JPH1151745A - Level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a level sensor by which the height of a liquid level or a powder level can be judged continuously and whose reliability is excellent. SOLUTION: A level sensor is constituted in such a way that at least two variable capacitors Cv1 , Cv2 which are arranged in parallel and which are composed of three or more long conductive linear or rod-shaped bodies are installed, that fixed resistances are connected respectively to the variable capacitors Cv1 , Cv2 , that integrating circuits IN1 , IN2 whose time constant is different are formed, that a clock whose frequency and duty are constant is input to the integrating circuits IN1 , IN2 , that outputs from the integrating circuits IN1 , IN2 are input to a logic IC and that the output of the logic IC is changed so as to correspond to a change in [the capacitance + the stray capacitance of the variable capacitors Cv1 , Cv2 ] due to a change in the immersion amount into a liquid or a powder of the variable capacitors Cv1 , Cv2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level sensor for detecting the level of a liquid or a particle surface.

[0002]

2. Description of the Related Art For example, there is a level sensor as shown in FIG. This sensor, as shown in FIG.
A pipe-like body 90 having a plurality of vertically arranged proximity switches 90a, and a float 91 extrapolated to the pipe-like body 90 and having a magnet 91a disposed on the inner peripheral surface side, the liquid level (water level) Float 91 magnet that moves up and down as it rises and falls
The liquid level can be determined by detecting which position of the proximity switch 90a the 91a faces.

[0003] However, the above-mentioned level sensor has the following problems. Since the liquid level is detected only when the float 91 reaches a certain position of the proximity switch 90a, the liquid level can be determined only discontinuously. Since the float 91 moves up and down with respect to the pipe 90, the liquid level cannot be detected when dust or the like is clogged between the pipe 90 and the float 91. In other words, reliability is poor because of many mechanical elements.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a level sensor which can continuously determine the height of a liquid surface or a particle surface and has excellent reliability.

[0005]

SUMMARY OF THE INVENTION A level sensor according to the present invention comprises at least two variable capacitors _C.sub.V1 , C.sub.3 composed of three or more long conductive linear members or rods arranged in parallel.
C _V2 is provided and fixed resistors are respectively connected to the variable capacitors C _V1 and C _V2 to integrate circuits IN having different time constants.
_1, IN ₂ and the formation receives the output from the integrating circuit IN _1, IN ₂ logic IC with said integrator circuit IN _1, frequency IN ₂ and duty to enter a constant clock,
Caused by漬浸amount of the liquid or granular material of the variable capacitor C _V1, C _V2 changes [variable capacitor C _V1, C
_V2 electrostatic capacitance + stray capacitance]
The output of C is changed.

Here, regarding the above level sensor,
Can be added. By changing the length of the linear member or the rod member constituting the variable capacitors C _V1 and C _V2 , it is possible to change the rate of change of the sensor output with respect to the liquid level or the particle surface height. The logic IC is an EX-OR circuit. The linear member or the rod member is covered with a resin member or a rubber member.

The function of the level sensor will be described in detail in the following embodiments of the invention.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings. (Embodiment 1) The level sensor of this embodiment is shown in FIGS.
As shown in FIG. _V1, C_V2Consisting of
The sensor main body 1 and the variable capacitor C_V1, C_V2Liquid
Caused by changing the amount of immersion
Sa C_V1, C_V2Capacitance + stray capacitance]
And an output detection circuit DK.

Hereinafter, a main configuration of the level sensor will be described. [Regarding sensor main body 1] The sensor main body 1 corresponds to FIGS.
As shown in the figure, two variable capacitors C _V1 ,
C _V2 was formed. In addition, this sensor main body 1
As shown in FIG. 3, a suction cup 2 for attaching to the fixed wall surface 80 of the container 8 is provided.

Here, when a voltage is applied to the conductive lines 1a and 1c and the conductive line 1b is connected to the ground potential, the variable capacitors C _V1 and C _V2 formed by the conductive lines 1a and 1b and the conductive lines 1b and 1c are formed. Has a capacitance, but since the dielectric constant of the part where the surrounding is air is different from the dielectric constant of the part in contact with the liquid, the capacitance of the variable capacitors C _V1 and C _V2 depends on the liquid level. The stray capacitance generated in the surroundings differs.

-Variable capacitor C_V1Capacitance: Cab_O ・ Variable capacitor C_V1The floating volume of the part where air is around
Amount: Cab₁ ・ Variable capacitor C_V1The floating volume of the part around which the liquid is liquid
Amount: Cab_Two ・ Variable capacitor C_V2Capacitance: Cbc_O ・ Variable capacitor C_V2The floating volume of the part where air is around
Quantity: Cbc₁ ・ Variable capacitor C_V2The floating volume of the part around which the liquid is liquid
Quantity: Cbc_Two Air permittivity ε₁, The dielectric constant ε of the liquid to be measured_Two(Ε₁<
ε_Two), The total capacitance generated by the conductive lines 1a and 1b is Cab_O
+ Cab₁+ Cab_TwoIs generated by the conductive wires 1b and 1c
Total capacity is Cbc_O+ Cbc₁+ Cbc_TwoBecomes Also, Ca
b₁, Cbc₁And Cab_Two, Cbc_TwoAre the conductive wires 1a, 1
Length L of b, 1c₁, L _Two(See FIG. 3). did
Therefore, the total capacity Cab = Cab_O+ Cab₁+ Cab_Two, Full capacity
Cbc = Cbc_O+ Cbc₁+ Cbc_TwoIs almost according to the liquid level
It will change linearly.[About detection circuit DK] The detection circuit DK is as shown in FIG.
And fixed resistance R₁, R_Two, R_ThreeAnd the above variable capacitor
C_V1, C_V2And an EX-OR logic IC [code IC1]
And the resistance R₁And variable capacitor C_V1By
Integrator circuit IN₁(Time constant: capacitance Cab_OX resistance R₁No
Resistance r₁) And the resistance R_TwoAnd variable capacitor C_V2By product
Branch circuit IN_Two(Time constant: capacitance Cbc_OX resistance R_TwoResistance
Value r_Two) Are respectively configured. In addition,
Fixed resistance R_ThreeIs provided to stabilize operation.
It works even if you don't.

The operation of the detection circuit DK when the liquid level in the container 8 changes will be described with reference to FIGS. Clock to P1 under the condition of fixed resistor R ₁ <fixed resistor R ₂
When CLK is input, P2 and P3 have a constant time constant Cab · r
_{According to 1} and the time constant Cbc · r ₂ , an integrated waveform as shown in the second stage from the top in FIG. 4 is obtained. The output of the EX-OR logic IC [IC1] is an output pulse P4 corresponding to the integrated waveform at points P2 and P3 as shown in the third row from the top in FIG. Here, the liquid level rises and L ₁ and L ₂ become L ₁ ′ and L ₂ ′.
(L ₁ ′ <L ₁ , L ₂ ′> L ₂ ), the above total capacities Cab, Cbc are Cab ′, Cbc ′ (Cab ′> C
ab, Cbc '> Cbc) (see FIG. 3).

[0013] Therefore, as shown in FIG. 4, P2, integrated waveform of point P3, as shown in the fourth stage from the top in FIG. 4, the time corresponding to the constant Cab '· r ₁ and the time constant Cbc' · r ₂ The duty of the output of the EX-OR logic IC [IC1] changes like P4 'shown in the fifth row from the top in FIG. If the output pulse of the EX-OR logic IC [IC1] is smoothed by a low-pass filter or the like, the output pulse corresponding to the liquid level can be handled as an analog voltage. FIG. 5 shows the detection circuit DK (r ₁ = 330 KΩ, r ₂
= 680Ω), the result of measuring the liquid level of water is shown. In FIG. 5, the output voltage is obtained by smoothing the output pulse.

As is clear from FIG.
Since the output voltage (mv) changes linearly during m, it can be sufficiently adopted as a level sensor.
Since the dielectric constant of water (approximately 80) is much higher than the dielectric constant of air (approximately 1), before and after the water surface comes into contact with the sensor body 1 composed of the conductive wires 1a, 1b, and 1c (water surface height 0 cm) However, if this range is outside the measured values, there is no problem at all. Further, this level sensor is a sensor
And the detection circuit DK, the cost is very low, and since there is no mechanically operating portion, the reliability is excellent. Further, since this level sensor employs the sensor main body 1 of FIG. 1 and the detection circuit DK of FIG. 2, measurement can be performed with a certain degree of accuracy even when the level of the highly viscous liquid drops.

When the liquid level drops, the state in which the liquid remains adhered around the sensor main body 1 continues for a long time as shown in FIG. to become slightly larger than the total volume of the original variable capacitor C _V1, C _V2 at full capacity both liquid level of the variable capacitor C _V1, C _V2 which are, as shown in the second stage from the top in FIG. 7 P2 , P3 become waveforms P2 +, P3 + having slightly larger time constants than the original. However, since the increase in the time constant is almost the same, as shown in the third and fourth rows from the top in FIG.
The duty of the output of [IC1] does not appear as a large fluctuation, and the phase of the clock slightly shifts. Therefore, the fluctuation of the voltage obtained by converting the output at the point P4 into an analog signal by the low-pass filter is small. This is because the EX-OR logic IC [IC1] works so as to cancel (differential) errors due to liquid components remaining on the sensor main body 1. (Embodiment 2) In the level sensor of this embodiment, as shown in FIG. 8, the lower end of the conductive line 1a is set 24 cm above the lower ends of the other conductive lines 1b and 1c. That is,
The conductive line 1a is set 24 cm shorter than the other conductive lines 1b and 1c. As the detection circuit DK, the same one as in the first embodiment is employed.

With this level sensor, as the liquid level of water is raised, the output increases until the liquid level reaches 24 cm, as shown in FIG. 9, but the liquid level rises to 24 cm. The output decreases from the point when it has passed. Therefore, in the case of a system in which the liquid level is set to a constant level, a level sensor of this type may be used to stop the liquid when the output decreases.

The 0 cm point of the liquid level in FIG. 9 is the lower end position of the conductive wires 1b and 1c. (Regarding Another Embodiment of Sensor Main Body 1) The sensor main body 1 shown in FIG. 10 is configured such that the conductive wires 1a, 1b, and 1c are connected to one another.
Two variable capacitors C _V1 and C _V2 are formed by disposing them in parallel at intervals of 20 ° and coating them with a synthetic resin 10. The sensor main body 1 shown in FIG. 11 includes conductive wires 1a and 1b and a conductive tube 1d surrounding the conductive wires 1a and 1b. The conductive tube 1d is filled with a synthetic resin 10. In this device, a voltage is applied to the conductive wires 1a and 1b, the conductive tube 1d is connected to the ground potential, and two variable capacitors are formed by the electric wire 1a and the conductive tube 1d, and the electric wire 1b and the conductive tube 1d. It is formed. In the sensor main body 1 of the first and second embodiments, three conductive wires 1
Although the sensor main body is constituted by a, 1b, and 1c, the sensor main body 1 may be constituted by four or more conductive wires.

Note that the conductive wire constituting the variable capacitor can be replaced with a conductive rod. (Other Embodiments of Detection Circuit DK) First Embodiment
The same operation and effect can be obtained by using the detection circuit DK shown in FIG. 12 instead of the detection circuit DK.

In the figure, symbols U1 and U2 are inverter ICs (open collector output), symbols R ₄ and R ₅ are resistors, symbol I
C2 indicates an EX-OR logic IC. (Regarding liquids targeted by this level sensor) Examples of liquids targeted by this level sensor include water, alcohol, petroleum, seawater, edible oil and the like.

Further, this level sensor can be used as a powdery material (powder,
Granules or a mixture thereof) can also be detected.
In the case of a granular material, it is preferable to form a variable capacitor with a conductive rod in consideration of the powder pressure and the like.

[0021]

Since the configuration of the present invention is as described above, the following effects can be obtained.

As is clear from the description of the means for solving the problems, it was possible to provide a level sensor that can continuously determine the height of the liquid surface or the particle surface and has excellent reliability.

[Brief description of the drawings]

FIG. 1 is a perspective view of a sensor main body of a level sensor according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a detection circuit of the level sensor.

FIG. 3 is a sectional view showing a state where the sensor main body is attached to a fixed wall surface of a container.

FIG. 4 is an explanatory diagram showing a relationship between an input clock, an output clock, and the like when the detection circuit is used.

FIG. 5 is a graph showing the relationship between the output of the level sensor and the water surface height.

FIG. 6 is a cross-sectional view showing a state in which the liquid remains on the outer peripheral surface of the sensor main body when the liquid in the container is drained and the liquid level is lowered.

FIG. 7 is an explanatory diagram showing a relationship between an integrated waveform at points P2 and P3 and a clock on the output side when the liquid in the container is drained and the liquid level is lowered.

FIG. 8 is a cross-sectional view showing a state in which the sensor main body of the level sensor according to Embodiment 2 of the present invention is attached to a fixed wall surface of a container.

FIG. 9 is a graph showing the relationship between output and water level in the level sensor according to the second embodiment.

FIG. 10 is a perspective view of a main part of a sensor main body according to another embodiment.

FIG. 11 is a perspective view of a main part of a sensor main body in another embodiment.

FIG. 12 is an explanatory diagram of a detection circuit according to another embodiment.

FIG. 13 is an explanatory diagram of a level sensor according to the prior art.

[Explanation of symbols]

C _V1 variable capacitor C _V2 variable capacitor R ₁ resistor R ₂ resistor IN ₁ integration circuit IN ₂ integration circuit IC1 EX-OR logic IC

Claims (4)

[Claims] 1. Three or more long conductive members arranged in parallel
At least two variable conditioners consisting of linear or rod-like objects
Sensor (C_V1) (C_V2) And the variable condenser
Sa (C_V1) (C_V2Connect a fixed resistor to each
Integrators with different numbers (IN₁) (IN_Two) Forming the
Integrator (IN₁) (IN_Two) Frequency and duty
A fixed clock is input and the integration circuit (IN₁)
(IN_Two) Is input to the logic IC, and the variable
Densa (C_V1) (C_V2) Of liquid or powder
[Variable capacitor (C_V1)
(C _V2) Of the capacitance + stray capacitance]
The output of the IC is changed
Liquid level sensor. 2. A ratio of a change in sensor output with respect to a liquid surface or a particle surface height is changed by changing a length of a linear body or a rod body constituting the variable capacitors (C _V1 ) and (C _V2 ). 2. The method according to claim 1, wherein
The level sensor as described. 3. The level sensor according to claim 1, wherein the logic IC is an EX-OR circuit. 4. The level sensor according to claim 1, wherein the linear member or the rod member is covered with a resin member or a rubber member.