JPH02147823A - Liquid level detecting device - Google Patents

Abstract

PURPOSE:To easily detect the presence/absence of a liquid, such as an applying liquid with a simple constitution, the container of which is not restricted in material, by enclosing a detecting and heat producing elements in a casing in which the elements are dipped in a liquid. CONSTITUTION:A thermistor 73 is enclosed in a casing 74 and the surrounding area of the thermistor 73 is filled up with a filler 75 which seals the front end section of the casing 74. The surface of the filler 75 is covered with the brazed section 75a at the front end of the casing 74. Moreover, the casing 74 is charged with a synthetic resin 75b so as to cover the thermistor 73. The casing 74 is dipped in a liquid to be detected while an electric current is made to flow to the thermistor 73. When the liquid exists around the thermistor 73, the heat produced from the thermistor 73 is absorbed by the liquid and the temperature of the thermistor 73 is low, but, when the liquid level is low and no sufficient quantity of liquid exists around the thermistor 73, the temperature of the thermistor 73 rises and the resistance value of the thermistor 73 changes, because the quantity of heat radiated from the thermistor 73 becomes less. A detection circuit 76 detects a change in the resistance value of the thermistor 73 and outputs a signal indicating the lowering of the liquid level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid level detection device for detecting the presence or absence of coating agents such as primers, paints, or adhesives, and other liquids.

[Conventional technology]

Conventionally, in order to supply coating agent to coating equipment,
A system is often used in which a pressure vessel is filled with a coating agent that is conveyed using pressure gas.

In such a system, when the coating agent in the pressure vessel becomes empty, it must be replenished, and for this purpose it is necessary to detect the presence or absence of coating agent in the pressure vessel.

Conventional detection devices for this purpose include float sinch,
Alternatively, a capacitive proximity sensor is used.

(Problems to be Solved by the Invention) However, when using the flow 1 switch, there is a problem that the float, which is the movable part, becomes inoperable due to adhesion or hardening of the coating agent, resulting in frequent malfunctions. It cannot be used depending on the type of coating agent.

In addition, when detecting the liquid level of the coating agent from the outside of the container using a capacitive proximity sensor, it is convenient because there are no moving parts and there is no contact, unlike in the case of a float switch. There is a restriction that metallic materials cannot be used due to the dielectric constant of the material.

In view of the above-mentioned problems, the present invention provides a liquid level detection device that has no moving parts, has no restrictions on the material of the container, and can easily detect the presence or absence of a liquid such as a coating agent with a simple configuration. The purpose is to

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention includes a detection element whose resistance value changes depending on temperature, a heating element that generates heat,
a casing for integrally or integrally enclosing the detection element and the heating element; a filler with good thermal conductivity filled between the detection element and the heating element and the casing; and the detection element. a detection circuit for detecting a change in the resistance value of the detection element, and is configured to detect a change in the heat dissipation state due to the presence or absence of a heat liquid generated by the heating element as a change in the resistance value of the detection element.

[For production]

The detection element and the heating element are immersed in the liquid to be detected via the filling or casing.

When there is liquid around the detection element and heating element, the heat generated by the heating element is dissipated by the liquid and the temperature decreases. However, if the liquid level drops and there is no more liquid, Since the amount of heat dissipated decreases, the temperature rises and the resistance value of the detection element changes.

The detection circuit detects a change in the resistance value of the detection element, and thereby outputs a signal indicating a drop in the liquid level.

In the present invention, it is also possible to use the same element as both the detection element and the heating element. For example, it is possible to use a thermistor as an element that serves as both a detection element and a heat generating element, and to measure the voltage value across the thermistor while causing it to generate heat by passing a current through the thermistor. Note that in the present invention, the resistance value includes reactance and capacitance.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a liquid level detection device 10 according to the present invention.

The liquid level detection device IO includes a thermistor 73 and a thermistor 73.
a casing 74 for enclosing the thermistor 73; a filler 75 filled around the thermistor 73 and sealing the tip of the casing 74; a brazing portion 75a applied to cover the surface of the filler 75; It is composed of a synthetic resin Jig 75b filled so as to cover the thermistor 73, and a detection circuit 76 that applies a current to the thermistor 73 to generate heat and detects a change in its resistance value.

The thermistor 73 generates heat due to the current supplied from the detection circuit 76, and assumes a resistance value corresponding to a temperature at which the heat generation (2) and the amount of heat radiation are balanced. Therefore, the current flowing through the thermistor 73 changes depending on the amount of heat dissipated. As the thermistor 73, one having a positive or negative temperature coefficient may be used.

The casing 74 is tubular and made of a material with excellent chemical resistance, such as stainless steel or Teflon.

The filler 75 protects the thermistor 73 and maintains good heat conduction between the thermistor 73 and the outside, and is made of a material with good heat conductivity such as magnesium or copper.

The detection circuit 76 includes a power supply circuit 77, a current detection circuit 78 that detects the magnitude of the current flowing from the power supply circuit 77 to the thermistor 73, and a setting circuit 79 that sets the detection level of the current detection circuit 78. There is.

The current detection circuit 78 is configured by, for example, a Wheatstone bridge incorporating the thermistor 73 on one side,
A constant current is supplied from a power supply circuit 77 to this, the voltage across the thermistor 73 is compared with a value set by a setting circuit 79, and if the set value is exceeded, an output signal S1 is output.

Alternatively, the amount of heat generated by the thermistor 73 may be controlled to be constant by supplying constant power from the power supply circuit 77 to the thermistor 73, and the voltage value across the thermistor 73 may be measured. Furthermore, in order to improve responsiveness, current may be caused to flow intermittently through the thermistor 73 using pulse signals of a constant period.

FIG. 2 is a sectional front view of a pressure feeding device 80 using the liquid level detection device 10 of FIG. 1. This pressure-feeding device 80 is configured to force-feed the black brimer BP with air, and the liquid level detection device 10 is used to detect that the blank brimer BP in the pressure-feeding device 80 has become empty.

In FIG. 2, the brimer tank 98 is composed of a tank body 116 and M117.

The tank body 116 is constructed by integrating a bottom plate 115 and a tube 116a by screws or welding, and an opening 116b at the top of the tank body 116 is formed by a lid 117 that is secured by a clamp device 118, 118, etc. It is sealed by being removably attached.

On the bottom plate 115 is a pedestal 119 made of synthetic resin or the like.
is removably mounted on the pedestal 119, and on the pedestal 119 is a cartridge-type brimer container 127 filled with black brimer BP, with its cap removed, with the inner circumferential surface 127a of the bottom facing the pedestal. It is positioned and placed so that it fits into the outer circumferential surface 119a of the convex portion 119.

A pipe 122 connected to the brimer line L N 8 through a connector 121 and a liquid level detection sensor 99 are each attached to 1111 in a sealed manner by screw type bushes 120 and 123. This brimer tank 98 is attached to the mounting plate 3 of the coating agent supply device 3.
A is mounted on a bolt (not shown) via a mounting fitting 128.

As shown by level LVI in FIG.
The heat generated by the thermistor 73 is conducted to the black brimer BP via the filling 75, the casing 74, and the brazing part 75a, and is diffused into the black brimer BP to promote heat dissipation, so that the temperature of the thermistor 73 is The output signal S1 is kept low and is off, but the level LV2
As shown, the liquid level of Black Brimer BP is thermistor 7.
When the temperature decreases below the point 3, the heat generated by the thermistor 73 does not diffuse into the black brimer BP, so the temperature of the thermistor 73 increases, and the current change due to this is detected by the current detection circuit 78 and output. A signal S1 is output.

As a result, it is detected that the blank brimer BP in the brimer container 127 is empty.

When the blank brimer BP in the brimer container 127 is empty, the air from the air lines 1 and N6 is stopped to release the pressure in the brimer tank 98, and then the clamp device 118 is operated to remove the lid 117. New unsettled t2. filled with blank primer BP and shaken thoroughly. Brimer container 127
exchange with.

According to the embodiment described above, since the liquid level detection sensor 99 has no moving parts, there is no risk of malfunction due to fζJ adhesion or hardening of the black brimer BP. Since it is inserted into the container, there are no restrictions on the quality of the container, and since the container can be sealed, it can be applied to volatile or flammable liquids, and the structure of the liquid level detection device 10 is simple. be.

In the above-mentioned implementation number, the detection element and the heating element are combined into one
Although the thermistor 73 is used for both purposes, a heating element may be provided separately. Various resistance wires or semiconductor elements other than the thermistor 73 can be used. The casing 74 may have a sealed bottom. Various shapes, qualities, or materials of the casing 74, the filler 75, the brazing portion 75a, and other members may be adopted. . Detection circuit 76 may have various configurations other than those described above. It is applicable to the detection of various liquids other than Black Brimer BP.

〔Effect of the invention〕

According to the present invention, there are no moving parts, there are no restrictions on the material of the container, and the presence or absence of a liquid such as a coating agent can be easily detected with a simple configuration.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a diagram showing the configuration of a liquid level detection device, and FIG. 2 is a sectional front view of a pumping device using the liquid level detection device of the present invention. DESCRIPTION OF SYMBOLS 10... Liquid level detection device, 73... Thermistor (detection element 1 heating element), 74... Casing, 75...
Filler, 76...Detection circuit, BP...Black Brimer (liquid). Applicant Sunstar Giken Co., Ltd. Agent Patent Attorney Yukio Kubo

Claims (1)

[Claims] (1) A detection element whose resistance value changes depending on temperature, a heating element that generates heat, a casing for enclosing the detection element and the heating element integrally or integrally, and the detection element and the heating element. a filling having good thermal conductivity filled between the element and the casing; and a detection circuit for detecting a change in the resistance value of the detection element, and a detection circuit for detecting a change in the resistance value of the detection element; A liquid level detection device configured to detect a change in heat dissipation state due to presence or absence as a change in resistance value of the detection element.