Abstract:
A particle signal processing apparatus which processes a particle signal representative of characteristics of particles includes an amplifier having input and output terminals for amplifying a particle signal including serial pulses to output an output signal including the amplified serial pulses, a filter section for extracting a low frequency component from the output signal of the amplifier so that the extracted component is fed back into the input terminal as a negative feedback signal, and a feedback signal control section for allowing the filter section to fix the negative feedback signal when each of the amplified pulses rises and to hold the fixed negative feedback signal while the amplified pulse is larger than a threshold value.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application is related to Japanese Patent Application No. 2000-120373 filed on Apr. 21, 2000, whose priority is claimed under 35 USC § 119, the disclosure of which is incorporated by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a particle signal processing apparatus and a particle measurement apparatus using the same, those apparatuses used for measurement of particles in body fluid and industrial particles.  
           [0004]    2. Description of the Related Art  
           [0005]    Conventionally, particle measurement apparatuses of the electric measurement type are provided with two chambers that communicate with each other through a micro through hole (orifice) and it is so arranged that when a particle-contained solution flows from one chamber to the other, a pulse-formed electric resistance change is detected as a particle signal each time a particle passes through the orifice. Since it is known that a peak value of the particle signal is proportional to a volume of the particle, the particle signal is utilized in calculating a particle diameter or in sorting out particles.  
           [0006]    But problems with such particle signal measurement apparatuses are that if bubbles contained in the particle-contained solution are present near the micro through hole, the obtained particle signal (pulse signal) fluctuates with respect to a base line (low frequency fluctuation) and it is difficult to determine the peak value of the particle signal accurately.  
         SUMMARY OF THE INVENTION  
         [0007]    In view of the prior art described above, it is an object of the present invention to provide a particle measurement apparatus in which a base line of a particle signal including serial pulses is stabilized to determine a peak value of each pulse signal accurately and which permits measurement of particles with precision.  
           [0008]    The object of the present invention is achieved by providing a particle signal processing apparatus which processes a particle signal representative of characteristics of particles, comprising: an amplifier having input and output terminals for amplifying a particle signal including serial pulses to output an output signal including the amplified serial pulses; a filter section for extracting a low frequency component from the output signal of the amplifier so that the extracted component is fed back into the input terminal as a negative feedback signal; a feedback signal control section for allowing the filter section to fix the negative feedback signal when each of the amplified pulses rises and to hold the fixed negative feedback signal while the amplified pulse is larger than a threshold value. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    A preferred embodiment of the present invention will be illustrated, and not by way of limitation, in conjunction with the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a block diagram of a particle measurement apparatus embodying the present invention.  
         [0011]    [0011]FIG. 2 is a detailed connection diagram of an essential part of the embodiment of the present invention.  
         [0012]    [0012]FIG. 3 is a detailed connection diagram of another essential part of the embodiment of the present invention.  
         [0013]    [0013]FIG. 4 is a waveform diagram of a particle signal in the embodiment.  
         [0014]    [0014]FIG. 5 is a waveform diagram showing the base line in the embodiment.  
         [0015]    [0015]FIG. 6 is a waveform diagram of a particle signal processed in the embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    The object particles to be determined in the present invention include a toner, graphite, silica, abrasive material, ceramic powder, pigment, powder paint, cultured cell, blood cell, yeast, plankton and magnetic powder. The particle measurement size ranges from submicrons to hundreds of microns in diameter.  
         [0017]    The particle signal processing apparatus according to the present invention is mainly applied to an electric resistance-type particle measurement apparatus but is not limited thereto, and may be applied to an optical-type particle measurement apparatus, for example.  
         [0018]    A commercial operational amplifier can be used as the amplifier in the particle signal processing apparatus.  
         [0019]    The filter section may be composed of a combination of an operational amplifier, a capacitor and a resistor - what is called a RC active filter.  
         [0020]    The feedback signal control section may be composed of a comparator for comparing the pulse output from the amplifier with the threshold value and an analog switch that is actuated by an output of the comparator.  
         [0021]    In the feedback signal control section, the output of the amplifier may be input to the comparator through a differential circuit. A commercially available comparator and analog switch may be used for the comparator and analog switch.  
         [0022]    The particle signal processing apparatus according to the present invention, when used in an electric resistance-type measurement apparatus, may include a flow cell having first and second chambers, an orifice section through which the first and second chambers communicate with each other, first and second electrodes provided in the first and second chambers respectively, and a detection section for detecting a change in impedance between the first and second electrodes as a particle signal.  
         [0023]    In this case, the particle measurement apparatus may further include an analysis section for analyzing the particle signal obtained from the particle signal processing apparatus.  
         [0024]    A microcomputer or personal computer may be used for the analysis section.  
         [0025]    The detection section in the above particle measurement apparatus may be include d.c. power source to supply a constant current between the first and second electrodes and a current/voltage conversion section to convert a change in a current flowing between the first and second electrodes into a voltage.  
         [0026]    [0026]FIG. 1 is a block diagram of a particle measurement apparatus embodying the present invention.  
         [0027]    In FIG. 1, a particle signal V 1  detected by a particle signal detecting section  1  is processed in waveform in a waveform processing section  20  and output to an analysis section  30  as particle signal V 2 . On the basis of the particle signal V 2 , the analysis section  30  counts and sorts out particles and calculates particle volumes and particle diameters. A results are output from an output section  40 .  
         [0028]    Configuration and operation of particle signal detection section  
         [0029]    In FIG. 1, the particle signal detection section  1  comprises a flow cell  2 , a sample liquid container  3  to hold a sample liquid containing particles to be measured, a suction nozzle  4  for sucking the sample liquid, valves  5 ,  6 ,  7 , a syringe  8 , a motor  9  for driving the syringe  8  and a sheath liquid container  10 . The flow cell  2  is composed of a first cell  2   a , a second cell  2   b , a orifice section  2   c  in which the first cell  2   a  communicates with the second cell  2   b  through a micro through hole (orifice) and a nozzle  2   d  to jet the sample liquid to the orifice section  2   c . In addition, an inlet port  2   e  to accept the sheath liquid from the container  10  through valve  7  is provided in the first cell  2   a , while an outlet port  2   f  to discharge the sheath liquid and sample liquid is provided in the second cell  2   b.    
         [0030]    Furthermore, inside the first cell  2   a  and the second cell  2   b  are provided electrodes  11 ,  12 , respectively. A d.c. power source  13  is provided to supply a constant current between electrodes  11 ,  12  through the orifice section  2   c.    
         [0031]    In such a particle signal detecting section  1 , if the valves  5 ,  6  are first opened for a predetermined period of time, the sample liquid is sucked by the suction nozzle  4  under a negative pressure until a flow path between the valves  5 ,  6  is filled with the sample liquid. Then, the sample liquid is discharged into the first cell  2   a  when the syringe  8  presses out the sample liquid between the valves  5 ,  6  to the sample nozzle  2   d  at a constant flow rate.  
         [0032]    The valve  7  is opened at the same time and thereby the sheath liquid is supplied to the first cell  2   a . And the sample liquid is sheathed with the sheath liquid, and further squeezed by the orifice section  2   c  to form a sheath flow.  
         [0033]    In the sheath flow, the particles contained beforehand in the sample liquid are aligned and flowed one by one in a line through the orifice  2   c . The sample liquid and the sheath liquid that have passed through the orifice  2   c  are discharged through the outlet port  2   f  of the second cell  2   b.    
         [0034]    An electric resistance or impedance between the electrodes  11  and  12  is determined by a conductivity (electrical conductivity) of the sheath liquid, an orifice size (sectional area) of the orifice section  2   c , an electrical conductivity of the sample liquid and a diameter of the sheath flow of the sample liquid.  
         [0035]    Meanwhile, as mentioned above, the constant current is supplied between the electrode  12  and the electrode  11  from the d.c. power source  13 . If a particle passes through the orifice section  2   c , the electric resistance at both ends of the orifice section  2   c  changes. Therefore, the current that flows between the electrode  12  and the electrode  11  changes in the form of pulse every time one particle passes. The maximum value of change (pulse height) is proportional with the size of the particle passing through the orifice section  2   c . This change in the current is converted into a voltage by a current/voltage converting section  14  and outputted as the particle signal V 1 . In this way, the particle signal detecting section  1  generates the particle signal V 1 .  
         [0036]    By the way, the current/voltage conversing section  14  can be formed of a condenser  1 , an operational amplifier M 1  and a resistor R 1  as shown in FIG. 2.  
         [0037]    Configuration and operation of waveform processing section  
         [0038]    The waveform processing section  20  shown in FIG. 1 includes a amplifier  21  to amplify the particle signal V 1  by a suitable degree of amplitude, a filter section  22  acting as a negative feedback element to extract a low frequency component from an output of the amplifier  21  as a feedback signal to be fed back into an input of the amplifier  21  and a feedback signal control section  23  to allow the filter section  22  to fix and hold the feedback signal from the output of the amplifier  21  while the pulse waveform output from the amplifier  21  is larger than a threshold value.  
         [0039]    [0039]FIG. 3 is a detailed connection diagram of the waveform processing section  20 . The amplifier  21  is formed of an operational amplifier M 2  and resistors R 2  to R 4 . And in the present embodiment, for example, the values of the resistors R 2  to R 4  are so set that the amplifier M 2  has a gain of 2.2.  
         [0040]    The filter section  22  is provided with an operational amplifier M 3 , a capacitor C 2 , resistors R 5  to R 8  to form an RC active filter. And the values of the capacitor C 2  and resistors R 5 , R 6  are so set that the filter section  22  works as a low pass filter with a cutoff frequency of 1 kHz. To a non-reversible input of the operational amplifier M 3  is applied with a reference voltage V 3 , for example, 2 V.  
         [0041]    The feedback signal control section  23  is provided with a comparator M 4  and a differential circuit composed of an analog switch SW, resistors R 9 , R 10  and a capacitor C 3 . To the comparator M 4 , a reference voltage (threshold voltage) V 4  is applied. The comparator M 4  turns on the analog switch SW when a signal V 5  output from the differential circuit is larger than the threshold voltage V 4 .  
         [0042]    As the operational amplifiers M 1 , M 2  and M 3  can be used Model LMV 824M made by National Semiconductor. As the comparator M 4  can be used Model LMV331M5 made by National Semiconductor. In case the output needs to be kept low in offset voltage, it is desirable to use an operation amplifier of a low offset voltage as the operational amplifier M 3 .  
         [0043]    The operation of the above described configuration will be explained.  
         [0044]    A pulse signal having a pulse waveform as shown in FIG. 4 is inputted to the amplifier  21  as the particle signal V 1  from the particle signal detecting section  1 . The pulse signal shown in FIG. 4 has a low frequency component as shown in FIG. 5, which causes the base line of the pulse waveform in FIG. 4 to fluctuate.  
         [0045]    The pulse signal output from the amplifier  21  is filtered through the filter section  22 , and the low frequency component shown in FIG. 5 is negatively fed back into the amplifier  21 . Therefore, the low frequency component shown in FIG. 5 is removed from the pulse signal shown in FIG. 4, and the output waveform of the amplifier  21  become a waveform with a stable base line as shown in FIG. 6.  
         [0046]    But it is difficult to sufficiently extract only the low frequency component shown in FIG. 5 from the output of the amplifier  21  by the filter section  22  and a pulse signal component (high frequency component) partially passes the filter section  22  and is negatively fed back into the amplifier  21 . That causes the pulse waveform shown in FIG. 6 to strain.  
         [0047]    It is the feedback signal control section  23  that is provided to eliminate that strain. In the feedback signal control section  23 , the comparator M 4  compares the voltage V 5 , i.e., a differentiated value of the output V 2  of the amplifier  21  with the reference voltage V 4  and turns on the analog switch SW while the voltage V 5  is larger than the voltage V 4 , that is, only during a period of time corresponding to the pulse width of each pulse contained in the output V 2 .  
         [0048]    When the analog switch SW turns on, the voltage V 3  (2 V) is applied to two input terminals of the operational amplifier M 3  in the filter section  22 . Therefore, the filter section  22  does not function as the filter, and the feedback signal is fixed to the voltage just before the analog switch SW is turned on. Thus, because the pulse waveform component is not fed back, an unstrained pulse waveform can be obtained from the amplifier  21 .  
         [0049]    In the feedback signal control section  23 , the output of the amplifier  21  is input to the comparator M 4  through the differential circuit composed of the condenser C 3  resistors R 9 , R 10 . That circuit is provided to quickly detect a rise of the pulse. A detection level of the pulse can be adjusted with the voltage V 4  and a differential constant determined by the capacitor C 3  and resistors R 9 , R 10 .  
         [0050]    In case the rise of the pulse is quick enough, the above-mentioned differential circuit may be removed to input the output of the amplifier  21  directly to the comparator M 4 .  
         [0051]    The signal shown in FIG. 6 should be reversed in polarity with respect to the polarity of pulse in FIG. 4 in the present embodiment. But for sake of clarity, an unreversed waveform is shown.  
         [0052]    Thus, the particle signal (pulse signal) V 2  with a stable base line is inputted into the analysis section  30 . Therefore, the analysis section  30  can count the particles from the particle signal V 2  and calculates the particle volume and particle size with high precision and outputs them to the output section  40 .  
         [0053]    According to the present invention, the base line of the particle signal can be stabilized, which permits an accurate measurement of particles on the basis of the particle signal.  
         [0054]    Since the feedback is stopped for the pulse corresponding to each particle, the present invention is more effective in preventing the particle signal from straining. In the present invention, the base line is kept from fluctuating and amplifies the particle signal to make good use of the voltage range in the circuit. Especially when the dynamic range of the signal handled is large or the source voltage in the circuit is low, good results can be achieved.