JP2000180245A - Liquid level detecting probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the output to be a fixed value and correctly detect a liquid level by coating fixed length from the tip of a liquid level detecting probe with an insulating film so as to keep insulation after the probe penetrates through a film until it contacts with a sample liquid level. SOLUTION: At the moment when a liquid level detecting probe 2 contacts with a film 8, it the film 8 is conductive, the probe 2 and the film 8 are in a conductive state, and change due to the contact appears in the output of an electrostatic capacity detecting circuit. When the probe 2 pierces through the film 8, the change disappears, and it returns to a signal in the non-conductive state. When the probe 2 contacts with the liquid level, change due to the contact with liquid appears in the output of the detecting circuit, and contact with liquid can be detected by a liquid level circuit. Even when an insulating film 22 is coated only on the way part of a metallic tube 21, after the probe 2 penetrates through the film, by contacting the film 22 with the film 8, it returns to the signal in the non-conductive state, and when the probe 2 contacts with liquid level, the output of the detecting circuit largely changes. In this way, insulation is kept up to contact with liquid, change of the detected signal at contacting with liquid becomes large, and hence it can be correctly detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detection probe used for sucking a sample in a container.

[0002]

2. Description of the Related Art In order to detect the liquid level of a sample, a mechanism for detecting a change in the capacitance of the liquid level detection probe using a nozzle itself as a liquid level detection probe has been used (Japanese Patent Application Laid-Open No. Hei 1-1990).
No. 178826). According to this configuration, the pipe for sucking the sample is used as a liquid level detection probe, and the output corresponding to the capacitance of the liquid level detection probe in a state not in contact with the sample liquid level is stored as a reference value. The output of the liquid level detection probe is taken into a comparison arithmetic unit and compared.

In a circuit configuration in which the output increases as the capacitance increases, when the output of the liquid level detecting probe exceeds a reference value, it is determined that the probe has come into contact with the sample liquid level, and a detection signal is output. . With a circuit configuration in which the output decreases as the capacitance increases, when the output of the liquid level detection probe falls below a reference value, it is determined that the sample has come into contact with the sample liquid level, and a detection signal is output.

[0004]

In some cases, a sample container is sealed with a conductive film such as an aluminum foil for preventing evaporation. In this case, since the conductive film is erroneously detected as the sample liquid surface and an output is output, the sample liquid surface may not be accurately detected. In addition to the conductive film, even if the film is sealed with a resin film such as polyethylene, it is erroneously detected that the inside of the film is wet with the sample and adheres to the liquid level detection probe and reaches the liquid level. May be.

As one solution, it is conceivable to use the output of the liquid level detection probe after the liquid level detection probe has penetrated the film and before contact with the sample liquid level as a reference value.
The difference between this reference value and the detection signal when it comes into contact with the sample liquid surface is very small. For this reason, even if the reference value is intended to be stored, the reference value itself cannot be distinguished from the output when it comes into contact with the sample liquid surface, and the possibility of erroneously detecting the sample liquid surface remains.

Accordingly, an object of the present invention is to provide a liquid level detection probe capable of accurately detecting a liquid level of a sample even when the sample container is sealed with a film for preventing evaporation.

[0007]

According to the liquid level detecting probe of the present invention, the liquid level detecting probe has the shape of a tube, and is coated with an insulating film from the tip of the tube to a certain length. (Claim 1). The location of the coating may be in the middle of the tube (claim 2).

According to these configurations, the moment the liquid level detection probe breaks the film, even if the capacitance temporarily decreases, the liquid level detection probe penetrates through the film and then comes into contact with the sample liquid level. Since the insulation is maintained up to this point, the output of the liquid level detection probe maintains a constant value. Therefore, a change in the detection signal when the sample liquid surface comes into contact with the sample liquid surface becomes large, and the sample liquid surface can be accurately detected.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a circuit configuration diagram of a liquid level detection device to which a liquid level detection probe is applied. The liquid level detecting device is provided in accordance with a mounting table 1 (working as a ground electrode) of the sample container 7, a liquid level detecting probe 2 arranged to be insertable into the sample container 7, and a capacitance of the liquid level detecting probe 2. A capacitance detection circuit 4 for outputting an AC output signal having a variable amplitude; and a liquid level detection circuit 6. 3 is a suction device.

FIG. 2 is a perspective view of the tip of the liquid level detection probe 2, and FIG. 3 is a sectional view of the tip of the liquid level detection probe 2. The liquid level detection probe 2 includes a metal tube 21 and is coated with an insulating film 22 from the tip of the metal tube 21 to a certain length. The composition of the insulating film 22 is not particularly limited, and for example, a silicon resin, a Teflon resin, or the like can be used. In addition, any method such as drying after application, vacuum evaporation, and sputtering can be adopted as the coating method.

FIG. 4A shows a state immediately before the liquid level detection probe 2 is inserted into the sample container 7 whose mouth is covered with the film 8, and FIG. FIG. 4 (c) shows a state before reaching the liquid level, and FIG. 4 (c) shows a state before reaching the liquid level. At the moment when the liquid level detection probe 2 in FIG. 4A comes into contact with the film 8, if the film 8 is conductive, the liquid level detection probe 2 and the film 8 conduct, and the output of the capacitance detection circuit 4 is in contact. Changes appear. Even if the film 8 is not conductive, the liquid level detection probe 2 touches a water droplet on the inner surface of the film 8 and a change in the output of the capacitance detection circuit 4 appears. This change is shown at time A in FIG. However, when the liquid level detection probe 2 breaks through the film 8, the change disappears, and the signal returns to the non-conductive state as shown at the time point B in FIG. When the liquid level detection probe 2 reaches the liquid level, the output of the capacitance detection circuit 4 shows a change b due to the liquid contact as shown at a time point C in FIG. The change due to the liquid contact is larger than the change b at the time point A in FIG.
Can be detected without overlooking the contact.

Here, when the liquid level detection probe is not coated with a film as in the prior art, the capacitance detection circuit 4
The change of the output will be described. FIG. 6 (a) shows the film 8
6 (b) shows a state before the liquid level detection probe 9 without a coating is inserted into the sample container 7 covered with the filter, FIG. 6 (b) shows a state where the liquid level detection probe 9 is in contact with the film 8, and FIG. FIG. 6D shows a state before the liquid level detection probe 9 has penetrated the film 8 and reached the liquid level, and FIG.

At the moment when the liquid level detection probe 9 contacts the film 8, the output of the capacitance detection circuit 4 changes due to the contact. This change is shown at time A in FIG. Even if the liquid level detection probe 9 breaks through the film 8, the change remains without disappearing as shown at the time point B in FIG. When the liquid level detection probe 9 reaches the liquid level, the output of the capacitance detection circuit 4 shows a change a due to the liquid contact as shown at time point C in FIG. Although the change a due to the liquid contact is larger than the change at the time point B in FIG. 7, it is smaller than the change b shown at the time point C in FIG. However, there is a risk that the liquid may be erroneously detected as being in contact with the liquid.

The embodiment of the present invention is not limited to the above-described embodiment. For example, as shown in FIG. 8, an insulating film 22 may be coated only on an intermediate portion of a metal tube 21. Also in this case, after the liquid level detection probe 2 breaks through the film 8, when the insulating film 22 comes into contact with the film 8, the signal returns to the non-conductive state, and when the liquid level detection probe 2 reaches the liquid level, the capacitance detection circuit The output of 4 shows a large change due to liquid contact.

[0015]

As described above, according to the liquid level detecting probe of the present invention, the insulation is maintained until the liquid level detecting probe penetrates the film and comes into contact with the sample liquid level. The change of the detection signal at the time of the detection becomes large, and the sample liquid level can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a liquid level detection device.

FIG. 2 is a perspective view of a distal end portion of the liquid level detection probe 2.

FIG. 3 is a sectional view of a distal end portion of the liquid level detection probe 2.

4A and 4B are diagrams for explaining a use state of the liquid level detection probe 2. FIG. 4A shows a sample container 7 whose mouth is covered with a film 8. FIG.
4B shows a state immediately before the liquid level detection probe 2 is inserted, FIG. 4B shows a state before the liquid level detection probe 2 penetrates the film 8 and reaches the liquid level, and FIG. Indicates the state of arrival.

FIG. 5 is a graph showing a change in output of the capacitance detection circuit 4 when the liquid level detection probe 2 is used.

6A and 6B are views for explaining a use state of a conventional liquid level detection probe 9; FIG. 6A shows a state before inserting an uncoated liquid level detection probe 9 into a sample container 7 whose mouth is covered with a film 8; 6 (b) shows a state in which the liquid level detection probe 9 is in contact with the film 8, and FIG. 6 (c) shows a state in which the liquid level detection probe 9 has penetrated the film 8 and has not yet reached the liquid level. FIG. 6D shows a state where the liquid has reached the liquid level.

FIG. 7 is a graph showing a change in output of the capacitance detection circuit 4 when the conventional liquid level detection probe 9 is used.

FIG. 8 is a view for explaining another embodiment of the present invention in which the insulating coating 22 is coated only on the middle part of the metal tube 21.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Installation stand 2 Liquid level detection probe 3 Suction unit 4 Capacitance detection circuit 6 Liquid level detection circuit 7 Sample container 8 Film 21 Metal tube 22 Insulation coating

Claims (2)

[Claims] 1. A ground electrode for grounding a sample container, a liquid level detection probe disposed so as to be inserted into the sample container, and a static electrode for outputting an AC output signal having an amplitude corresponding to the capacitance of the liquid level detection probe. A liquid level detection probe used in a liquid level detection device having capacitance detection means, wherein the liquid level detection probe has the shape of a tube, and has an insulating coating from the tip of the tube to a certain length. A liquid level detection probe characterized by being coated with: 2. A ground electrode for grounding a sample container, a liquid level detection probe insertably inserted into the sample container, and a static electricity output signal having an amplitude corresponding to the capacitance of the liquid level detection probe. A liquid level detection probe used in a liquid level detection device including a capacitance detection means, wherein the liquid level detection probe has a tube shape, and an intermediate portion of the tube is coated with an insulating film. A liquid level detection probe, comprising: