Liquid level detection system based on multivibrator and algorithm thereof

Abstract

The invention belongs to the technical field of biological sample detection equipment, and relates to a liquid level detection system based on a multivibrator and an algorithm thereof. The liquid level detection system based on the multivibrator comprises a pipetting needle and a liquid level detection plate which are connected in sequence, the liquid level detection plate comprises a multivibrator module, a frequency divider module, an MCU unit and an external interface which are connected in sequence; the front end of the multivibrator module is connected with a pipetting needle; the multivibrator module comprises a resistor and a capacitor, and the output frequency of the multivibrator module is jointly determined by the resistor and the capacitor; when the pipetting needle is in contact with the liquid level, the output frequency of the multivibrator circuit is changed; the frequency divider module is used for carrying out frequency reduction processing on the frequency signal output by the multivibrator module; the frequency divider module accumulates square waves generated by the multi-harmonic oscillation module, the period of a counter output signal is N times of the period of an input signal of the multi-harmonic oscillation module, and the frequency is 1 / N of the original frequency; the MCU unit processes an output signal of the frequency divider module; and the external interface performs single-board communication and power supply.

Description

Technical Field

[0001] The present invention belongs to the technical field of biological sample detection equipment, and in particular relates to a liquid level detection system based on a multivibrator and an algorithm thereof. Background Art

[0002] Most of the fully automatic clinical analytical instruments are equipped with automatic pipetting systems. The pipetting accuracy and liquid detection accuracy play an important role in the analytical accuracy of these instruments.

[0003] The accuracy of pipetting is mainly affected by the liquid carryover on the outer surface of the pipette needle. Liquid carryover is affected by the viscosity and adhesion of the liquid and the depth of the pipette needle into the liquid, resulting in an unstable carryover amount. The instrument will not produce a stable system error. The accuracy of liquid detection is mainly affected by the response speed of liquid level detection, resulting in an increase in liquid carryover if the liquid detection depth is too large.

[0004] Minimizing the amount of liquid carried on the outer surface of the pipette needle and increasing the response speed of liquid level detection are the main methods to reduce carryover contamination and improve analytical accuracy. There are many ways to reduce carryover, for example, coating the outer surface of the pipette needle with materials that are not easily stained by liquids, such as TEFLON; slowing down the speed of the pipette needle when it withdraws from the liquid; using the liquid level detection (LLD) function to control the depth of the pipette needle into the liquid, etc. The method to improve the response speed can be digital or software optimization.

[0005] The most commonly used method at present is to use the LLD function, which can not only control the depth of the pipette needle into the liquid, but also detect whether the liquid is exhausted or missing, thereby avoiding false addition of samples by the instrument.

[0006] The existing LLD technologies mainly include contact LLD technology and contactless LLD technology.

[0007] 1. Contact LLD technology mainly includes resistance method, capacitance method, air pressure method and mechanical vibration method, and its basic principles are as follows;

[0008] (1) Resistance method: Two metal electrodes (usually the metal pipette needle is one of the electrodes) installed on the pipette needle move downward with the pipette needle. When the two electrodes come into contact with the conductive liquid, the resistance between the electrodes suddenly decreases, which can be used to determine that the pipette needle has come into contact with the liquid.

[0009] (2) Capacitance method: Generally, the pipette needle is regarded as one plate of the capacitor (moving plate), and the metal casing of the liquid container is regarded as the other plate (fixed plate). The capacitance value of the capacitor formed by the pipette needle and the casing gradually increases as the pipette needle moves downward. When the pipette needle touches the sample, it is equivalent to the area of ​​the moving plate suddenly increasing and the distance between the two plates suddenly decreasing, causing the capacitance value to suddenly increase. Detecting the sudden change in the capacitance value can determine whether the pipette needle has touched the liquid surface.

[0010] (3) Air pressure method: When the pipette needle moves downward under the drive of the transmission mechanism, the syringe piston moves upward slowly to blow the air in the syringe out through the pipette needle. Once the pipette needle mouth touches the liquid surface, the air outflow is blocked, and the air pressure in the pipeline suddenly increases, which is detected by the pressure sensor.

[0011] (4) Mechanical vibration method: When the pipette needle system mechanically resonates under the action of external force, once it contacts the liquid, the natural frequency of the system changes. By detecting this change, it is possible to detect whether the pipette needle contacts the liquid surface.

[0012] 2. Non-contact LLD technologies include ultrasonic method, laser method and CCD imaging method, and their basic principles are as follows;

[0013] (1) Ultrasonic method: The liquid level is calculated by detecting the time difference between the transmission and reflection of ultrasonic waves. Since the speed of sound waves in the air is related to the temperature, the measurement error of ultrasonic ranging will change with the change of air temperature. Fortunately, the working environment of clinical laboratory instruments is relatively stable, and with the use of temperature compensation technology, ultrasonic ranging technology can fully meet the requirements of clinical laboratory instruments.

[0014] (2) Laser method: The laser tube and photosensitive device are fixed on the left and right sides of the pipette needle and form a certain angle with the pipette needle. Only when the pipette needle moves down to a certain fixed height from the liquid surface, the light emitted by the laser tube is reflected by the liquid surface and illuminates the photoelectric detector, thereby detecting the liquid level.

[0015] (3) CCD imaging method: Use a CCD camera to capture the side image of the sample tube, identify the boundaries of various liquid phases from the image to determine the liquid level.

[0016] The capacitance method in the above-mentioned contact LLD technology is commonly used in automated clinical analysis instruments, but the existing contact LLD technology circuit design is too complex, the response speed is slow, and the minimum capacitance detection amount in different background capacitance systems is difficult to evaluate, resulting in poor detection accuracy. The application cost of non-contact LLD technology is relatively high and it has not yet been widely used.

[0017] The present invention hopes to provide a liquid level detection system based on a multivibrator and an algorithm thereof, which can reduce the design difficulty and cost of a crystal oscillator LLD hardware circuit and greatly improve the liquid level detection accuracy. Summary of the invention

[0018] The object of the present invention is to provide a liquid level detection system based on a multivibrator to solve the problems raised in the above background technology.

[0019] To achieve the above object, the present invention provides the following technical solutions:

[0020] A multivibrator-based liquid level detection system comprises a pipette needle and a liquid level detection board connected in sequence; the liquid level detection board comprises a multivibrator module, a frequency divider module, an MCU unit and an external interface connected in sequence; the front end of the multivibrator module is connected to the pipette needle;

[0021] The multivibrator module includes a resistor and a capacitor, and the output frequency of the multivibrator module is determined by the resistor and the capacitor. The resistor is a fixed value, and the capacitor is a variable value. When the pipette needle contacts the liquid surface, the capacitor changes, and the output frequency of the multivibrator circuit changes.

[0022] The frequency divider module performs frequency reduction processing on the frequency signal output by the multivibrator module; the frequency divider module accumulates the square waves generated by the multivibrator module, and generates an overflow signal after reaching a certain number, and the period of the counter output signal is N times the period of the input signal of the multivibrator module, and the frequency is 1 / N of the original;

[0023] The MCU unit processes the output signal of the frequency divider module;

[0024] The external interface performs single-board communication and power supply.

[0025] Preferably, the pipetting needle is a single-layer needle or a double-layer needle.

[0026] Preferably, an EMC protection circuit is provided between the pipette needle and the multivibrator module; the EMC protection circuit comprises a common-mode inductor, a clamping diode and a magnetic bead; the common-mode inductor suppresses the common-mode noise of the circuit, the clamping diode limits the voltage of the pipette needle, and the magnetic bead absorbs high-frequency noise.

[0027] Preferably, the multivibrator module includes a multivibrator circuit composed of TLC555. After the pipette needle is connected to the connector, due to the existence of the basic capacitor of the pipette needle, the power supply will charge the capacitor through resistors RA and RB. When the voltage VC on the capacitor is less than 1 / 3VDD, the TLC555 output is a high level, and the capacitor is continuously charged. When VC is between 1 / 3VDD and 2 / 3VDD, the output remains at a high level. When the voltage on VC is greater than 2 / 3VDD, the output becomes a low level, and the internal discharge circuit is turned on at the same time, the capacitor is discharged to zero voltage, and the power supply starts charging again, so that the circuit outputs periodic high and low levels.

[0028] Preferably, the frequency divider module is a hardware frequency divider module, and the hardware counter module adopts SN74HC393. The SN74HC393 is a dual-channel 4-bit binary counter, each channel counter can achieve 16-bit counting, and the combination of two channels can achieve a maximum of 256-bit counting.

[0029] Preferably, the frequency divider module is a software frequency divider module, and the software frequency divider module is implemented in software through an MCU unit, and the process of the software implementation is as follows:

[0030] (1) The MCU unit starts working, TIM&EXIT is initialized, and it waits for a rising edge to determine whether a rising edge occurs. If it is determined that no rising edge occurs, it returns to determine whether a rising edge occurs again.

[0031] (2) If it is determined that a rising edge occurs, the interrupt service function is entered to determine the number of interrupts;

[0032] (3) If the first interrupt is triggered, TIM is turned on, TIM is cleared, and self-increment is started. After completion, the process returns to determine whether a rising edge occurs. If the 1-n interrupts are triggered, self-increment is turned on. After completion, the process returns to determine whether a rising edge occurs. If the nth interrupt is triggered, the value of the divider module is obtained, the cycle is calculated, the capture is cleared, TIM is turned off after completion, and the process returns to wait for a rising edge.

[0033] An algorithm based on a multivibrator liquid level detection system comprises the following steps: (1) starting the system and initializing a liquid detection panel; (2) a timer module collecting frequency and filtering frequency data; (3) determining whether the frequency data is greater than a threshold frequency; if the frequency data is less than or equal to the threshold frequency, a frequency divider module is reset to zero, and after completion, the frequency is returned to the timer module to collect the frequency; (4) if the frequency data is greater than the threshold frequency, determining whether the sampling times and the sampling time are greater than the threshold at the same time; if so, the liquid detection is successful; if not, the liquid detection panel is returned to the initialization.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention provides a liquid level detection system based on a multivibrator, which can significantly improve the accuracy of liquid level detection. The EMC protection circuit includes a common-mode inductor, a clamping diode and a magnetic bead. The common-mode inductor is used to suppress the common-mode noise in the circuit, and the clamping diode is used to limit the voltage on the pipette needle. The magnetic bead is used to absorb high-frequency noise. The function of the entire EMC protection module is to improve the stability and anti-interference ability of the detection circuit;

[0036] (2) The present invention provides a liquid level detection system based on a multivibrator. The output frequency of the multivibrator module is determined by resistance and capacitance. When the resistance is a constant value, changes in capacitance will cause changes in frequency. When the pipette needle contacts the liquid surface, changes in capacitance value cause changes in the output frequency of the multivibrator circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is the overall structural block diagram of the pipetting needle-liquid level detection circuit of the present invention;

[0038] Figure 2 The schematic diagram of the multivibrator composed of TLC555 in the present invention;

[0039] Figure 3 It is a block diagram of the frequency divider module in the present invention;

[0040] Figure 4 is a schematic diagram of the hardware counter in the present invention;

[0041] Figure 5 It is a software implementation flow chart when the MCU unit in the present invention is used as a counter;

[0042] Figure 6 It is the liquid level detection algorithm flow of the present invention;

[0043] Figure 7 It is a software control flow chart of the liquid detection process in the present invention;

[0044] Figure 8 It is the fluctuation diagram of the height of the liquid surface in the present invention;

[0045] Fig. 9 It is a schematic diagram of the capacitance detection module in the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] A liquid level detection system based on a multivibrator includes a pipette needle and a liquid level detection board connected in sequence; the liquid level detection board includes a multivibrator module, a frequency divider module, an MCU unit and an external interface connected in sequence; the front end of the multivibrator module is connected to the pipette needle. For specific connection methods, see Figure 1 .

[0048] Pipette needle: The pipette needle is used to sense the liquid surface. Its structure is usually single-layer or double-layer. The basic capacitance of single-layer and double-layer needles is quite different. EMC protection circuit: It consists of common-mode inductors, clamping diodes and magnetic beads. The common-mode inductors are used to suppress the common-mode noise in the circuit, and the clamping diodes are used to limit the voltage on the pipette needle. The magnetic beads are used to absorb high-frequency noise. The function of the entire EMC protection module is to improve the stability and anti-interference ability of the detection circuit. Multivibrator module: The output frequency of the multivibrator module is determined by the resistor and capacitor. When the resistor is a fixed value, the change of the capacitor will cause the change of the frequency. When the pipette needle contacts the liquid surface, the change of the capacitance value causes the output frequency of the multivibrator circuit to change. Divider module: The high-frequency signal output by the multivibrator module is appropriately down-converted, and at the same time it plays a role in reducing noise. MCU unit: Processes the output signal of the divider module. External interface: Including single-board communication and power supply.

[0049] 1. TLC555 multivibrator solution

[0050] The multivibrator circuit composed of TLC555 is as follows Figure 2 As shown, due to the existence of the equivalent capacitor C1 of the pipette needle, the power supply will charge the capacitor through the resistors RA and RB. When the voltage VC on the capacitor is less than 1 / 3VDD, the TLC555 output is high level, and the capacitor continues to charge. When VC is between 1 / 3VDD and 2 / 3VDD, the output remains high level. When the voltage on VC is greater than 2 / 3VDD, the output becomes low level. At the same time, the internal discharge circuit is turned on, the capacitor discharges to zero voltage, and the power supply starts charging again, so that the circuit outputs periodic high and low levels.

[0051] 2. Implementation plan of frequency divider module

[0052] Frequency divider module see Figure 3 . Since the output frequency of the multivibrator is high, the frequency measurement error is large when the single-chip microcomputer is used to collect the frequency, and it is necessary to frequently enter the MCU interrupt, thereby consuming resources. Therefore, the divider module is introduced. The divider module accumulates the square waves generated by the multivibrator module and generates an overflow signal after reaching the set number. According to different implementation methods of the divider module, the set number may be determined by the hardware circuit configuration or software configuration. The period of the divider output signal is N times the period of the multivibrator input signal, and the frequency is 1 / N of the original.

[0053] The frequency divider can be implemented by a hardware counter circuit or a software counter module. The specific implementation method is as follows:

[0054] a. Hardware counter circuit solution

[0055] like Figure 4 As shown, U2 is a counter circuit, which uses SN74HC393, a dual 4-bit binary counter. Each counter can achieve 16-bit counting, and the combination of the two can achieve a maximum of 256-bit counting. Figure 4 The resistors R1 to R4 are used to adjust the number of counting bits.

[0056] b. Software counter module solution

[0057] The counter module can also be implemented in software through the MCU unit. Compared with the hardware frequency division chip, it is more flexible and can realize arbitrary counting. Figure 5 Software flow chart for using timers and external interrupts to implement arbitrary counting.

[0058] 3. Liquid level detection algorithm process

[0059] Turn on the device and initialize the liquid detection panel. The timer starts to collect the frequency and further filter the frequency data. The filtered frequency data is judged to determine whether it is greater than the threshold frequency.

[0060] If not, the counter is cleared and returns to the timer to re-collect the frequency.

[0061] If yes, then determine whether the sampling times and sampling values ​​are greater than the threshold. If yes, the liquid detection is successful; if not, return to the initialization liquid detection panel.

[0062] Among them, the liquid level detection software control process is shown in Figure 7 .

[0063] 4. Accuracy test

[0064] The liquid level detection accuracy is determined by the liquid level trigger position, and the difference between the detection position and the liquid level position is recorded. Figure 8 For more than 70,000 consecutive liquid surface accuracy tests, the position difference in the figure is controlled within ±30 steps.

[0065] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A liquid level detection system based on a multivibrator, characterized in that: It includes a pipetting needle and a liquid level detection board connected in sequence; the liquid level detection board includes a multivibrator module, a frequency divider module, an MCU unit and an external interface connected in sequence; the front end of the multivibrator module is connected to the pipetting needle; The multivibrator module includes a resistor and a capacitor, and the output frequency of the multivibrator module is determined by the resistor and the capacitor. The resistor is a fixed value, and the capacitor is a variable value. When the pipette needle contacts the liquid surface, the capacitor changes, and the output frequency of the multivibrator circuit changes. The frequency divider module performs frequency reduction processing on the frequency signal output by the multivibrator module; the frequency divider module accumulates the square waves generated by the multivibrator module, and generates an overflow signal after reaching a certain number, and the period of the counter output signal is N times the period of the input signal of the multivibrator module, and the frequency is 1 / N of the original; The MCU unit processes the output signal of the frequency divider module; The external interface performs single-board communication and power supply.

2. A liquid level detection system based on a multivibrator according to claim 1, characterized in that: The pipetting needle is a single-layer needle or a double-layer needle.

3. The multivibrator-based liquid level detection system according to claim 1, characterized in that: An EMC protection circuit is provided between the pipette needle and the multivibrator module; the EMC protection circuit comprises a common mode inductor, a clamping diode and a magnetic bead; the common mode inductor suppresses the common mode noise of the circuit, the clamping diode limits the voltage of the pipette needle, and the magnetic bead absorbs high frequency noise.

4. A multivibrator-based page detection system according to claim 1, characterized in that: The multivibrator module includes a multivibrator circuit composed of TLC555. After the pipette needle is connected to the connector, due to the existence of the basic capacitor of the pipette needle, the power supply will charge the capacitor through resistors RA and RB. When the voltage VC on the capacitor is less than 1 / 3VDD, the TLC555 output is high level, and the capacitor is continuously charged. When VC is between 1 / 3VDD and 2 / 3VDD, the output remains high level unchanged. When the voltage on VC is greater than 2 / 3VDD, the output becomes low level, and the internal discharge circuit is turned on at the same time, the capacitor is discharged to zero voltage, and the power supply starts charging again, so that the circuit outputs periodic high and low levels.

5. The multivibrator-based liquid level detection system according to claim 1, characterized in that: The frequency divider module is a hardware frequency divider module, and the hardware counter module adopts SN74HC393, which is a dual-channel 4-bit binary counter. Each channel counter can achieve 16-bit counting, and the combination of two channels can achieve a maximum of 256-bit counting.

6. The multivibrator-based liquid level detection system according to claim 1, characterized in that: The frequency divider module is a software frequency divider module, which is implemented in software through the MCU unit. The process of the software implementation is as follows: (1) The MCU unit starts working, TIM&EXIT is initialized, and it waits for a rising edge to determine whether a rising edge occurs. If it is determined that no rising edge occurs, it returns to determine whether a rising edge occurs again. (2) If it is determined that a rising edge occurs, the interrupt service function is entered to determine the number of interrupts; (3) If the first interrupt is triggered, TIM is turned on, TIM is cleared, and self-addition is started. After completion, it returns to determine whether a rising edge occurs; If the 1-nth interrupt is triggered, the capture self-add is turned on, and after completion, it returns to determine whether a rising edge occurs; If the nth interrupt is triggered, the value of the divider module is obtained, the cycle is calculated, the capture is cleared, and TIM is closed after completion, and finally returns to wait for the rising edge.

7. An algorithm based on a multivibrator liquid level detection system, characterized in that: The following steps are involved: (1) Turn on the system and initialize the liquid detection panel; (2) The timer module collects the frequency and filters the frequency data; (3) It determines whether the frequency data is greater than the threshold frequency; if the frequency data is ≤ the threshold frequency, the divider module is cleared and returns to the timer module to collect the frequency after completion; (4) If the frequency data is greater than the threshold frequency, it determines whether the sampling times and sampling time are greater than the threshold at the same time; if so, the liquid detection is successful; if not, it returns to the initialization liquid detection panel.

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