JP3200048B2 - 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 automatic dispensing apparatus used for analyzing body fluids such as blood, and a carry-over (a blood cell reagent used for a sample or a test of blood or the like of a patient or a donor) is used at the time of an initial test. The present invention relates to a liquid level detecting apparatus used for efficient stirring while reducing the amount of residual liquid remaining on a pipette, which affects measurement errors at the next inspection, and particularly to a liquid level detecting apparatus in a dispensing apparatus.

[0002]

2. Description of the Related Art Conventionally, in a hospital or a blood center, blood types such as ABO type and Rh type have been examined for the purpose of ensuring the safety of blood transfusion from a donor (or donor) to a patient (recipient). Antibody screening for identifying (confirming the presence or absence of) irregular antibodies, or cross-matching tests (tests in which blood is mixed and the result of agglutination is checked) are being carried out.

In these tests and tests, in order to completely eliminate the possibility of the carry-over, that is, to remove the possibility that the sample remaining on the pipette during the first test has a measurement error effect on the next test. In addition, disposable sample chips are used and are discarded after use.

In addition, instead of a disposable sample chip, an apparatus using a single nozzle or a plurality of nozzles capable of simultaneously dispensing at a plurality of locations for the purpose of shortening the measurement time is also provided.

In these apparatuses, in order to aspirate a sample or a predetermined amount of a sample from a reagent container, first, the nozzle position at the time when the sample chip or the nozzle itself contacts the liquid surface of the sample is determined. A predetermined amount of liquid is suctioned after the nozzle is further lowered from that position by a distance corresponding to the above-mentioned predetermined amount.

[0006]

SUMMARY OF THE INVENTION In the prior art,
The disposable sample chip is an effective means for eliminating the possibility of carryover, but it requires replacement for each specimen or for each reagent, complicating the equipment for replacement, and discarding each time. Therefore, there was a problem that the operating cost was increased.

When a nozzle is used instead of a disposable sample chip, carryover becomes a problem particularly when one nozzle comes in contact with a plurality of specimens or reagents. Specifically, when a nozzle is inserted into the liquid in order to aspirate a liquid such as a sample or a reagent, the liquid adheres not only to the inside of the nozzle but also to the outer wall of the nozzle. Or, when it comes into contact with the reagent, the attached liquid diffuses into the next sample or reagent, which hinders accurate measurement.

In order to avoid this carry-over, many automatic dispensers use an overflow-type washing mechanism to wash the inside and outside of the nozzle after aspirating and discharging a sample or a reagent, and to perform a test necessary for a test. By determining the nozzle position so as to aspirate only a desired amount of the sample or the reagent, the amount of adhesion to the outer wall of the nozzle is reduced.

[0009] On the other hand, for the specimens and reagents in the test tubes,
It is essential to stir before dispensing. As a stirring method, generally, a sample or a reagent in a container is repeatedly sucked and discharged by a nozzle to perform stirring. In order to perform this stirring operation efficiently, it is necessary that an appropriate amount of liquid remains in the container, and therefore, a liquid level detection operation for constantly monitoring the amount of liquid in the test tube is indispensable.

As a known liquid level detection method, first, a method of detecting a minute change in pressure generated at the time of suction of a liquid,
Secondly, a method of detecting a change in capacitance between the tip of a chip or a nozzle and a liquid surface and a third method of detecting a change in electric resistance using a conductive chip are known.

However, the conventional technique has the following problems. In the first method using a pressure difference, a relatively inexpensive polypropylene chip is used. Particularly, in the case of a blood (whole blood) sample, a lump called a blood-specific clot (also called fibrin) is contained in the blood. In some cases, if the clot is clogged in the tip of the tip or the nozzle during blood suction, there is a problem that an error occurs in the suction amount and the operating cost increases.

In the second method for detecting a change in capacitance, the capacitance is detected as a change in the frequency (the number of pulses). Therefore, the method is affected by an external stray capacitance due to an external electric field or the like. There is a problem that the detection operation is easily unstable.

In the third method for detecting a change in electric resistance, a conductive tip is attached to the tip of the nozzle, but there is a problem that the cost of the conductive tip is high.

An object of the present invention is to eliminate the influence of carryover, to enable the detection of clots, if any, to operate stably without being affected by external stray capacitance, and to reduce operating costs. Another object of the present invention is to provide a liquid level detecting device in a dispensing device.

[0015]

According to an embodiment of the present invention, there is provided a dispensing apparatus including at least a nozzle (12) used for dispensing a liquid of a dispensing apparatus, and a predetermined circuit. According to the circuit, the nozzle (12) and the liquid container (6, 7,
9, 10), a liquid level detecting device in a dispensing device for measuring a change in stray capacitance and detecting that the nozzle tip has reached a liquid level position of the liquid. A frequency generation circuit (24) and a reference side for outputting a reference pulse signal (TP1) having a pulse width defined by a reference capacitance in synchronization with a rise or fall of an input signal from the reference frequency generation circuit (24). A one-shot circuit (25) and a variable pulse width defined by a time constant that changes in proportion to the stray capacitance in synchronization with the rise or fall of the input signal from the reference frequency generation circuit (24). A detection-side one-shot circuit (26) that outputs a pulse width signal (TP2), and integrates a difference (TP3) between the reference pulse signal (TP1) and the variable pulse signal (TP2). Thus, an integrating circuit (28) for detecting a change amount of the pulse width as a change amount of the DC voltage (E), and a control circuit for outputting a liquid level detection signal when the detected change amount is a predetermined amount or more. (32) A liquid level detecting device in a dispensing device, comprising:

With this arrangement, a sudden change in the stray capacitance at the moment when the nozzle comes into contact with or separates from the liquid surface is detected as a change in the pulse width, and this is detected as a stable change in the DC voltage value by the integration circuit. Therefore, the detection state can be stabilized and the detection accuracy can be improved.

Further, since the position of the liquid surface is detected not only when the nozzle comes in close contact with the liquid surface but also when the nozzle moves upward away from the liquid surface, the fact that the clot is clogged in the nozzle can be prevented. Can be detected.

Further, since one nozzle can be used directly,
The operation cost can be greatly reduced as compared with the case where an expensive conductive tip is attached to the tip of the nozzle. Further, the liquid level detecting device according to the present invention includes at least a predetermined probe (12) and a predetermined circuit, and the probe (12) and the liquid container (6, 7, 9, 10) are connected by the predetermined circuit. A liquid level detecting device that measures a change in stray capacitance between the liquid crystal layer and the liquid crystal and detects that the probe tip has reached the liquid level of the liquid.
A reference-side one-shot circuit (25) for outputting a reference pulse signal (TP1) having a pulse width defined by a reference capacitor in synchronization with a rise or fall of an input signal from the reference frequency generation circuit (24); A variable pulse width signal (TP) having a pulse width defined by a time constant that changes in proportion to the stray capacitance in synchronization with the rise or fall of the input signal from the reference frequency generation circuit (24).
2) and the difference (TP3) between the reference pulse signal (TP1) and the variable pulse signal (TP2) by integrating the detection one-shot circuit (26) that outputs the pulse width change amount with the DC voltage ( An integration circuit (28) for detecting the change amount of E), and a control circuit (32) for outputting a liquid level detection signal when the detected change amount is equal to or more than a predetermined amount.
And

Thus, the present invention can be applied not only to a dispensing apparatus but also to a sensor for detecting a liquid level using a floating capacity. Also preferably, an earth electrode (23) is provided in the middle of the nozzle (12) or the pipes (15a, 15b) communicating with the nozzle (12), in contact with the liquid flowing in the pipe.

As a result, a stable floating capacitance can be obtained. Preferably, the control circuit stores the predetermined change amount calculated from experimental data of a stray capacitance to be measured and a change amount of the pulse width.

Thus, the actual change amount of the pulse width can be compared with the stored predetermined change amount, and the liquid level can be detected regardless of whether the nozzle or the like approaches or separates from the liquid level. is there.

Preferably, a stabilizing diode (3) is connected to the connection line between the detection-side one-shot circuit and the stray capacitance.
0) is connected. This eliminates the effects of ambient noise and capacitance.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of an automatic dispensing device used for a blood transfusion test, and FIG. 2 is a schematic configuration layout diagram of reagents and samples of the device. In each drawing, as one embodiment, a case where a blood type is tested and a case where there is one specimen (blood) will be described.

In FIG. 1, an automatic dispensing apparatus 1 includes a fixed table 2, an upper movable unit 3, and a pipette unit 4 attached to the movable unit 3 and capable of moving up and down and back and forth.
And a dispensing unit 5.

On the fixed table 2, a plurality of first-row test tubes 6 containing whole blood after centrifugation as a specimen, a plurality of second-row test tubes 7 for preparing a blood cell suspension, blood type determination A plurality of gel cassettes 8 (only one is shown in FIG. 2) for carrying out the above are mounted, and a buffer diluent container 9 and a pair of blood cell reagent containers 10 (10a, 10b) are further mounted.
The gel cassette 8 includes first to sixth gel cassettes as shown in FIG.
Has a total of six holes 8a to 8f.

The pipette unit 4, as shown in FIG.
Generally, the liquid level detection device 11 (to be described in detail later) and the nozzle 1
Consists of two. As shown in FIGS. 2 and 3, the dispensing unit 5 includes a glass syringe 1 that is a plunger / piston mechanism.
3 and a three-way valve 14.
5a is connected to the washing container 21 and the pipe 15
The nozzle 12 is connected via b. In FIG. 3, the illustration of the liquid level detecting device 11 is omitted. In FIG. 2, reference numeral 22 denotes a nozzle cleaning tank, and the nozzle 12 is immersed in the nozzle cleaning tank 22 at an appropriate time.

Reference numeral 23 denotes a guard electrode provided in the middle of the pipe 15b, which is grounded. Liquid level detecting device 11
Is, as shown in FIG. 4, roughly the reference frequency generation circuit 24,
It has a reference one-shot circuit 25, a detection-side one-shot circuit 26, an integration circuit 28 including a comparison unit 27, and a power supply 29 (see FIG. 5). Specifically, as shown in FIG. 5, the reference frequency generation circuit 24 includes three NOR circuits IC1 to IC
3, the resistors R1 and R2, and the capacitor C1, and the reference one-shot circuit 25 is a one-shot circuit element IC4.
The detection one-shot circuit 26 has a one-shot circuit element IC5. The integration circuit 28 has a NAND circuit IC6 as a comparison unit 27, a resistor R3, and a capacitor C2. Having. The variable resistor Vr of the reference-side one-shot circuit 25, together with the reference fixed capacitance capacitor CP, provides an output time of an output pulse after a trigger signal is input, that is, a time constant for determining a pulse width, and adjusts the variable resistor Vr. By doing so, the output pulse width can be set. One-shot circuit element IC5 of detection-side one-shot circuit 26
Are connected to the nozzle 12 via the resistor R4 and the capacitance detection terminal 31. The stray capacitance CS and the resistors R4 and R5 existing between the nozzle 12 and the ground provide a time constant for determining the output pulse width of the detection one-shot circuit 26. The circuit stabilizing diode 30 is connected to the resistors R4 and R
It is connected to the C terminal to eliminate the influence of ambient noise and capacitance. A control circuit 32 determines an interrupt signal to the computer.

Next, the general operation of the automatic dispensing apparatus 1 will be described. First, at the start of operation of the apparatus or when the measurement method is changed, first, the inside and the outside of the nozzle 12 are washed to reduce carryover. Specifically, the nozzle 12 is inserted into the cleaning liquid in the cleaning tank 22 (FIG. 2), and the cleaning liquid in the cleaning container 21 is once sucked into the syringe 13 using the syringe 13 and the three-way valve 14, and then the syringe is again used. 1
The cleaning liquid is guided to the nozzle 12 by using the three-way and three-way valves 14 to be discharged and overflow from the cleaning tank 22.
Thereby, the nozzle 12 is cleaned.

Next, first, a blood cell suspension of the blood recipient (or blood donor) is prepared in order to determine the blood type of the blood recipient (or blood donor). First, the nozzle 12 is moved downward with respect to the diluent container 9 shown in FIG. 2 to detect the liquid level by a liquid level detection method described later, and then further lowered by a predetermined distance to a desired amount (for example, 990 microliters). A) Aspirate the diluent. Thereafter, the nozzle 12 is pulled up and moved to the test tube 7 shown in FIG. 2, and the desired amount of the diluent is discharged into the test tube 7. In this case, since the nozzle 12 is moved down only by a distance corresponding to the desired amount of the diluent with respect to the diluent container 9, the diluent adhering to the outer wall of the nozzle 12 can be minimized, and carry-over can be prevented. Can contribute to the reduction.

Next, the nozzle 12 is moved with respect to the first-row test tube 6 shown in FIGS. 1 and 2 and containing the centrifuged recipient blood (separated into blood cells and serum) as a specimen. Then, a desired amount (for example, 10 microliters) of blood cells settled at the bottom of the test tube 6 is aspirated, then moved to the second-row test tube 7 and discharged therefrom. After a while, nozzle 1
(2) After the tip is lowered to the vicinity of the bottom of the liquid in the second row of test tubes 7, stirring is performed by repeating the suction and discharge of the entire amount a plurality of times, whereby a desired amount of a uniform state (for example, 10 microliters) is obtained. (1000 microliters) containing the blood cells is prepared, and the nozzle 12 is once pulled up.

Next, the nozzle 12 is moved down again with respect to the test tube 7 in the second row, and then moved down by a predetermined distance after the liquid surface position is detected, which corresponds to the dispensed amount to the gel cassette 8 in the next step. The blood cell suspension is aspirated by a desired amount (eg, 160 microliters).

Thereafter, the nozzle 12 is moved to the gel cassette 8 for blood type test, and the above-mentioned blood cell suspension is used for the so-called blood type determination table test and Rh factor determination to be described later. A predetermined amount (for example, 40 microliters) is sequentially dispensed into the gel cassette units 8a to 8d from No. to No. Thereafter, the nozzle 12 is moved to the cleaning tank 22.
And wash again. Note that the gel cassettes 8a and 8
b is filled with anti-A serum and anti-B serum, respectively, for blood type determination, and the gel cassette 8c is filled with anti-D serum for determination of Rh (D) factor. The gel cassette 8d is filled with a buffer solution for control.

On the other hand, the nozzle 12 is moved downward with respect to the first row of test tubes 6 and is moved downward by a predetermined distance after detecting the liquid surface position, which corresponds to the dispensed amount to the gel cassette 8 in the next step. Aspirate the desired amount of serum (eg, 80 microliters),
The nozzle 12 is moved to the gel cassette 8, and the serum is
For a back test, a predetermined amount (for example, 40 microliters) is sequentially dispensed into the fifth and sixth gel cassette portions 8e and 8f of the gel cassette 8. Thereafter, the nozzle 12 is cleaned again in the cleaning tank 22.

Thus, a desired amount of a blood cell suspension for the front test is present in each of the gel cassette portions 8a to 8d of the gel cassette 8, and a desired amount of the blood cell suspension for the other test is present in the other gel cassette portions 8e and 8f. Of serum is present. Next, a blood type test will be described.

The blood cell reagent container 10a is
(FIG. 2) The blood cell reagent A in the liquid level position is detected, the remaining amount of the reagent is calculated, the effective agitation is carried out, and after the liquid level is detected again, a desired amount is sucked and then transferred to the gel cassette section 8e. Dispense and mix with serum. Thereafter, the nozzle 12 is cleaned in the same manner as described above.

Next, the blood cell reagent container 1 is
The blood cell reagent B prepared at 0b is similarly stirred and sucked, dispensed into the gel cassette section 8f, and mixed with serum. Thereafter, the nozzle 12 is cleaned in the same manner as described above.

Thereafter, the gel cassette 8 was reacted at a constant temperature (for example, 37 ° C.) using an incubation device, and further subjected to a centrifugal separator. Based on the results of the back test, blood type determination and Rh factor determination are performed.

Next, a method of detecting the liquid level by the nozzle 12 will be described. As shown in FIGS. 4 and 5, the stray capacitance C is set between the nozzle 12 and a container (test tubes 6, 7 or a diluent container 9) for storing the liquid sucked by the nozzle 12.
Suppose that S exists.

A trigger pulse (not shown) having a predetermined frequency is generated in the reference frequency generation circuit 24 and is input to the one-shot circuits 25 and 26 on the reference side and the detection side. Then, in synchronization with the positive rise of the trigger pulse, the reference-side one-shot circuit 25 has a binary logic having a pulse width corresponding to the time constant defined by the reference fixed capacitance CP, as shown in FIG. It outputs a positive pulse signal TP1. The pulse width of the reference side pulse signal TP1 is always constant because the reference capacitance CP is constant (the variable capacitance Vr is also held constant). At the same time, in the detection-side one-shot circuit 26, as shown in FIG. 5B, a binary logic negative pulse signal TP2 (to a negative value) having a pulse width corresponding to the time constant defined by the changing stray capacitance CS. Output). The pulse width of the detection-side pulse signal TP2 is small when the stray capacitance CS is small, because the frequency is high, so that the pulse width is small. On the other hand, when the stray capacitance CS is large, the frequency is small, so that the pulse width is large.

NAND circuit IC6 as comparison section 27
Receives the inverted pulses of the reference side pulse signal TP1 and the detection side pulse signal TP2, and outputs the reference side pulse signal TP1.
1 and only when the detection-side pulse signal TP2 is negative, FIG.
As shown in (c) and (d), both signals TP1 and TP2
Difference pulse signal TP3 (TP3-1 or TP3-2)
Is output. In this example, the differential pulse signal TP3 rises in synchronization with the fall of the reference side pulse signal TP1 and falls in synchronization with the fall of the detection side pulse signal TP2.

Accordingly, reference numeral 12a of the nozzle 12 in FIG.
As shown by (b) and (b), when the distance between the nozzle 12 and the liquid surface is still relatively large, the frequency becomes high because the stray capacitance CS is relatively small, and the pulse width of the detection-side pulse signal TP2 becomes small. That is, the detection-side pulse signal TP2 is
In FIG. 6B, the signal falls at a time t2 when a relatively short time T1 has elapsed from the time t1 when the reference pulse signal TP1 falls and the differential pulse signal TP3 rises. Accordingly, the differential pulse signal TP3 has a relatively small pulse width as shown in FIG.
It falls as 1 at the time t2. Accordingly, in the integration circuit 28, as shown in FIG. 6E, a relatively small pulse width of the differential pulse signal TP3-1 is integrated, and a DC voltage indicating a relatively small DC voltage value E1 proportional to the pulse width is obtained. It is converted to a voltage signal TP4-1. This signal TP4-1 is output to the control circuit 32 (FIG. 4), where it is compared with a predetermined voltage change value. Since it is still smaller than the predetermined voltage change value, it is determined that the liquid level detection has not been performed. Is done. The control circuit 32 supplies a DC voltage signal TP4 with respect to a change in the stray capacitance CS obtained by an experiment in advance.
Of the voltage signal TP4, and monitors a sudden voltage change of the voltage signal TP4. If the voltage change between the previous voltage signal TP4 and the current voltage signal TP4 is equal to or greater than a predetermined voltage change value, the liquid level contact signal or It is configured (programmed) to output a liquid level separation signal. The reference pulse signal TP
1, the above operation is performed.
As can be seen from the graph, as the nozzle 12 approaches the liquid surface, the floating capacitance CS gradually increases, so that the time T1, that is, the DC voltage E1, gradually increases.

Next, as shown by the nozzle symbol 12c in FIG. 7, when the nozzle 12 comes in close contact with the liquid surface, the stray capacitance CS rapidly increases, so that the frequency sharply decreases, and the pulse on the detection side is reduced. The signal TP2 suddenly changes so as to fall at time t3 after a relatively long time T2 has elapsed from time t1 in FIG. 6B. Therefore, the difference pulse signal TP3
Falls at the time t3 as the differential pulse signal TP3-2 having a large pulse width as shown in FIG. 6D. Accordingly, as shown in FIG. 6F, the integration circuit 28 integrates a relatively large pulse width of the difference pulse signal TP3-2 and outputs the result as a DC voltage signal TP4-2 having a large DC voltage value E2. . In FIG. 7, a vertical straight line Q indicates a liquid surface contact state. When the DC voltage signal TP4-2 is input, the control circuit 32
It is determined that it is larger than a predetermined voltage change value, and a liquid level detection signal is output. Thus, after the descent of the nozzle 12 is once stopped, next, the suction operation of the desired amount of liquid is started.

That is, as shown by a nozzle symbol 12d in FIG. 7, the nozzle 12 descends by a predetermined distance from the above-mentioned liquid level detection position and sucks a desired amount of liquid. Meanwhile, the straight line R in FIG.
As shown by, the stray capacitance CS gradually increases. But,
During the period of the straight line R, for example, the DC voltage signal TP4 is TP4-2.
Even if it becomes larger, the voltage change does not reach the predetermined voltage change value, so that no signal is output from the control circuit 32.

Next, when the suction of the liquid is completed, the liquid level is lowered by a predetermined amount, and as shown by the nozzle symbol 12e in FIG. Rapidly decreases, the frequency rapidly increases, and the detection side pulse signal T
P2 falls after a lapse of time T1, which has been sharply shortened,
At the same time, the difference pulse signal TP3-
1 is output. As a result, a small pulse width is integrated and a small DC voltage signal TP4-1 is output. The control circuit 32 determines that the voltage change value has become larger than the predetermined voltage change value because the voltage value sharply decreases, and outputs a liquid level separation detection signal. In FIG. 7, a vertical straight line S indicates this state. Further, as shown by the nozzle symbols 12f and 12g, when the nozzle 12 further moves upward, the stray capacitance CS gradually decreases as shown by the straight line U.

Here, as described above, when the liquid level detected by moving the nozzle 12 away from the liquid level does not coincide with the calculated liquid level calculated after the completion of the suction operation, It is determined that the clot is sucked and clogged at the tip of the nozzle 12, the operation is stopped, and the sample is replaced. As one specific example, even if the nozzle 12 after suction is separated from the liquid surface by 2 to 3 mm, the difference pulse signal TP
When the falling edge of 3-1 does not occur, it is determined that the clot has been sucked.

Next, the function of the guard electrode 23 at the ground potential will be described with reference to FIG. The washing solution in the washing container 21 used for the measurement of a general body fluid (blood sample in the example) is a buffer solution having a conductivity of several hundred microsiemens or more (for example, a physiological solution obtained by dissolving 9 g of sodium chloride in 1 liter of distilled water). Salt). The buffer is a conductor having a low electric resistance and a current flowing therethrough. The pipes 15a and 15b
When the buffer is filled therein, it has a resistance value corresponding to the length of the pipe and forms a predetermined electric circuit. Under these conditions, assuming that the guard electrode 23 of the ground potential is not provided, one end of the pipes 15a and 15b connected to each other is connected to the nozzle 12 as is clear from the flow path diagram shown in FIG. Further, since the other end is only immersed in the washing container 21, neither the washing container 21 nor the test tubes 6, 7 (or the diluent container 9) are electrically grounded. As described above, in a state where the flow path system is not grounded, the electric resistance value changes and the circuit constant easily changes, whereby the space capacity is changed due to changes in the surrounding environment, for example, an external electric field such as bringing a hand closer to the device. And the input potential of the detection-side one-shot circuit 26 changes, so that stable operation cannot be performed.
Accurate measurement of stray capacitance is not possible.

However, when the guard electrode 23 having the ground potential is provided in the middle of the pipe as described above, one end of this electric circuit is always grounded, so that the electric resistance value of the buffer solution in the pipe is constant. Thus, a change in the circuit constant is unlikely to occur, thereby making it possible to provide a liquid level detecting device which is not affected by a change in the surrounding environment, that is, an external electric field.

Although the guard electrode 23 is provided in the middle of the nozzle-side pipe 15b in FIG. 3, the guard electrode 23 is not limited to this and may be provided in the middle of the cleaning vessel-side pipe 15a. In some cases, the washing container 21 or the test tubes 6 and 7 (or the diluent container 9 and the reagent containers 10a and 10b) may be grounded without providing a guard electrode, and the same effect is obtained. be able to.

In the above embodiment, the liquid level detecting device is applied to the automatic dispensing device. However, the present invention is not limited to this embodiment. The present invention can also be used as a sensor for detecting the liquid surface of a liquid related to blood type determination or various liquids without being limited thereto. Of course, when the nozzle 12 is used, the present invention can be applied to dispensing various liquids other than the liquid related to blood type determination.

[0050]

According to the present invention, the following effects can be obtained. The stray capacitance between the nozzle and the liquid container is determined by integrating the difference signal TP3 between the reference pulse signal TP1 from the reference one-shot circuit 25 and the variable pulse width signal TP2 from the detection-side one-shot circuit 26 to obtain the pulse width. Is detected as a change in the DC voltage (E), so that a sudden change in the stray capacitance at the moment when the nozzle contacts or separates from the liquid surface is regarded as a sudden change in the DC voltage (E). Because it is detected, that is, not as a change in frequency (number of pulses) as in the conventional method of detecting stray capacitance, but as a change in pulse width, this is detected as a stable change in DC voltage value by an integration circuit. When the amount of change is equal to or greater than a predetermined amount of change, it is determined that the nozzle has reached the liquid level, so that the detection state can be stabilized and the detection accuracy can be improved.

As described above, since the detection is made as the amount of change in the DC voltage value, not only when the nozzle comes in close contact with the liquid surface but also when the nozzle moves upward away from the liquid surface, the liquid surface position is detected. Can detect the fact that the clot is clogged in the nozzle, preventing erroneous detection, compared to the conventional pressure detection method that can only detect the liquid level when it comes into close contact with the liquid surface, Detection accuracy can be further improved.

Since one nozzle can be used repeatedly, the operation is more difficult than the one using an expensive conductive tip which needs to be replaced according to the type of liquid at the tip of the nozzle as in the conventional electric resistance method. Costs can be significantly reduced.

The liquid level detecting device of the present invention is not limited to a dispensing device, but can be used as a sensor for detecting a liquid level using, for example, a floating capacity, and has a wide range of applications. Since the ground potential electrode is provided in the middle of the nozzle or the pipe connected to the nozzle, a stable floating capacitance can be obtained, and the detection accuracy can be further improved.

Since the control circuit stores the predetermined change amount calculated from the experimental data of the stray capacitance to be measured and the change amount of the pulse width, the control circuit stores the predetermined change amount as described above. The liquid level can be detected both when the nozzle or the like approaches or separates from the liquid level.

Further, since a stabilizing diode is provided on the connection line from the one-shot circuit on the detection side to the stray capacitance, the influence of ambient noise and capacitance can be eliminated.

[Brief description of the drawings]

FIG. 1 is a side view of an automatic dispensing device used for a blood transfusion test.

FIG. 2 is a schematic configuration diagram of a reagent and a sample of the apparatus.

FIG. 3 is a view showing a channel configuration of a dispensing unit, a washing container, and a nozzle portion of the apparatus.

FIG. 4 is a schematic configuration diagram of a circuit applied to the device.

FIG. 5 is a circuit diagram showing details of the circuit shown in FIG. 4;

FIG. 6 is a diagram showing signal waveforms of the circuit,
FIG. 6A shows an output pulse signal of the reference one-shot circuit, FIG. 6B shows an output pulse signal of the detection one-shot circuit, and FIG. 6C shows a comparison circuit when the stray capacitance CS is small. FIG. 6D shows an output pulse signal from the comparison circuit when the stray capacitance CS suddenly increases due to the nozzle contacting the liquid surface.
(E) and (f) show DC voltage signals output from the integrating circuit corresponding to FIGS. 6 (c) and (d), respectively.

FIG. 7 is a diagram showing a state in which the stray capacitance CS changes in accordance with a change in the position of the nozzle with respect to the liquid level.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Automatic dispensing apparatus 2 ... Fixed table 3 ... Moving unit 4 ... Pipette unit 5 ... Dispensing unit 6, 7 ... Test tube 8 ... Gel cassette 9 ... Diluent container 10 ... Blood cell reagent container 11 ... Liquid level detecting device 12 ... Nozzle 13 ... Syringe 14 ... Three-way valve 15a, 15b ... Pipe 21 ... Cleaning container 22 ... Nozzle cleaning tank 23 ... Guard electrode 24 ... Reference frequency generation circuit 25 ... Reference-side one-shot circuit 26 ... Detection-side one-shot circuit 27 ... Comparison Part 28 ... integration circuit 29 ... power supply 30 ... circuit stabilizing diode 31 ... capacitance detection terminal 32 ... control circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-10-197539 (JP, A) JP-A-8-122338 (JP, A) JP-A-5-175425 (JP, A) JP-A 52-1982 90075 (JP, A) JP-A-8-220161 (JP, A) JP-A-8-271556 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 35/10

Claims (6)

(57) [Claims] A nozzle (1) used for dispensing of a dispensing device.
2) and at least a predetermined circuit, the predetermined circuit is used to measure a change in the stray capacitance between the nozzle (12) and the liquid container (6, 7, 9, 10), and that the tip of the nozzle is a liquid. In the liquid level detecting device for detecting that the liquid level has been reached, the predetermined circuit is synchronized with a reference frequency generation circuit (24) and a rise or fall of an input signal from the reference frequency generation circuit (24). A reference-side one-shot circuit that outputs a reference pulse signal (TP1) having a pulse width defined by a reference capacitance; and a rising or falling edge of an input signal from the reference frequency generation circuit (24). A detection-side one-shot circuit that outputs a variable pulse width signal (TP2) having a pulse width defined by a time constant that changes in proportion to the stray capacitance; An integration circuit (28) for detecting a change amount of the pulse width as a change amount of the DC voltage (E) by integrating a difference (TP3) of the variable pulse signal (TP2); and increasing the detected change amount. Is greater than or equal to a predetermined voltage change value.
In the case where the liquid level detection signal is
A control circuit (32) for outputting a liquid level separation detection signal when the voltage change value is equal to or more than a predetermined voltage change value; and a nozzle (15a, 1
In the course of step 5b), the contact with the liquid flowing through the pipe
And a ground electrode (23) . 2. At least a predetermined probe (12) and a predetermined circuit are provided, and the probe (1) is provided by the predetermined circuit.
2) A liquid level detecting device for measuring a change in a floating capacity between a liquid container and a liquid container (6, 7, 9, 10) and detecting that a nozzle tip has reached a liquid level position of the liquid. A predetermined circuit comprises: a reference frequency generation circuit (24); and a reference pulse signal (TP1) having a pulse width defined by a reference capacitance in synchronization with a rise or fall of an input signal from the reference frequency generation circuit (24). And a pulse width defined by a time constant that varies in proportion to the stray capacitance in synchronization with the rise or fall of the input signal from the reference frequency generation circuit (24). By integrating a detection one-shot circuit that outputs a variable pulse width signal (TP2) and a difference (TP3) between the reference pulse signal (TP1) and the variable pulse signal (TP2), An integrating circuit (28) for detecting a change amount of the pulse width as a change amount of the DC voltage (E), wherein an increase of the detected change amount is equal to or more than a predetermined voltage change value;
In the case where the liquid level detection signal is
Given a control circuit for outputting a liquid surface spaced detection signal (32) in the case of more than the voltage change value, a pipe communicating with the probe or probes (15
a, contact with the liquid flowing in the pipe in the middle of 15b)
And a ground electrode (23) . 3. The liquid level detecting device according to claim 1,
The control circuit calculates a liquid level position of the nozzle,
The nozzle moves upward at least a predetermined distance from the calculated liquid level.
If the separation detection signal is not output, the
A liquid level detecting device . 4. The liquid level detecting device according to claim 1, wherein the control circuit includes a predetermined capacitance calculated from experimental data of a stray capacitance to be measured and a change amount of the pulse width. A liquid level detecting device, wherein the amount of change of the liquid level is stored. 5. The liquid level detecting device according to claim 1, wherein a stabilizing diode (30) is connected to a connection line from the detection-side one-shot circuit (26) to the stray capacitance. A liquid level detecting device. 6. The liquid level detecting device according to claim 1, wherein the liquid is any one of blood, a buffer dilution station, a blood cell reagent, and a blood cell suspension. Detection device.