Abstract:
Disclosed is an analyzer comprising: a container holder configured to hold a container containing a liquid; an aspirating tube configured to aspirate the liquid from the container held by the container holder; a drive part configured to transfer the aspirating tube; a detector configured to output a signal based on a physical characteristic between the aspirating tube and a liquid surface of the liquid in the container; and a memory configured to store, as a reference signal, the signal output from the detector when the aspirating tube is being transferred under a condition that the container containing the liquid which can be aspirated by the aspirating tube is not being held by the container holder; and a controller configured to detect the liquid level position of the liquid in the container, based on the reference signal and a real signal that the detector outputs, when the aspirating tube is transferred for an aspiration operation of the liquid.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from prior Japanese Patent Application No. 2014-060393, filed on Mar. 24, 2014, entitled “ANALYZER, AND METHOD OF DETECTION LIQUID LEVEL IN AN ANALYZER”, the entire contents of which are incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to an analyzer and a method of detecting liquid level in an analyzer. More specifically, the present invention relates to an analyzer and method of detecting liquid level in an analyzer capable of accurately detecting the level of a liquid such as a sample and reagent aspirated from a container by an aspirating tube. 
       BACKGROUND 
       [0003]    Conventional sample analyzers are known to dispense a sample such as blood or urine from a sample container to a reaction vessel where the sample is mixed with a reagent corresponding to the measurement criteria, and then perform various types of measurements and analyses. The liquids, such as sample and reagent, used in this sample analyzer are stored in predetermined containers and aspirated by an aspirating tube which is inserted into the container. There is known art for preventing contamination and minimizing the amount of insertion of the nozzle in the liquid by detecting the liquid level in the container (refer to Japanese Laid-Open Patent Application No. H11-271319). 
         [0004]    The art disclosed in Japanese Laid-Open Patent Application No. H11-271319 detects changes in the electrostatic capacity between the liquid and the aspirating tube to detect the liquid level within the container. The static electricity is eliminated to prevent inaccurate detection of the liquid level due the influence of the static electricity charging the container. 
         [0005]    Static electricity is just one of several factors obstructing liquid level detection. For example, when detecting the liquid level based on changes in electrostatic capacity as in the art disclosed in Japanese Laid-Open Patent Application No. H11-271319, there may be conductors such as metal panels and screws around the container and these conductors can act as electrodes to greatly change the electrostatic capacity. Therefore, when there is a change in electrostatic capacity while detecting the liquid level, it becomes difficult to recognize the change in electrostatic capacity when the aspirating tube approaches a nearby conductor and the liquid level cannot be accurately detected. There also is concern that liquid level detection also will become inaccurate due to changes in the detected electrostatic capacity caused by loosening of a metal screw around the container and by a replaced metal part. There is further concern that liquid level detection will be inaccurate due to changes in detected voltage caused by differences in the shapes of containers holding the liquid when liquid level detection is performed by a voltage sensor. Hence, the environment surrounding the liquid level sensor greatly affects the detection signal of the liquid level sensor. 
       SUMMARY OF INVENTION 
       [0006]    The scope of the present invention is defined solely by the appended claims, and is not affected to any degree by the statements within this summary. 
         [0007]    A first aspect of the present invention is An analyzer comprising: a container holder configured to hold a container containing a liquid; an aspirating tube configured to aspirate the liquid from the container held by the container holder; a drive part configured to transfer the aspirating tube; a detector configured to output a signal based on a physical characteristic between the aspirating tube and a liquid surface in the container; and a memory configured to store, as a reference signal, the signal output from the detector when the aspirating tube is being transferred under a condition that the container containing the liquid which can be aspirated by the aspirating tube is not being held by the container holder; and a controller configured to detect a liquid level position in the container, based on the reference signal and a real signal output by the detector when the aspirating tube is transferred for an aspiration operation of the liquid. 
         [0008]    A second aspect of the present invention is an analyzer comprising: a container holder configured to hold a container containing a liquid; an aspirating tube configured to aspirate the liquid from the container held by the container holder; a drive part configured to transfer the aspirating tube; a controller configured to control the drive part; a detector configured to output a signal based on a physical characteristic between the aspirating tube and a liquid surface in the container; and a memory configured to store the signal output by the detector; wherein the controller is configured to; store as a reference signal in the memory, the signal output by the detector when the aspirating tube is being transferred under a condition that the container containing the liquid which can be aspirated by the aspirating tube is not being held by the container holder; and detect the liquid level position in the container, based on the reference signal and a real signal output by the detector when the aspirating tube is transferred for an aspiration operation of the liquid. 
         [0009]    A third aspect of the present invention is a method of detecting a liquid level in an analyzer comprising: a step of transferring an aspirating tube to aspirate a liquid from a container held in a container holder; a step of outputting, as a real signal, a signal based on a physical characteristic between the aspirating tube and a liquid surface in the container, when the aspirating tube is being transferred for an aspiration operation of the liquid; and a step of detecting the liquid level position in the container based on the real signal and a reference signal that is based on a physical characteristic between the aspirating tube and the liquid surface in the container when the aspirating tube is being transferred under a condition that the container containing the liquid which can be aspirated by the aspirating tube is not being held by the container holder. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view showing the general structure of an immunoanalyzer  1  as an embodiment of the sample analyzer; 
           [0011]      FIG. 2  is a plan view of the immunoanalyzer of  FIG. 1 ; 
           [0012]      FIG. 3  is a perspective view of a reagent installation unit; 
           [0013]      FIG. 4  is a side view briefly showing the structure of a reagent dispensing unit; 
           [0014]      FIG. 5  is a block diagram showing the structure of a liquid level detector; 
           [0015]      FIG. 6  is a block diagram showing the structure of a capacitance detector; 
           [0016]      FIG. 7  illustrates the correspondence between the position of the aspirating tube in the vertical direction and the background signal; 
           [0017]      FIG. 8  illustrates the correspondence between the position of the aspirating tube in the vertical direction, the liquid level detection signal, and the differential signal; 
           [0018]      FIG. 9  is a flow chart showing the procedure of obtaining the background signal; 
           [0019]      FIG. 10  is a flow chart showing the control sequence of the reagent aspirating operation by the aspirating tube; 
           [0020]      FIG. 11  is a flow chart showing the control sequence of the reagent aspirating operation by the aspirating tube; 
           [0021]      FIG. 12  is a flow chart showing the control sequence of the aspirating tube washing process; and 
           [0022]      FIG. 13  is a cross sectional view of the aspirating tube washing unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The preferred embodiments will be described hereinafter with reference to the drawings. 
       [General Structure of Immunoanalyzer  1 ] 
       [0024]    The immunoanalyzer  1  examines various items such as hepatitis type-B, hepatitis type-C, tumor marker, and thyroid hormone contained in a plasma sample (hereinafter referred to simply as “sample”) by utilizing an antigen/antibody reaction. The immunoanalyzer  1  has a measuring section  2 , sample transporting section  3 , and a control device  4 . The measuring section  2  is connected to the sample transporting section  3  and the control device  4  with communication enabled. The sample transporting section  3  is configured to transport a rack holding a plurality of test tubes containing sample collected from a subject. The control device  4  has a main body  400  and a display/input section  410 . The display/input section  410  has a touch panel, and incorporates a display section and input section. 
         [0025]    As shown in  FIG. 2 , the measuring section  2  includes a sample dispenser  5 , R 1  reagent dispenser  6 , R 2  reagent dispenser  7 , R 3  reagent dispenser  8 , reactor  9 , cuvette supplier  10 , Primary BF separator  11 , secondary BF separator  12 , pipette tip supplier  13 , measuring unit  14 , R 4 /R 5  reagent supplier  15 , reagent installation section  16 , disposal unit  17 , and measurement controller  200  (refer to  FIG. 1 ). 
         [0026]    The sample transporting section  3  is configured to transport a rack holding a plurality of test tubes containing unprocessed sample. 
         [0027]    In the immunoanalyzer  1 , the sample to be measured is mixed with a buffer solution R 1  reagent, and an R 2  reagent which contains magnetic particles carrying a capture antibody for binding to the antigen in the sample is added to the liquid mixture. The components in the sample that are not bound to the capture antibody are eliminated when magnetic particles carrying the capture antibody bound to the antigen are attracted to a magnet (not shown in the drawing) of the primary BF (bound free) separator  11 . After an R 3  reagent containing a labeled antibody has been added, the magnetic particles carrying the capture antibody bound to the antigen and the labeled antibody are attracted to a magnet of the secondary BF separator  12  (not shown in the drawing) to eliminate the R 3  reagent that contains the unreacted labeled antibody. After adding an R 5  reagent containing a luminescent substrate, which luminesces via reaction between the labeled antibody and the R 4  reagent which is a dispersion liquid, the amount of light produced by the reaction between the labeled antibody and the luminescent substrate is measured. The antigen contained in the sample bound to the labeled antibody can be quantified through this process. 
         [0028]    The cuvette supplier  10  is configured to accommodate a plurality of cuvettes, and sequentially supplies the cuvettes one by one to the discharge position  1   b.    
         [0029]    An aspirating tube  6   a  for aspirating and discharging R 1  reagent is attached to the R 1  reagent dispenser  6 , as shown in the drawing. A pipette is used as the aspirating tube  6   a  in the present embodiment. The R 1  reagent dispenser  6  aspirates the R 1  reagent from the reagent container installed in the reagent installation section  16 , and discharges the aspirated R 1  reagent to a cuvette placed at the discharge position  1   b  using the aspirating tube  6   a.    
         [0030]    The pipette tip supplier  13  moves a plurality of loaded pipette tips (not shown in the drawing) one by one to the tip installation position (not shown in the drawing). Thereafter, a pipette tip is mounted on the pipette end of the sample dispenser  5  at the tip installation position. 
         [0031]    The sample dispenser  5  aspirates the sample in the test tube moved to the sample aspirating position  1   a  by the sample transporting section  3  using the installed pipette tip. This aspiration is accomplished through a hole  31   a  formed in a cover  31  that covers the transport path of the sample transporting section  3 . The sample dispenser  5  discharges the aspirated sample into a cuvette at the discharge position  1   b . The R 1  reagent was previously dispensed to the cuvette by the R 1  reagent dispenser  6 . Thereafter, the cuvette is moved to the reactor  9  by a catcher (not shown in the drawing) of the R 1  reagent dispenser  6 . 
         [0032]    As shown in the drawing, an aspirating tube  7   a  for aspirating and discharging R 2  reagent is attached to the R 2  reagent dispenser  7 . A pipette is used as the aspirating tube  7   a  in the present embodiment. The R 2  reagent dispenser  7  aspirates the R 2  reagent from the reagent container installed in the reagent installation section  16 , and discharges the aspirated R 2  reagent to a cuvette containing the R 1  reagent and the sample. 
         [0033]    The reactor  9  has an annular shape so as to circumscribe the reagent installation section  16 , which is circular, as shown in the drawing. The reactor  9  has a plurality of cuvette holders  9   a  arranged at predetermined spacing along the exterior. Cuvettes set in the cuvette holders  9   a  are heated to approximately 42° C. Hence, the heating promotes reaction of the various reagents and the sample in the cuvette. The reactor  9  is configured to be horizontally rotatable in a clockwise direction, and moves the cuvette set in the cuvette holder  9   a  to each processing position where various processes, such as dispensing reagent, are performed. 
         [0034]    The cuvette containing the sample and R 1  and R 2  reagents is moved by a catcher (not shown in the drawing) from the reactor  9  to the primary BF separator  11 . Primary BF separation is performed by the primary BF separator  11 . The components in the sample that are not bound to the capture antibody of the R 2  reagent are thus removed from the sample within the cuvette. Having completed primary BF separation, the cuvette is returned to the reactor  9  by the catcher (not shown). 
         [0035]    An aspirating tube  8   a  for aspirating and discharging R 3  reagent is attached to the R 3  reagent dispenser  8 , as shown in the drawing. A pipette is used as the aspirating tube  8   a  in the present embodiment. The R 3  reagent dispenser  8  uses the aspirating tube  8   a  to aspirate the R 3  reagent set at the reagent installation section  16 . The R 3  reagent dispenser  8  also uses the aspirating tube  8   a  to discharge the aspirated R 3  reagent into the cuvette which was moved from the primary BF separator  11  to the reactor  9 . 
         [0036]    After the elimination process by the primary BF separator  11 , the cuvette containing the R 3  reagent and the sample already processed by the primary BF separator  11  is moved from the reactor  9  to the secondary BF separation section  12  by a catcher (not shown in the drawing). Secondary BF separation is performed in the secondary BF separator  12 . The R 3  reagent including the unreacted labeled antibody is thereby eliminated. Having completed secondary BF separation, the cuvette is returned to the reactor  9  by the catcher (not shown). 
         [0037]    The R 4 /R 5  reagent supplier  15  sequentially dispenses R 4  and R 5  reagents to the cuvette containing the sample after the elimination process performed by the secondary BF separator  12  via a catcher not shown in the drawing. 
         [0038]    The reagent installation section  16  holds a plurality of reagent containers which accommodate R 1  reagent, R 2  reagent, and R 3  reagent, respectively, for each measurement item. The reagent installation section  16  also holds a container of BSA duffer as a sample buffering solution, which is used to dilute the sample when dilute sample measurements are performed. 
         [0039]    The measuring unit  14  obtains the amount of light produced during the reaction process between the luminescent substrate and the labeling antibody bound to the antigen of the ample subjected to predetermined processing via a photomultiplier tube. The measuring unit  14  sends signals corresponding to the amount of light to the measurement controller  200  (refer to  FIG. 1 ). 
         [0040]    The disposal unit  17  is a unit for the disposal of cuvettes and waste fluid within the cuvettes after detection is completed, and the disposal unit has an aspiration part (not shown) for aspirating the waste fluid within the cuvette, and a disposal hole (not shown). After detection, the cuvette is moved from the measuring unit  14  to the disposal unit  17  by a catcher (not shown), the waste fluid within the cuvette is aspirated by the aspiration part and the cuvette from which the waste fluid has been aspirated is discarded through the disposal hole in the disposal unit  17 . 
         [0041]    The measurement controller  200  of the measuring section  2  has a CPU and a memory configured by a ROM, RAM or the like. The measurement controller  200  is configured to control each part of the measuring section  2  in accordance with signals output by the main body  400  of the control device  4  shown in  FIG. 1 . The controller  200  receives the signals sent from the measuring unit  14 , converts the signals to measurement values, and analyzes the converted measurement values. The measurement controller  200  transmits the analysis results to the main body  400  of the control device  4 . 
         [0042]    As shown in  FIG. 3 , the reagent installation section  16  includes an annular table  162  on the inner side, and an annular table  163  on the outer side, when viewed from above. 
         [0043]    The inner table  162  has a plurality of container holders capable of holding the R 1  reagent container  100  which contains R 1  reagent, and a plurality of container holders capable of holding R 3  reagent container  120  which contains R 3  reagent. These container holders accommodate a plurality of R 1  reagent containers  100  on the inner side of the table  162  in an annular configuration, and the R 1  reagent containers  100  are circumscribed on the outer side by the R 3  reagent containers  120  which are arranged along the circumference, as shown in the drawing. 
         [0044]    The outer table  163  has a plurality of container holders capable of holding the R 2  reagent container which contains R 2  reagent. These container holders accommodate R 2  reagent containers  110  on the outside table  163  in an annular configuration so as to circumscribe the R 1  reagent containers  100  on the outer side, as shown in the drawing. 
         [0045]    The inner table  162  and the outer table  163  are configured to be horizontally rotatable in the circumferential direction via step motors which are not shown in the drawing. The reagent containers  100 ,  110 , and  120  placed in the container holders are disposed at the reagent aspirating position to aspirate reagent through the reagent dispensers  6  through  8  by rotating the inner table  162  and the outer table  163 . 
         [0046]    Note that a cover which is not shown in the drawing is provided on the top surface of the reagent installation section  16  so as to cover both the reagent installation section  16  and the reactor  9 , and an opening is formed in this cover to permit the insertion of the aspirating tubes  6   a  through  8   a  of the reagent dispensers  6  through  8 . 
         [0047]    As shown in  FIG. 4 , the reagent dispensers  6  through  8  have arms  6   b  through  8   b , drive units  60  configured to move arms  6   b  through  8   b  vertically and rotate the alms  6   b  through  8   b  on shaft  6   c  through  8   c , and aspirating tubes  6   a  through  8   a  attached at the tip of the arms  6   b  through  8   b  to aspirate and discharge the reagent in reagent containers  100 ,  110 , and  120  which are held in container holder  16 A of reagent installation section  16 . 
         [0048]    The drive unit  60  has a rotation motor  61 , elevator motor  62 , and a transmission unit  63  for transmitting the drive force of the rotation motor  61  and the elevator motor  62  to a shaft. The transmission unit  63  is configured by a rack and pinion mechanism and belt transmission unit for reducing the rotational force of, for example, the rotation motor  61 , and converting the rotational force of the elevator motor  62  gear devices and belt transmission for transmitting force to the shafts  6   c  through  8   c  to a direct force in vertical directions and transmitting this force to the shafts  6   c  through  8   c . Encoders  64  and  65  are provided to output signals according to the amount of rotational displacement of the rotation motor  61  and elevator motor  62 , and the output signals of the encoders  64  and  65  are sent to the measurement controller  200 . The measurement controller  200  detects the rotational position and vertical position of the aspirating tubes  6   a  through  8   a  by counting the output signals of the encoders  64  and  65 . The encoders  64  and  65  therefore configure a position detection unit for detecting the position of the aspirating tubes  6   a  through  8   a . Note that alternative configurations may be used as the position detection unit such as configurations which directly detect the position of the aspirating tubes  6   a  through  8   a  or configurations using an optical sensor or the like to detect a member which moves in association with the aspirating tubes  6   a  through  8   a.    
         [0049]    The measuring section  2  of the present embodiment also has, in addition to the various parts mentioned above, a liquid level detecting unit  20  (refer to  FIG. 5 ) configured to detect the liquid level of reagent within the reagent containers  100 ,  110 , and  120  installed in the reagent installation section  16 . The structure of the liquid level detecting unit  20  will be described in detail later. 
         [0050]    As shown in  FIG. 1 , the control device  4  is configured by a body part  400 , and display/input part  410 . The body part  400  has a CPU, a memory part such as a ROM, RAM, and hard disk, I/O interface, and image output interface. 
         [0051]    The CPU of the body part  400  executes various programs installed in the memory part. 
         [0052]    The I/O interface of the body part  400  receives the signals output from the display/input section  410 . The image output interface of the body part  400  outputs image signals corresponding to the image data to the display/input part  410 . 
         [0053]    The display/input part  410  displays images based on the image signals received from the image output interface, and outputs instructions received from the user through the screen of the display/input part  410  to the I/O interface  406 . 
         [0054]    The communication interface of the body part  400  transmits signals from the body part  400  to the measurement controller  200  of the control section  2  on the body part  400  side, and receives signals sent from the measurement controller  200 . 
         [0055]    Reagent Aspiration Operation of the Reagent Dispensing Unit 
         [0056]    As shown in  FIG. 5 , the liquid level detecting unit  20  has a position detector  65  which detects the vertical position of the aspirating tubes  6   a  through  8   a , capacitance detector  21  which detects the change in capacitance between the aspirating tubes  6   a  through  8   a  and the surrounding environment, controller  22  which receives the output signals of the position detector  65  and capacitance detector  21 , detects the liquid surface LS of the reagent L, and controls the drive unit  60  in accordance with the detected liquid level, and memory  23  which stores the background signal used to detect the reagent liquid level. The controller  22  and memory  23  are configured by the CPU and memory of the measurement controller  200 . 
         [0057]    The position detector  65  is configured by an encoder which outputs pulse signals corresponding to the rotation of the elevator motor  62  in the reagent dispensers  6  through  8 , as previously described. The output of the position detector  65  is input to the controller  22 . 
         [0058]    Note that when a step motor is used as the elevator motor  62 , a possible configuration will detect the position by the pulse count of a drive signal applied to the elevator motor  62  without providing the position detector  65 . 
         [0059]    The capacitance detector  21  is a capacitance sensor which detects changes in electrostatic capacity between the aspirating tubes  6   a  through  8   a  and the surrounding conductors, such changes being produced by the vertical movements of the aspirating tubes  6   a  through  8   a . Specifically, the capacitance detector  21  incorporates an oscillation circuit  25  which oscillates a high frequency pulse, a peak-hold circuit  26  which obtains the peak value output of the oscillation circuit  25 , and a differentiating circuit  27  which obtains the change in output of the peak-hold circuit  26 , as shown in  FIG. 6 . Note that examples of the output signals s 1 , s 2 , and s 3  of the circuits  25 ,  26 , and  27  are shown in  FIG. 6 . 
         [0060]    When the aspirating tubes  6   a  through  8   a  are lowered, the capacitance changes due to the change in distance between the aspirating tubes  6   a  through  8   a  and the reagent liquid level in the reagent containers  100 ,  110 , and  120 , and the capacitance changes greatly when the aspirating tube  6   a  through  8   a  contacts the liquid surface. The change in capacitance manifests as a change in amplitude of the output signal s 1  which represents the output voltage of the oscillation circuit  25 . Specifically, the amplitude of the output signal s 1  of the oscillation circuit  25  increases when the capacitance is small, and the amplitude decreases when the capacitance increases. 
         [0061]    The peak-hold circuit  26  obtains the peak value of the output signal s 1  of the oscillation circuit  25  which corresponds to the magnitude of the capacitance C and output this peak value to the differentiating circuit  27 . Although the output signal s 2  of the peak-hold circuit  26  corresponds to the magnitude of the capacitance, the change itself is slight. Therefore, the rate of change in the output signal s 2  of the peak-hold circuit  26  is obtained by the differentiating circuit  27 . The output signal s 3  of the differentiating circuit  27  therefore increases when the capacitance C changes rapidly due to the aspirating tube  6   a  through  8   a  contacting the liquid surface LS, and the contact between the liquid surface and the aspirating tube  6   a  through  8   a  can be detected in this way. 
         [0062]    The output signal of the capacitance detector  21  is input to the controller  22 . The controller  22  detects the position of the liquid surface LS of the reagent L from the output signal of the position detector  65  and the output signal of the capacitance detector  21 . The controller  22  also controls the drive unit  60  to further lower the aspirating tubes  6   a  through  8   a  to a position at which the reagent L can be aspirated based on the detected position of the liquid surface LS of the reagent L 
         [0063]    Although the reagent containers  100 ,  110  and  120  are installed in the reagent installation section  16 , there are various conductive member such as metal panels and screws surrounding the reagent installation section  16  as well as the reagent installation section  16  itself. The output of the capacitance detector  21  is affected not only by the reagent L within the reagent containers  100 ,  110 , and  120 , but also by conductors surrounding the aspirating tubes  6   a  through  8   a . Since the capacitance changes rapidly as the aspirating tubes  6   a  through  8   a  are moved in vertical directions and approach these conductors and move from these conductors, it becomes difficult to identify the change when the aspirating tube  6   a  through  8   a  makes contact with the liquid surface LS, and hence it becomes difficult to accurately detect the liquid surface LS. Since the capacitance changes rapidly when the aspirating tubes  6   a  through  8   a  move in vertical direction while accelerating or decelerating, it also becomes difficult to identify the change when the aspirating tubes  6   a  through  8   a  make contact with the liquid surface LS in this case. 
         [0064]    The liquid level detecting unit  20  of the present embodiment is configured to accurately detect the liquid surface LS of the reagent L by considering the change in capacitance between the aspirating tubes  6   a  through  8   a  and the surrounding environment other than the reagent L within the reagent containers  100 ,  110 , and  120 , as described below. 
         [0065]    Specifically, when reagent containers  100 ,  110 ,  120  are empty of reagent or reagent is consumed to the point the reagent cannot be aspirated by the aspirating tubes  6   a  through  8   a , that is, the reagent containers  100 ,  110 ,  120  installed in reagent installation section  16  contain reagent below the dead volume level, the controller  22  of the liquid level detecting unit  20  moves the aspirating tubes  6   a  through  8   a  in a vertical direction and obtains the change in capacitance corresponding to the position of the aspirating tube  6   a  through  8   a  in a vertical direction. The controller  22  then stores this signal as the “background signal” (referred to as “reference signal” below) in the memory  23 . In the present embodiment, the signal representing the capacitance when the aspirating tube  6   a  through  8   a  is moved is stored as the reference signal. The background signal is compared to the output signal of the capacitance detector  21  when the reagent is actually aspirated from the reagent containers  100 ,  110 ,  120  (referred to as “liquid level detection signal” or “real signal” below) to detect the liquid surface of the reagent L by eliminating the environmental influences around the reagent L. 
         [0066]    Note that “when the aspirating tubes  6   a  through  8   a  are moving” refers to the interval from the starting point of the aspirating tube (for example, dead bottom point) to the arrival point (for example, dead top point). The operation of moving the aspirating tube is not specifically limited insofar as overall the operation moves from the starting point to the arrival point, and may be an operation of continuously moving from the starting point to the arrival point, or may be an operation of repeatedly moving with intermittent starts and stops. 
         [0067]    Note that the background signal can be obtained and stored in memory  23  just once when the immunoanalyzer  1  is manufactured or installed, or can be obtained and stored in memory  23  automatically each time the power source of the immunoanalyzer  1  is turned on, that is, whenever the immunoanalyzer  1  is started. The output signal of the capacitance detector  21  changes when the metal parts are replaced and metal screws loosen around the containers. The background signal acquisition time and liquid level detection time are preferably closer than not in order to more accurately detect the liquid level. In the present embodiment, the background signal is automatically obtained at startup to cope with changes in the environment around the aspirating tubes  6   a  through  8   a.    
         [0068]    As shown in  FIG. 7 , conductors K such as metal panels and the like are present around the reagent containers  100 ,  110 ,  120 . Reagent is not accommodated within the reagent containers  100 ,  110 ,  120 . When the aspirating tube  6   a  through  8   a  is moved vertically in this situation, the obtained output signal of the capacitance detector  21  is on the right side of the graph. This output signal fluctuates greatly when the aspirating tube  6   a  through  8   a  approaches the conductor K and moves from the conductor K. This output signal also fluctuates greatly depending on the velocity change due to acceleration when the aspirating tube  6   a  through  8   a  starts to move downward from a higher stopped position. 
         [0069]    As shown in  FIG. 8 , a reagent L is contained in the reagent container  100 ,  110 ,  120 , and can be aspirated by the aspirating tube  6   a  through  8   a . When the aspirating tube  6   a  through  8   a  is moved vertically in this situation, the obtained output signal of the capacitance detector  21  is in the center of the graph. This output signal fluctuates greatly when the aspirating tube  6   a  through  8   a  accelerates, when the aspirating tube  6   a  through  8   a  makes contact with the reagent L, and when the aspirating tube  6   a  through  8   a  approaches a nearby conductor K and moves from a nearby conductor K. 
         [0070]    If the relationship between the background signal of  FIG. 7  and the liquid level detection signal is considered, it becomes possible to grasp the change of the liquid level detection signal based only on the influences when contact is made with the reagent L. Specifically, just the signal when the reagent L is contacted may be obtained by acquiring the differential between the background signal and the liquid level detection signal. A graph representing the differential signals is shown at the right side in  FIG. 8 . In the graph, the change when the aspirating tube  6   a  through  8   a  approaches and moves from the nearby conductor K, and the change when the aspirating tubes  6   a  through  8   a  are accelerating are canceled, and the only remaining signal represents when the aspirating tube makes contact with the reagent L in the reagent container  100 ,  110 ,  120 . 
         [0071]    A bubble or membrane (the term “bubble” covers the concept of both hereinafter) LB produced during transport or the like may be simply present within the reagent container  100 ,  110 ,  120 . The capacitance changes when the aspirating tube  6   a  through  8   a  makes contact with the bubble LB. In the graph showing the differential signals, it is understood that the differential signal changes when the not only when contact is made with the liquid surface LS of the reagent, but also when contact is made with the bubble LB. 
         [0072]    The change in the differential signal which accompanies contact with the bubble LB is difficult to recognize as the change in the differential signal which accompanies contact with the liquid surface LS. In the present embodiment, measures are therefore taken to discriminate between when the aspirating tube  6   a  through  8   a  makes contact with the liquid surface LS and when the tube makes contact with the bubble LS. Specifically, the memory  23  of the liquid level detecting unit  20  stores an estimated position of the liquid surface LS of the reagent L beforehand. Then, when the differential signal changes between the background signal and the liquid level detection signal, whether or not the aspirating tube  6   a  through  8   a  has made contact with the liquid surface LS is determined by comparing the position of the aspirating tube  6   a  through  8   a  and the estimated position of the liquid level. 
         [0073]    The specific control sequences of the acquisition of the background signal, and reagent liquid level detection mentioned above, are described in detail below with reference to  FIGS. 9 through 11 . Note that in  FIGS. 9 through 11  the term “background signal” is abbreviated to “BG signal.” 
       [Background Signal Acquisition] 
       [0074]    Empty reagent containers  100 ,  110 ,  120  or reagent containers  100 ,  110 ,  120  containing reagent below dead volume are pre-installed by a service person at predetermined positions on the inner table  162  and outer table  163  of the reagent installation section  16 . 
         [0075]    As shown in  FIG. 9 , the controller  22  controls the drive unit  60  to lower the aspirating tubes  6   a  through  8   a  when the power is switched on to the immunoanalyzer  1  (step S 1 ). 
         [0076]    The controller  22  obtains the position of the aspirating tubes  6   a  through  8   a  in the vertical direction from the position detector  65  (step S 2 ), and obtains the output signal of the capacitance detector  21  as the background signal B 1  (step S 3 ). 
         [0077]    The controller  22  associates the background signal B 1  with the position of the aspirating tube  6   a  through  8   a  in the vertical direction, and stores the data in the memory  23  (step S 4 ). 
         [0078]    The controller  22  then determines whether the aspirating tube  6   a  through  8   a  has arrived at the dead bottom point (step S 5 ). The dead bottom point is set at a position near but not touching the bottom of the reagent container  100 ,  110 ,  120  installed in the reagent installation section  16 . The process returns to step S 2  when the aspirating tube  6   a  through  8   a  has not arrived at the dead bottom point, and the process advances to step S 6  when the aspirating tube  6   a  through  8   a  has reached the dead bottom point. 
         [0079]    In step S 6 , the controller  22  raises the aspirating tubes  6   a  through  8   a , and obtains a background signal B 2  and the position of the aspirating tube  6   a  through  8   a  in the vertical direction (steps S 7 , S 8 ). The controller  22  associates the background signal B 2  with the position of the aspirating tube  6   a  through  8   a  in the vertical direction, and stores the data in the memory  23  (step S 9 ). The controller  22  repeats steps S 7  through S 9  until the aspirating tubes  6   a  through  8   a  are at the dead top point, and the process of stopping the aspirating tubes  6   a  through  8   a  ends (step S 11 ) when the controller  22  determines (that the aspirating tubes  6   a  through  8   a  have reached the top dead point (step S 10 ). 
         [0080]    When the aspirating tubes  6   a  through  8   a  are lowered background signals B 1  and B 2  are obtained by the operation described above when raising the tubes, and the data are stored in memory  23 . 
         [0081]    Note that the acquisition of background signals B 1  and B 2  as per above is accomplished for each reagent dispenser  6  through  8  containing reagents R 1  through R 3 , respectively. Suitable background signals B 1  and B 2  therefore are obtained for each reagent dispenser  6  through  8 . 
         [0082]    When the background signals B 1  and B 2  obtained by the controller  22  differ in magnitude from the background signals stored in the memory  23  (for example, when the differential of the former and latter background signals exceeds a predetermined threshold value), an error is considered to have occurred due to some large environmental fluctuation around the aspirating tubes  6   a  through  8   a , as well as dysfunction of a circuit or sensor in the system obtaining the background signals. Therefore, the controller  22  sends a summary to the control device  4 , and an error message is shown on the display/input section  410 , and an audio or optical warning is issued to alert the user by warning part. 
       [Reagent Aspiration Operation] 
       [0083]    As shown in  FIGS. 10 and 11 , the controller  22  controls the drive units  60  to lower the aspirating tubes  6   a  through  8   a  (step S 21 ). The positions of the aspirating tubes  6   a  through  8   a  in the vertical direction are obtained from the position detector  65  (step S 22 ), and the output signal of the capacitance detector  21  is obtained as the liquid level detection signal A 1  (step S 23 ). 
         [0084]    The controller  22  reads the background signals B 1  corresponding to the positions of the aspirating tube  6   a  through  8   a  from the memory  23  (step S 24 ), compares the background signal B 1  to the liquid level detection signal A 1  and determines the differential signal C 1  (C 1 =A 1 −B 1 ) (step S 25 ). The differential signal C 1  obtained at this time is equivalent to a signal represented in the graph on the right side of  FIG. 8 . 
         [0085]    The controller  22  determines whether the differential signal C 1  is greater than a predetermined threshold value D 1  (refer to  FIG. 8 ) (step S 26 ), and the process returns to step S 22  when the signal C 1  is less than the threshold D 1 , and the process advances to step S 27  when the signal C 1  is greater than the threshold D 1 . 
         [0086]    In step S 27 , the controller  22  determines whether the aspirating tubes  6   a  through  8   a  are at the estimated position of the liquid surface LS. The estimated position is obtained in step S 37  and will be described later. When initially performing the process of step S 27 , since the estimated position does not yet exist, the position of the liquid surface corresponding to the capacity when, for example, a new reagent container  100 ,  110 ,  120  is installed in reagent installation section  16  is set as the estimated position, and stored in memory  23 . 
         [0087]    Although the estimated position of the liquid surface LS may be a value represented by a point in the vertical direction, a predetermined width (for example, about 1 mm) in the vertical direction is set as the value in the present embodiment. When the leading end of the aspirating tube  6   a  through  8   a  matches the liquid level estimated position, that is, when the value is within the predetermined width, the position is determined to be the liquid surface LS of the reagent L, and the process advances to step S 28 . When the leading end of the aspirating tube  6   a  through  8   a  does not match the liquid level estimated position, the process advances to step S 30 , then the process returns to step S 22 . 
         [0088]    The controller  22  stops the lowering operation of the aspirating tubes  6   a  through  8   a  in step S 28 , and suctions the reagent L within the reagent containers  100 ,  110 ,  120  in step S 29 . The aspirating operation of the reagent L includes an operation of lowering the aspirating tubes  6   a  through  8   a  only a predetermined amount from the liquid level detection position of the reagent L. This predetermined amount is set at an amount which allows the aspirating tubes  6   a  through  8   a  to remain in the liquid even though the liquid surface LS declines in conjunction with the aspiration of the reagent L. 
         [0089]    On the other hand, in step S 30  the controller  22  sets the bubble contact flag to [1]. In step S 26 , when the differential signal C 1  is determined to be greater than the predetermined threshold value D 1 , the aspirating tubes  6   a  through  8   a  are considered to have made contact with the liquid surface LS of the reagent L or contact with the bubble LB above the liquid surface LS. In step S 27 , when the leading end of the aspirating tube  6   a  through  8   a  does not match the estimated position of the liquid level, there is a very high possibility that the aspirating tube  6   a  through  8   a  has made contact with the bubble LB. Therefore, in this case the aspirating tube  6   a  through  8   a  is determined to have made contact with the bubble LB, and the bubble contact flag is raised. Note that the bubble contact flag is used when the aspirating tube  6   a  through  8   a  is washed after reagent aspiration in step S 41  to be described later. 
         [0090]    The controller  22  then raises the aspirating tubes  6   a  through  8   a  (step S 31 ), obtains the vertical direction position of the aspirating tubes  6   a  through  8   a  from the position detector  65  (step S 32 ), and obtains the output signal of the capacitance detector  21  as the liquid level detection signal A 2  (step S 33 ). 
         [0091]    The controller  22  reads the background signals B 2  corresponding to the positions of the aspirating tube  6   a  through  8   a  from the memory  23  (step S 34 ), compares the background signal B 2  to the liquid level detection signal A 2  and determines the differential signal C 2  (C 1 =A 2 −B 2 ) (step S 35 ). The differential signal C 2  obtained at this time is equivalent to a signal represented in the graph on the right side of  FIG. 8 . 
         [0092]    The controller  22  determines whether the differential signal C 2  is greater than a predetermined threshold value D 2  (step S 36 ), and the process returns to step S 32  when the signal C 2  is less than the threshold D 2 , and the process advances to step S 37  when the signal C 2  is greater than the threshold D 2 . 
         [0093]    When the differential signal C 2  is greater than the threshold value D 2 , the controller  22  stores the positions of aspirating tubes  6   a  through  8   a  as the next estimated position of the liquid level being used in memory  23 , in step S 37 . 
         [0094]    Thereafter, the controller  22  obtains the position of the aspirating tubes  6   a  through  8   a  (step S 38 ), determines whether the aspirating tube  6   a  through  8   a  has reached the top dead point (step S 39 ), and stops the raising of the aspirating tube  6   a  through  8   a  when the tube has reached the top dead point (step S 40 ). 
         [0095]    Thereafter, the washing process of the aspirating tubes  6   a  through  8   a  is executed (step S 41 ), and the process ends. 
       [Aspiration Tube Washing Unit Structure and Operating Sequence] 
       [0096]    The aspirating tube washing process of step S 41  in  FIG. 11  is described in detail below. 
         [0097]    The measuring section  2  of the present embodiment is structurally described above, however, an aspiration tube washing unit  220  is also provided to wash the aspirating tubes  6   a  through  8   a  after reagent is aspirated and discharged. The aspirating tube washing unit  220  has a wash container  221 , and the wash container  221  has a washing orifice  222  through which the aspirating tubes  6   a  through  8   a  are inserted, and a washing nozzle  223  which discharges washing liquid into the wash container  221 . The wash container  221  is arranged within the range of movement of the aspirating tubes  6   a  through  8   a.    
         [0098]    The washing orifice  222  is an opening on the top end of the wash container  221 , and the aspirating tubes  6   a  through  8   a  can be inserted from this opening. The washing nozzle  223  is configured to wash the aspirating tubes  6   a  through  8   a  by discharging washing liquid obliquely from above through the washing orifice  222 , and spraying the washing liquid on the aspirating tubes  6   a  through  8   a  inserted in the washing orifice  222 . The washing range of the aspirating tubes  6   a  through  8   a  can be changed by changing the amount of insertion of the aspirating tubes  6   a  through  8   a  through the washing orifice  222 . 
         [0099]    The aspirating tube washing process of step S 41  of  FIG. 11  is described below referring to  FIG. 12 . 
         [0100]    The controller  22  determines whether the bubble contact flag obtained in step  30  of  FIG. 10  is set to [ 1 ] (step S 51 ). 
         [0101]    The process advances to step S 52  when the bubble contact flag is set to [1], and the process continues to step S 53  when the flag is not set to [ 1 ]. 
         [0102]    Since there is a high possibility that the aspirating tube  6   a  through  8   a  has made contact with the bubble LB when the bubble contact flag is set to [1] as previously described, the leading end of the aspirating tube  6   a  through  8   a  makes contact with the reagent L in a relatively broad range. Therefore, when the bubble contact flag is set to [1], a wider range of 70 mm from the bottom end of the aspirating tube  6   a  through  8   a  is washed in step S 52 . When the bubble contact flag is not set to [1], a narrower range of 10 mm from the bottom end of the aspirating tube  6   a  through  8   a  is washed in step S 53 . In this way the aspirating tubes  6   a  through  8   a  are reliably washed even when contact has been made with the bubble, and contamination is prevented. 
         [0103]    In step S 54 , the controller  22  initializes the bubble contact flag to [0] and the process ends. 
         [0104]    Note that the specific numerical values of the washing range of the aspirating tubes  6   a  through  8   a  are examples, and the present invention is not limited to these values. When the bubble contact flag is set to [1] as described previously, a signal may be sent to the control device  4  to display a message in the control device  4  indicating the aspirating tube  6   a  through  8   a  has made contact with the bubble. 
         [0105]    Since the liquid level is detected by the liquid level detecting unit  20  when the reagent L is aspirated from the reagent container  100 ,  110 ,  120  in the present embodiment described above, the aspirating tubes  6   a  through  8   a  can be reliably inserted into the reagent L for aspiration, the aspirating tubes  6   a  through  8   a  can be minimally inserted into the reagent L, and contamination can be prevented. 
         [0106]    Since the liquid level detecting unit  20  detects the liquid surface LS of the reagent L based on the liquid level detection signals (real signals) A 1  and A 2  and the background signals (reference signals B 1  and B 2 ) stored in memory  23 , the liquid surface LS of the reagent L can be accurately detected by excluding the influence of conductors K present around the reagent containers  100 ,  110 ,  120 , influence of changes in the moving speed of the aspirating tubes  6   a  through  8   a , and the influence of loosening metal screws and replaced metal parts around the containers. Because the influence of changes in moving speed of the aspirating tubes  6   a  through  8   a  is eliminated, the aspirating tubes  6   a  through  8   a  can operate at higher speed and the measurement cycle time can be reduced. 
         [0107]    The liquid level detecting unit  20  appropriately recognizes whether the aspirating tubes  6   a  through  8   a  have made contact with the liquid surface LS or made contact with the bubble LB by using the estimated position of the liquid surface LS of the reagent L. Erroneous aspiration of reagent L therefore is prevented when the bubble LB is mistakenly detected as the liquid surface LS. 
         [0108]    The measuring section  2  of the present embodiment can reliably prevent contamination because the liquid level detecting unit  20  detects whether the aspirating tubes  6   a  through  8   a  make contact with the bubble LB, and wash a wide range of the aspirating tubes  6   a  through  8   a  when the aspirating tube has made contact with the bubble LB. 
         [0109]    Note that the present invention is not limited to the above described embodiment and may be variously modified insofar as such modifications are within the scope of the claims. 
         [0110]    For example, although empty reagent containers or reagent containers holding reagent below dead volume are installed in the container holders of the reagent installation section when obtaining the background signal, the reagent need not necessarily be installed inasmuch as the background signal also may be obtained when the reagent container is not installed. However, an actually accurate background signal can be obtained by installing the reagent containers. 
         [0111]    Although the background signal is automatically obtained each time the power is switched on for the immunoanalyzer  1  in the above embodiment, the present invention is not limited to this configuration. For example, the background signal can be automatically obtained and stored in memory  23  when the reagent containers  100 ,  110 ,  120  are empty, or the liquid L within the reagent containers  100 ,  110 ,  120  is below dead volume. In this case, for example, the estimated position can be stored and whether the estimated position is less than the liquid level when the reagent in the container is at dead volume can be determined in step S 37  of  FIG. 11 . When it is determined that the estimated position is less than the liquid level when the reagent in the container is at dead volume, this determination result preferably becomes a trigger to start the background signal acquisition process shown in  FIG. 9 . 
         [0112]    Although the previously described liquid level detecting unit detects the liquid level of the reagent contained in a reagent container, the liquid level detecting unit also is applicable to detecting the liquid level of a sample held in a sample container. 
         [0113]    Although the control device in the above embodiment is integrated with a measuring section, the control device also may be configured as a stand alone personal computer or the like. 
         [0114]    Although the background signal in the device is obtained and stored in memory when the power is switched on to the immunoanalyzer, when the reagent container is empty, when the apparatus is manufactured, or at the time of installation in the above embodiment, the background signal also may be obtained by a separate immunoanalyzer, for example a prototype or master device. 
         [0115]    Although the immunoanalyzer  1  is described by way of example of an analyzer of the present invention in the above embodiment, the present invention is not limited to this embodiment. For example, the present invention also is applicable to other clinical analyzers such as blood coagulation measuring apparatus, multi item blood cell analyzer, urine component analyzer, gene amplification measuring apparatus and the like. 
         [0116]    Although the output signal of the capacitance detector is associated with the position in the vertical direction of the aspirating tubes  6   a  through  8   a  and stored as the reference signal representing a signal when the aspirating tube is moving in the above embodiment, the present invention is not limited to this embodiment. For example, the output signal also may be associated and stored when a predetermined time has elapsed since the start of movement of the aspirating tubes  6   a  through  8   a , or the output signal may be associated and stored with the travel distance of the aspirating tubes  6   a  through  8   a.    
         [0117]    Although an electrostatic capacity sensor is used as the capacitance detector  21  in the above embodiment, the detector is not specifically limited insofar as the capacitance detector  21  can detect changes in the physical characteristics between the aspirating tube and the environment surrounding the aspirating tube including the liquid level of the liquid within a liquid container. For example, in addition to an electrostatic capacity sensor, a voltage sensor, ultrasonic sensor, electrical resistance sensor or the like may be used as the capacitance detector  21 .