JPH0431718A - Liquid level sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect a liquid level accurately even if the depth of electrolyte is shallow by independently providing a plurality of depth detecting electrodes in approximately parallel with a resistor film on the insulating substrate of a liquid level sensor, and setting the tips of the depth detecting electrodes at the different positions in specified depth regions from the bottom surface of the insulating substrate. CONSTITUTION:When a region wherein the impedance of electrolyte is large and measurement becomes unstable is, e.g. about 5 mm, the positions of the tips of depth detecting electrodes 50 are determined at the different depths in a depth region. Lead electrodes 52-1 - 52-11 are connected to the upper end sides of the electrodes 50 and further connected to an external processing circuit with connectors. The electrolyte is sequentially brought into contact with the tips of the electrodes 50 in conformity with standards. Therefore, the lower ends of the electrodes 50 correspond to the windows of a water repelling layer 40. As the depth of the electrode increases, the electrodes 50 sequentially come into contact with the electrolyte one by one. The depth detecting electrode 50-1 forms the reference electrode. The other depth detecting electrodes 50-2 - 50-11 output the specified liquid-level signals based on the conduction with the reference-depth detecting electrode 50-1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid level sensor, and particularly to an improvement of a liquid level sensor suitable for easily measuring changes in the liquid level of an electrolytic solution.

[Prior Art] Several liquid level sensors have been proposed for detecting the liquid level position, which makes it possible to measure the amount of liquid stored or the flow rate.

In normal cases, these liquid level sensors detect l? It consists of a structure that optically or magnetically detects the position of the floating float.

According to the conventional liquid level sensor, regardless of the type of liquid,
Although the liquid level can be detected, there is a problem in that it is relatively difficult to determine the exact position of the liquid level, and it is not possible to detect the liquid level with a simple and small sensor.

When the liquid to be measured is an electrolytic solution, a sensor that utilizes electrical continuity of the electrolytic solution can be used without using the float.

Examples of such electrolytes include electrolytes used in various chemical treatments, as well as electrolytes in which body fluids such as urine have relatively good electrical conductivity when body fluids are collected from patients in hospitals. Therefore, it is also suitable for measuring the amount of body fluid collected.

FIG. 3.4 shows an example of a conventional liquid level sensor for detecting the electrolyte level, in which a liquid level sensor 20 is attached inside a container 10 to measure the amount of body fluid collected from a patient. The condition is shown.

This liquid level sensor 20 has a pair of resistor films 24a and 24b provided vertically in parallel on an insulating substrate 22 made of plastic or the like by printing, vapor deposition, or the like.

Such resistor coatings 24a and 24b are made of carbon resistors, for example, and in the conventional example shown in the figure, the insulating substrate 2
2 is printed on.

A plurality of electrodes 26a-1 to 26a- are disposed on the resistor coatings 24a and 24b intermittently along their length.
n, and 26b-1 to 26b-m are provided by vapor deposition or the like.

These electrodes 26 are made of, for example, a thin silver film, and are arranged in a staggered manner with respect to the pair of resistor coatings 24a so as to be offset from each other.

In the embodiment, the uppermost electrodes 26a-1, 26b-1
are integrated into lead electrodes 28a and 28b, respectively, and are connected to a liquid level detection circuit via external connector terminals 30a and 30b.

On the other hand, at the lowest end of the resistor coating 24, the common electrode 3
2 connects both paper antibody coatings 24a and 24b.

Therefore, when the measurement liquid is sequentially injected into the container 10 as shown by the arrow 100, the liquid level 200 at that time changes sequentially depending on the injection amount, and at this time, the antibody coating 24a,
The electrodes 26 provided on the electrodes 24b are successively connected to each other by an electrolytic solution, and the resistance value between the lead terminals 2ga and 28b is successively decreased as the liquid level rises, thereby making it possible to electrically detect the liquid level very easily. can.

FIG. 5 shows an equivalent circuit of a conventional liquid level sensor, in which an AC signal for measurement is supplied from an AC source 32 to the sensor, and its output is supplied from an impedance conversion circuit 34 to a signal processing section 36. Then, the liquid level 200 is electrically processed and displayed by the calculation/display unit 38.

In the figure, as the liquid level 200 rises, the left and right electrodes 26 are successively and intermittently brought into conduction. A water-repellent layer is formed on the surface except for the electrode portion.

That is, the ordinary insulating substrate 22, resistor film 24, and electrode 26 are relatively easily wetted by liquid, and as a result, the liquid level 20
There is a problem in that the electrodes above the liquid level 200 become conductive during zero fluctuation or liquid scattering, which causes measurement errors.

The water repellent layer is suitable for preventing such a situation,
By providing a water-repellent layer 40 and exposing only the central part of each electrode 26 to the liquid as shown by the chain line in the figure, the water-repellent layer repels most of the water, so that the liquid surface 200 shakes or splashes are prevented. This has the advantage that even if this happens, electrical continuity is completely cut off and measurement errors do not occur.

Therefore, the liquid level sensor 20 using such a water repellent layer 40
According to Fig. 6, the resistance value output becomes a stepwise output that sequentially conducts each electrode depending on the liquid level position, that is, the water depth, and by appropriately setting the distance between the electrodes, a predetermined measurement resolution can be achieved. It becomes possible to obtain.

[Problems to be Solved by the Invention] However, in such a conventional liquid level sensor, when the depth of the electrolyte is shallow, the electrolyte impedance between the two paper antibody coatings is greater than the impedance of the resistor coating. As a result, when the amount of electrolyte is small, the measured value becomes extremely unstable and contains a large error.

In other words, if the depth of the electrolyte is sufficiently large, there is sufficient conductivity between the resistor films, but if the depth is shallow, the impedance of the electrolyte itself will affect the measured value. Therefore, the unstable measurement value described above occurs.

This characteristic is shown in Figure 7. When the electrolyte depth shown on the horizontal axis is shallow, the impedance of the electrolyte increases rapidly, and as a result, the impedance change of the resistor film becomes linear. Even so, there was a problem in that the overall impedance characteristic could not exhibit sufficient linearity in a shallow region, as shown by the chain line.

The present invention has been made in view of the above-mentioned conventional problems,
The purpose is to provide a liquid level sensor that can accurately detect the liquid level even in areas where the depth of the electrolyte is shallow, which cannot be measured conventionally.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a plurality of depth-search electrodes are independently provided on the insulating substrate of the liquid level sensor substantially parallel to the resistor coating, and It is characterized in that the tips of the deep electrodes are set at different positions within a predetermined depth region from the bottom surface of the insulating substrate.

[Function] Therefore, according to the present invention, when the electrolyte depth is shallow,
Liquid level detection is performed using depth-seeking electrodes, and the conductivity of the depth-seeking electrodes at different depths is detected at the liquid level of the electrolyte.After passing this small depth area, a resistor is detected as in a normal liquid level sensor. It is characterized by detecting the liquid level through conduction of the coating.

As described above, according to the present invention, it is possible to perform optimum liquid level detection according to the electrolyte depth, so that accurate liquid level detection is always possible for all electrolyte depths.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a preferred embodiment of the liquid level sensor according to the present invention, and the same members as those of the conventional liquid level sensor shown in FIG. .

As is clear from the figure, two parallel resistor coatings 24a
, 24b and electrodes 26a arranged intermittently thereon.
, 26b are the same as the conventional one.

A characteristic feature of the present invention is that a plurality of depth sensing electrodes 50-1 to 50-11 are provided on the insulating substrate 22 almost parallel to the parallel resistor coating 24 by printing or vapor deposition. It is.

These electrodes provide good electrical conductivity by, for example, silver electrodes, and in the present invention, their tips, that is, the ends on the bottom surface 22a side of the insulating substrate 22, extend to different depths, These are evenly arranged within a predetermined depth from the bottom surface 22a.

In the embodiment, if the region where the electrolyte impedance is large and the measurement becomes unstable is, for example, about 5 mm, the tips of the depth-search electrodes 50 are positioned at different depths within this depth region.

A lead electrode 5 is provided on the upper end side of each of the depth sensing electrodes 50.
2-1 to 52-11 are connected to each other, and are connected to an external processing circuit by a connector (not shown) in the same manner as the lead electrode 28 of the conventional resistor film.

In order to bring the electrolyte into contact with the tip of each probing electrode 50 in a controlled manner, the lower end of each probing electrode 50 corresponds to the window of the water-repellent layer 40, so that as the depth of the electrolyte increases, the probing is carried out sequentially. The deep electrodes 50 come into contact with the electrolyte one by one.

In the embodiment, the depth-seeking electrode 50-1 forms a reference electrode, and generates a predetermined liquid level detection signal by being electrically connected to the other depth-seeking electrodes 50-2 to 50-11 or the reference depth-seeking electrode 50-1. Output.

FIG. 2 shows an example of the processing circuit of this embodiment.
The CPU arithmetic circuit 60 receives the liquid level detection signal from the resistor film supplied from the terminals 62, 64 as well as the small depth detection signal from the encoder 66 as in the conventional case, switches between the two, and outputs the output terminal 68. The detection result is output to 70.

In FIG. 2, the depth sensing electrode is a reference depth sensing electrode 50-1.
forms the ground side electrode, and the other electrodes 50-2 to 50-1
1 forms the other terminal of equivalent switches SWI to 5WIO.

Therefore, as the electrolyte depth increases sequentially, SWI
This is equivalent to sequentially connecting the switches SW2, .

The encoder 66 converts the ten input terminals into four digit signals and outputs them to the CPU arithmetic circuit 60.

Therefore, according to the liquid level detection using the depth-seeking electrode 50, even when the impedance of the electrolyte is unstable or large, the encoder 66 can reliably detect the reference depth-seeking electrode 5.
It is possible to electrically detect and output the connection between 0-1 and other probing electrodes.

When the output from the encoder 66 reaches a predetermined value, for example, when the depth of the electrolyte increases to the top of a predetermined depth region, the CPU arithmetic circuit 60 inputs a signal from the encoder 66 to the conventional terminals 62 and 64. Switch to the detection signal of
Thereafter, the liquid level detection function is performed in the same manner as in the conventional case.

As described above, according to this embodiment, for example, the liquid level is detected at ten different depths at equal intervals in the area until the depth of the electrolytic solution reaches 5 mm, and thereby 0.5 mm
Accurate measurement signals can be obtained at each time, and when there is a sufficient electrolyte depth beyond this point, it is possible to detect the liquid level using a resistor film as in the past.

[Effects of the Invention] As explained above, according to the present invention, a sensor that detects the liquid level using conduction of the electrolyte can accurately detect the liquid level even when the depth of the electrolyte is small. do.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a preferred embodiment of the liquid level sensor according to the present invention, FIG. 2 is a circuit diagram showing a part of a processing circuit suitable for the liquid level sensor according to the present invention, and FIG. 3 is a conventional example. 4 is a cross-sectional view taken along line IV-IV in FIG. 3, FIG. 5 is an equivalent circuit diagram of a conventional resistive liquid level sensor, and FIG. 6 is a conventional resistive liquid level sensor with an intermittent electrode. Figure 7 is a characteristic diagram of conventional electrolyte depth and impedance. 20... Insulating substrates 24a, 24b... Resistor coatings 26a, 26b
=-electrode 50... depth-seeking electrode

Claims (1)

[Claims] A pair of resistor films are provided in parallel on an insulating substrate, electrodes are provided intermittently along the length direction of the resistor film, and the length direction of the resistor film is perpendicular to the resistor film. A liquid level sensor that detects the liquid level by immersing it in an electrolytic solution to be measured and changing the resistance value by connecting the resistor films arranged in parallel with the electrolytic solution through both electrodes, wherein: A plurality of depth-seeking electrodes are provided independently from each other substantially parallel to the resistor film, and the tips of the depth-seeking electrodes are set at successively different depths up to a predetermined distance from the bottom surface of the insulating substrate, and the liquid level on the bottom side of the substrate is a liquid level sensor characterized in that detection is performed by conduction of a depth-seeking electrode.