CN115790775A

CN115790775A - Liquid level detection equipment, method and device and storage medium

Info

Publication number: CN115790775A
Application number: CN202211485222.8A
Authority: CN
Inventors: 许铭杰
Original assignee: Guangzhou Heygears IMC Inc
Current assignee: Guangzhou Heygears IMC Inc
Priority date: 2022-11-24
Filing date: 2022-11-24
Publication date: 2023-03-14

Abstract

The embodiment of the application provides liquid level detection equipment, a liquid level detection method, a liquid level detection device and a storage medium, and relates to the technical field of liquid level detection. This liquid level detection device includes: the first excitation circuit is used for outputting a first voltage signal according to an input first excitation signal and the current liquid level; a first detection circuit for extracting a peak voltage of the first voltage signal; and the comparison amplifying circuit is used for outputting a second voltage signal according to the peak voltage and a preset reference voltage. And the second voltage signal is used for representing the height corresponding to the current liquid level. The excitation circuit of the device obtains a voltage signal through detection according to the signal generated by the current liquid level, compares the voltage signal with the reference voltage, amplifies the voltage signal, and then calculates the height of the liquid level, and has the advantages of small occupied size and high detection precision.

Description

Liquid level detection equipment, method and device and storage medium

Technical Field

The application relates to the technical field of liquid level detection, in particular to liquid level detection equipment, method, device and storage medium.

Background

The traditional liquid level detection device comprises a hydraulic type detection device, a floating ball type detection device, an ultrasonic wave detection device and the like, and the problems of large occupied volume, low detection precision and high construction cost exist. In 3D printing based on uv curing, for example, it is necessary to measure the level of a liquid photosensitive resin material. The photosensitive resin is used as a non-conductive liquid material, and the traditional detection method based on the connectivity change caused by liquid conductivity is not applicable. The hydraulic, floating ball, ultrasonic and other detection devices need to occupy a large volume, or have low detection precision or high construction cost, and are not suitable for being used in 3D printer equipment with sensitive cost. The laser type has the advantage of non-contact, but cannot detect the liquid level of the transparent resin, and has no universality.

Therefore, how to design the liquid level detection equipment with low cost and high detection precision is a technical problem to be solved.

Disclosure of Invention

The application aims to provide liquid level detection equipment, a liquid level detection method, a liquid level detection device and a storage medium, so as to solve the technical problems of high cost and low detection precision in the prior art.

In order to achieve the above purpose, the embodiments of the present application adopt the following technical solutions.

In a first aspect, an embodiment of the present application provides a liquid level detecting apparatus, including:

the first excitation circuit is used for outputting a first voltage signal according to an input first excitation signal and the current liquid level;

a first detection circuit for extracting a signal characteristic of the first voltage signal; wherein the signal characteristic comprises a peak value, a peak-to-peak value and/or a minimum value;

the comparison amplifying circuit is used for outputting a second voltage signal according to the signal characteristics and the first preset reference voltage; and the second voltage signal is used for representing the height corresponding to the current liquid level.

The excitation circuit of the device generates a first voltage signal according to a first excitation signal and the current liquid level, then obtains the signal characteristics of the first voltage signal through detection, compares the signal characteristics with a reference voltage, amplifies the signal characteristics to obtain a second voltage signal representing the current liquid level height, further obtains the liquid level, does not need hydraulic, floating ball, ultrasonic and other detection devices, and is small in occupied size and low in cost. The comparison amplification circuit can perform differential amplification on the signals, so that the amplification factor and the detection precision are improved.

In one embodiment, the first excitation circuit comprises a detection capacitor and a divider resistor; the detection capacitor is formed according to a probe extending into the container;

the first end of the detection capacitor is grounded, and the second end of the detection capacitor is electrically connected with the input end of the first detection circuit and the first end of the divider resistor; the second end of the divider resistor is used for receiving a first excitation signal; or the like, or, alternatively,

the first end of the divider resistor is electrically connected with the first detection circuit and the second end of the detection capacitor, the second end of the divider resistor is grounded, and the first end of the detection capacitor is used for receiving the first excitation signal.

In one embodiment, the first excitation circuit further comprises an excitation voltage follower;

the output end of the excitation voltage follower is electrically connected with the input end of the first detection circuit, and the input end of the excitation voltage follower is connected with the connection point of the detection capacitor and the divider resistor.

In one embodiment, the first detector circuit comprises a detector diode, a peak detector capacitor and a first resistor, wherein the anode of the detector diode is electrically connected with the output end of the first excitation circuit; the first end of the peak detection capacitor is electrically connected with the cathode of the detection diode, the first end of the first resistor and the input end of the comparison amplification circuit respectively; the second terminal of the peak detection capacitor and the second terminal of the first resistor are both grounded.

In one embodiment, the first detection circuit further includes a detection voltage follower, and the first end of the peak detection capacitor is electrically connected to the input terminal of the comparison amplification circuit through the detection voltage follower.

In one embodiment, the first detection circuit comprises a comparator, a first input end of the comparator is electrically connected with the first excitation circuit, and a second input end of the comparator is used for connecting a preset detection reference voltage;

the comparator is used for outputting a square wave with a variable duty ratio according to the comparison between the first voltage signal output by the first excitation circuit and a preset detection reference voltage, and the duty ratio is in direct proportion to the peak value of the first voltage signal;

the first detection circuit also comprises an active filter circuit or an average detection circuit, the output end of the comparator is connected with the input end of the active filter circuit or the input end of the average detection circuit, and the output end of the active filter circuit or the average detection circuit is electrically connected with the comparison amplification circuit;

an active filter circuit or an average detection circuit is used to obtain an average value of the square wave, which is proportional to the duty cycle of the square wave.

In one embodiment, the liquid level detection apparatus further comprises a first reference voltage circuit for providing a first preset reference voltage.

In one embodiment, the first reference voltage circuit comprises a reference voltage follower and a low-pass filter circuit, wherein the output end of the low-pass filter circuit is connected with the input end of the reference voltage follower, and the input end of the low-pass filter circuit is connected with the processing circuit; the output end of the reference voltage follower is electrically connected with the comparison amplifying circuit.

In one embodiment, the number of the low-pass filter circuits is multiple, the output end of the series connection of the low-pass filter circuits is connected with the input end of the reference voltage follower, and the input end of the series connection of the low-pass filter circuits is used for connecting the processing circuit.

In one embodiment, the low-pass filter circuit comprises a filter resistor and a filter capacitor; the first end of the filter resistor is the input end of the low-pass filter circuit, the second end of the filter resistor is electrically connected with the first end of the filter capacitor, the first end of the filter capacitor is the output end of the low-pass filter circuit, and the second end of the filter capacitor is grounded.

In one embodiment, the first reference voltage circuit comprises a DAC circuit, and the input end of the comparison amplification circuit is connected with the DAC circuit.

In one embodiment, the comparison amplification circuit comprises a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor and an operational amplifier;

the non-inverting input end of the operational amplifier is respectively connected with the first end of the fourth resistor and the first end of the sixth resistor, the inverting input end of the operational amplifier is respectively connected with the first end of the fifth resistor, the first end of the seventh resistor, and the output end of the operational amplifier is connected with the second end of the seventh resistor and is used for being connected with the MCU; the second end of the fourth resistor is connected to a first preset reference voltage, and the second end of the fifth resistor is connected to the output end of the first detection circuit; and the second end of the sixth resistor is grounded.

In one embodiment, the liquid level detection apparatus further comprises:

the second excitation circuit is used for outputting a third voltage signal according to the input second excitation signal and the current liquid level; the input end of the second excitation circuit is connected with the input end of the first excitation circuit;

a second detection circuit for extracting a signal characteristic of the third voltage signal;

a second reference voltage circuit;

the first input end of the subtraction circuit is connected with the output end of the first detection circuit and the output end of the second detection circuit, the second input end of the subtraction circuit is connected with the second reference voltage circuit, and the output end of the subtraction circuit is connected with the input end of the comparison amplification circuit; the subtraction circuit is used for obtaining the signal characteristic of a fourth voltage signal according to the signal characteristic of the first voltage signal, the signal characteristic of the third voltage signal and a second preset reference voltage provided by the second reference voltage circuit;

the comparison amplifying circuit is used for outputting a fifth voltage signal according to the signal characteristic of the first voltage signal, the signal characteristic of the fourth voltage signal and the first preset reference voltage.

In one embodiment, the first excitation circuit comprises a first detection capacitor and a first divider resistor; the first detection capacitor is formed according to the first probe and the second probe which extend into the container; the second probe is used for contacting the liquid at the first liquid level;

the first end of the first detection capacitor is grounded, the second end of the first detection capacitor is electrically connected with the first detection circuit and the first end of the first divider resistor, and the second end of the first divider resistor is used for connecting a first excitation signal; or the first end of the first divider resistor is electrically connected with the first detection circuit and the second end of the first detection capacitor, the second end of the first divider resistor is grounded, and the first end of the first detection capacitor is used for connecting the first excitation signal;

the second excitation circuit comprises a second detection capacitor and a second divider resistor; the second detection capacitor is formed by the first probe and the third probe; the third probe is used for contacting the liquid at the second liquid level; the resistance value of the second divider resistor is larger than that of the first divider resistor; the first liquid level is lower than the second liquid level;

the first end of the second detection capacitor is grounded, the second end of the second detection capacitor is electrically connected with the first detection circuit and the first end of the second divider resistor, and the second end of the second divider resistor is used for connecting a second excitation signal; or, the first end of the second voltage-dividing resistor is electrically connected with the first detection circuit and the second end of the second detection capacitor, the second end of the second voltage-dividing resistor is grounded, and the first end of the second detection capacitor is used for connecting the second excitation signal.

In one embodiment, the second reference voltage circuit includes a buck diode and a ground resistor, a cathode of the buck diode is grounded through the ground resistor, and an anode of the buck diode is used for connecting the reference power supply and outputting the second preset reference voltage after the voltage of the reference power supply is reduced.

In a second aspect, an embodiment of the present application further provides a liquid level detection method, which is applied to the liquid level detection apparatus as described above, where the liquid level detection method includes:

acquiring a second voltage signal;

confirming that the zero setting is successful under the condition that the voltage value corresponding to the second voltage signal falls into the preset interval;

reading a current second voltage signal and/or a current temperature signal according to the received liquid reading instruction;

and obtaining the current liquid level according to the current second voltage signal and/or the current temperature signal.

In a third aspect, an embodiment of the present application further provides a liquid level detection apparatus, which is applied to the above liquid level detection device, and includes:

the zero setting unit is used for acquiring a second voltage signal and confirming that zero setting is successful under the condition that a voltage value corresponding to the second voltage signal falls into a preset interval;

the computing unit is used for reading the current second voltage signal and/or the current temperature signal according to the received liquid reading instruction under the condition of successful zero setting; obtaining the current liquid level according to the current second voltage signal; or obtaining the current liquid level according to the current second voltage signal and the current temperature signal.

In a fourth aspect, the present application further provides a computer-readable storage medium, in which a computer program or instructions are stored, and when the computer program or instructions are executed by a computing device, the liquid level detection method as described above is implemented.

Drawings

To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.

FIG. 1 is a first schematic view of a liquid level detection apparatus provided by an embodiment of the present application;

FIG. 2 is a second schematic view of a liquid level detection apparatus provided by an embodiment of the present application;

FIG. 3 is a schematic diagram of a first detector circuit according to an embodiment of the present disclosure;

FIG. 4 is a schematic view of a liquid level detection apparatus with high limit detection provided by an embodiment of the present application.

Description of the reference numerals:

10-level detection device, 11-first excitation circuit, 12-first detection circuit, 121-active filter circuit or mean detection circuit, 13-comparison amplification circuit, 14-first reference voltage circuit, 15-second excitation circuit, 16-second detection circuit, 17-second reference voltage circuit, 18-subtraction circuit.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and the described embodiments are some embodiments, but not all embodiments, of the present application. The components of the embodiments of the present application, as generally described in the figures herein, may be arranged and designed in a wide variety of different configurations. The embodiments described below and the features of the embodiments can be combined with each other without conflict.

In the description of the present application, it should be noted that the relational terms such as first and second, and the like are only used for distinguishing one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. The term "connected" is to be interpreted broadly, e.g., as a fixed connection, a removable connection, or an integral connection; may be directly connected or indirectly connected through an intermediate.

In 3D printing based on uv curing, the level of liquid photosensitive resin material needs to be measured. The photosensitive resin is used as a non-conductive liquid material, and the traditional detection method based on connectivity change caused by liquid conduction is not applicable. The hydraulic, floating ball, ultrasonic and other detection devices need to occupy a large volume, or have low detection precision or high construction cost, and are not suitable for being used in cost-sensitive 3D printer equipment; the laser type has the advantage of non-contact, but cannot detect the liquid level of the transparent resin, and has no universality.

In order to overcome the above problem, referring to fig. 1, an embodiment of the present application provides a liquid level detection apparatus 10 including: the first excitation circuit 11 is used for outputting a first voltage signal according to an input first excitation signal and the current liquid level; a first detection circuit 12 for extracting a signal characteristic of the first voltage signal; the signal characteristic comprises a peak value, a peak-to-peak value and/or a minimum value; and the comparison amplifying circuit 13 is configured to output a second voltage signal according to the signal characteristic of the first voltage signal and the first preset reference voltage. And the second voltage signal is used for representing the height corresponding to the current liquid level.

The first excitation signal may be a PWM signal, which is applied to the first excitation circuit. The first excitation circuit comprises an equivalent capacitor formed by a probe, and the capacitance reactance of the equivalent capacitor is determined by the current liquid level and the frequency of the first excitation signal, so that the signal characteristic of the first voltage signal is further influenced.

It should be noted that, the comparison amplification circuit performs differential amplification on the signal characteristic of the first voltage signal and the first preset reference voltage to increase the amplification factor of the liquid level of the resin, and the second voltage signal of the first embodiment is in a mapping relationship with the current liquid level, so that when the second voltage signal is obtained, the height value of the liquid level can be obtained according to the mapping relationship.

This application embodiment can obtain the second voltage signal of present liquid level height of sign through first excitation circuit, first detection circuit and comparison amplifier circuit, and then obtains the liquid level, need not the detection device of fluid pressure type, floater formula, ultrasonic wave etc. and occupy smallly. The comparison amplification circuit can improve the amplification factor and the detection precision. To sum up, the probe type resin liquid level detection equipment based on the capacitance variation has the advantages of small equipment volume, high detection precision, low construction cost and strong universality.

In one embodiment, a contact type sensor is used for liquid level detection, a probe of the contact type sensor can be arranged on a tray of the 3D printer, and the probe is connected with a subsequent first excitation circuit, a subsequent first detection circuit and a subsequent comparison amplification circuit through a contact point and a contact head. The probes of the sensor are discarded together when the tray needs to be discarded. In another embodiment, the first excitation circuit and the first detection circuit can be disposed on the tray, and the first reference voltage circuit, the comparison and amplification circuit, the controller and other devices can be disposed on the printer body, the first detection circuit and the comparison and amplification circuit can be electrically connected in the form of contacts and contacts, when the tray needs to be discarded, the probes and the circuit board provided with the first excitation circuit and the first detection circuit can be discarded together with the tray, so that the problem that the resins pollute each other when the resin is replaced on the tray can be avoided.

The first excitation signal input by the first excitation circuit can be a PWM1 waveform with the excitation frequency of f sent by an output end IO1 of the MCU, and a detection probe in the excitation circuit is inserted into the resin tray and fixed; although the resin is not conductive, the change of the resin liquid level can affect the medium between the two detection probes (changing air into resin, namely changing the dielectric constant), thereby changing the equivalent capacitance of the probes; the change of the capacitance is converted into a change of a direct current voltage amount through the first excitation circuit and the first detection circuit. The final output signal is an analog voltage value which can be sampled by the ADC due to the capacitance change caused by the resin liquid level change, and the MCU can calculate the current liquid level of the resin according to the sampled digital value.

It should be noted that the dielectric constant of each resin material is slightly different, and they are influenced by self temperature differently, if there is a liquid level reading that needs to be more accurate, can carry out the independent experiment to each resin material, obtain the proportionality coefficient of ADC numerical value and liquid level, and add temperature sensor and survey the resin temperature, MCU when calculating current liquid level, can take the resin temperature value as auxiliary parameter and carry out corresponding compensation.

In one embodiment, the first excitation circuit includes a detection capacitor and a voltage divider resistor. The detection capacitor and the divider resistor are connected in series for voltage division, and the voltage of one device of the detection capacitor and the divider resistor can be correlated with the liquid level information. The voltage of the detection capacitor can be taken, and the voltage of the divider resistor can also be taken. Namely the following two cases:

1) A first end of the detection capacitor is grounded, and a second end of the detection capacitor is electrically connected with the input end of the first detection circuit 12 and is electrically connected with a first end of the divider resistor; and the second end of the divider resistor is used for accessing the first excitation signal.

2) A first end of the voltage dividing resistor is electrically connected to the first detection circuit 12 and to a second end of the detection capacitor, a second end of the voltage dividing resistor is grounded, and a first end of the detection capacitor is used for receiving the first excitation signal.

As shown in fig. 2, fig. 2 shows a way of taking the voltage of the detection capacitor, i.e. the probe equivalent capacitor C, wherein the first excitation circuit 11 further includes an excitation voltage follower U1A, and the excitation voltage follower U1A is used to avoid the influence of the first detection circuit 12 on the voltage of the detection capacitor. The output end of the excitation voltage follower U1A is electrically connected to the input end of the first detection circuit 12, and the input end of the excitation voltage follower U1A is connected to the connection point of the detection capacitor and the divider resistor.

For the first detector circuit 12, a diode and a capacitor may be provided to realize detection. As shown in fig. 2, the first detector circuit 12 includes a detector diode D1, a peak detector capacitor C1, and a first resistor R1. The detector diode D1 prevents the reverse flow of the charge of the capacitor C1, the anode of the detector diode D1 is the input terminal of the first detector circuit 12, the first terminal of the peak detector capacitor C1 is electrically connected to the cathode of the detector diode D1, the first terminal of the first resistor R1, and the input terminal of the comparator amplifier circuit 13, respectively, and the second terminal of the peak detector capacitor C1 and the second terminal of the first resistor R1 are both grounded.

After the quasi-sine wave output from the first excitation circuit passes through the detector diode D1, the peak detection capacitor C1 is charged with the maximum value of the voltage at the time of voltage rise for each cycle, and the peak detection capacitor C1 is substantially maintained at the voltage fall edge for each cycle because of the unidirectional conductivity of the detector diode D1, and cannot return to the previous stage for discharge. The first resistor R1 has the function that when the peak value given to the peak detection capacitor C1 is reduced (due to liquid level change), C1 can discharge to the ground through R1 to reduce the voltage, so that the C1 voltage can follow the peak value of the quasi-sine wave in real time, in one embodiment, the time constant formed by the first resistor R1 and the peak detection capacitor C1 is in the ms level, otherwise, if the value of R1 is too small, the capacitor is completely discharged through the resistor at the voltage falling edge of the quasi-sine wave, and the effect of following the peak value cannot be achieved; if the value of R1 is too large, when the peak value is reduced due to the liquid level change, the voltage of the capacitor is reduced too slowly, and the measurement delay is higher.

In fig. 2, the first detector circuit 12 includes a detection voltage follower U1B, and the first end of the peak detection capacitor C1 is electrically connected to the input end of the comparison amplifier circuit 13 via the detection voltage follower, so that the first detector circuit 12 can be isolated from the signal on the output side thereof.

Unlike the structure of the first detector circuit 12 in fig. 2, in one example, the function of the first detector circuit 12 can also be realized by: the signal output by the first excitation circuit 11 is compared with a preset detection reference voltage to output a comparison result, and the comparison result is a square wave because the signal output by the first excitation circuit 11 is a sine-like wave, and presents different duty ratios along with different outputs of the first excitation circuit 11, and the duty ratios are related to the liquid level. The square wave with the duty ratio can obtain an average value of the square wave through an active filter circuit or an average detection circuit, and the average value is proportional to the duty ratio of the square wave, i.e. the peak value of the sine-like wave of the signal output by the first excitation circuit 11 can also be obtained. I.e. the first detector circuit 12 may comprise an active filter circuit or an average detector circuit.

In one embodiment, referring to FIG. 3, the first detector circuit comprises a comparator U1E, the first input of the comparator U1E is the input of the first detector circuit 12, and the second input of the comparator is used for connecting to the predetermined detection reference voltage V _ ref. The comparator is configured to output a square wave with a varying duty ratio according to a comparison between the first voltage signal of the first excitation circuit 11 and a preset detection reference voltage, where the duty ratio is proportional to a peak value of the first voltage signal, that is, a peak value of the quasi-sine wave can also be obtained.

The output of the comparator is connected to the input of the active filter circuit or mean detector circuit 121, and the output of the active filter circuit or mean detector circuit 121 is the output of the first detector circuit 12. An active filter circuit or mean detection circuit 121 is used to obtain the average value of the square wave, which is proportional to the square wave duty cycle. I.e. the voltage at the output is a voltage proportional to the square wave duty cycle, i.e. also reflecting the level height.

With continued reference to fig. 2, the liquid level detection device further comprises a first reference voltage circuit 14, which may be used to provide a first preset reference voltage for the comparison and amplification circuit 13. The first reference voltage circuit 14 includes a reference voltage follower U1C and a low-pass filter circuit (including a resistor and a capacitor), an output terminal of the low-pass filter circuit is connected to an input terminal of the U1C, and an input terminal is used for connecting another output terminal IO2 of the MCU. The output terminal of U1C is the output terminal of the first reference voltage circuit 14. Through the first reference voltage circuit, the first preset reference voltage which is stably adjustable can be obtained. It should be noted that, as long as the first reference voltage circuit can output the stable first preset reference voltage, other types of reference voltage circuits in the art should also be included in the protection scope of the present application.

In fig. 2, two lowpass filter circuits are adopted, that is, a second-order RC lowpass filter is adopted, and the steep drop characteristic of the filter in the cut-off region is enhanced, so that the ripple of the output voltage of the stage is smaller. Wherein the cut-off frequency of the filter is set below kHz.

The order may be freely selected, and may be a first order, a second order, a higher order, or the like.

As a further alternative to deriving the reference voltage, the reference voltage can be derived by a DAC circuit, i.e. the first reference voltage circuit 14 comprises a DAC circuit to which the input of a comparison and amplification circuit is connected, the DAC circuit being arranged to convert a digital quantity into an analog quantity, the output voltage being adjustable in dependence on the input digital value.

In one embodiment, the comparison amplification circuit comprises a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7 and an operational amplifier U1D;

Specifically, two input ends of the operational amplifier are respectively electrically connected with a first end of the fourth resistor and a first end of the fifth resistor, and a second end of the fourth resistor and a second end of the fifth resistor are two input ends of the comparison amplification circuit;

the non-inverting input end of the operational amplifier is grounded through a sixth resistor, a seventh resistor is connected between the output end and the inverting input end of the operational amplifier, and the output end of the operational amplifier is the output end of the comparison amplifying circuit.

Referring now to fig. 4, in order to avoid detection failures at high levels, a second excitation circuit 15 for detecting a second level is also provided in fig. 4, the second excitation circuit 15 being arranged to output a third voltage signal depending on the input second excitation signal and the current level. The input end of the second excitation circuit is connected with the input end of the first excitation circuit. Similarly, a second detector circuit 16 is provided, and the second detector circuit 16 is used to extract the signal characteristics of the third voltage signal, and the circuit configuration thereof may be the same as that of the first detector circuit. The signal characteristic includes a peak value, a peak-to-peak value, and a minimum value. The first input end of the subtraction circuit 18 is connected with the output end of the second detection circuit, the second input end is connected with the second reference voltage circuit, and the output end is connected with the input end of the comparison amplification circuit; the subtraction circuit is used for obtaining the signal characteristic of the fourth voltage signal according to the signal characteristic of the third voltage signal and the second reference voltage provided by the second reference voltage circuit 17; the comparison amplifying circuit 13 is configured to output a fifth voltage signal according to the peak voltage of the first voltage signal, the peak voltage of the fourth voltage signal, and the first preset reference voltage. And when the liquid level is higher than the second liquid level, the change rate of the fifth voltage signal along with the liquid level is greater than that of the fifth voltage signal along with the liquid level when the liquid level is lower than the high limit.

Specifically, the second reference voltage circuit 17 is used for providing a second preset reference voltage. The subtraction circuit 18 is configured to subtract the superimposed value of the signal characteristic of the first voltage signal and the signal characteristic of the third voltage signal from the second preset reference voltage, and input the obtained signal to the input terminal of the comparison and amplification circuit. In one embodiment, the required reference voltage can be obtained from a constant supply voltage through diode voltage reduction, i.e. as shown in fig. 4, the second reference voltage circuit 17 is provided to include the voltage reduction diodes D2, D4 and the ground resistor R8, the number of the voltage reduction diodes can be set as required, and in one example, the number of the voltage reduction diodes can be two. The cathode of the series connection of the voltage reduction diodes D2 and D4 is grounded through a grounding resistor, and the anode of the series connection of the voltage reduction diodes D2 and D4 is used for connecting a reference power supply and outputting a preset reference voltage Vref after the voltage of the reference power supply is reduced. The voltage drop of the diodes in the first and second detector circuits can be cancelled by the voltage dropping diodes D2 and D4. Subtracting circuit 18 may be any subtracting circuit known in the art. For example: the subtraction circuit may include an operational amplifier U1E, a resistor R12, and a resistor R13; one end of the resistor R12 is connected with one end of the grounding resistor R8 and the cathode of the voltage reduction diode D4 respectively, the other end of the resistor R12 is connected with the inverting input end of the operational amplifier U1E and one end of the resistor R13 respectively, and the other end of the resistor R13 is connected with the output end of the operational amplifier U1E and the comparison amplification circuit.

Second excitation circuit 15 and first excitation circuit 11 share a single probe, as follows.

The first excitation circuit 11 comprises a first detection capacitor C formed by a first probe and a second probe projecting into the container. Wherein the second probe is adapted to contact the liquid at a first level, the first level being lower than the second level. The second liquid level is the high limit of the material tray.

The second excitation circuit 15 comprises a second detection capacitor C10, the second detection capacitor C10 being formed for the first probe and the third probe. Wherein the third probe is adapted to contact the liquid at a high limit (i.e. a second liquid level). And the resistance value of the second divider resistor R10 is larger than that of the first divider resistor R in the figure. Further, the resistance value of the second divider resistor R10 is different from the resistance value of the first divider resistor R by orders of magnitude.

Therefore, when the liquid level is low, the liquid level change cannot cause the capacity value change of the second detection capacitor C10, so that the liquid level can be detected along with the change of the liquid level according to the capacity value of the first detection capacitor C.

When liquid is added to enable the liquid level to gradually transit to a position above the second liquid level, the capacitance value of the third probe is obviously changed due to the fact that the third probe touches the liquid, and therefore the liquid level can be detected according to the change of the capacitance value of the second detection capacitor C10 along with the liquid level. In this case, even if the first detection capacitor fails, the liquid level is detected to be too high, so that a warning can be given to further avoid overflowing due to too much added liquid. In the present application, the number of probes is not limited, and three probes may be used or a plurality of probes may be used.

It should be further noted that, in the case that the inputs of the first excitation circuit and the second excitation circuit originate from the same interface, the first excitation signal and the second excitation signal may be alternately sent out from the same interface. Due to the difference of the resistance values of the first divider resistor and the second divider resistor, the paths of the first excitation circuit and the first detection circuit and the paths of the second excitation circuit and the second detection circuit can alternately function. Wherein the first driving signal and the second driving signal also have a difference of several orders of magnitude. Through the circuit, liquid level detection and high liquid level early warning can be realized simultaneously under the condition that the interface is not increased.

Based on the foregoing embodiment, an embodiment of the present application further provides a liquid level detection method, which is applied to the foregoing liquid level detection device, and the method includes:

s1, acquiring a second voltage signal;

s2, confirming that the zero setting is successful under the condition that the voltage value corresponding to the second voltage signal falls into a preset interval;

s3, reading a current second voltage signal and/or a current temperature signal according to the received liquid reading instruction;

and S4, obtaining the current liquid level according to the current second voltage signal and/or the current temperature signal.

Through the zero setting step, the initial second voltage signal can be controlled in a proper range, so that the subsequent second voltage signal can be reflected more accurately when being changed. And error compensation can be performed on temperature by increasing a temperature signal, so that the influence of temperature change on the measured liquid level is avoided.

The above method can be used for the MCU in fig. 1, fig. 2, fig. 4. IO1, IO2 in fig. 4 may output PWM signals. The MCU can be an independent 8-bit or 32-bit microprocessor and is communicated with an upper computer through interfaces such as UART (universal asynchronous receiver/transmitter), I2C (inter-integrated circuit) and the like; the MCU can also be a CPU of a printer core board, and the system is constructed by directly using PWM1, PWM2 and ADC resources in the CPU. The overall process is as follows: the method comprises the steps of initializing I/O attributes, setting PWM1 and PWM2 frequencies and initial duty ratios, completing ADC and UART configuration, circularly executing and receiving instructions of an upper computer, exiting circulation until power failure, and ending. The upper computer may send a zero setting instruction and a liquid level reading instruction, and the MCU respectively performs zero setting action or liquid level reading action according to the zero setting instruction or the liquid level reading instruction at any time.

The zero setting voltage is a second voltage signal obtained by comparing and amplifying a first preset reference voltage and the peak voltage of the first voltage signal, wherein the preset reference voltage can be formed by PWM 2. When the system is at the resin zero liquid level, the MCU sends a PWM2 waveform with adjustable duty ratio, and the PWM2 waveform generates a preset reference voltage for zero setting through the active filter circuit.

The zero setting mechanism greatly reduces the influence of the parasitic parameters of active devices in the system and the precision problems of passive devices such as resistors, capacitors and the like on errors.

In addition, the capacitance change caused by the resin liquid level change is very small, about 0.5pf, the capacitance grade of a multimeter can only measure the capacitance of the uF level, a light probe of a general oscilloscope has an input capacitance of 10pf, the parasitic parameter is overlarge, the capacitance of the pf level can be detected by general LCR equipment, but the LCR equipment is extremely expensive, the difficulty in constructing a low-cost detection device is high, and a simple method and accurate theoretical calculation need to be considered. Because the PWM function that ordinary 8 bit singlechips all had, realize the accurate seizure of electric capacity change. This application only utilizes ordinary 8 bit singlechips machines can realize the accurate measurement to the liquid level, can see the outstanding contribution that this application made to reduce cost.

In fig. 2, a PWM1 of the MCU may be set to output a square wave signal with a duty ratio of 50% as Vin, and the resistor R, the probe equivalent capacitor C, and the first stage operational amplifier U1A form a first-order active low pass filter. After being expanded by the fourier series, the square wave signal can be regarded as a composite signal composed of a direct current component, a sine wave component with a fundamental frequency of the frequency (which may also be called an excitation frequency) f of the square wave signal, and odd harmonics thereof. After active low-pass filtering, the direct current component completely passes through, the higher harmonics are basically attenuated, the fundamental frequency signal is distributed with the input voltage according to the complex voltage division rule by the resistor R and the capacitive reactance 1/j omega C of the capacitor C, finally Vout is a similar sine signal (with the direct current component) with the amplitude smaller than Vin and the frequency of the fundamental frequency f, and the change of the capacitor influences the voltage division ratio and further influences the amplitude of the output voltage.

The waveform obtained by the first excitation circuit is a sine-like wave, and the original direct current component of the PWM1 square wave is superposed, and the magnitude of the direct current component is generally half of the power supply voltage VCC. Since the change in capacitance does not affect the magnitude of the dc component but only the peak-to-peak value of the sine-like wave, the first detector circuit shown in fig. 2 is designed to capture the magnitude of the peak value in real time.

After the quasi-sine wave passes through the diode D1, when the voltage of each period rises, the maximum value of the voltage charges the capacitor C1, and at the voltage falling edge of each period, the capacitor C1 can not return to the previous stage to discharge due to the unidirectional conductivity of the diode, and basically maintains the voltage, so that the C1 has larger capacitance as much as possible to ensure lower output ripple waves. The resistor R1 has the effects that when the peak value of the capacitor C1 is reduced (due to liquid level change), the voltage can be reduced by discharging the resistor R1 to the ground, so that the C1 voltage can follow the peak value of the quasi-sine wave in real time, the value of the resistor R1 cannot be too small, otherwise, the capacitor is completely discharged through the resistor when the voltage of the quasi-sine wave is reduced, the effect of following the peak value cannot be achieved, the value of the resistor R1 cannot be too large, otherwise, when the peak value is reduced due to liquid level change, the voltage of the capacitor is reduced too slowly, the measurement delay is higher, and the time constant formed by the resistor R1 and the capacitor C1 is generally in the ms level. The second-stage operational amplifier U1B is used as an emitter follower and can isolate front and rear two-stage loads, so that device parameters of the front and rear two stages cannot be influenced mutually.

As described above, the waveform output from the first detector circuit is a dc voltage waveform carrying a large dc component of the original square wave, and the voltage change due to the changed capacitance is small, and if the voltage of the first detector circuit is simply amplified, the amplification factor is not even 2 times due to the limitation of the power supply voltage. As shown in fig. 2, the present invention uses an operational amplifier to build an add-subtract amplifying circuit, where R4= R5, R6= R7, vpeak is the output voltage of peak detection, vref is the output voltage of an active filter circuit, and the final output voltage Vadc is:

as the liquid level increases, the capacitance increases, the capacitive reactance decreases, vpeak begins to decrease, and the resulting Vadc begins to increase, with the magnitude of the increase depending on the change in liquid level and the setting of the magnification. Under the circuit design, the amplification factor can reach more than 20 times, which is far higher than the effect of directly amplifying Vpeak (less than 2 times).

For PWM2, the initial duty cycle may be set using empirical values obtained during actual debugging, and then adjusted according to the zeroing sub-process. The zeroing sub-process is as follows:

step1: ADC samples a digital value Vdig, the sampling is added with a digital filtering mode, and a method of averaging a plurality of continuous sampling values is adopted, so that errors are reduced; calculating the current detected voltage value according to the bit number n of the ADC and the reference voltage Vr

Step2: if Vadc is less than 0.01V, it means that the duty ratio of the current PWM2 is too small, vref is not enough to exceed the output Vpeak of the peak detection circuit, and the duty ratio needs to be increased; adding 1 to the PWM2 duty ratio register, and returning to Step1; if Vadc is greater than 0.02V, the duty ratio of the current PWM2 is too large, a test result is coupled with a part of direct current components to influence the judgment of the liquid level, and the PWM2 duty ratio register returns to Step1 after being reduced by 1; if Vadc is more than or equal to 0.01V and less than or equal to 0.02V, the zeroing is considered to be successful, and the Step3 is entered.

Step3: and sending information of zero setting completion to the upper computer through the UART.

The sub-process of the reading liquid level instruction is as follows:

step1: ADC samples a digital value Vdig, digital filtering is added in the sampling, after Vadc is obtained by using a formula 3-3, a proportionality coefficient Ktype which should be used at the moment is obtained according to the current material type given by an upper computer, and the final liquid level height H is as follows:

H＝KtypeVadc

because the temperature can influence the measurement, a temperature sensor can be added to test the resin temperature T, the temperature compensation coefficient of the material is set to Ktem, and the final liquid level height H is as follows:

step2: and sending the information of the liquid level H to an upper computer through a UART.

Based on the above liquid level detection method, an embodiment of the present application further provides a liquid level detection apparatus for executing the above liquid level detection method, the apparatus including:

the zero setting unit is used for acquiring an initial second voltage signal and confirming that zero setting is successful under the condition that a voltage value corresponding to the second voltage signal falls into a preset interval;

the computing unit is used for reading the current second voltage signal and/or the current temperature signal according to the received liquid reading instruction under the condition of successful zero setting, and obtaining the current liquid level according to the current second voltage signal; or obtaining the current liquid level according to the current second voltage signal and the current temperature signal.

Optionally, a temperature compensation unit may be provided in the liquid level detection device for generating a temperature signal depending on the ambient temperature.

Based on the liquid level detection method, an embodiment of the present application further provides a computer-readable storage medium, in which a computer program or an instruction is stored, and when the computer program or the instruction is executed by a computing device, the liquid level detection method is implemented.

Generally speaking, the application provides a liquid level detection equipment, liquid level detection method, liquid level detection device and storage medium, through the signal that generates of detecting and reference voltage comparison, and amplify, and then calculate the liquid level height, it is small to occupy, and it is high to detect the precision.

The above-described embodiments of the apparatus and system are merely exemplary, and some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

The above description is only for the preferred embodiments of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A liquid level detection apparatus, comprising:

a first detection circuit for extracting a signal characteristic of the first voltage signal; wherein the signal characteristic comprises a peak value, a peak-to-peak value, and/or a minimum value;

the comparison amplification circuit is used for outputting a second voltage signal according to the signal characteristic and a first preset reference voltage; and the second voltage signal is used for representing the height corresponding to the current liquid level.

2. The fluid level detection apparatus of claim 1, wherein the first excitation circuit comprises a detection capacitor and a voltage divider resistor; the detection capacitor is formed according to a probe extending into the container;

the first end of the detection capacitor is grounded, and the second end of the detection capacitor is electrically connected with the input end of the first detection circuit and the first end of the divider resistor; the second end of the divider resistor is used for receiving the first excitation signal; or the like, or, alternatively,

3. The fluid level detection device of claim 2, wherein the first excitation circuit further comprises an excitation voltage follower;

the output end of the excitation voltage follower is electrically connected with the input end of the first detection circuit, and the input end of the excitation voltage follower is connected to the connection point of the detection capacitor and the divider resistor.

4. The fluid level sensing apparatus of claim 1, wherein the first detector circuit comprises a detector diode, a peak detector capacitor, and a first resistor, the detector diode having an anode electrically connected to the output of the first excitation circuit; the first end of the peak detection capacitor is electrically connected with the cathode of the detection diode, the first end of the first resistor and the input end of the comparison amplification circuit respectively; the second end of the peak detection capacitor and the second end of the first resistor are both grounded.

5. The liquid level detecting apparatus as claimed in claim 4, wherein the first detector circuit further comprises a detector voltage follower, and the first terminal of the peak detector capacitor is electrically connected to the input terminal of the comparison amplifier circuit through the detector voltage follower.

6. The fluid level sensing apparatus of claim 1, wherein the first detector circuit comprises a comparator having a first input electrically connected to the first excitation circuit and a second input for receiving a predetermined detector reference voltage;

the comparator is used for outputting a square wave with a variable duty ratio according to the comparison between the first voltage signal output by the first excitation circuit and the preset detection reference voltage, and the duty ratio is in direct proportion to the peak value of the first voltage signal;

the first detection circuit further comprises an active filter circuit or an average detection circuit, the output end of the comparator is connected with the input end of the active filter circuit or the input end of the average detection circuit, and the output end of the active filter circuit or the output end of the average detection circuit is electrically connected with the comparison amplification circuit;

the active filter circuit or the average detection circuit is used for obtaining the average value of the square wave, and the average value is in direct proportion to the duty ratio of the square wave.

7. The fluid level detection apparatus of claim 1, further comprising a first reference voltage circuit for providing the first preset reference voltage.

8. The liquid level detection apparatus of claim 7, wherein the first reference voltage circuit comprises a reference voltage follower and a low pass filter circuit having an output connected to an input of the reference voltage follower and an input for connection to a processing circuit; and the output end of the reference voltage follower is electrically connected with the comparison amplifying circuit.

9. The liquid level detection apparatus of claim 8, wherein the number of the low pass filter circuits is plural, and an output terminal of the plural low pass filter circuits connected in series is connected to an input terminal of the reference voltage follower, and an input terminal of the plural low pass filter circuits connected in series is used for connecting the processing circuit.

10. The fluid level detection device of claim 8, wherein the low pass filter circuit comprises a filter resistor and a filter capacitor; the first end of the filter resistor is the input end of the low-pass filter circuit, the second end of the filter resistor is electrically connected with the first end of the filter capacitor, the first end of the filter capacitor is the output end of the low-pass filter circuit, and the second end of the filter capacitor is grounded.

11. The fluid level sensing apparatus of claim 7, wherein the first reference voltage circuit comprises a DAC circuit, and wherein the input of the comparison and amplification circuit is coupled to the DAC circuit.

12. The fluid level sensing apparatus of claim 1, wherein the comparison amplification circuit comprises a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, and an operational amplifier;

the non-inverting input end of the operational amplifier is connected with the first end of the fourth resistor and the first end of the sixth resistor respectively, the inverting input end of the operational amplifier is connected with the first end of the fifth resistor respectively, the first end of the seventh resistor and the second end of the seventh resistor are connected with the output end of the operational amplifier, and the operational amplifier is used for being connected with the MCU; a second end of the fourth resistor is connected to the first preset reference voltage, and a second end of the fifth resistor is connected to an output end of the first detection circuit; and the second end of the sixth resistor is grounded.

13. The fluid level detection apparatus of claim 1, further comprising:

a second reference voltage circuit;

a subtraction circuit, a first input terminal of which is connected to the output terminal of the first detection circuit and the output terminal of the second detection circuit, a second input terminal of which is connected to the second reference voltage circuit, and an output terminal of which is connected to the input terminal of the comparison amplification circuit; the subtraction circuit is used for obtaining the signal characteristic of a fourth voltage signal according to the signal characteristic of the first voltage signal, the signal characteristic of the third voltage signal and a second preset reference voltage provided by the second reference voltage circuit;

the comparison amplification circuit is used for outputting a fifth voltage signal according to the signal characteristics of the first voltage signal, the signal characteristics of the fourth voltage signal and the first preset reference voltage.

14. The fluid level detection apparatus of claim 13, wherein the first excitation circuit comprises a first detection capacitor and a first divider resistor; the first detection capacitor is formed according to a first probe and a second probe which extend into the container; the second probe is used for contacting liquid at a first liquid level;

a first end of the first detection capacitor is grounded, a second end of the first detection capacitor is electrically connected with the first detection circuit and is electrically connected with a first end of the first divider resistor, and a second end of the first divider resistor is used for connecting the first excitation signal; or a first end of the first divider resistor is electrically connected with the first detection circuit and a second end of the first detection capacitor, a second end of the first divider resistor is grounded, and a first end of the first detection capacitor is used for connecting the first excitation signal;

the second excitation circuit comprises a second detection capacitor and a second divider resistor; the second detection capacitor is formed by the first probe and the third probe; the third probe is used for contacting the liquid at a second liquid level; the resistance value of the second divider resistor is larger than that of the first divider resistor; the first liquid level is lower than the second liquid level;

a first end of the second detection capacitor is grounded, a second end of the second detection capacitor is electrically connected with the first detection circuit and the first end of the second divider resistor, and a second end of the second divider resistor is used for connecting the second excitation signal; or, a first end of the second voltage-dividing resistor is electrically connected to the first detector circuit and to a second end of the second detection capacitor, a second end of the second voltage-dividing resistor is grounded, and a first end of the second detection capacitor is used for connecting the second excitation signal.

15. The liquid level detection apparatus of claim 13, wherein the second reference voltage circuit comprises a buck diode and a ground resistor, wherein a cathode of the buck diode is grounded through the ground resistor, and an anode of the buck diode is connected to a reference power source and is configured to step down a voltage of the reference power source to output the second preset reference voltage.

16. A liquid level detection method applied to the liquid level detection apparatus according to any one of claims 1 to 15, the liquid level detection method comprising:

acquiring a second voltage signal;

confirming that the zero setting is successful under the condition that the voltage value corresponding to the second voltage signal falls into a preset interval;

17. A liquid level detection apparatus, applied to the liquid level detection device according to any one of claims 1 to 15, comprising:

18. A computer-readable storage medium, having stored thereon a computer program or instructions, which, when executed by a computing device, carry out the method of claim 16.