CN213239100U

CN213239100U - Accurate capacitanc liquid level detection circuit

Info

Publication number: CN213239100U
Application number: CN202022005705.6U
Authority: CN
Inventors: 王伟意; 林富能
Original assignee: Xiamen Crystal Microelectronics Technology Co ltd
Current assignee: Xiamen Crystal Microelectronics Technology Co ltd
Priority date: 2020-09-15
Filing date: 2020-09-15
Publication date: 2021-05-18
Anticipated expiration: 2030-09-15

Abstract

The utility model discloses a precise capacitance type liquid level detection circuit, which comprises a liquid level detection sensor; the liquid level detection sensor is connected with a capacitive liquid level detection chip, and the capacitive liquid level detection chip is respectively connected with an open-drain output circuit, a capacitance comparison circuit, a discharge circuit, a charge collector, a decoupling circuit and a filter circuit; the open-drain output circuit is output to external host equipment through R4, and needs to be connected with a power supply end of a capacitive liquid level detection chip through a pull-up resistor R2. The water level control device has the advantages that the circuit layout is simple, the sensitivity is high, and the influence of water drop wall hanging can be effectively avoided by reasonably adjusting the water level point.

Description

Accurate capacitanc liquid level detection circuit

Technical Field

The utility model relates to an accurate liquid level detection circuit and adjustment mode, more specifically say, relate to a capacitanc liquid level detection circuit through binary channels comparison method, high accuracy adjustment.

Background

In many industrial processes, it is often necessary to detect the level of the liquid and the presence or absence of a change in the state of the liquid to provide an effective prompt signal and to notify the host computer to take appropriate action to protect some peripherals of the device from operating effectively, to reduce energy consumption, to reduce the service life of some peripherals, and so on.

The liquid level sensor that adopts in the market at present is various, there is the floater formula, photoelectric type, capacitanc, ultrasonic wave etc. all have respective corresponding advantage and disadvantage, any object all has the electric capacity, and the electric capacity size is related to by dielectric constant and volume size, and liquid level sensor judges the height of liquid level or has the state of liquid through detecting object capacitance variation, hugs closely the container wall with liquid level sensor now after, and the capacitor of similar parallel polar plate is formed with between the liquid, and the capacitance value of this capacitor is influenced by the dielectric constant of liquid and sensor interactive area and container wall.

SUMMERY OF THE UTILITY MODEL

In order to overcome the problems, the influence of the wall thickness of the container is broken through, the change of the liquid level in the container or the pipeline can be detected through the medium, the container does not need to be provided with holes, the reliability is high, the cost is low, and the mass production is easy to realize. The technical proposal is that the method comprises the following steps,

a precise capacitance type liquid level detection circuit comprises a liquid level detection sensor; the liquid level detection sensor is connected with a capacitive liquid level detection chip, and the capacitive liquid level detection chip is respectively connected with an open-drain output circuit, a capacitance comparison circuit, a discharge circuit, a charge collector, a decoupling circuit and a filter circuit; the open-drain output circuit is output to external host equipment through R4, and needs to be connected with a power supply end of a capacitive liquid level detection chip through a pull-up resistor R2.

Furthermore, the capacitance comparison circuit comprises a capacitor C1, wherein one end of the capacitor C1 is grounded, and the other end of the capacitor C1 is connected with the capacitive liquid level detection chip through R1.

Further, the liquid level detection sensor is connected with the capacitance type liquid level detection chip through R3, and the resistor R3 is used for improving the conduction anti-interference degree and the radiation anti-interference degree.

Further, the charge collector comprises a CMOD capacitance for collecting the variation of all the additional parasitic capacitances of the capacitive liquid level detection sensor; the discharge circuit includes a CDC discharge capacitor for discharging the CMOD capacitor.

Furthermore, the decoupling circuit comprises a capacitor C2, and two ends of the capacitor C2 are respectively connected with a power supply end and a ground end of the capacitive liquid level detection chip.

Further, the filter circuit comprises a capacitor C3 and an inductor or a magnetic bead, the C3 is connected with the C2 in parallel and connected with the inductor or the magnetic bead in series, and the inductor or the magnetic bead is connected with a power supply or a ground wire in series.

Furthermore, the liquid level detection sensor is arranged at the bottom or the side wall of the insulating container wall, or attached to the pipeline or clamped on the pipeline, or used as a probe mode to penetrate into the pipeline and the container.

Advantageous effects

This application has adopted advanced signal processing technique and high-speed signal processing's chip, has broken through the influence of container wall thickness, can separate the change of medium detection container or the inside liquid level of pipeline, and the container need not the trompil, and the reliability is high, and is with low costs, realizes mass production easily.

Drawings

Fig. 1 is the utility model discloses a schematic diagram of accurate capacitanc liquid level detection circuit.

Fig. 2 is a block diagram of an accurate capacitive liquid level detection circuit of the present invention.

Fig. 3 is the utility model discloses an accurate capacitanc liquid level detection circuit work flow chart.

The system comprises a pipeline 10, a container 20, a liquid level detection sensor 30, a discharge circuit 40, an open-drain output circuit 50, a decoupling circuit 60, a charge collector 70, a capacitance type liquid level detection chip 80, a capacitance comparison circuit 90 and a filter circuit 100.

Detailed Description

For a further understanding of the invention, reference is made to the detailed description of the invention taken in conjunction with the accompanying fig. 1-3 and the examples.

Referring to fig. 1, the precise capacitive liquid level detection circuit of the present embodiment includes a liquid level detection sensor, a capacitive liquid level detection chip, a charge collector, a capacitance comparison circuit, a discharge circuit, an open-drain output circuit, a decoupling circuit, and a filter circuit. The embodiment provides an accurate capacitanc liquid level detection circuit, can be applied to the water purifier, intelligence machine of sweeping the floor, cleaning machine, dish washer, intelligence is cultivated in a pot etc. but not limited to this.

As shown in fig. 2, the threshold value of the capacitive liquid level detection chip 80 is set internally by the liquid level chip, or is set internally by collecting external data, and both applications are within a limited range. The present embodiment takes SC01 as an example。

As shown in fig. 2, the liquid level detection sensor 30 is connected to the CIN2 of the capacitive liquid level detection chip 80 through a resistor R3, the liquid level detection sensor 30 includes a flat top spring, a coil spring, a conductive cotton, a conductive cloth,

the PCB copper foil, conductive medium materials such as probe or miniature copper pipe copper post, general liquid level detection sensor 30 design requirement will have certain response area, and the area is better for the rectangle, and liquid level detection sensor 30 will design the response area as big as possible, and liquid level detection sensor 30 parasitic capacitance is as little as possible, controls within 10PF, and the response area designs as far as possible between 4 x 4mm-30 x 30mm, ensures great response area, just can guarantee high sensitivity and precision height. The level detection sensor 30 collects the capacitance change caused by the liquid level change, and the capacitance change is logically judged by the interior of a liquid level chip introduced by a resistor R3. The R3 resistor is mainly used to improve the conduction interference rejection, the radiation interference rejection, and the like, and is helpful for the EMC performance of the product, the selection range is 0 to 10K Ω, and the general recommended value is 3K Ω, in other optional embodiments, other types of liquid level detection sensors 30 may also be used, and this embodiment is not limited thereto.

The liquid level detecting sensor 30 may be disposed at the bottom or the side wall of the insulating container 20 as shown in fig. 2, attached to the pipeline 10 or clamped on the pipeline 10, or may be in the form of a probe extending into the pipeline and the container, but is not limited thereto.

As shown in fig. 2, the decoupling circuit 60 and the filter circuit 100, different power environments, need to enhance the problem of EMC and other interference, the decoupling circuit 60 includes a capacitor C2, which is generally recommended to be 100 nF; the filter circuit 100 comprises a large capacitor C3 and an inductor or a magnetic bead which are connected in series between a power supply and a ground wire, wherein the C3 and the C2 are connected in parallel and are connected in series with the inductor or the magnetic bead, a front-end power supply is connected with the inductor L1/magnetic bead or the ground wire is connected in series with the inductor L1/magnetic bead, and the selection of components of the circuits is determined according to the characteristics of the power supply. This embodiment is not limited thereto.

As shown in fig. 2, the open-drain output circuit 50 requires an external pull-up resistor R2 for open-drain output, and the series resistor R4 is mainly used to protect the capacitive liquid level detection chip 80 and prevent the capacitive liquid level detection chip 80 from being damaged by an external applied voltage and a reverse-flow large current. When detecting that liquid exists or the liquid height reaches the position to be detected, the output is low level, and when detecting that no liquid exists or the liquid height does not reach the position to be detected, the output is low level. In this operation, a level signal to be outputted can be changed by adding a circuit such as an inverter to the signal according to the level to be outputted. This embodiment is not limited thereto.

As shown in FIG. 2, the charge collector 70 includes a CMOD capacitor, which is typically set at 1nF to 10nF, preferably 4.7 nF. For collecting the variation of all the additional parasitic capacitances of the capacitive level detection sensor.

As shown in FIG. 2, the discharge circuit 40 includes a CDC capacitor for discharging the CMOD charge collectors, which is primarily used to adjust the sensitivity of the level detection sensor to liquid, with less CDC capacitor being more sensitive to liquid and less sensitive, conversely. The CDC capacitance adjustment range is generally between 5PF and 50 PF. The NPO material or the COG material is adopted, the higher the precision is, and the better the consistency is.

As shown in fig. 2, the capacitance comparison circuit 90, including the capacitor C1, may be connected in series with a resistor R1 between the channels C1 and CIN1 to enhance the anti-interference and stability, and the capacitor C1 connected in series needs to use a high-precision capacitor, and the precision of the capacitor directly determines the liquid level detection precision. The capacitance is used for matching the current environment, and forms a difference value with the capacitance of the liquid level detection sensor electrode to judge whether the liquid changes, namely, the capacitance value of the liquid level detection sensor minus the capacitance value of C1 is larger than a set threshold value, and the liquid level of the container changes or whether the container changes in water or not is judged. Generally, the capacitance of the C1 capacitor needs to be NPO material capacitance, and the accuracy level needs to be as high as possible. The value range is determined by the parasitic capacitance of the liquid level detection sensor, the design is generally recommended to be between 0PF and 10PF, and the specific design value is determined by PCB layout and the sensor.

The capacitive liquid level detection chip is mainly used for acquiring the capacitance of the liquid level detection sensor and the capacitance of the capacitance comparison circuit channel, and acquiring high and low level signal output through internal logic processing, as shown in fig. 3, which is a working flow chart of the circuit. The method comprises the specific steps of carrying out,

s1, the capacitance type liquid level detection chip charges and discharges a liquid level detection sensor channel and a capacitance comparison circuit channel through a pseudo-random code switch, the liquid level detection sensor channel and the capacitance comparison circuit channel are scanned for multiple times, and the capacitance type liquid level detection chip transfers charges charged each time to a CMOD (charge-to-discharge) capacitor for collection and storage. The scanning time of the capacitance type liquid level detection chip to the liquid level detection sensor channel and the capacitance comparison circuit channel is the same and fixed, and the scanning time is mutually independent, so that the channel capacitance change corresponding to each time period is collected in a time-sharing mode only by one CMOD.

S2, when the capacitance type liquid level detection chip is used for charging and discharging a liquid level sensor channel, the CMOD continuously collects the transferred charge amount of the sensor channel, as the capacitance value of the CMOD is fixed, the more the CMOD collects the charge, the larger the voltage of the corresponding CMOD is, the comparator is arranged in the capacitance type liquid level detection chip, the voltage reference value of the comparator is the voltage of a power supply of 1/2, when the CMOD voltage exceeds the voltage of a power supply of 1/2, the output level of the comparator is turned over, the CDC capacitance gating switch is triggered, the CMOD voltage is discharged by the CDC capacitance at the moment, until the CMOD voltage is reduced to be lower than the voltage of a power supply of 1/2, the output level of the comparator is turned over again, the CDC capacitance gating switch is closed at the moment, the CMOD charge is continuously increased, the CDC capacitance gating switch is repeatedly switched on and when the capacitance of the, that is, the capacitance change analog quantity of the liquid level detection sensor channel is converted into the switching times of the CDC capacitance gating switch. And finally converting the variable capacitance value of the channel of the capacitance comparison circuit into the switching times of the CDC capacitance gating switch.

S3, after acquiring the channel switching times of the liquid level detection sensor and the channel switching times of the capacitance comparison circuit, the capacitance type liquid level detection chip performs logic judgment;

s4, when the fact that all additional parasitic capacitances of the liquid level detection sensor channel are larger than the sum of all existing parasitic capacitances of the capacitance comparison circuit channel and a threshold value set in the capacitance liquid level detection chip is detected in the capacitance liquid level detection chip, after the judgment of shake elimination processing, the parasitic capacitances are continuously established for many times, the leakage output circuit outputs a low level, the liquid level point is judged to reach a set position, or the container and the pipeline are in a liquid state, otherwise, the leakage output circuit outputs a high level, and the liquid level point is judged to not reach the set position, or the container and the pipeline are in an anhydrous state.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An accurate capacitance type liquid level detection circuit is characterized by comprising a liquid level detection sensor; the liquid level detection sensor is connected with a capacitive liquid level detection chip, and the capacitive liquid level detection chip is respectively connected with an open-drain output circuit, a capacitance comparison circuit, a discharge circuit, a charge collector, a decoupling circuit and a filter circuit; one path of the open-drain output circuit is output to external host equipment through R4, and the other path of the open-drain output circuit is connected with a power supply end of the capacitive liquid level detection chip through a pull-up resistor R2.

2. The accurate capacitive liquid level detection circuit according to claim 1, wherein the capacitance comparison circuit comprises a capacitor C1 and a resistor R1, one end of the capacitor C1 is grounded, and the other end is connected with the capacitive liquid level detection chip through the R1.

3. The accurate capacitive liquid level detection circuit of claim 1, wherein the liquid level detection sensor is connected to the capacitive liquid level detection chip through R3, and the resistor R3 is used to improve the conduction interference resistance and the radiation interference resistance.

4. A precision capacitive liquid level detection circuit according to claim 1 wherein the charge collector comprises a CMOD capacitance for collecting the variation of all additional parasitic capacitances of the capacitive liquid level detection sensor; the discharge circuit includes a CDC discharge capacitor for discharging the CMOD capacitor.

5. The accurate capacitive liquid level detecting circuit according to claim 1, wherein the decoupling circuit comprises a capacitor C2, and two ends of the capacitor C2 are connected to a power terminal and a ground terminal of the capacitive liquid level detecting chip, respectively.

6. The accurate capacitive liquid level detection circuit according to claim 1, wherein the filter circuit comprises a capacitor C3, an inductor or a magnetic bead, the C3 is connected in parallel with the C2 and in series with the inductor or the magnetic bead, and the inductor or the magnetic bead is connected in series with a power supply or a ground line.

7. The circuit of claim 1, wherein the liquid level sensor is disposed at the bottom or the sidewall of the insulating container, or attached to or clamped on the pipe, or used as a probe extending into the pipe and the container.