Capacitance liquid level sensor

Abstract

The utility model discloses a capacitance liquid level sensor, which is mounted in a vacuum excrement collector of a sanitation system of a railway passenger vehicle, and comprises a protective shell, an inductive probe, a signal generation module, a signal conditioning module, an MCU (Microprogrammed Control Unit) control module and a power supply module, the signal generation module comprises a voltage follower, an oscillating circuit, a first NOT gate, a second NOT gate and other matched circuits; the oscillating circuit is composed of variable capacitance diodes, the first NOT gate is connected with the oscillating circuit in parallel, and the first NOT gate serves as an amplifier and provides gain for the oscillating circuit; the input end of the second NOT gate is connected with the output end of the first NOT gate, and the output end of the second NOT gate is connected with the inductive probe after passing through other matched circuits; the voltage follower amplifies the voltage of an input signal and outputs a signal with the same amplitude, and the output end of the voltage follower is connected with the oscillating circuit.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of liquid level sensor, concretely relates to a kind of capacitive liquid level sensor, applied in railway passenger vehicle sanitation system vacuum toilet. BACKGROUND

[0002] For traditional railway passenger vehicle, floating ball liquid level switch and capacitive liquid level sensor are usually used, i.e., floating ball liquid level switch and capacitive liquid level sensor are installed in passenger train sewage toilet box to detect the liquid level of sewage in the body, but floating ball liquid level switch and capacitive liquid level sensor are prone to false alarm due to hanging pollution, resulting in abnormal or failure of system operation. INVENTION CONTENT

[0003] The utility model provides a kind of capacitive liquid level sensor for railway passenger vehicle sanitation system vacuum toilet to solve the problem that existing liquid level sensor is prone to false alarm due to hanging pollution, resulting in abnormal or failure of system operation, which can accurately detect the liquid level of sewage in railway passenger vehicle sanitation system vacuum toilet.

[0004] Technical scheme: a kind of capacitive liquid level sensor, comprising: protective shell, inductive probe being arranged on the protective shell, signal generating module being arranged in the protective shell and being electrically connected one by one, signal conditioning module, MCU control module and power module;

[0005] The signal generating module is used to receive the control of MCU control module and output corresponding waveform;

[0006] The signal conditioning module is used to enhance and eliminate direct current bias for the waveform output by signal generating module;

[0007] The MCU control module is used to output control signal to signal generating module and receive signal from signal conditioning module;

[0008] The power module is used to power each module;

[0009] Among them, the signal generating module includes voltage follower, oscillation circuit, first NOT gate, second NOT gate and other supporting circuits;The oscillation circuit is composed of varactor, the first NOT gate is connected with the oscillation circuit in parallel, and the first NOT gate is used as an amplifier to provide gain for the oscillation circuit;The input end of the second NOT gate is connected with the output end of the first NOT gate, and the output end of the second NOT gate is connected with the inductive probe after passing through other supporting circuits;The voltage follower amplifies the voltage of input signal and outputs signals with the same amplitude, and the output end of the voltage follower is connected with the oscillation circuit.

[0010] Further, the capacitive liquid level sensor is installed in a vacuum excrement collector of a railway passenger vehicle sanitation system.

[0011] Further, the signal conditioning module comprises a radio frequency signal amplifier, an operational amplifier and other supporting circuits; an input end of the radio frequency signal amplifier is connected with an output end of the signal generating module, an output of the radio frequency signal amplifier is input to a positive input end of the operational amplifier, and an output end of the operational amplifier is connected with the MCU control module.

[0012] Further, the MCU control module is composed of an MC9S08SH8 chip and peripheral circuits thereof.

[0013] Further, the power module is composed of an LM357 chip and peripheral circuits thereof.

[0014] Beneficial effects: compared with the prior art, the utility model has the following advantages:

[0015] (1) as the dielectric constant value of air is different from the dielectric constant value of water-based liquid, by determining the capacitance value of the front end and the dielectric constant value of the medium, the capacitive liquid level sensor can stably identify two states: covered and uncovered, and the problem that false alarm is easily caused by contamination, leading to abnormal or ineffective system operation is solved;

[0016] (2) the capacitive liquid level sensor can be used for liquid level measurement and industrial process control in high-speed rail motor train units, airplanes, intelligent manufacturing, food and pharmaceutical industries and the like;

[0017] (3) the capacitive liquid level sensor utilizes self-developed technology, adopts modular design ideas, and has simple and reliable circuit and structure design, and is easy to mass produce. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a simplified equivalent model and measurement working principle schematic diagram of a capacitive liquid level sensor used in a vacuum excrement collector of a railway passenger vehicle sanitation system;

[0019] Figure 2 It is an outline structure schematic diagram of a capacitive liquid level sensor used in a vacuum excrement collector of a railway passenger vehicle sanitation system;

[0020] Figure 3 It is a circuit diagram of a signal generating module of a capacitive liquid level sensor used in a vacuum excrement collector of a railway passenger vehicle sanitation system;

[0021] Figure 4 It is a circuit diagram of a signal conditioning module of a capacitive liquid level sensor used in a vacuum excrement collector of a railway passenger vehicle sanitation system;

[0022] Figure 5 It is a circuit diagram of a power module for a capacitive liquid level sensor in a vacuum toilet of a railway passenger vehicle sanitation system.

[0023] Figure 6 It is a circuit diagram of a power module for a capacitive liquid level sensor in a vacuum toilet of a railway passenger vehicle sanitation system. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the utility model more clear and obvious, the utility model is further explained in detail below in combination with specific implementation manners and with reference to the drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the utility model.

[0025] The embodiment provides a capacitive liquid level sensor for a vacuum toilet of a railway passenger vehicle sanitation system, which mainly comprises a signal generating module, a signal conditioning module, an MCU control module and a power module which are electrically connected one by one.

[0026] Figure 2 The appearance structure of the capacitive liquid level sensor is shown. The capacitive liquid level sensor is externally provided with a stainless steel protective shell, and an inductive probe made of PEEK material is arranged on the stainless steel protective shell. The signal generating module, the signal conditioning module, the MCU control module and the power module are arranged in the inductive probe, and the inductive probe is externally connected with a PLC device through a multi-core cable. Specifically, the stainless steel protective shell of the embodiment is a salt mist resistant 316L stainless steel protective shell, the inductive probe made of PEEK material has corrosion resistance and high strength hardness, the multi-core cable comprises a power line and an output switch signal line, the overall structure is fully sealed, the design is compact, the inside is filled with high-performance sealing glue, the vibration resistance, impact resistance and corrosion resistance are high, and the overall protection level can reach IP67.

[0027] As shown in Figure 3 The signal generating module used in the embodiment comprises a voltage follower, an oscillation circuit, a first NOT gate, a second NOT gate and other supporting circuits. The oscillation circuit is composed of a varactor diode, and the first NOT gate is connected in parallel with the oscillation circuit. The input end of the second NOT gate is connected with the output end of the first NOT gate, and the output end of the second NOT gate is connected with the inductive probe after passing through other supporting circuits. The voltage follower amplifies the voltage of the input signal and outputs a signal with the same amplitude. Since the input resistance is large and the output resistance is small, a larger load can be driven. The output end of the voltage follower is connected with the oscillation circuit, and the oscillation circuit composed of the varactor diode is connected in parallel with the first NOT gate, which can be used as an amplifier to provide gain for the oscillation circuit. A second NOT gate is connected in series behind the first NOT gate, which plays a role in signal shaping and output isolation. Finally, the signal is emitted through the inductive probe.

[0028] As Figure 4 shown, the signal conditioning module used in this embodiment includes a radio frequency signal amplifier, an operational amplifier and other supporting circuits; the input end of the radio frequency signal amplifier is connected with the output end of the signal generating module, the output of the radio frequency signal amplifier is input to the positive input end of the operational amplifier, and the output end of the operational amplifier is connected with the MCU control module. In this embodiment, the radio frequency signal amplifier is used to enhance the signal strength, the operational amplifier is used to stabilize the oscillation and eliminate the DC bias. The operational amplifier used in this embodiment is chip AD8544.

[0029] The MCU control module of this embodiment is used for overall software and hardware management and control of the entire circuit, and is used to realize signal generation, collection, conditioning, switching signal output and delay control. The MCU control module integrates many complex functions, so that the number of peripheral devices and the complexity of circuit board design can be greatly reduced when designing the liquid level circuit, and the cost of the entire system circuit is reduced. The working range of the MCU is relatively wide, and it is very suitable for field use. As Figure 5 shown, the MCU control module used in this embodiment is composed of MC9S08SH8 chip.

[0030] Considering that the application range of the liquid level sensor is mainly for industrial measurement, an industrial + 24V DC power supply is used as the power supply mode here, and the communication with the related instruments can realize the modification of the response data on the PC side. As Figure 6 shown, the power module used in this embodiment is LM357.

[0031] Figure 1 A simplified equivalent model of the capacitive liquid level sensor of this embodiment is shown, the output end of the signal generating module is connected with one end of the coil L through the signal conditioning module, the other end of the coil L contacts the surrounding environment of the to-be-detected object, the surrounding environment of the to-be-detected object constitutes a capacitor, and the capacitance value of the capacitor is related to the dielectric constant (DK value) of the surrounding environment of the to-be-detected object. The capacitor and the coil L form an LC oscillation circuit. The resonant frequency generated by the LC oscillation circuit is sent to the single-chip microcomputer for processing, in the single-chip microcomputer, the obtained resonant frequency is compared with the trigger threshold value to obtain a comparison result, a control signal is generated according to the comparison result, and the single-chip microcomputer sends the control signal to the subsequent alarm circuit. The alarm circuit includes but is not limited to an indicator light or a buzzer.

[0032] The equivalent model and the measurement working principle of the capacitive radio frequency liquid level sensor proposed in this embodiment are as follows:

[0033] In the actual measurement process, the dielectric constant has two change conditions:

[0034] Case one: for a single medium, as the probe insertion depth is different, the mixing ratio of air and medium is different, resulting in the change of ε.

[0035] Case two: the medium itself changes, resulting in the change of ε.

[0036] For case one:

[0037] Since the capacitance value In the formula, ε is the dielectric constant of the measured medium, and during the process of sewage overflowing the probe, ε changes from small to large, and the capacitance value C also changes accordingly.

[0038] The resonant frequency generated by the LC oscillation circuit is represented as:

[0039]

[0040] During the process of sewage overflowing the probe, ε changes from small to large, and the capacitance value C also changes accordingly, and the resonant frequency f changes from large to small, and when the resonant frequency f is less than the alarm setting value, the alarm is given.

[0041] The sensor of the embodiment determines the capacitance value at the end of the sensor and the dielectric constant value of the medium through the electric field. Since the dielectric constant value of air is different from that of water-based liquid, the switch can stably identify the two states: covered and not covered. The liquid level switch uses independent research and development technology, adopts modular design idea, and the circuit and structure design are simple and reliable, easy to mass produce.

Claims

1. A capacitive liquid level sensor, characterized by: Include: The protective shell, the inductive probe arranged on the protective shell, the signal generating module arranged in the protective shell and electrically connected one by one, the signal conditioning module, the MCU control module and the power module; The signal generating module is used for receiving the control of the MCU control module and outputting corresponding waveforms; The signal conditioning module is used for signal enhancement and DC offset elimination of the waveforms output by the signal generating module; The MCU control module is used for outputting control signals to the signal generating module and receiving signals from the signal conditioning module; The power module is used for power supply for each module; Wherein, the signal generating module includes: voltage follower, oscillation circuit, first NOT gate and second NOT gate; the oscillation circuit is composed of varactor, the first NOT gate is connected with the oscillation circuit in parallel, the first NOT gate is used as an amplifier to provide gain for the oscillation circuit; the input end of the second NOT gate is connected with the output end of the first NOT gate, the output end of the second NOT gate is connected with the inductive probe after passing through other supporting circuits; the voltage follower amplifies the voltage of the input signal and outputs signals with the same amplitude, and the output end of the voltage follower is connected with the oscillation circuit.

2. A capacitive liquid level sensor according to claim 1, characterized in that: The capacitive liquid level sensor is installed in a vacuum toilet of a railway passenger vehicle sanitation system.

3. A capacitive liquid level sensor according to claim 1, wherein: The signal conditioning module includes a radio frequency signal amplifier and an operational amplifier; the input end of the radio frequency signal amplifier is connected with the output end of the signal generating module, the output of the radio frequency signal amplifier is input to the positive input end of the operational amplifier, and the output end of the operational amplifier is connected with the MCU control module.

4. A capacitive liquid level sensor according to claim 1, wherein: The MCU control module is composed of an MC9S08SH8 chip and its peripheral circuit.

5. A capacitive liquid level sensor according to claim 1, wherein: The power module is composed of an LM357 chip and its peripheral circuit.

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