JP6989359B2 - Liquid level detection device and liquid level detection method - Google Patents

Description

The present invention relates to a liquid level detecting device and a liquid level detecting method.

Conventionally, the nozzle itself that sucks liquid from the liquid storage container is used as a liquid level detection sensor that detects the electrostatic capacity in the liquid storage container, and a liquid that outputs a liquid level detection signal based on the electrostatic capacity detected by the sensor. There is a liquid level detection device having a surface detection circuit. The liquid level detection device utilizes the fact that the relative permittivity of water is higher than the relative permittivity of air, and detects the liquid level by capturing the change in capacitance due to the nozzle coming into contact with the liquid surface (Patent Document 1). ).

Japanese Unexamined Patent Publication No. 2-254365

In the above-mentioned liquid level detection device, an automatic adjustment function is provided to eliminate the influence of peripheral members, but even if the nozzle comes into contact with the liquid level, the amount of change in the oscillation frequency does not exceed the threshold value, and the liquid level rises. In some cases, it was not detected.

An object of the present invention is to provide a liquid level detection device capable of improving the accuracy of liquid level detection.

One aspect of the present invention is an oscillation circuit that oscillates with a time constant that depends on the capacitance between the first electrode and the second electrode.
A drive unit that moves the first electrode in the vertical direction,
The difference between the oscillation frequency of the oscillation circuit in the first state where the first electrode and the liquid surface are not in contact with each other and the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered exceeds the threshold value. In some cases, the detector that detects the liquid level and
A calculation unit that calculates the amount of deviation between the oscillation frequency of the oscillation circuit in the first state and the set value prepared in advance.
A correction unit for correcting the threshold value or the oscillation frequency of the oscillation circuit based on the deviation amount is provided.

Further, in another aspect of the present invention, the first electrode and the second electrode are described by using an oscillation circuit that oscillates at a time constant depending on the capacitance between the first electrode and the second electrode that can contact the liquid surface. A step of calculating the amount of deviation between the oscillation frequency of the oscillation circuit in the first state where the liquid level is not in contact with the set value prepared in advance, and
The step of correcting the threshold value or the oscillation frequency of the oscillation circuit based on the deviation amount, and
A step of detecting the liquid level when the difference between the oscillation frequency of the oscillation circuit in the first state and the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered exceeds the threshold value. It is a liquid level detection method including.

According to the present invention, the accuracy of liquid level detection can be improved.

It is a perspective view which showed the schematic structure of the analysis apparatus including the liquid level detection apparatus which concerns on embodiment. It is a figure which shows the control system of the analyzer which concerns on embodiment. It is a figure which shows typically the capacitance between a nozzle and a housing of a device. It is a figure which shows the structural example of the liquid level detection apparatus which concerns on embodiment. It is a figure which shows an example of an oscillation circuit. It is a sequence diagram which shows an example of a liquid level detection process. It is a flowchart which shows the example of the liquid level detection processing. It is explanatory drawing of the liquid level detection threshold value.

The liquid level detection device according to the embodiment of the present invention includes the following.
(1) Oscillation circuit that oscillates with a time constant that depends on the electrostatic capacitance between the first electrode and the second electrode (2) Drive unit that moves the first electrode in the vertical direction (3) The first electrode When the difference between the oscillation frequency of the oscillation circuit in the first state where the liquid surface is not in contact with each other and the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered exceeds the threshold value, the liquid Detection unit that detects the surface (4) Calculation unit that calculates the amount of deviation between the oscillation frequency of the oscillation circuit in the first state and the set value prepared in advance (5) The threshold value or the above based on the deviation amount. Correction unit that corrects the oscillation frequency of the oscillation circuit

According to the liquid level detection device according to the embodiment, the threshold value or the oscillation frequency of the oscillation circuit is corrected based on the amount of deviation between the oscillation frequency of the oscillation circuit in the first state and the set value prepared in advance. As a result, even if the oscillation frequency deviates from the set value, the accuracy of the liquid level detection can be improved by the correction by the correction unit.

The oscillation frequency may be measured as the number of oscillations per unit time of the oscillation circuit, or may be measured as the length of time required for the oscillation circuit to oscillate a predetermined number of times. The oscillation frequency in the first state used for liquid level detection and the oscillation frequency in the first state used for correction may be measured at the same timing or at different timings.

In the liquid level detection device according to the embodiment, when the oscillation frequency of the oscillation circuit in the first state is smaller than the set value, the correction unit performs correction to make the threshold value larger than the threshold value set value prepared in advance. It is also good. Further, when the oscillation frequency of the oscillation circuit in the first state is larger than the set value, the correction unit may make a correction to make the threshold value smaller than the threshold value set value prepared in advance.

In the liquid level detection device, the correction unit is based on the following formula.
The threshold value may be corrected by using the threshold value = correction coefficient (measured value of time length-set value of time length) + set value of threshold value.

Further, in the liquid level detection device, the correction unit has a capacitance setting value C used for calculating the time constant, an oscillation frequency setting value F of the oscillation circuit, and an oscillation frequency F'of the oscillation circuit in the first state. , The following formula,
C'= CC × (F / F'-1)
And may be used to make a correction to change the capacitance used for calculating the time constant to C'.

Further, in the liquid level detection device, the correction unit uses the resistance value setting value R used for calculating the time constant, the oscillation frequency setting value F of the oscillation circuit, and the oscillation frequency F'of the oscillation circuit in the first state. The following formula,
R'= RC × (1-F' / F)
And may be used to make a correction to change the resistance value used for calculating the time constant to R'.
Both F and F'described above indicate the oscillation frequency of the oscillation circuit in the first state. F assumes the oscillation frequency at a fixed temperature and humidity at normal temperature and humidity, and F'assumes the oscillation frequency at high temperature and high humidity or low temperature and low humidity.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the configuration of the embodiment. For example, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention to those alone unless otherwise specified.

(Embodiment)
FIG. 1 is a perspective view showing a schematic configuration of an analyzer 1 including a liquid level detection device according to an embodiment. The analyzer 1 is an apparatus that performs a predetermined analysis on a sample. In this embodiment, a urine analyzer using a reagent pad will be described as an example, but other analyzers may be used. Further, the liquid level detection device may be mounted on a device other than the analyzer, or may be a single device. It includes a control unit 3, a mounting unit 4, a nozzle 10, and a display unit 18 housed in a housing 2 of the analyzer 1. A container 30 (see FIG. 3) containing a liquid sample is placed on the placing portion 4. The nozzle 10 sucks and collects a sample from the container 30 placed on the mounting portion 4, and drops (dotted) the sample onto a plurality of reagent pads placed on a test paper. Examples of the sample include urine, blood, and body fluid. Further, as the sample container, a urine collection cup, a test tube (including Spitz), or the like can be exemplified.

Reflection or absorption at a specific wavelength is measured by an optical system installed inside the analyzer 1 for the sample spotted on the reagent pad, and the inspection result based on the measurement result is output to the display unit 18.

FIG. 2 is a diagram illustrating a control system included in the analyzer 1 according to the embodiment. The control unit 3 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, and a RAM.
It includes a (Random Access Memory) 13, an EEPROM (Electrically Erasable Programmable Read-Only Memory) 14, and an interface circuit (I / F) 15, and is connected to each other by a bus line 16.

A display unit (display) 18, an operation unit 19, a motor drive unit 21, a pump drive unit 22, a valve drive unit 23, and a liquid level detection unit 24 are connected to the interface circuit 15.

The CPU (central processing unit) 11 operates based on a program stored in the ROM (read only memory) 12 and read in the RAM (random access memory) 13, and controls the entire analyzer 1. The ROM 12 stores programs and data for operating the CPU 11. The RAM 13 provides a work area to the CPU 11 and temporarily stores various data and programs. The EEPROM 14 stores various setting data and the like. The EEPROM 14 is an example of an auxiliary storage device, and a non-volatile storage medium other than the EEPROM (hard disk, SSD (Solid State Drive), etc.) can be applied. The interface circuit 15 controls communication between the CPU 11 and various circuits.

The display unit 18 includes an LCD (liquid crystal display), a light emitting diode, and the like, and is controlled by the CPU 11 to display various information and inspection results. The operation unit 19 includes keys, buttons, switches, and the like, and supplies operation signals according to user operations to the CPU 11.

The nozzle 10 is moved horizontally and vertically by the motor drive unit 21. The liquid level detection unit 24 detects the liquid level 32 in the container 30. The display unit 18, the operation unit 19, the motor drive unit 21, the valve drive unit 23, and the liquid level detection unit 24 are controlled by the CPU 11 of the control unit 3.

The liquid level 32 of the sample (an example of "liquid") 31 housed in the container 30 is detected by the liquid level detection unit 24. The liquid level 32 can be detected as follows. For example, consider a capacitor C1 whose electrodes are the nozzle 10 and the housing 2 of the grounded analyzer 1, as shown in FIG. The wall surface of the housing 2 referred to here is a side wall surface facing the nozzle 10 via the container 30. The capacitance of the capacitor C1 is calculated by the following equation 1.
Capacitance = ε ₀ × ε _r × S / d ・ ・ ・ (Equation 1)
However, ε ₀ is the permittivity of the vacuum, ε _r is the relative permittivity, S is the electrode surface area, and d is the distance between the electrodes.

The relative permittivity takes a value according to the substance. For example, the relative permittivity of air is about 1.0 and the relative permittivity of water is about 80. Therefore, the capacitance when the nozzle 10 is in contact with the liquid surface 32 is 80 times the capacitance before the nozzle 10 is in contact with the liquid surface 32. By capturing such a change in capacitance, the liquid level can be detected. In this way, when the nozzle comes into contact with the liquid surface, the capacitance changes significantly, so we thought that the effects of the environment such as humidity and temperature could be ignored. However, as a result of analyzing the cause of the false detection of the liquid level, it was found that it was affected by environmental factors more than expected.

However, since it is difficult to directly measure the capacitance, an oscillation circuit (also referred to as an RC oscillation circuit or CR oscillation circuit) including the capacitor C1 shown in FIG. 3 in the RC circuit is prepared, and the unit time of the oscillation circuit is set. The change in capacitance is captured by the number of oscillations per hit (including the oscillation frequency).

In the example shown in FIG. 3, the nozzle 10 is one of the two electrodes forming the capacitor C1 (corresponding to the first electrode capable of contacting the liquid surface), and the wall surface of the grounded housing 2 forms the capacitor C1. The case where it becomes the other of one electrode (corresponding to the second electrode) is illustrated. However, a member other than the nozzle 10 that comes into contact with the liquid surface 32 may be used as the first electrode.

FIG. 4 is a diagram showing a configuration example of a liquid level detection device including a liquid level detection unit 24, and FIG. 5 shows an example of an oscillation circuit. The liquid level detection unit 24 includes a CPU 41, an oscillation circuit 42, and a memory 45 connected to the CPU 41.

As shown in FIG. 5, the oscillation circuit 42 includes a comparator 43. The comparator 43 compares the voltage at point A and the voltage at point B, which are inputs. When the voltage at point A is lower than the voltage at point B, the output V _out of the comparator 43 (oscillation circuit 42) becomes 0 [V], and when the voltage at point A is higher than the voltage at point B, the comparator 43 _{The output V out} of (oscillation circuit 42) is the power supply voltage V _cc [V].

The resistance element R4 and the capacitor C1 constitute an RC circuit 44, and the output V _out of the oscillation circuit 42 is a time constant τ (τ =) determined by the resistance value of the resistance element R4 and the capacitance of the capacitor C1.
It becomes an oscillation waveform (hereinafter referred to as pulse) of the transmission frequency according to resistance × capacitance). The capacitor C1 is the capacitor C1 shown in FIG. 3, and one electrode forming the capacitor C1 is provided on the nozzle 10 and the other electrode is provided on the housing 2. When the nozzle 10 comes into contact with the liquid surface 32, the capacitance of the capacitor C1 increases, so that the time constant τ increases and the oscillation frequency (the number of oscillations per unit time) decreases. The pulse output from the oscillation circuit 42 is input to the CPU 41.

The CPU 41 performs a liquid level detection process (also referred to as a sample detection process) by executing a program stored in the memory 45. In the liquid level detection process according to the embodiment, the time length of a predetermined number of pulses output from the oscillation circuit (that is, the time length required for the oscillation circuit to oscillate a predetermined number of times) is measured and measured as the oscillation frequency. The threshold is corrected based on the value. Therefore, the liquid level detection process includes a process of measuring the time length of a predetermined number of pulses, a process of detecting a liquid level (sample) using a predetermined number of pulse time lengths and a threshold value, and a process of correcting the threshold value. I do. That is, the CPU 41 operates as a measurement unit, a detection unit, a calculation unit, and a correction unit by executing the program.

The memory 45 is a storage medium for storing a program and data, and as data, for example, a predetermined number of pulse time length set values (hereinafter referred to as “time length set value”) and a threshold value, which are prepared in advance, respectively. (Hereinafter referred to as "threshold setting value") and the like are stored.

The time length set value is output from the oscillation circuit 42 when the nozzle 10 (first electrode) and the liquid surface 32 are not in contact with each other (corresponding to the first state) under reference conditions in which the environmental condition and the measurement position are fixed. The time length of a predetermined number of pulses is shown. The time length of a predetermined number of pulses may be expressed in time units (seconds, etc.), but here, the value obtained by dividing the time length by the unit time length (that is, a unit included in the time length of a predetermined number of pulses). Notated by the number of time lengths). The predetermined number and unit time length can be appropriately selected.

The time length of a predetermined number of pulses depends on the number of oscillations (oscillation frequency) per unit time, and becomes larger as the number of oscillations (oscillation frequency) becomes smaller. The threshold value setting value is determined in consideration of the time length of a predetermined number of pulses increased by the contact between the nozzle 10 and the liquid surface 32 and the reference time length setting value. That is, the liquid level 32 is detected when the difference between the time length of a predetermined number of pulses and the time length set value, which corresponds to the amount of change in the number of oscillations, is equal to or greater than the threshold set value.

As an example, the CPU 41 measures the time length of a predetermined number of pulses at the start of liquid level detection as follows. As described above, the measurement is performed by counting the number of unit time lengths included in the time lengths of a predetermined number of pulses. The CPU 41 repeats the extraction of a predetermined number of pulses from the oscillation circuit 42 n times. Although n is, for example, 5, the value of n may be more or less than 5, and a value of 1 or more can be appropriately set. Of the count values of the number of unit time lengths for n times, the maximum count value and the minimum count value are discarded, and the average value of the remaining count values is obtained as the first time length. In addition, the number of unit time lengths obtained by one count may be used as the first time length. When n is twice, the average value may be set as the first time length. When n is 3 times, the first time length may be the one excluding the minimum value and the maximum value of the count value. The first time length corresponds to "the oscillation frequency of the oscillation circuit in the first state where the first electrode and the liquid surface are not in contact with each other".

The CPU 41 starts and ends the liquid level detection process according to an instruction from the CPU 11 that controls the operation of the nozzle 10. The CPU 11 supplies the nozzle unit 31 with control amount data of the nozzle 10 including the rotation amount of a motor (not shown). The nozzle unit 31 includes a motor drive unit 21 (corresponding to a drive unit), a motor (not shown), an actuator for the nozzle 10 (not shown), a nozzle 10, and the like. The motor drive unit 21 drives the motor and the actuator according to the control amount supplied from the CPU 11, moves the nozzle 10 in the vertical direction and the horizontal direction, and arranges the nozzle 10 at a predetermined position. The liquid level detection unit 24 may be provided in the same device as the CPU 11 and the nozzle unit 31, or may be retrofitted to the device including the CPU 11 and the nozzle unit 31. When the CPU 11, the nozzle unit 31, and the liquid level detection unit 24 are provided in the same device, the processing performed by the CPU 11 and the processing performed by the CPU 41 may be performed by the same CPU (processor). The first electrode may be attached to the nozzle 10 so that the first electrode moves up and down together with the nozzle 10.

FIG. 6 is a sequence diagram showing an example of the liquid level detection process. At the start of the liquid level detection process, the CPU 11 (first CPU) controls the motor drive unit 21 to move the lower end of the nozzle 10 to a position facing the liquid level 32 of the container 30. The CPU 11 supplies a start instruction for the liquid level detection process to the CPU 41 (second CPU) (FIG. 6 <1>). Upon receiving the start signal of the liquid level detection process, the CPU 41 calculates the first time length by the method described above (FIG. 6 <2>). The CPU 11 lowers the nozzle 10 while increasing the lowering speed of the nozzle 10 (FIG. 6 <3>). After a lapse of a certain period of time, the CPU 11 changes the descending speed so that the nozzle 10 descends at a constant speed (FIG. 6 <4>). The measurement timing of the first time length of <2> may be before the nozzle 10 comes into contact with the liquid surface or before the start of the descent of the nozzle 10 described above, and the nozzle 10 is descending (liquid). It may be before contact with the surface 32). For example, the first time length may be measured when the tip of the nozzle reaches the upper end of the container 30.

Subsequently, the CPU 41 performs threshold value correction and a second time length measurement process (FIG. 6 <5>). Then, the CPU 41 determines the presence or absence of the liquid level (sample) by using the second time length and the threshold value measured after the measurement of the first time length (FIG. 6 <6>).

FIG. 7 is a flowchart showing the details of the processing of the CPU 11 and the CPU 41, and FIG. 8 is an explanatory diagram of the threshold value correction. The CPU 41 receives a start signal (start instruction) of the liquid level detection process from the CPU 11 (S01). Upon receiving the start signal, the CPU 41 measures the first time length (S02).

The CPU 41 calculates the liquid level detection threshold value (S03). That is, the CPU 41 has a threshold value (liquid level detection) used for the liquid level detection determination from the first time length measured in S02 and the time length set value and the threshold value set value prepared in advance in the memory 45 and read from the memory 45. Threshold) is calculated. The CPU 41 calculates the liquid level detection threshold value using the following equation 2.
Liquid level detection threshold =
Correction coefficient x (first time length-time length setting value) + threshold value setting value ... (Equation 2)
However, in Equation 2, the correction coefficient, the time length setting value, and the threshold value setting value are constants. “(First time length-time length set value)” in Equation 2 corresponds to “amount of deviation between the measured value of the value related to the oscillation frequency and the set value of the value related to the oscillation frequency”. The unit of the first time length, the time length setting value, and the threshold value setting value is "pieces". However, the first time length, the time length setting value, and the threshold value setting value may be expressed in the unit of time [sec] obtained by multiplying the number by the unit time length. As described above, the first time length is used to calculate the liquid level detection threshold value, "measurement of the value related to the oscillation frequency measured in a state where the first electrode and the liquid surface are not in contact with each other. It is also an example of "value". However, the time length measured at a timing different from the first time length may be used for correcting the liquid level detection threshold value.

For example, it is assumed that the correction coefficient = −0.5, the threshold setting value = 50 [pieces], and the time length setting value = 100 [pieces]. In this case, if the measured value of the first time length is, for example, 90, the liquid level detection threshold value is 55 [pieces]. On the other hand, if the first time length is, for example, 120, the liquid level detection threshold is 40 [.
Pieces]. As described above, when the first time length is smaller than the time length set value, the liquid level detection threshold value is corrected to a value larger than the threshold value set value. When the first time length is larger than the time length set value, the liquid level detection threshold value is corrected to a value smaller than the threshold value set value. In this way, the difference between the time length set value prepared in advance and the first time length which is the actually measured time length is absorbed by increasing or decreasing the threshold value. An allowable range is set in the correction range of the threshold value. In the example of FIG. 8, the correction range of the reference threshold value is defined so that the upper limit value and the lower limit value of the threshold value are ± 50% of the threshold value setting value (allowable range coefficient 1). However, the method of adopting the allowable range coefficient x (0 <x ≦ 1) can be appropriately set. If the correction of the threshold value exceeds the permissible range, the correction may not be performed, the error may be determined, and the user may be notified by outputting to that effect to the display unit 18.

Returning to FIG. 7, the CPU 41 that has calculated the liquid level detection threshold determines whether or not the liquid level detection is continuing (S04). This determination can be made based on whether or not the CPU 41 has received the end signal of the liquid level detection from the CPU 11. Alternatively, it can be determined by whether or not the CPU 41 continuously receives the liquid level detection instruction (same as the liquid level detection start signal) from the CPU 11. If it is determined that the liquid level detection is not ongoing, the CPU 41 determines that there is no sample (liquid level 32).

The CPU 41, which determines that the liquid level detection is ongoing, measures a predetermined number of pulses from the output of the oscillation circuit 42, and divides the time length of these predetermined number of pulses by the unit time length (second time length). Is calculated (S05). The second time length corresponds to "the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered".

In S06, the CPU 41 determines whether or not the difference between the first time length and the second time length (value obtained by subtracting the first time length from the second time length) exceeds the liquid level detection threshold value. do. This determination is made using, for example, the following equation 3.
Second time length ≥ first time length + liquid level detection threshold ... (Equation 3)

That is, the CPU 41 determines whether or not the second time length measured after the measurement of the first time length is equal to or greater than the sum of the first time length and the liquid level detection threshold value. When the nozzle 10 comes into contact with the liquid surface 32, the capacitance of the capacitor C1 increases, so that the value of the time constant τ increases and the number of oscillations per unit time decreases. That is, the second time length increases.

If it is determined in S06 that the difference between the second time length and the first time length is equal to or greater than the liquid level detection threshold value (Yes in S06), the CPU 41 advances the process to S07, and if not, the process proceeds to S07. (No of S06), the CPU 41 returns the process to S04. In S07, the CPU 41 determines whether or not a certain time has elapsed after detecting that the difference between the second time length and the first time length is equal to or greater than the liquid level detection threshold value. If it is determined that a certain time has elapsed (Yes in S07), the CPU 41 determines that there is a sample (liquid level 32), and if not (No in S07), the CPU 41 returns the process to S04. In this way, when the state in which the difference between the second time length and the first time length is equal to or higher than the liquid level detection threshold value continues for a certain period of time, it is determined that the sample (liquid level) is present. The loop of S04 to S07 is repeated until the above-mentioned conditions of S06 and S07 are satisfied or it is determined in S04 that the liquid level detection is not continuing. In the process of FIG. 7, it is determined that the sample (liquid level 32) is detected after waiting for the continuation for a certain period of time, but it may be determined that the sample (liquid level) is detected without waiting for the continuation for a certain period of time. ..

Returning to FIG. 6, when the CPU 41 determines that the sample (liquid level 32) is present, the CPU 41 sends a signal indicating the presence of the sample to the CPU 11. The CPU 11 receives a signal with a sample (FIG. 6 <7>). Then, the CPU 11 starts decelerating the descending speed of the nozzle 10 (FIG. 6 <8>), stops the descending of the nozzle 10 after a lapse of a predetermined time (FIG. 6 <9>), and signals the end of the liquid level detection process. It is sent to the CPU 41 (FIG. 6 <10>). The CPU 41 receives the end signal and ends the liquid level detection process. After that, the CPU 11 performs predetermined control for analysis such as collection of a sample (liquid) by suction of the nozzle 10.

When measured under the reference conditions, the time length of a predetermined number of pulses is constant, but fluctuates due to the influence of the surrounding environment such as humidity and temperature. According to the liquid level detection device according to the embodiment, the liquid level detection threshold value is corrected according to the difference between the first time length and the time length set value, so that the temperature of the place where the liquid level detection device is placed and the temperature of the place where the liquid level detection device is placed can be determined. Even if the oscillation frequency of the oscillation circuit 42 deviates due to humidity, the deviation can be absorbed and the liquid level can be detected with high accuracy.

<Modification 1>
In the above-described embodiment, a predetermined number of pulses are extracted, and the time length of the predetermined number of pulses (the time length required for the oscillation circuit to oscillate a predetermined number of times) is measured as the "oscillation frequency". The time length of this predetermined number of pulses depends on the number of oscillations (oscillation frequency) per unit time of the oscillation circuit 42. Therefore, instead of the time length of a predetermined pulse, the number of oscillations per unit time can be measured as the oscillation frequency.

For example, instead of the first time length, the CPU 41 sets the number of oscillations per unit time at a predetermined timing (for example, at the start of the liquid level detection process) as the first oscillation number (oscillation frequency of the oscillation circuit in the first state). The number of oscillations per unit time after that is calculated as the second number of oscillations (corresponding to the oscillation frequency of the oscillation circuit in the second state), and the difference between the first number of oscillations and the second number of oscillations. When is equal to or greater than the liquid level detection threshold value (| first number of oscillations-second number of oscillations | ≧ liquid level detection threshold value), the liquid level may be detected. The first number of oscillations may be obtained by finding the number of oscillations per n times unit time, discarding the maximum value and the minimum value, and finding the average value of the remaining number of oscillations. In the first modification, the oscillation number setting value is prepared in advance in the memory 45 instead of the time length setting value. The liquid level detection threshold value is obtained by the formula of "liquid level detection threshold value = correction coefficient x (first oscillation number-oscillation number setting value)) + reference threshold value". However, the measured value of the number of oscillations used for calculating the liquid level detection threshold value may be one measured at the same timing as the measurement timing of the first oscillation number, or one measured at a different timing. .. In short, the number of oscillations per unit time measured in a state where the nozzle 10 (first electrode) and the liquid surface 32 are not in contact with each other may be used.

<Modification 2>
In the first embodiment and the first modification, the liquid level 32 is detected by using the liquid level detection threshold value obtained by correcting the threshold value set value. Instead of the configuration for correcting the threshold value, it is conceivable to correct the oscillation frequency and use the threshold value set value fixedly. In this case, for example, the oscillation frequency is corrected by changing the capacitance and the resistance value of the RC circuit included in the oscillation circuit 42.

For example, the set oscillation frequency, which is the set value of the oscillation frequency of the oscillation circuit 42, can be expressed by the following equation 4.
F = 1 / A × R × C ... (Equation 4)
However, A is a constant, R is a resistance value, and C is a capacitance.

When the actual oscillation frequency F'is deviated from the set oscillation frequency F due to humidity, temperature change, or the like, the capacitance changes from C to C + δC. The oscillation frequency F'is expressed by the following equation 5.
F'= 1 / A × R × (C + δC) ・ ・ ・ (Equation 5)
The oscillation frequency F'can be corrected by either a method of changing the capacitance of the RC circuit (first method) or a method of changing the resistance value (second method).

(First method)
The ratio between the oscillation frequency F'and the oscillation frequency set value F is expressed by the following equation 6.
F'/ F = {1 / A x R x (C + δC)} x {A x R x C / 1}
= C / (C + δC) ... (Equation 6)
From the formula 6, the capacitance C is changed to C'represented by the following formula 7. Specifically, the capacitance of the capacitor C1 is changed to C'by changing the dielectric between the electrodes of the capacitor C1 (FIG. 5) forming the RC circuit 44 in the oscillation circuit 42, and the frequency is corrected. do. This will result in
The deviation of the oscillation frequency can be eliminated, and the liquid level 32 can be detected by determining whether the difference between the first and second measured values is equal to or greater than the threshold set value without changing the threshold set value.
C'= C-δC = C-C × (F / F'-1) ... (Equation 7)

(Second method)
When correcting with the resistance value, it is necessary that the following equation 8 is satisfied for the ratio F'/ F of the oscillation frequency.
F'/ F = {1 / A × (R-δR) × (C + δC)} × (A × R × C / 1) = 1 ... (Equation 8)
At this time, it is sufficient that the following equation 9 holds.
C / (C + δC) = R-δR / R ... (Equation 9)
Here, since δC = C × (F / F'-1), the resistance R is changed to R'represented by the following equation 10. For example, the resistance value R'can be changed by applying a variable resistance to the resistance element R4 (FIG. 5) forming the RC circuit 44 in the oscillation circuit 42 and changing the resistance value of the resistance element R4. ..
R'= R-δR = R-R × (1-F' / F) ... (Equation 10)
Thereby, the same effect as the first method can be obtained. The embodiments described above and the configurations described in the first and second modifications can be combined as appropriate.

1 ... Analytical device 3 ... Control unit 10 ... Nozzle 24 ... Liquid level detection unit 11, 41 ... CPU
42 ... Oscillation circuit

Claims (9)

An oscillating circuit that oscillates with a time constant that depends on the capacitance between the first electrode and the second electrode.
A drive unit that moves the first electrode in the vertical direction,
A calculation unit that calculates the amount of deviation between the oscillation frequency of the oscillation circuit in the first state where the first electrode and the liquid surface are not in contact with each other and the oscillation frequency set value prepared in advance.
A correction unit that obtains a liquid level detection threshold value based on the deviation amount and a threshold value set in advance.
If the oscillation frequency of the oscillation circuit in the first state, the difference between the oscillation frequency of the oscillation circuit in the second state is lowered the first electrode exceeds the liquid level detection threshold, detecting the liquid level Detection unit and
A liquid level detector equipped with. When the oscillation frequency of the oscillation circuit in the first state is smaller than the oscillation frequency set value, the correction unit, the liquid level detection threshold, to have magnitude than the threshold setting value,
The liquid level detection device according to claim 1. If the larger oscillation frequency is the oscillation frequency setting value of the oscillation circuit in the first state, the correction unit, the liquid level detection threshold, to a value not smaller than the threshold setting value,
The liquid level detection device according to claim 1 or 2. The oscillation frequency of the oscillation circuit is measured as the length of time required for the oscillation circuit to oscillate a predetermined number of times.
The liquid level detection device according to any one of claims 1 to 3. The correction unit is based on the following formula.
The liquid level detection threshold value is obtained by using the liquid level detection threshold value = correction coefficient (measured value of the time length-set value of the time length) + the threshold value set value.
The liquid level detection device according to claim 4. The oscillation frequency of the oscillation circuit is measured as the number of oscillations per unit time of the oscillation circuit .
The liquid level detection device according to any one of claims 1 to 3. An oscillating circuit that oscillates with a time constant that depends on the capacitance between the first electrode and the second electrode.
A drive unit that moves the first electrode in the vertical direction,
The difference between the oscillation frequency of the oscillation circuit in the first state where the first electrode and the liquid surface are not in contact with each other and the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered exceeds the threshold value. In some cases, the detector that detects the liquid level and
A calculation unit that calculates the amount of deviation between the oscillation frequency of the oscillation circuit in the first state and the oscillation frequency set value prepared in advance.
A correction unit that corrects the oscillation frequency of the oscillation circuit based on the deviation amount is provided.
The correction unit has the following: a set value C of the capacitance used for calculating the time constant, a set value F of the oscillation frequency of the oscillation circuit, an oscillation frequency F'of the oscillation circuit in the first state, and the following. formula,
C'= CC × (F / F'-1)
A liquid level detection device that makes corrections to change the capacitance used for calculating the time constant to C'using. An oscillating circuit that oscillates with a time constant that depends on the capacitance between the first electrode and the second electrode.
A drive unit that moves the first electrode in the vertical direction,
The difference between the oscillation frequency of the oscillation circuit in the first state where the first electrode and the liquid surface are not in contact with each other and the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered exceeds the threshold value. In some cases, the detector that detects the liquid level and
A calculation unit that calculates the amount of deviation between the oscillation frequency of the oscillation circuit in the first state and the oscillation frequency set value prepared in advance.
A correction unit that corrects the oscillation frequency of the oscillation circuit based on the deviation amount is provided.
The correction unit has the following equations, the set value R of the resistance value used for calculating the time constant, the set value F of the oscillation frequency of the oscillation circuit, the oscillation frequency F'of the oscillation circuit in the first state, and the following equation. ,
R'= RC × (1-F' / F)
A liquid level detection device that makes corrections to change the resistance value used for calculating the time constant to R'using. A first state in which the first electrode and the liquid surface are not in contact with each other by using an oscillating circuit that oscillates at a time constant depending on the capacitance between the first electrode and the second electrode that can contact the liquid surface. The step of calculating the amount of deviation between the oscillation frequency of the oscillation circuit and the oscillation frequency set value prepared in advance in
A step of obtaining a liquid level detection threshold value based on the deviation amount and a threshold value set in advance, and
The liquid level is detected when the difference between the oscillation frequency of the oscillation circuit in the first state and the oscillation frequency of the oscillation circuit in the second state in which the first electrode is lowered exceeds the liquid level detection threshold value. A liquid level detection method including a process.

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