JPH0310888B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a roll-up liquid level measuring device equipped with a tension detector capable of detecting displacement using a Hall element.

[Prior art] One of the liquid level measuring devices that requires high accuracy is the 7th one.
There is a self-balancing retractable liquid level gauge as shown in the figure.

This liquid level gauge suspends a liquid level sensor 2 called a displacer in a tank 1 with a string-like body 3 such as a wire or tape, and detects the tension of this string-like body 3 with a tension detector 4. , if the tension is greater than the reference value, the motor 6 for the winding drum 7 is "feeding out" the string-like body.
direction, and if it is smaller than the reference value, it is driven in the same "winding" direction to keep the tension of the string body 3 constant at all times. The liquid level is measured by following the liquid level fluctuations so that it is always constant, and by the length of the string-like body.

There are various types of tension detectors for liquid level gauges, but basically it is desirable that the following conditions be satisfied.

a) Low voltage and low power consumption, without the risk of sparks, so that it can be used in tanks that store flammable liquids.

b The output at least at the reference value must be unaffected by temperature, humidity, etc. and always be constant.

c It must be highly sensitive to detect even the slightest change in tension.

d The structure is simple and the installation space is small;
Low cost.

Although some of the tension detectors currently in use do satisfy the above conditions to some extent,
However, it is still desired to develop a tension detector that can more fully satisfy the above conditions.

[Objective of the present invention] The present invention can fully satisfy the conditions a to d above by skillfully utilizing a Hall element as a displacement detection element, and in particular, the condition a is set by the Industrial Safety Research Institute of the Ministry of Labor. It has become possible to provide a roll-up type liquid level measuring device equipped with a tension detector that can fully satisfy the regulations of intrinsically safe explosion-proof construction.

[Embodiments of the present invention] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, reference numeral 10 is a tank, 11 is a displacer as a liquid level sensor, 12 is a wire as a string-like body for hanging the displacer, and a motor 15 is shown in FIG.
The wire is wound around a winding drum 16 via a pulley 13 and a pulley 14, which is rotated in forward and reverse directions.

The pulley 13 is attached to an arm 18 whose base end is supported by a bearing 17 so that it can rotate around a horizontal axis within the tank 10, and this arm 18 is supported by a spring 20 in the direction in which its free end is raised. It is given a rotational return force to form a so-called balancer.

Also, near the free end of the arm, there is a vertical rod 19 that has a magnet 21 at the upper end with the NS up and down, and the magnet of the rod is inserted into a lead pipe 22 that projects from the top of the tank 10. has been done.

In the above balancer mechanism, the arm 18 becomes horizontal when the tension of the wire 12 and the tension of the spring 20 are balanced, and when the tension of the wire 12 increases, the arm 18 rotates downward, and conversely, the tension of the wire 12 decreases. Then, the arm 18 rotates upward, and the magnet 21 at the upper end of the rod 19 rises or falls within the lead pipe 22.

A Hall element 23 is provided on the outside of the lead pipe 22. A power supply line 25 from a power source in a control circuit 24 is connected to two of the four terminals of the Hall element 23, and an output terminal is connected to the other two terminals. A signal line 26 for the winding drum 16 is connected thereto, and a signal from the control circuit 24 is input to the motor 15 for the winding drum 16.

The Hall element 23 is disposed so that its magnetic flux sensitive surface is parallel to the NS direction of the magnet 21 that moves up and down in the lead pipe, and when the displacer 11 is in a predetermined state, the center of the magnet P
The position is set so that C is at the same level as the center C of the Hall element.

In the liquid level measuring device of the embodiment described above, when the level of the liquid in the tank rises, the displacer 11
As the amount of water increases, the buoyant force acting on the displacer 11 increases, so that the displacer 1
The tension in the wire suspending 1 is reduced and the arm is rotated upward by the spring. As a result, the magnet at the upper end of the rod moves upward and is displaced upward from the reference position relative to the Hall element.

Conversely, when the level of the liquid in the tank decreases, the amount of water in the displacer 11 decreases, the buoyant force acting on the displacer 11 decreases, and the tension of the hanging wire increases due to the load of the displacer 11. The arm is then rotated downward. As a result, the magnet at the upper end of the rod moves downward and is displaced downward from the reference position with respect to the Hall element.

By the way, as shown in Figure 2, when a voltage is applied between power supply terminals A and B to generate a magnetic field, the Hall element generates a voltage between the output terminals that is proportional to the product of the magnetic flux passing through the magnetic flux sensitive surface and the supplied current. It has the property of occurring in

To explain this in more detail, when the displacer 11 has a predetermined amount of water and the center P of the magnet is above the center C of the Hall element as shown in FIG. Conversely, when the center P of the magnet is lower than the center C of the Hall element as shown in FIG. 5, the magnetic flux passes through the Hall element from the front to the back.

Further, when the center P of the magnet is at the same height as the center C of the Hall element, the magnetic flux becomes parallel to the magnetic flux sensitive surface 23a of the Hall element, and the magnetic flux passing through the magnetic flux sensitive surface becomes almost zero.

Furthermore, as can be seen from Figures 3 to 5, as the deviation between the center P of the magnet and the center C of the Hall element increases, the slope of the magnetic lines of force increases, and therefore the amount of magnetic flux passing through the magnetic flux sensitive surface of the Hall element increases. increases, the output voltage becomes high, and the output voltage E of the Hall element 23 changes approximately as shown in FIG. 6 with respect to the displacement of the magnet 21.

As can be understood from this change, the Hall element 2
3, due to the displacement of the magnet 21, an electromotive force corresponding to this displacement is generated.

In this embodiment, when the displacer 11 is on the liquid level with a predetermined level of water, the center of the magnet is at the same level as the center of the Hall element, which is the reference position, and the electromotive force of the Hall element in this state is is 0.

However, when the magnet is displaced above or below the Hall element as described above when the liquid level changes, a positive or negative electromotive force is generated in the Hall element. This electromotive force is detected and amplified by the control circuit 24, and if the voltage is positive, the motor 15 rotates in the forward direction, and if the voltage is negative, it is reversed, and the motor is controlled so that the output voltage of the Hall element is always 0. By doing this, the center P of the magnet 21 can always be at the same level as the center C of the Hall element, and thereby the displacer 11 can faithfully follow liquid level fluctuations so as to achieve a predetermined stuttering. Accurate liquid level measurements can be made.

There are various known mechanisms for measuring and indicating the liquid level, but one example is a known rotation angle detector (not shown) that measures the forward and reverse rotation angle (rotation amount) of the winding drum shaft. The angle of rotation is converted to an analog or digital liquid level value and displayed on an indicator.

As described above, according to the present invention, accurate liquid level measurement can be carried out, and in addition, the following functions and effects can be achieved.

a) The supply current required for the Hall element is very small, and many of them now operate at less than 10 mA, so the power consumption of the entire device can be reduced.

b. Since there is no need to use a differential transformer with large inductance or a large capacitor like conventional ones in the configuration of the electronic circuit, it is possible to provide a tension detector that is highly explosion-proof and complies with the aforementioned safety standards.

c When the centers of the magnet and Hall element are at the same height, the output voltage of the Hall element is physically 0, so even if the output characteristics of the Hall element change due to temperature etc., the position of the 0 output will not shift. do not have.

Therefore, in a liquid level gauge using this device,
Adjust the relative position of the magnet Hall element in advance so that the centers of the magnet and Hall element are at the same height when the tension is specified, and control the motor so that the output voltage of the Hall element is always 0. For example, even if the electrical characteristics of the Hall element change, the tension is always kept constant, making it possible to measure the liquid level with high precision.

d The output voltage of the Hall element changes as shown in Figure 6, and as mentioned in c above, the stability at the 0 point is extremely good, so even if the output voltage E is amplified by a large amplification factor, the tension cannot be controlled. It does not become unstable or inaccurate.

Therefore, it becomes technically easy to increase the tension detection sensitivity.

e Since the Hall element is extremely small in size and the detection circuit is simple, the device can be made small and lightweight. Also, the cost can be reduced.

As described above, according to the present invention, it is possible to provide a highly accurate roll-up type liquid level measuring device that is small and has high tension detection sensitivity.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the winding type liquid level measuring device according to the present invention, Fig. 2 is a diagram showing how the Hall element is used, and Figs. 3 to 5 are diagrams showing the relationship between the Hall element and the magnetic flux generated by the magnet. FIG. 6 is a diagram showing the relationship between the displacement of the magnet and the output of the Hall element, and FIG. 7 is a diagram showing the conventional liquid level measuring device. In the figure, 10... Tank, 11... Displacer, 13... Pulley, 14... Pulley, 15... Motor, 16... Winding drum, 18... Arm, 1
9... Rod, 20... Spring, 21... Magnet, 22... Lead pipe, 23... Hall element, 24... Control circuit, 25... Power supply line, 26...
…Signal line.

Claims (1)

[Claims] 1 An arm whose base end is rotatably supported on a horizontal axis, whose free end is given a rotational restoring force in the upward direction by a spring, and a pulley is attached to the horizontal axis. A liquid level measuring device comprising a balancer mechanism consisting of a balancer mechanism, and a liquid level sensing body suspension means for suspending a liquid level sensing body at the starting end from the liquid surface through a string-like body from a drum rotated forward and backward by a motor via the pulley of the arm. In the device, a magnet is provided that moves substantially linearly as the arm swings up and down, and a Hall element corresponding to the magnet is arranged so that its magnetic flux sensitive surface is substantially parallel to the direction of both poles of the magnet. In addition, the magnetic flux from the magnet is provided so that when the liquid level sensing body is at the reference position of the predetermined stuttering, the magnetic flux from the magnet is approximately parallel to the magnetic flux sensing surface of the Hall element, and the magnet is positive with respect to the reference position.
A roll-up type liquid level measuring device in which the drum is rotated in forward and reverse directions by positive and negative electromotive force of the Hall element when the drum is negatively displaced until the liquid level sensor reaches a predetermined level of water.