distance changes, the magnetostrictive signal, in particular, the amplitude of vibration greatly changes, and the accurate position of the float 4 cannot be known by the conventional means. The present invention provides a means for always detecting the position of the float 4 accurately even if the magnetostrictive signal fluctuates in this way. Looking at FIG. 9 in detail, even if the magnetostrictive signal as shown by the circle 37 fluctuates near the zero crossing point 26 of the magnetostrictive signal (at this time, even if the separation distance changes, the liquid level 2 indicated by the float 4 assume that there is no fluctuation), it can be seen that there is a point indicating the arrival of the magnetostrictive signal as a specific time. In this specification, the aforementioned circle 37 is referred to as a magnetostrictive signal node. Therefore, in the present invention, the node 37 that gives the specific time of the magnetostrictive sensor 7 is identified in advance. Specifically, the magnet is provided so as to be displaceable in directions toward and away from the magnetostrictive line, and when the distance between the magnet and the magnetostrictive line is varied while the axial position of the magnet is held constant, a plurality of Measure the magnetostriction signals of Among the waveforms of these multiple magnetostrictive signals, a specific time, that is, a node 37, which does not change even if the distance between the magnet and the magnetostrictive line changes, is identified. For example, as a factor for determining the node 37, a potential 37v at an intersection point where a plurality of magnetostrictive signals intersect immediately after the peak of the maximum peak waveform may be determined. Since this potential 37v is not constant for all magnetostrictive sensors, it is advisable to determine the potential 37v for each individual magnetostrictive sensor. In the actual detection work, if the potential 37v is known, the node 37 cannot be determined immediately, and it is necessary to determine the node 37 by logical judgment as described later. By measuring the time T between the application time of the current pulse 9 and the time indicated by the node 37 of the magnetostrictive signal, it is possible to know the accurate position of the float 4 . It is also possible to use the potential of the zero point 26 near the node 37 instead of the node 37 .

FIG. 10 shows the magnetostrictive signal 34 and the inverting Schmidt trigger comparators 33 and 2 shown in FIG. The output signals 41, 42, 43 of the inverting comparators 28a, 28b are shown. In FIG. 10, each trigger reference point (trigger voltage) 38, 39, 40 of each comparator 33, 28a, 28b is indicated by a dashed line. Among them, one comparator is preferably a so-called inverted Schmidt trigger comparator 33 whose trigger ON and OFF levels are different. The absolute value of the ON voltage 38 of the Schmitt trigger comparator 33 is lower than the absolute values of the trigger voltages 39, 40 of the other comparators 28a, 28b.

Inverting Schmitt-trigger comparator 33 is a comparator with hysteresis that turns ON when input 19 falls below potential 38 and turns OFF when it exceeds potential 37v. This potential 37v is the potential of the node 37 determined in the identification step described above, but it is also possible to use zero potential. As is clear from comparing output signals 41, 42, and 43 of the comparators shown in FIG. The downstream time coincides with the node 37 time. Although general comparators are used as the two inverting comparators 28a and 28b in this example, it is of course possible to replace them with inverting Schmidt trigger comparators. When all the comparators 33, 28a, and 28b are inverted Schmitt trigger comparators and their OFF voltages are set to a potential of 37 V, the second pulse of the output signal 41 and the first pulse of the output signal 42 are , the falling time of the pulse of the output signal 43 indicates the same time T.

Since the magnetostrictive signal 34 is relatively large, it is also below the trigger reference point 39, resulting in two pulse trains as in the output signal 42 of the comparator, and furthermore the peak voltage of the magnetostrictive signal 34 is below the trigger reference point 40. , the output signal 43 of the comparator obtains one pulse. In this way, obtaining a pulse signal that turns ON/OFF at a specific potential from an electrical signal (meaning the magnetostrictive signal 34 in FIG. 10) that changes in a continuous sinusoidal shape is also called "wave shaping".

FIG. 11 shows the case of the magnetostrictive signal 35 when the distance between the outer circumference of the float 4 and the outer circumference of the rod portion 7r of the sensor 7 is 15 mm. One and one. In this case, the time width T to be measured can be obtained by paying attention to the fall time of the first pulse of the output signal 41 of the inverted Schmitt trigger comparator 33 .

FIG. 12 shows the case of the magnetostrictive signal 36 when the distance between the outer circumference of the float 4 and the outer circumference of the rod portion 7r of the sensor 7 is 20 mm. 1 and then 0. In this case, the fall time of the first pulse of the output signal 41 of the inverting Schmidt trigger comparator 33 should be noted as the time T to be measured.

10, 11 and 12, it can be seen that if there is only one comparator for obtaining the specific arrival time of the magnetostrictive signal, the output signal 41 of the inverting Schmidt trigger comparator 33 is the only one available. As a result, it is impossible to determine which part of which pulse of the three pulses of the output signal 41 indicates the correct time. However, if the number of independent comparators is increased and the respective trigger reference points are set to be different, which time indicated by the plurality of pulses of the output signal 41 of the inverting Schmidt trigger comparator 33 can be specified by logical judgment. You can easily find out if it's good or not. For example, as an example of logical judgment, among the three pulses of the output signal 41, the pulse (the second pulse) that overlaps with the pulses of the other output signals 42 and 43 the most may be selected. In other words, this is synonymous with selecting the maximum peak waveform. Since the falling time of the second pulse of the output signal 41 is equal to the previously identified node 37, this can be used as the "specified time".

In the case of FIG. 10, from the output signals 42 and 43 of the comparator, the time point of the second pulse of the output signal 41 of the inverting Schmidt trigger comparator 33 can be set as the specified time. In the same way, from the output signals 42 and 43 of the comparator, the time point of the first pulse of the output signal 41 of the inverting Schmitt trigger comparator 33 can be easily determined as the specified time. From the output signals 42 and 43 of the comparator, it can be easily understood that the fall point of the first pulse of the output signal 41 of the comparator should be set to the specified time. In this way, it is possible to uniquely determine the desired time T. This time T does not change even if the distance between the magnets varies.

As described above, the logical operation method for obtaining the time T has been explained using an analog circuit, but these logical operations can be easily performed using a DSP or microprocessor. Even if the signal changes due to large fluctuations in the usage environment, it is possible to always achieve the position detection of the object to be measured or the position of the float accurately. In the present invention, in order to determine the specific time of the obtained magnetostrictive signal that varies sinusoidally and also varies in amplitude, the node 37 described in this specification is determined in advance, and three independent comparators are used. However, two comparators may be used if the fluctuation of the magnetostrictive signal is not so large, or one comparator may be used if the vibration mode or amplitude of the magnetostrictive signal does not change in any environment.

As is clear from the above description, the number of comparators need not be limited to three, and the larger the number, the more logical judgment conditions for determining the specific time, which is preferable. Next, the configuration of the controller 203 shown in FIG. 13 will be described, but it is not limited to this, and it is a matter of course that other configurations may be used as long as the same purpose can be obtained. The functions of the AND element 29, the comparators 33, 28a and 28b in FIG. 13 may be provided to a semiconductor integrated circuit such as a DSP or microprocessor.

FIG. 13 is an example of a controller according to the invention. The controller 203 includes an amplifier 27 for amplifying the magnetostrictive signal observed by the detection means 12 of FIG. 4, an inverting Schmidt trigger comparator 33, two inverting comparators 28, three AND elements 29, a logical judgment circuit 32, and a control circuit. 30 and a current pulse drive circuit 31 . The magnetostrictive signal 19 in the figure shows the output of the amplifier 27 mentioned above, but it is clear from the above description that it also means the magnetostrictive signals 34, 35, 36 of FIGS. At this point, we would like to discuss how logic decision circuit 32 works in the present invention. Since the control circuit 30 also transmits the information of the application time of the current pulse 9 to the logic judgment circuit 32, the necessary time T is measured based on that time.

In the case of FIG. 10, since the output 43 of the comparator appears, the time between the fall time of the second pulse of the output 41 of the comparator including the pulse generation time and the application time of the current pulse 9 is measured. Let T be the time to be taken. Since the output 43 also appears in the case of FIG. 11, the time between the fall time of the first pulse of the output 41 of the comparator including the pulse generation time and the application time of the current pulse 9 should be measured. Let the time be T. In the case of FIG. 12, after confirming that no pulse appears at the output 43, the fall time of the first pulse of the output 41 of the comparator including the pulse generation time of the output 42 and the application of the current pulse 9 are calculated. It suffices to set the time between the times as the time T to be measured.

As described above, the magnetostrictive sensor position detection method of the present invention is very effective when the magnet can move toward and away from the magnetostrictive line. That is, as shown in FIG. 3, when the magnets are biased (offset) on one side of the outer periphery of the magnetostrictive sensor, the magnetostrictive signal fluctuates due to the change in the separation direction of the magnets. This is because it is difficult to accurately detect the position. By applying the present invention, it becomes possible to stably and accurately detect the position of the float. Needless to say, the magnetostrictive sensor of the present invention is not limited to the application of detecting the position of the float of the magnet gauge liquid level gauge as shown in FIG.

1 tank 3 communicating pipe,
4 Float 4m Magnet in float 5 Magnet gauge type liquid level gauge 6 Liquid level indicator of magnet gauge type liquid level gauge 7 Magnetostrictive sensor 8 Magnetostrictive wire 9 Current pulse 10 Magnet 12 Magnetostrictive signal detector 19 Magnetostrictive signal 20 Magnetostrictive Signal zero potential 21, 22 Trigger voltage 23-25 Comparator output signal 26 Zero-crossing point 28 Inverting comparator 30 Control circuit 31 Current pulse driving circuit 32 Logic judgment circuit 33 Inverting Schmitt trigger comparator 34-36 Magnetostrictive signal 37 Magnetostrictive signal A specific point (node) indicating arrival
37v Schmitt trigger comparator OFF trigger voltage 38 Schmitt trigger comparator ON trigger voltage 39-40 Comparator trigger voltage 41 Schmitt trigger comparator output pulses 42-43 Comparator output pulse 201 Controller example 1
202 Controller Example 2
203 Example of controller of the present invention T Time to be specified

Claims (6)

An object to be measured having a magnet is provided movably along the magnetostrictive line, and a current pulse is caused to flow in the axial direction of the magnetostrictive line to generate a torsional elastic wave at a portion of the magnetostrictive line adjacent to the magnet. A magnetostrictive sensor that detects the axial position of the magnet by detecting the torsional elastic wave with a detector provided at a specific part of the magnet and measuring the propagation time of the torsional elastic wave from the magnet to the detector,
converting a torsional elastic wave into an electrical signal by the detector to obtain a magnetostrictive signal;
a step of waveform shaping the magnetostrictive signal using a plurality of comparators with different trigger voltages;
A single waveform that defines a specific time related to the axial position of the magnet is selected from among the shaped waveforms indicating a plurality of times, regardless of the amplitude variation of the magnetostrictive signal, and the arrival of the waveform is selected. determining the axial position of the magnet based on the time between the time and the application time of the current pulse applied to the magnetostrictive wire;
has
At least one of the plurality of comparators is a Schmitt trigger comparator, and one waveform defining the specific time is obtained by the output waveform of the Schmitt trigger comparator,
The ON level of the Schmitt trigger comparator has a lower absolute value than the ON level of other comparators, and the OFF level of the Schmitt trigger comparator is a potential level identified in advance to define a specific time.
Position detection method for magnetostrictive sensors. An object to be measured having a magnet is provided movably along the magnetostrictive line, and a current pulse is caused to flow in the axial direction of the magnetostrictive line to generate a torsional elastic wave at a portion of the magnetostrictive line adjacent to the magnet. A magnetostrictive sensor that detects the axial position of a magnet by measuring the propagation time of a torsional elastic wave to a specific portion of a magnetostrictive line,
a detector provided at a specific portion of the magnetostrictive wire to obtain a magnetostrictive signal by converting a torsional elastic wave into an electrical signal;
a plurality of comparators with different trigger voltages for waveform shaping the magnetostrictive signal;
selecting one waveform defining a specific time related to the axial position of the magnet irrespective of amplitude fluctuations of the magnetostrictive signal from among the waveforms shaped by the plurality of comparators and indicating a specific time; a logical judgment circuit that determines the axial position of the magnet based on the time between the arrival time of the waveform and the application time of the current pulse applied to the magnetostrictive wire;
with
At least one of the plurality of comparators is a Schmitt trigger comparator, and one waveform defining the specific time is obtained by the output waveform of the Schmitt trigger comparator,
The ON level of the Schmitt trigger comparator has a lower absolute value than the ON level of other comparators, and the OFF level of the Schmitt trigger comparator is a potential level identified in advance to define a specific time.
Magnetostrictive sensor. a non-magnetic communicating pipe which is installed in a communicating state along the liquid container whose liquid surface is to be detected and accommodates a float having a magnet so as to be movable up and down;
a liquid level display device in which a large number of liquid level indicators that are rotated by receiving a magnetic field from the magnet are arranged in the longitudinal direction along the communication pipe, and the liquid level is indicated by the rotation of the liquid level indicator;
and a magnetostrictive sensor according to claim 2 arranged longitudinally along the communicating pipe,
The magnet of the magnetostrictive sensor is a magnet provided on the float,
Liquid level indicator. An object to be measured having a magnet is provided movably along the magnetostrictive line, and a current pulse is caused to flow in the axial direction of the magnetostrictive line to generate a torsional elastic wave at a portion of the magnetostrictive line adjacent to the magnet. A magnetostrictive sensor that detects the axial position of the magnet by detecting the torsional elastic wave with a detector provided at a specific part of the magnet and measuring the propagation time of the torsional elastic wave from the magnet to the detector,
The magnet is provided so as to be displaceable in a direction toward or away from the magnetostrictive line, and when the distance between the magnet and the magnetostrictive line is varied while the axial position of the magnet is held constant, the detector a step of respectively measuring a plurality of magnetostrictive signals obtained by converting the torsional elastic waves into electrical signals by
identifying a specific time that does not change even if the distance between the magnet and the magnetostrictive line changes, among the plurality of magnetostrictive signals;
A magnetostrictive signal arrival time identification method. The identifying step includes:
determining a signal level at an intersection point where the plurality of magnetostrictive signals intersect, the intersection point immediately after the peak of the maximum peak waveform;
The arrival time identification method of the magnetostrictive signal according to claim 4 . The specific time is a time at or near the zero point immediately after the peak of the maximum peak waveform of the pre-magnetostrictive signal,
6. The method for identifying arrival times of magnetostrictive signals according to claim 4 or 5 .

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