JPS63233302A - Displacement sensor - Google Patents

Abstract

PURPOSE:To obtain the title sensor having a long measuring effective range, by forming the leading end of the plunger, which is connected to a float for detecting displacement quantity and formed of a magnetic body so as to be movable in the through-hole of a coil, into a tapered shape. CONSTITUTION:When a liquid 12 is injected in a container 10, a float 14 rises and a plunger 16 also rises along with said float 14. At this time, since the plunger 16 has ridges 24a, 24b, 24c, 24d formed thereto in a tapered shape toward the leading end thereof at four places, the cross-sectional area of the plunger 16 corresponding to the lower end surface of a coil 18 gradually increases and the reactance of the coil 18 gradually changes. Therefore, when an oscillation circuit is connected to the coil 18, the rising quantity of the plunger 16 is measured as the change of oscillation frequency and a displacement sensor almost linear in the relation between the stroke of the plunger and the oscillation frequency and having a long measuring effective range can be realized.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a displacement sensor.

(Prior Art) Conventionally, there has been known a method of measuring the amount of displacement as a change in reactance (frequency) or the like in a self-excited manner using a magnetic body moving in the thrust direction through a central hole of a coil. As an example, there is a technique disclosed in Japanese Patent Application Laid-Open No. 172011/1983. This is a displacement sensor that has a coil and a diaphragm, and a magnetic body that slides inside the coil is attached to the diaphragm.The end face of the magnetic body is located outside the end face of the coil. The change in the reactance (frequency) of the coil when the connected magnetic body moves toward and away from the coil in accordance with the displacement of the diaphragm is measured as the amount of displacement of the diaphragm (pressure).

(Problems to be Solved by the Invention) However, the above displacement sensor has the following problems.

When the opposite end faces of the magnetic body are brought close to each other from the outside of the coil end face, the reactance of the coil changes rapidly as the distance between the two approaches O, and when the end of the magnetic body enters the central hole of the coil, the reactance changes. It is not possible to obtain a large change in Therefore, the amount of displacement of a displaceable body such as a diaphragm can be obtained as a change in coil reactance from a position where the end face of the magnetic body is close to the end face of the opposing coil until the end face of the magnetic body enters the central through hole of the coil. limited to a range. In other words, since the displacement stroke is within an extremely limited range, there is a problem in that it is not possible to measure the amount of displacement over a large stroke.

In addition, since the stroke of the magnetic material and the change characteristics of the reactance of the coil change in a curved manner (quadratic curve), converting the change in reactance into the amount of displacement requires an expensive microcomputer with a large capacity. There are also some problems.

Therefore, an object of the present invention is to provide an inexpensive displacement sensor in which the stroke of the magnetic body is long and the effective measurement range is also long, and furthermore, the stroke of the magnetic body can arbitrarily set the changing characteristics of the reactance of the coil.

6 (Means for solving the problem) That is, a plunger formed of a coil and a magnetic material movable in the thrust direction within the through-hole of the coil.

In a displacement sensor, the coil or plunger is connected to a displacement body for detecting the displacement of a measured object such as a diaphragm or a float, and the displacement of the displacement body is measured by a reactance change of the coil. The plunger is characterized in that its end portion has one or more tapered portions close to the inner wall of the through hole.

(effect) The operation will be explained with reference to the drawings.

When the amount of liquid 12 in the container 10 changes and the height of the liquid changes, the plunger 16 formed of a magnetic material moves the coil 1
8 through the through hole 20a. The reactance in the coil 18 then changes as the plunger 16 moves. At this time, the reactance change characteristic has a linear characteristic because the plunger 16 is provided with the tapered surfaces 22a, 22b, 22c, 22d, . . . . Therefore, the reactance (
The amount of change in the frequency) can be measured as the amount of displacement of the flow 14 which is the displacement body, that is, the amount of displacement of the liquid level.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the configuration will be explained.

FIG. 1 shows a liquid level sensor.

A container 10 contains a liquid 12 as an object to be measured.

A float 14 is a displacement body, is made of a rigid resin such as polyacetal, and floats on the liquid 12.

16 is a plunger made of magnetic material,
The lower end is fixed to the upper surface of the float 14. The planar shape of the tip of the plunger 16 is formed in a cross shape as shown in FIG. 1(b), and the clearance with the inner wall of the central through hole 20a varies depending on the application, etc., and there is a sufficient clearance for sliding contact. Even things are included. The plunger 16 has tapered surfaces 22a, 22b, 22 having the length shown in A.
C122d, 22e, 22f, 22g, 22h are formed at appropriate angles, and four tapered peaks 24a, 24b, 24
c, 24d are formed.

Note that the tapered surface 22 a 122 b% 22 c 12
2 d-.

22e, 22f, 22g, and 22h do not necessarily have to be linear tapered surfaces, but may be formed in curved or stepwise shapes, and may have arbitrary angles.

Alternatively, a hole or a recess may be formed in the center of the tip surface shown in FIG. 1(b).

18 is a coil, which is fixed within the frame 26. The coil 18 is formed by winding a conductive wire around a bobbin 28, but the bobbin 28 may not be necessary depending on the case.

A through hole 20b having the same diameter as the through hole 20a of the coil 18 (a diameter through which the plunger 16 can enter) is bored in the lower surface of the flange 30 of the frame 26, and communicates with the inside of the container 10. Note that when the liquid 12 is not present in the container 10, the upper end of the plunger 16 slightly enters the through hole 20a of the coil 18.

Reference numeral 32 denotes a pressing member, which is screwed onto the upper part of the frame I/-A 26 to press and fix the coil 18 to the inner bottom surface of the frame 26.

Note that an oscillation circuit (not shown) is connected to the coil 18.

A liquid level sensor, which is an embodiment of the displacement sensor according to the present invention, is constructed as described above.

Next, we will discuss the operation.

When the liquid 12 is injected into the container 10, the float 14 rises, and the plunger 16 also rises accordingly. At this time, the coil 18 is energized in advance and magnetic flux is generated in the coil 18, so when the plunger 16, which is a magnetic body, approaches the coil 1, the magnetic flux increases and the reactance of the coil 18 changes. At this time, the plunger 16 has four peaks 24 a, 24 b, and 24 c tapering toward the upper end.
, 24d, the cross-sectional area of the plunger 16 corresponding to the lower end surface of the coil 18 gradually increases (proportional to the rise of the plunger 16).

When the reactance of the coil 18 changes, the change in the oscillation frequency of the oscillation circuit connected to the coil 18 is proportional to the change in reactance, so the amount of rise (displacement) of the plunger 16 can be measured as a change in the frequency of the oscillation circuit. Can be done. The measurement results may be displayed using a microcomputer for arithmetic processing and an appropriate display method.

In the above embodiment, the plunger roll 6 has peaks 24a, 24b, 2
4c and 24d were formed at four locations, but for example, plunger 1
6 may be cut diagonally, or the plunger 16 may have two or three peaks, and the lower end cross section of the plunger 16 does not necessarily have to be circular (for example, a prismatic shape).

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments; for example, the displacement body may be a diaphragm or the like instead of a float to measure pressure changes, Also, it is not the plunger that is displaced together with the displacement body, but the plunger is fixed,
Of course, many further modifications can be made without departing from the spirit of the invention, such as allowing the coil to be displaced integrally with the displacement body.

(Effects of the Invention) When the displacement sensor according to the present invention is used, the relationship between the stroke of the plunger and the measured oscillation frequency exhibits a nearly linear characteristic as shown in Figure 2 (Figure 3 shows the relationship between the stroke of the plunger and the measured oscillation frequency). ). Therefore, from a comparison between Figures 2 and 3, the frequency change was 3kHz for a plunger stroke of 4mm in the conventional system, but in the displacement sensor according to the present invention, the frequency change was 41kHz.
Since we were able to obtain a frequency change of 9 Kllz for a stroke of , it is possible to realize a sensor with three times the resolution compared to the conventional one, making it possible to perform highly accurate measurements.

Further, since the oscillation frequency has a linear characteristic, it is possible to increase the length of the tapered peak of the plunger to realize a displacement sensor with a long stroke and a long effective measurement range. Change characteristics are linear By changing the angle and shape of the tapered surface formed to make the plunger tapered, it is also possible to arbitrarily set the change characteristics of reactance (frequency).

Further, unlike conventional displacement sensors, the tip of the plunger can be inserted into the central through hole of the coil in advance, which makes it possible to downsize the sensor, which is technically and economically advantageous.

[Brief explanation of drawings]

Figure 1 shows (a) a front sectional view of a liquid level sensor using a displacement sensor according to the present invention, (b) a plan view of a plunger of the displacement sensor, and Figure 2 shows the oscillation frequency of the displacement sensor with respect to the plunger stroke. FIG. 3 is a graph showing the relationship between the oscillation frequency and the plunger stroke of a conventional displacement sensor. 14...Float, 16...Plunger, 18
...Coil, 20a...Through hole, 22a, 22b,
22c, 22d, 22e, 22f. 22g, 22h...Tapered surface, 24a, 24b, 24c, 24d-peak.

Claims (1)

[Claims] 1. A coil and a plunger made of a magnetic material that is movable in the thrust direction within the through-hole of the coil, and the coil or plunger is used to adjust the amount of displacement of an object to be measured such as a diaphragm or a float. In a displacement sensor that is connected to a displacement body for detecting the displacement body and measures the amount of displacement of the displacement body based on a reactance change of a coil, the plunger has an end close to the inner wall of the through hole and a tapered portion. A displacement sensor characterized by having one or more locations.