JP2001004642A - Liquid level detection mechanism having bias voltage in shield drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an arm head in a liquid level detection mechanism from lowering and fluctuation in a floating capacity due to rotational motion so as to detect a liquid level more precisely even in a minute amount of a sample by forming the same potential low impedance drive in an outer tube as that of an inner tube without dropping the outer tube to the ground. SOLUTION: In a case of a liquid level detection mechanism, for example, wherein a probe is used as a shield drive 20, bias power is applied to an input signal by using an adding circuit 40 and a transolver circuit is included, a shield drive is constructed of an operational amplifier between a probe inner tube and a probe outer tube constructed coaxially with each other, and a low impedance is accomplished at the same potential as that of the inner tube without dropping the outer tube to the ground. Apparently, an electrostatic capacity between the inner tube and the outer tube becomes zero. Even if the probe is lowered or a wiring position is shifted, no fluctuation is caused in electrostatic capacity. An electrostatic capacity increased by the contact of probe with a liquid surface is that between the probe and the liquid carrying container. The adding circuit 40 uses an operational amplification adding circuit and the like. The transolver protects an IC in a base board from noise or electrostatic discharge from the probe.

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 mechanism, and more particularly to an automatic analyzer, in which a sample, a reagent or a liquid as a reaction liquid thereof is dispensed into a container using a probe, and the dispensed liquid is dispensed. The present invention relates to a liquid level detection mechanism that detects a surface using the 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 the probe. A liquid level detection mechanism of a type may be used.

[0003] There are several types of liquid level detection methods, and a capacitance type effective for minimizing the amount of probe penetrating into the liquid at the time of liquid level detection is often used.

In the conventional capacitance type liquid level detection method, it is necessary to form a pair of electrodes for generating capacitance. In general, a probe is used as one electrode and simultaneously as a live part, and is grounded. A method of detecting the capacitance between the liquid container holding unit and the liquid container holding unit is used. 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.

In Japanese Patent Application Laid-Open No. Hei 6-3395, since the bias voltage cannot be reduced to 0 by a balance circuit such as a bridge circuit, the capacitance at the time of contact with the liquid surface is compared with the capacitance at the time when the probe moves downward. Then, the presence or absence of a liquid level is determined based on the amount of change in capacity. The circuit converts the capacitance at the time when the probe performs the downward movement into impedance, and stores it in the form of a voltage in the sample and hold circuit. Then, using a comparator, the stored voltage is compared with the voltage at the time of liquid surface contact, and the voltage at the time of liquid surface contact is several tens of meters from the stored voltage.
If V is high, it is determined that there is a liquid level.

[0006]

In the current liquid level detecting mechanism, when the sampling arm is moving up and down and rotating, the probe, the pattern of the liquid level detecting board, the wiring connecting the probe and the liquid level detecting board, etc. Because of the stray capacitance, a change in capacitance occurs due to wiring displacement, a change in the distance between the substrate pattern and the ground, and vibration of the globe. As a result, a change in the capacitance occurs before the liquid comes into contact with the liquid surface, which causes the probe to stop in the air and to be unable to detect the liquid surface.

In the above liquid level detection mechanism, if noise or electrostatic discharge enters through a probe during maintenance, the IC on the substrate may be broken.

In the above liquid level detection mechanism, when the sampling arm is charged by natural charging such as contact or movement of a person, the capacitance of the substrate pattern in the sampling arm and the wiring changes, and the reference hold voltage becomes unstable. , Causing false detection. In a balance circuit such as a bridge circuit of a detection circuit of a liquid level detection circuit, the capacity management of the probe is very important for achieving a good balance. The probe is made of double inner and outer metal tubes, and the quality is controlled in p-farat units.
Yields are getting worse and costs are rising.

In the liquid level detecting board, a circuit for storing the voltage at the time when the sampling arm is lowered is stored in the sample and hold circuit, and the voltage at the time of contact with the liquid level is compared with a comparator to determine whether the liquid level is detected. Judge. By incorporating the sample-and-hold circuit into Kiban, the size of the substrate and the number of components used increase, so that the reliability of the entire apparatus decreases and the cost increases.

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 substrate and variations in capacitance of a probe connected to the substrate affect the bias voltage. In some cases, this variation may make it impossible to detect the liquid level.

An object of the present invention is to eliminate the influence on the liquid level detection due to a change in stray capacitance due to the vertical and rotational movements of the sampling arm, protect the IC on the substrate from external noise and electrostatic discharge via the probe, and detect the liquid level. An object of the present invention is to provide an automatic analyzer that can simplify a circuit.

[0012]

In order to achieve the purpose of preventing the stray capacitance from being changed by the probe of the capacitance change detecting metal double tube due to the vertical movement of the arm, etc., the outer tube must be dropped to GND without dropping it to GND. This is a low impedance drive with the same potential as the tube.

In order to achieve the purpose of preventing the destruction of the IC on the substrate due to noise or electrostatic discharge through the probe, a bias voltage is applied to the input circuit signal of the liquid level detection circuit, and a transorb circuit is introduced as a protection circuit. is there.

In order to achieve the purpose of preventing the change of the floating capacitance of the substrate pattern due to the charging of the arm head, the vertical movement of the arm, etc., the substrate is placed inside the arm head and metal or metal is deposited on the inner layer side of the arm head. The shield drive is composed of metal plague.

In order to achieve the purpose of preventing the stray capacitance of the wiring between the substrate and the probe from being changed by vibrations caused by vertical and rotational movements, the wiring connecting the probe to the substrate is a shield line.

In order to achieve the object of not increasing the number of parts to be used when the probe is used as a shield drive, it is necessary to use a transistor or an IC used in the shield drive without using a dedicated one. It is a thing that uses the thing of.

In order to achieve the purpose of reducing the size of the substrate by reducing the number of components used on the substrate, the reference value voltage used for liquid level detection is set to a steady value of 0, and the sample and hold circuit that uses the reference voltage value for storage is stopped. That's what I did.

In order to achieve the purpose of reducing the size of the substrate by reducing the number of components used on the substrate, a bias voltage is applied to the input signal used for liquid level detection, and the circuits thereafter can be realized with a single power supply. The connector is omitted.

In order to achieve the purpose of eliminating the need for managing the capacitance of the probe in the production of the probe, the probe is made to be a shield drive so that the capacitance is apparently regarded as zero on the balance circuit. It was made.

Even if the probe has a bend that does not affect dispensing, in order to achieve the purpose of requiring no maintenance such as replacement of the probe, it is necessary to use a shield drive for the probe so that electrostatic bending due to the bend of the probe can be achieved. The change in capacitance is set to 0 apparently.

By applying a bias voltage to the input circuit signal of the liquid level detection circuit, it is possible to introduce a protection circuit such as a transorb, and to prevent the destruction of the IC on the substrate due to noise through the probe or electrostatic discharge.

When the outer tube of the metal double tube probe for detecting a change in capacitance is driven to the same potential and low impedance as the inner tube without dropping it to GND, the change in stray capacitance due to the vertical movement of the arm, etc. is prevented. Can be.

When a liquid level detection substrate is placed inside the arm head and a shield drive is formed by metal or metal deposition or metal plaster on the inner layer side of the arm head, the substrate pattern due to arm head charging, arm vertical movement, etc. The change in the stray capacitance of the device can be prevented.

When the wiring connecting the probe to the substrate is a shield line, it is possible to prevent a change in the stray capacitance of the wiring between the substrate and the probe due to vibrations caused by vertical and rotational movements.

In the case where the first one originally provided in the detection circuit is used without using a dedicated transistor or IC for the shield drive and using a dedicated one, the number of parts used when the probe is used for the shield drive is not increased. be able to.

When the reference value voltage used in the liquid level detection is set to the steady value 0 and the sample and hold circuit that uses the reference voltage value for storage is stopped, the number of components used on the substrate is reduced,
Substrate size can be reduced.

When a bias voltage is applied to the input signal of the liquid level detection and the subsequent circuit portion is constituted by a single power supply, the number of connectors used on the substrate can be reduced, and the substrate size can be reduced.

In the case where the capacitance is regarded as zero on the balance circuit by making the probe a shield drive, it is not necessary to manage the capacitance of the probe in the production of the probe. .

By making the probe a shield drive, the change in capacitance due to the bending of the probe is apparently zero.
In this case, even when the probe has a bend that does not affect dispensing, the liquid level can be accurately detected without maintenance such as probe replacement.

[0030]

FIG. 2 schematically shows a mechanism of a liquid dispensing apparatus according to one embodiment of the present invention. This is essentially the same as the generally known example. The sampling arm 2 of the sampling mechanism 1 moves up and down and rotates, and the liquid 5 which is a sample is placed in the container 3 placed in the liquid container holder 4.
The liquid level of the dispensed liquid is detected by a liquid level detecting device described later using the probe 6. The dispensed liquid 5 is sucked by the sampling mechanism 1 using the probe 6.

FIG. 3 shows an embodiment of a liquid level detecting device of a generally known liquid dispensing device. This liquid level detecting device is of a capacitance type. The AC signal output from the AC transmission circuit 7 is input to the detection circuit 8 to detect a change in the capacitance value detected through the probe 6. A sine wave is generally 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 AC state, and the amplified signal is input to the rectification circuit 9. 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 the input capacitance before and after the change, and obtains a detection signal 15 indicating whether or not the probe 6 is in contact with the liquid surface of the liquid in the container 3, that is, whether or not the liquid surface is detected. Can be The reason why the comparison circuit 10 is operated with a DC signal is that the circuit is simplified and the cost is reduced. In the case of a small amount of sample, the change in capacitance is usually 10 ^-12 farat (1 pF) or less, and the change in output voltage corresponding to this change is also several tens mV. Therefore, it is sufficiently possible that a change in the stray capacitance causes a false detection.

FIG. 1 schematically shows a main part of a liquid level detecting device of a liquid dispensing device according to an embodiment of the present invention. The probe is used as a shield drive 20, and a bias voltage is applied to the input signal using an adder circuit 40, and the
5 shows a liquid level detection mechanism included in circuit 0. A shield drive is formed by an operational amplifier between the inner tube and the outer tube of the coaxial structure probe, and the impedance becomes low at the same potential as the inner tube without dropping the outer tube to GND. Apparently, the capacitance between the inner tube and the outer tube becomes zero. Even if the probe goes down,
Even if the position of the wiring is displaced, the fluctuation of the capacitance due to these is eliminated. The capacitance increased due to the contact of the probe with the liquid surface is the capacitance between the probe and the liquid holding container. The addition circuit 40 uses an operational amplifier addition circuit or the like. The transorb 40 protects the IC in the substrate from noise from the probe and electrostatic discharge.

FIG. 4 shows the change in the detected capacitance at the time when the probe descends, immediately before reaching the liquid surface, and when the probe comes into contact with the liquid surface. FIG. 7A shows a situation where there is no change in the stray capacitance due to the lowering of the probe. If the capacity change is larger than ΔC, it is determined that there is a liquid level, and if it is smaller, it is determined that there is no liquid level. The amount of change in the capacitance a is the capacitance between the probe and the liquid container holding portion, C1> ΔC, and the liquid level can be detected normally. Looking at the case b, due to the lowering of the probe, the floating capacitance immediately before coming into contact with the liquid surface also increased C4 from the time of the lowering. The capacitance change when contacting the liquid surface is C2 = C1 + C4.
Even at this time, the liquid level can be normally detected. However, since the change in the capacity immediately before the liquid level is present is large, there is a possibility that the air stops immediately when noise is mixed.

Referring to the figure c, the capacitance change due to the lowering of the probe is C5. Since the capacity immediately before the liquid level is low is the capacity at the time of descent, the change in the capacity at the time of contact with the liquid level is C3 = C1−C5. If C3 is smaller than ΔC, the liquid level cannot be detected.

FIG. 5 shows the transorb circuit introduced this time. By applying a bias to the input signal, the transorb element is activated. When noise or electrostatic discharge enters from the probe, a reverse voltage is generated at both ends of the transorb element, and by canceling the reverse voltage, protection of the IC on the substrate is realized.

FIG. 6 is a schematic diagram of a commonly used liquid level detection comparison circuit. Resistance 10A, 10B, capacitor 1
It comprises an output switch 10C, an analog switch 10G, and a comparator 10D. 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. The analog switch 10G is configured to open and close contacts according to a probe 6 descent position detection signal. The capacitor 10C is configured as a reference value storage unit for capacitance change, and the comparator 10D is configured as a liquid level detection unit.

The probe 6 lowering position detection signal is generated when the probe 6 rotates and the probe 6 enters the lowering position. When the probe 6 starts to descend, no signal is output, the analog switch 10G is opened, and the output voltage of the capacitance detection circuit in the same state is set as the reference voltage for the capacitor 10C. During the discharging time of the capacitor 10C, Maintain the reference voltage.

When the probe 6 further falls during the discharging time of the capacitor 10C and the probe 6 comes into contact with the liquid surface, the output voltage of the capacitance detecting circuit rises by several tens mV and the comparator
The voltage at the negative terminal of 10D becomes higher than the reference voltage discharged from the capacitor 10D. Therefore, a signal is output from the terminal 10F as a liquid level detection signal.

As shown in FIG. 7, in the present invention, it is possible to simplify an analog switch and a voltage holding capacitor used in a generally used comparison circuit.
The output voltage of the capacitance detection circuit is compared with the divided voltage of 10J using only the comparator 10D. Theoretically, the bias voltage of the comparison circuit becomes the value V of the bias voltage applied to the input circuit. However, considering the dispersion of elements such as resistors and capacitors, the divided voltage of 10 J is given a certain tolerance from V in consideration of variations in elements such as resistors and capacitors. , V plus tens of mV, the output voltage of the capacitance detection circuit rises by several tens of mV to the 10F terminal when the probe comes down and comes into contact with the liquid level, and the comparator 10D divides the voltage by 10J of V plus tens of mV. And outputs a liquid level detection signal. Since the reference value to be compared can be greatly reduced from the current level, the liquid level can be accurately detected even with a very small amount of sample.

According to the embodiment described above, by using the probe 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 operation of the sampling arm. At the same time, the liquid level detection circuit can be simplified. Further, by applying a bias voltage and introducing a transorb circuit, it is possible to prevent the destruction of the IC due to noise from the probe and electrostatic discharge. In the above embodiment, the liquid to be dispensed into the container 3 may be not only the sample but also a reagent, or a reaction liquid of the sample and the reagent. The container holding unit may be not only a sample disk but also a sample rack on a line.

[0041]

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.

[Brief description of the drawings]

FIG. 1 is a diagram showing a liquid level detection mechanism in which a probe is a shield drive and a transorb protection circuit is provided.

FIG. 2 is a diagram showing a liquid level detection mechanism of a generally known liquid dispensing apparatus.

FIG. 3 is a schematic diagram of a generally known liquid level detection circuit.

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

FIG. 5 is a schematic diagram of a transorb circuit.

FIG. 6 is a diagram showing a part of a comparison circuit of a general liquid level detection circuit.

FIG. 7 is a diagram showing a part of a comparison circuit of the liquid level detection circuit used in the present invention.

[Explanation of symbols]

1. Sampling mechanism 2. Sampling arm 3.
Vessel, 4 sample disk, 5 liquid, 6 probe, 7 AC oscillation circuit, 8 detection circuit, 9 rectifier circuit,
10: comparison circuit, 10A, 10B, 10J, 10K, 4
0A, 40B, 40C, 40E: resistance, 10C: capacitor, 10D: comparator, 10E, 10F: terminal,
10G: analog switch, 20, 40D: operational amplifier, 30: schematic diagram of liquid level detection circuit, 40: addition circuit.

Claims (7)

[Claims] 1. A dispensing probe for dispensing a sample or a reagent such as blood or urine, the probe serving as a liquid level detecting sensor, and a change in capacitance when the probe comes into contact with the liquid level. In an automatic analyzer that performs surface detection, the outer tube of the metal double tube probe for capacitance change detection should be driven to the same potential and lower impedance as the inner tube without dropping it to ground, and a bias voltage should be applied to the input signal. An automatic analyzer characterized by a liquid level detection mechanism having a function of inputting a liquid level detection signal to a liquid level detection circuit via a shield drive. 2. A voltage surge protection element having a high-speed Zener diode characteristic in a liquid level detection mechanism having a shield drive between the inside and outside of the probe and a circuit for applying a bias voltage to an input signal. For example, a device having a transorb or the like. 3. A liquid level detecting mechanism having a shield drive between the inside and outside of the probe and a circuit for applying a bias voltage to an input signal, wherein a circuit portion thereafter comprises a single power supply. An apparatus characterized in that: 4. A liquid level detecting mechanism having a shield drive between an inner layer and an outer layer of the probe and applying a bias voltage to an input signal, wherein the liquid level detecting circuit board is housed inside the arm head. The apparatus further comprising an inner layer of the arm head made of metal, metal vapor deposition, or metal plague. 5. A liquid level detecting mechanism having a shield drive between an inner layer and an outer layer of the probe and applying a bias voltage to an input signal, wherein the shield drive is formed between the inner layer and the outer layer of the probe. A device that uses a liquid level detection circuit without using a dedicated transistor, IC, or the like. 6. A liquid level detecting mechanism having a shield drive between an inner layer and an outer layer of the probe and applying a bias voltage to an input signal, wherein the liquid level is detected only by a comparison circuit using a comparator. An apparatus characterized by being able to. 7. A liquid level detecting mechanism having a shield drive between an inner layer and an outer layer of a probe and a circuit for applying a bias voltage to an input signal does not require management of the capacitance of the probe. An apparatus characterized by the above.