JP3064487B2 - Liquid level detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analyzer for detecting a liquid level of a liquid in an analyzer using a liquid such as a specimen or a reagent for a clinical test.

[0002]

2. Description of the Related Art In an automatic biochemical analyzer, as a device for detecting the level of a test solution such as plasma and blood cells in a test solution container, as disclosed in Japanese Utility Model Laid-Open No. 54-19790, There is one that detects the liquid level using the conductivity of a test solution. That is, when a pair of liquid level detecting needles (electrodes) interlocked with the test liquid sampling probe are inserted into the test liquid container and lowered together with the probe toward the test liquid surface, when these come into contact with the liquid surface, The pair of liquid level detection needles is electrically connected by the conductivity of the test solution. The level of the test liquid can be detected by detecting the electrical conduction.

It is also known to form one of a pair of liquid level detecting needles as a probe by forming the probe from a conductive material such as stainless steel. In this case, only one liquid level detecting needle other than the probe is required.

[0004]

However, since the former uses two needles, handling is extremely dangerous. On the other hand, the latter requires only one liquid level detecting needle other than the probe.
Although it is a book only, although handling is safe, a conductive material having high conductivity must be used as a material of the probe, and the probe itself becomes expensive. Especially in blood tests such as immunoassays, contamination of the sample blood adversely affects the test data, so the probe is usually discarded after one use, and the use of expensive probes is uneconomical. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the risk of handling and to detect the liquid level with high accuracy without requiring an expensive probe. It is to provide a liquid level detecting device.

[0006]

In order to solve the above-mentioned problems, a liquid level detecting apparatus according to the present invention comprises a container for containing a liquid whose liquid level is to be detected, and a ground electrode provided near the container. A liquid level detecting needle inserted into the container and moved up and down relatively to the liquid level of the liquid; a signal oscillating means for oscillating an electric signal; and the liquid level detecting needle and the liquid level are non-contact. The capacitance value in the case of contact is set so that sensitivity is increased at the frequency of the electric signal, and the electric signal is set according to the capacitance value between the liquid level detection needle and the ground electrode. A differentiating circuit for differentiating and outputting an output value according to the differentiated value;
Detecting means for detecting the liquid level based on the output value of the differentiating circuit.

[0007]

According to the above arrangement, the capacitance between the liquid level detecting needle and the ground electrode changes depending on whether the liquid level detecting needle is in contact with the liquid level or not. If the sensitivity to the input signal frequency of the differentiating circuit is set to be higher at the frequency of the electric signal of the signal oscillating means in the non-contact state between the liquid level detection needle and the liquid level, the liquid level detection needle In the state of contact with the liquid surface, the sensitivity of the input signal frequency of the differentiating circuit decreases. As the sensitivity decreases, the output value of the differentiating circuit also changes. Therefore, the liquid level can be detected by detecting a change in the output value of the differentiating circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the liquid level detecting device of the present invention is applied to an automatic biochemical analyzer will be described below.

FIG. 1 shows a first embodiment of the present invention. In the figure, the lifting arm 1 is moved up and down by a lifting drive mechanism (not shown) in the vertical direction indicated by the arrow Z while supporting the probe 2 and the liquid level detecting needle 3. When the lifting arm 1 is lowered, the probe 2 and the liquid level detecting needle 3 are inserted into a test solution container 4 disposed below the probe 2 and the probe 2 is moved to the container 4.
The test solution 4a inside is sucked and collected. Here, the probe 2 and the liquid level detecting needle 3 are immersed in the test liquid 4a so that the probe 2 can collect the test liquid 4a in the container 4, and the tip 3a of the liquid level detecting needle 3 is It is arranged so as to be in contact with the liquid level 4b of 4a. When the sampling of the test solution 4 a is completed, the probe 2 and the liquid level detecting needle 3 are raised again by the raising of the lifting arm 1. The liquid level detecting needle 3 is made of a conductive material,
The material of the probe 2 is arbitrary. A grounded metal plate 5 is arranged near the container 4. Oscillation circuit 6
The signal oscillated from is input to the differentiating circuit 13.

The differentiating circuit 13 includes resistors 7 and 8, capacitors 9 and 10, and an operational amplifier 11, and is adjusted so that the input sensitivity increases at the frequency of the oscillation circuit 6.
The liquid level detecting needle 3 is connected to a positive input terminal of the differentiating circuit 13 via a lead wire. Further, the positive input terminal of the differentiating circuit 13, the oscillation circuit 6, and the metal plate 5 are connected through an earth line. A voltage detection circuit 14 is connected to an output terminal of the differentiating circuit 13.

The signal from the oscillating circuit 6 is differentiated by a differentiating circuit 13 according to the capacitance value between the liquid level detecting needle 3 and the metal plate 5 and output to a voltage detecting circuit 14. The capacitance value changes between a case where the liquid level detecting needle 3 and the test solution 4a in the test solution container 4 are not in contact with each other and a case where they are in contact with each other. Here, the differentiating circuit 13 is adjusted so that the sensitivity is increased at the frequency of the oscillator 6 by the capacitance value at the time of non-contact.

Next, the operation of the above-described liquid level detecting device will be described with reference to FIGS. 1 and 2 (A) to 2 (D). When the liquid level detecting needle 3 and the test solution 4a in the test solution container 4 are in a non-contact state and a contact state, the capacitance value between them changes. For this reason, as shown in FIG. 2A, the differentiating circuit 13 adjusted so that the sensitivity is increased at the frequency of the oscillation circuit 6 by the capacitance value in the non-contact state is not shown in the capacitance value in the contact state. The sensitivity is reduced as shown in FIG. Therefore, when the signal of the oscillation circuit 6 is a sine wave, FIG.
The output voltage V _{out at the} capacitance value in the non-contact state as shown in FIG. 2C is different from the output voltage V _{out at the} capacitance value in the contact state as shown in FIG.
The output voltage changes to a small output voltage as shown in FIG. Therefore, by detecting the output of the differentiating circuit 13 with the voltage detecting circuit 14, it is possible to determine whether the contact state is a non-contact state or a contact state according to the detected value, and the liquid level 4b can be detected.

In the above embodiment, the signal oscillated by the oscillation circuit 6 is a sine wave, but may be a rectangular wave. Also in this case, the output waveform of the differentiating circuit 13 changes in amplitude between the contact state and the non-contact state between the liquid level detecting needle tip 3a and the test liquid level, and the liquid level 4b can be detected by this change. The metal plate (ground electrode) 5 is for reducing the influence of the surroundings of the liquid level detecting device on the differentiating circuit 13. It goes without saying that the ground electrode can be omitted if the surrounding environment is stable.

In the above embodiment, the voltage detection circuit 14
, The change in the output voltage V _out of the differentiating circuit 13 is detected, but the same effect as in the above embodiment can be obtained even if the change in the phase is detected. Also, in FIG. 1, the one shown in FIG. 1 is used as a differentiating circuit because a peak can be set in a high frequency characteristic of the differentiating circuit 13 due to the capacitance of the capacitors 9 and 10 and the liquid level detecting needle. However, other various known differentiating circuits may be employed.

[0015]

As described above, according to the liquid level detecting device of the present invention, the liquid level can be reliably detected even though only one liquid level detecting electrode is used. Also, handling is safer than in the case of using two liquid level detecting electrodes as in the related art.

Further, since only one liquid level detecting electrode is to be brought into contact with the liquid level for detecting the liquid level, when the liquid level detecting apparatus of the present invention is combined with, for example, a probe, the material of the probe is required. Regardless. Further, when a conductive probe such as a metal is used, the probe itself can be used as a liquid level detection electrode by applying an electric signal to the probe.

[Brief description of the drawings]

FIG. 1 is a configuration diagram schematically showing an overall configuration of a liquid level detection device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an output waveform of a differentiating circuit corresponding to a frequency characteristic.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lift arm, 3 ... Liquid level detection needle, 4 ... Container, 4a ... Test liquid (liquid), 4b ... Liquid level, 5 ... Metal plate (ground electrode), 6
... Oscillation circuit (oscillation means), 13... Differentiation circuit, 14... Voltage detection circuit (determination means).

Claims (1)

(57) [Claims] 1. A liquid level detection device for detecting the liquid level of a liquid contained in a container using capacitance, comprising: a container for containing a liquid whose liquid level is to be detected; A liquid level detection electrode for contacting the liquid level; a signal oscillating means for oscillating an electric signal; and a capacitance value when the liquid level detection electrode is not in contact with the liquid level. A differentiator that is set so that the sensitivity becomes higher at the frequency of the electric signal, differentiates the electric signal according to a capacitance value related to the liquid level detection electrode, and outputs an output value according to the differential value. A liquid level detection device comprising: a circuit; and a determination unit that determines whether or not the liquid level is present based on an output value of the differentiation circuit.