JP2000213978A - Liquid level detector with shield drive - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To perform high-precision liquid level detection while suppressing the influence on the liquid level detection due to the floating capacity change due to the vertical and rotational movement of the sampling arm, while being inexpensive with a simple configuration. A liquid level detection device that can be realized. A liquid is dispensed into a container of a holding unit, and the liquid level is detected by a probe. The liquid level detection device is a probe 6 in which the probe 6 is shield-dried. A shield drive is formed by an operational amplifier between the inner tube 6a and the outer tube 6b of the probe 6, and the outer tube 6b is at the same potential as the inner tube 6a without being grounded. At low impedance. Inner tube 6a and outer tube 6
Since the potential is the same as b, the capacitance between them is 0, and the capacitance when the probe 6 comes in contact with the liquid surface and the probe 6 drop when there is no change in the capacitance due to the drop of the probe 6 or the displacement of the wiring. The difference between the capacities at the time becomes the capacity between the probe 6 and the holding section 4, and stable liquid level detection becomes possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detecting device, and more particularly to an automatic analyzer in which a sample, a reagent, or a liquid as a reaction solution thereof is dispensed into a container by using a probe,
The present invention relates to a liquid level detection device that detects the liquid level of the dispensed liquid using a probe.

[0002]

2. Description of the Related Art In an automatic analyzer, a sample, a reagent, or a liquid which is a reaction solution thereof is dispensed into a container using a probe, and the level of the dispensed liquid is detected using a probe. May be used.

There are several types of liquid level detection systems in the above-described liquid level detection device. Among them, there is a capacitance type which is effective for minimizing the amount of the probe penetrating into the liquid at the time of liquid level detection. Many are used.

[0004] As a conventional capacitance type liquid level detection method,
Although it is necessary to configure a pair of electrodes for detecting the capacitance, the probe generally serves as one electrode, and at the same time, acts as a live part, and the capacitance between the probe and the grounded liquid container holding part. Is used. Then, using the capacitance between the probe and the liquid container holding unit as a detection parameter, a change in impedance is taken into the liquid level detection unit using a bridge circuit or the like, and the presence or absence of the liquid level is detected.

For example, in the device described in Japanese Patent Application Laid-Open No. Hei 6-3395, the bias current cannot be reduced to zero by a balance circuit such as a bridge circuit. The presence or absence of the liquid level is determined based on the amount of change in the volume by comparing the volume at the time of exercise.

That is, in the above-mentioned publication,
The capacitance at the time when the probe performs the downward movement is converted into impedance and stored in the sample and hold circuit in the form of a voltage. Then, using a comparator, compare the voltage stored in the sample and hold circuit with the voltage at the time of liquid contact of the probe. If the voltage at the time of liquid contact is several tens mV higher than the stored voltage, there is a liquid level. Judge.

[0007]

However, in the conventional liquid level detecting apparatus, the probe, the pattern of the liquid level detecting board, and the probe and the liquid level detecting board are connected when the sampling arm is moving up and down and rotating. Since the wiring or the like has a stray capacitance, a change in the capacitance occurs due to a displacement of the wiring, a change in the distance between the pattern on the substrate and the ground, or a vibration of a globe.

As a result, a change in the capacity occurs before the probe comes into contact with the liquid surface, and the probe stops in the air with the probe not in contact with the liquid surface, causing a liquid level detection failure. I have.

In the above-mentioned liquid level detecting device, when the sampling arm is charged by natural charging due to contact or movement of a person, the floating capacitance of the substrate pattern in the sampling arm and the floating capacitance of the wiring change. Hold voltage becomes unstable, which causes a liquid level error detection.

In the liquid level detection circuit, the capacity is balanced by a circuit such as a bridge circuit. For this reason,
Variations in elements such as resistors and capacitors used on the board and the capacitance of the probe connected to the board affect the bias voltage, and in some cases,
Liquid level detection may not be possible.

The capacitance change is regarded as noise, and a capacitance type liquid level detecting device for reducing the noise is disclosed in Japanese Patent Application Laid-Open No. Hei.
No. 340789. In this publication, a signal electrode and a compensation electrode which are coaxially arranged on a probe (liquid transfer needle) are arranged, and a shield drive is used between the signal electrode and the compensation electrode so as to prevent a voltage difference between both ends. To reduce noise.

However, in the capacitive liquid level detecting device described in the above publication, the arrangement of the coaxial electrodes is arranged on the probe, so that the production of this probe is difficult and the production cost is increased. Problem.

Here, in a balance circuit such as a bridge circuit of a liquid level detection circuit, it is very important to manage the capacity of the probe in order to achieve a good balance. The probe is made of a double inner and outer metal tube, and quality control is performed on a picofarat basis. Therefore, the yield in probe manufacturing is low and the cost is increased.

In the liquid level detecting circuit, as described above, the voltage at the time when the sampling arm is lowered is stored in the sample and hold circuit, and the stored voltage and the voltage when the probe comes into contact with the liquid level are stored. The voltage is compared with a comparator to determine the presence or absence of liquid level detection. in this way,
The incorporation of the sample and hold circuit into the liquid level detection circuit board increases the size of the board and the number of components used, thereby lowering the reliability of the entire liquid level detection device and increasing the cost.

In the liquid level detection circuit, the capacity is balanced by a circuit such as a bridge circuit. For this reason,
Variations in elements such as resistors and capacitors used on the board and variations in the capacitance of the probe connected to the board affect the bias voltage, and in some cases,
Liquid level detection may not be possible.

SUMMARY OF THE INVENTION It is an object of the present invention to suppress the influence on the liquid level detection due to the change in the floating capacitance due to the vertical and rotational movement of the sampling arm and to perform the liquid level detection with high accuracy, while having a simple configuration and being inexpensive. It is an object of the present invention to realize a liquid level detecting device capable of performing the above.

[0017]

In order to achieve the above object, the present invention is configured as follows. (1) There is a dispensing probe for dispensing a liquid such as a sample or a reagent such as blood or urine, and the dispensing probe is used to detect a liquid level of a liquid contained in a container. In a liquid level detection device that functions as a sensor and performs liquid level detection by a change in capacitance between the probe and the container holding unit when the probe comes into contact with the liquid level, the probe is used for detecting a change in capacitance. And a shield drive means for performing low impedance drive on the inner tube and the outer tube, wherein the outer tube and the inner tube of the metal double tube are not grounded and have the same potential. A liquid level detection circuit for detecting whether or not the probe has contacted the liquid level based on an output signal from the shield drive means.

(2) Preferably, in the above (1),
A rotatable arm head supporting the probe, the arm head having the liquid level detection circuit therein, and an inner layer of the arm head being shielded by metal, metal deposition, or metal paste .

(3) Preferably, in the above (1), a connection line between the probe and the liquid level detection circuit is a shield line.

(4) Preferably, in the above (1), the liquid level detection circuit has a comparison circuit for comparing an output signal from the shield drive means with a predetermined reference value.

(5) Preferably, in the above (1), the probe is shielded.

Since the outer tube of the metal double tube probe for detecting a change in capacitance is not grounded and is driven with a low impedance at the same potential as the inner tube, it is possible to prevent a change in stray capacitance due to the vertical movement of the probe. Can be.

When the liquid level detection circuit is placed inside the arm head and the inner layer of the arm head is shielded by metal or metal vapor deposition or metal paste, the floating of the substrate pattern due to the charging of the arm head, the vertical movement of the arm, etc. A change in capacity can be prevented.

When the wiring connecting the probe and the liquid level detecting circuit is a shielded wire, it is possible to prevent a change in the stray capacitance of the wiring between the liquid level detecting circuit and the probe due to the vibration caused by the vertical and rotational movements.

If the reference value voltage used in the liquid level detection is set to the steady value 0, the sample and hold circuit used for storing the reference voltage value can be omitted in the liquid level detection circuit.

If the apparent capacity is set to 0 by using a shield drive for the probe, it becomes unnecessary to manage the capacity of the probe in the production of the probe, which facilitates the production.

By using a shield drive for the probe, even if the probe is bent, the change in capacitance can be apparently reduced to zero, and the probe can be bent as long as the probe does not affect dispensing. In addition, maintenance such as probe replacement is unnecessary, and accurate liquid level detection can be maintained.

[0028]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall schematic configuration diagram of a liquid dispensing device to which a liquid level detecting device according to an embodiment of the present invention is applied, and FIG. 2 is a liquid level of the liquid level detecting device to which an embodiment of the present invention is applied. It is the schematic of a dispensing mechanism part.

First, referring to FIG.
Sampling arm 2 moves up and down and rotates. The liquid 5 as a sample is stored in the container 3 placed in the liquid container holder 4.
The liquid level of the dispensed liquid 5 is
Is detected by a liquid level detection device described later. The dispensed liquid 5 is sucked by the sampling mechanism 1 using the probe 6.

Here, the sampling arm 2 (arm head) has a liquid level detection circuit described later therein, and the inner layer of the sampling arm 2 is shielded by metal, metal deposition, or metal paste. With this configuration, it is possible to prevent a change in the stray capacitance of the substrate pattern due to charging of the arm head, vertical movement of the arm, and the like.

FIG. 3 is a diagram showing a liquid level detection circuit in the liquid dispensing apparatus shown in FIG. This liquid level detection circuit 30
Is a capacitance type. In FIG. 3, an AC signal output from an AC oscillation circuit 7 is input to a detection circuit 8 to detect a change in a capacitance value detected through a probe 6. Generally, a sine wave is used as the AC signal, but a square wave, a triangular wave, or the like may be used.

The detection circuit 8 amplifies the detected change in the capacitance in the state of the AC signal, and inputs the amplified signal to the rectification circuit 9. Then, the rectifier circuit 9 converts the input AC signal into a DC signal, and inputs the DC signal to the comparison circuit 10.

The comparison circuit 10 compares the change in capacitance before and after the change based on the input DC signal, and determines whether or not the probe 6 is in contact with the liquid surface of the liquid in the container 3, that is, the liquid surface detection. And outputs a detection signal 15 indicating the presence or absence of.

The reason why the comparison circuit 10 operates with a DC signal is that the circuit is simplified and the cost is reduced. When the amount of the sample is small, the change in capacitance is usually 10 ⁻¹² farad (1 pF) or less, and the change in output voltage corresponding to this change is several tens mV. For this reason, the fluctuation of the floating capacity may cause erroneous detection of the liquid level.

Next, referring to FIG. 1, in this liquid level detecting device, the detecting circuit 8 has an operational amplifier 20, and the non-inverting input terminal of the operational amplifier 20 is connected to the inner tube 6 a of the probe 6. Inverting input terminal is probe 6
Is connected to the outer tube 6b. And operational amplifier 2
The output terminal of 0 is connected to the inverting input terminal of the operational amplifier 20. As described above, in one embodiment of the present invention, the probe 6 is a shield drive, and the shield drive is configured by the operational amplifier between the inner tube 6a and the outer tube 6b of the probe 6, and the outer tube 6b is Without dropping to the ground (GND), the same potential as the inner tube 6a and low impedance are used.

Since the inner tube 6a and the outer tube 6b have the same potential, the capacitance between the inner tube 6a and the outer tube 6b is apparently zero. Therefore, even if the probe 6 descends,
Even if the position of the wiring is displaced, the fluctuation of the capacitance due to these is eliminated. The capacitance that has increased due to the contact of the probe 6 with the liquid surface is the capacitance between the probe 6 and the liquid holding container 3.

The connection line between the probe 6 and the liquid level detection circuit 30 is a shield line.

FIG. 4 is a diagram showing changes in the detected capacitance when the probe 6 descends, immediately before reaching the liquid level, and when the probe 6 comes into contact with the liquid level. FIG. 4A shows a situation in which the stray capacitance does not change due to the lowering of the probe 6. When the change in capacitance is larger than ΔC (capacitance C1), it is determined that there is a liquid surface, and when the change is smaller, there is no liquid surface.

The change in the capacitance shown in FIG.
The capacitance C1 is larger than ΔC (C1> ΔC), and the liquid level can be detected normally.

Next, in the case of FIG.
This is an example of the case where the floating capacitance immediately before contact with the liquid surface is increased by C4 from the time of the drop due to the drop of the liquid. In the case of the example of FIG. 4B, the capacitance change C2 when contacting the liquid surface is C2 = C1 + C4. Even at this time, the liquid level can be normally detected, but the capacitance change (C4) immediately before the probe 6 enters the liquid level is large.
The noise is added to the capacitance change C4, which becomes larger than ΔC, and the probe 6 may be stopped immediately in the air.

Next, in the case of FIG.
Is a negative capacitance change by C5. Since the capacitance immediately before the probe 6 comes into contact with the liquid surface is small, and the capacitance at the time of descent is minus, the capacitance change when the probe 6 comes into contact with the liquid surface is C3 = C1-C5.
When C3 is smaller than ΔC, the liquid level cannot be detected.

FIG. 5 shows a liquid level detection comparison circuit 10 employing a shield drive according to one embodiment of the present invention.
FIG. 6 is a diagram for comparing the configuration with the circuit of FIG. 5, and is a schematic diagram of a liquid level detection comparison circuit that does not employ a shield drive. In FIG. 6, the liquid level detection comparison circuit includes detection resistors 10A, 10B, 10C, a capacitor 10
D, an analog switch 10H, and a comparator 10E. The output voltage of the capacitance detection circuit is applied from a terminal 10F, and a liquid level detection detection signal is output from a terminal 10G.

That is, the terminal 10F is connected to the plus input terminal of the comparator 10E via the analog switch 10H.

The terminal 10F and the analog switch 10
The connection point with H is grounded via the resistors 10A and 10B. The connection point between the resistors 10A and 10B is connected to the minus input terminal of the comparator 10E via the resistor 10C. Further, the analog switch 10
H is connected to the comparator 10E by a capacitor 10E.
Grounded via D. The output terminal of the comparator 10E is connected to the terminal 10G.

The analog switch 10H is configured to open and close the contact in accordance with a stop control signal generated based on a detection signal of the lowering position of the probe 6.
0D is configured as a reference value storage unit for capacitance change,
The comparator 10E is configured as a liquid level detecting unit.

The lowering position detection signal of the probe 6 is generated when the probe 6 rotates and moves and the probe 6 enters the lowering position. When the probe 6 starts lowering, the lowering position detection signal is not output, the analog switch 10H is opened by the stop control signal, and the output voltage of the capacitance detecting circuit 8 in the same state is set as the reference voltage to the capacitor 10D. Is done. Then, the reference voltage is maintained during the discharging time of the capacitor 10D.

When the probe 6 further falls during the discharging time of the capacitor 10D and the probe 6 comes into contact with the liquid surface, the output voltage of the capacitance detecting circuit 8 increases by several tens of mV, and the voltage of the minus terminal of the comparator 10E decreases. Capacitor 10D
Higher than the reference voltage discharged from. Therefore, a signal is output from the terminal 10G as a liquid level detection signal.

On the other hand, in FIG.
0 is the detection resistance 10A, 10B, 10C, the voltage dividing resistance 10
K, 10J, and a comparator 10E.
Apply the output voltage of the capacitance detection circuit from terminal 10F,
A liquid level detection detection signal is output from the terminal 10G.

That is, the terminal 10F is grounded via the resistors 10A and 10B. The connection point between the resistors 10A and 10B is connected to the minus input terminal of the comparator 10E via the resistor 10C. Further, a connection point between the analog switch 10H and the comparator 10E is grounded via a capacitor 10D.

The plus input terminal of the comparator 10E is a connection point between the resistors 10K and 10J. A stop control signal is supplied to the resistor 10K, and the resistor 10J is grounded. The output terminal of the comparator 10E is
Connected to terminal 10G.

As shown in FIG. 5, the present invention simplifies the circuit by omitting the analog switch and the voltage holding capacitor used in the commonly used comparison circuit (the circuit shown in FIG. 6). Can be That is,
Using only the comparator 10E, the output voltage of the capacitance detection circuit is compared with the divided voltages of the resistors 10K and 10J.

Theoretically, the bias voltage of the comparison circuit is 0 V. However, in consideration of variations in elements such as resistors and capacitors, the divided voltage of the resistor 10 J has a certain margin, and is set to tens of mV. When the probe 6 is lowered and comes into contact with the liquid surface, the output voltage of the capacitance detection circuit rises by several tens mV to the terminal 10F, and the divided voltage of the resistors 10K and 10J of more than ten mV is calculated by the comparator 10E. A liquid level detection signal is output by comparing with an output voltage of the capacitance detection circuit.

According to the liquid level detection and comparison circuit 10 shown in FIG. 5, the reference value to be compared can be greatly reduced compared with the conventional circuit (the circuit of FIG. 6), so that even a very small amount of sample can be accurately detected. Detection can be performed.

When a shield drive is formed between the inner and outer layers 6a and 6b of the probe 6, the one on the liquid level detecting and comparing circuit 10 is used without using a dedicated transistor or IC for this purpose. It is also possible.

According to the embodiment of the present invention described above, by using the probe 6 as a shield drive,
It is possible to eliminate the influence on the liquid level detection due to the change in the stray capacitance of the probe wiring and the substrate pattern due to the lowering and rotating operations of the sampling arm, and at the same time, simplify the liquid level detection circuit.

According to the embodiment of the present invention, the inner tube and the outer tube of the probe 6 do not need to be coaxial with each other as long as they have the same potential. Thus, the manufacture of the probe is easy and can be realized at low cost.

Therefore, according to the embodiment of the present invention, the influence on the liquid level detection due to the change in the floating capacitance due to the vertical and rotational movements of the sampling arm is suppressed, and the liquid has a high accuracy. A liquid level detection device capable of performing surface detection can be realized.

Further, if the capacitance changes due to the bending of the probe to such an extent that does not affect the dispensing, there is no adverse effect on the liquid level detection, so that maintenance such as probe replacement is not required.

In the embodiment of the present invention described above, the liquid to be dispensed into the container 3 may be not only a sample but also a reagent, or a reaction liquid of a sample and a reagent. Is also good. Further, the liquid container holding section 4 may be not only a sample disk but also a sample rack on a line.

[0060]

According to the present invention, it is possible to prevent the fluctuation of the floating capacity due to the lowering and rotating movement of the arm head of the liquid level detecting mechanism, and it is possible to detect the liquid level more accurately even with a small amount of sample.

Further, the liquid level detection circuit can be simplified, and the reliability of the substrate can be improved. In addition, since it is not necessary to manage the capacity of the probe, the yield of production is increased and the cost of the product is reduced.

Therefore, while having a simple structure and being inexpensive, the influence on the liquid level detection due to the change in the floating capacity due to the vertical and rotational movement of the sampling arm can be suppressed, and the liquid level detection can be performed with high accuracy. The device can be realized.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of a liquid dispensing device to which a liquid level detecting device according to an embodiment of the present invention is applied.

FIG. 2 is a schematic view of a liquid dispensing mechanism of a liquid level detecting device to which an embodiment of the present invention is applied.

FIG. 3 is a diagram showing a liquid level detection circuit in the liquid dispensing apparatus shown in FIG.

FIG. 4 is a diagram showing a change in detected capacitance when a probe descends, immediately before reaching a liquid level, and when the probe comes into contact with the liquid level.

FIG. 5 does not show a liquid level detection comparison circuit employing a shield drive according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of a liquid level detection comparison circuit that does not employ a shield drive.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sampling mechanism 2 Sampling arm 3 Container 4 Liquid container holding part 5 Liquid 6 Probe 6a Inner tube 6b Outer tube 7 AC oscillation circuit 8 Detection circuit 9 Rectification circuit 10 Comparison circuit 10A Resistance 10B Resistance 10C Resistance 10E Comparator 10F terminal 10G terminal 10H Analog Switch 10J Resistance 10K Resistance 20 Operational amplifier 30 Liquid level detection circuit

Claims (5)

[Claims] 1. A dispensing probe for dispensing a liquid such as a specimen or a reagent such as blood or urine, and the dispensing probe is used to detect a liquid level of a liquid contained in a container. A liquid level detection device that functions as a surface detection sensor and performs liquid level detection by a change in capacitance between the probe and the container holder when the probe comes into contact with the liquid level. A metal double tube for detection, wherein the outer tube and the inner tube of the metal double tube are not grounded and have the same potential, and a shield drive means for performing low impedance driving of the inner tube and the outer tube; , Based on the output signal from the shield drive means,
A liquid level detection circuit for detecting whether or not the probe has contacted a liquid level; and a liquid level detection device having a shield drive. 2. A liquid level detecting device having a shield drive according to claim 1, further comprising a rotatable arm head for supporting said probe, said arm head having said liquid level detecting circuit therein. A liquid level detecting device having a shield drive, wherein an inner layer of the arm head is shielded by metal, metal deposition, or metal paste. 3. The liquid level detecting device having a shield drive according to claim 1, wherein a connection line between the probe and the liquid level detecting circuit is a shield line. 4. A liquid level detection device having a shield drive according to claim 1, wherein said liquid level detection circuit has a comparison circuit for comparing an output signal from said shield drive means with a predetermined reference value. A liquid level detection device having a shield drive. 5. A liquid level detecting device having a shield drive according to claim 1, wherein said probe is shielded.