A method and circuit for detecting material parameters

Abstract

The present invention provides a method and circuit for detecting material parameters, belonging to the field of parameter detection technology. The detection method is based on an LC network including an ultrasonic transducer, and the ultrasonic transducer is in direct or indirect contact with the material to be measured; the detection method includes the following steps: S1. Energizing; S2. Detection; S3. Calculation and judgment; S4. Delay; the detection circuit includes an enabling circuit, an LC network, a residual vibration extraction circuit, a shaping / post-processing circuit, and a central processing unit. An embodiment of the present invention provides a feasible method for detecting material parameters, which can simultaneously detect multiple parameters of the same material or distinguish different materials through calibration; in ultrasonic atomization applications, the ultrasonic transducer can have both atomization and liquid level detection functions, which is conducive to simplifying the structure and reducing costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of traffic facilities, and in particular relates to a method and circuit for detecting material parameters. Background Art

[0002] Currently, in ultrasonic atomization applications, multiple parameters of the same substance are difficult to detect and determine, and different substances are also difficult to detect and distinguish. The ultrasonic transducer cannot have both atomization and liquid level detection functions, resulting in a more complex structure and higher cost for the ultrasonic transducer, which urgently needs improvement. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the technical problem to be solved by the embodiments of the present invention is to provide a method and circuit for detecting material parameters.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for detecting material parameters is based on an LC network including an ultrasonic transducer, wherein the ultrasonic transducer is in direct or indirect contact with the material to be measured, and the detection method comprises the following steps:

[0006] S1. Energizing: delivering at least one excitation cycle of driving power to the LC network to cause it to enter a stable oscillation state, wherein the driving power has a consistent or known energy per cycle or is measured;

[0007] S2. Detection: Stop supplying the drive signal to the LC network and detect residual vibration parameters of the LC network. The residual vibration parameters include, but are not limited to, amplitude, period, and / or the number of residual vibration periods with an amplitude greater than a set threshold, and / or the duration of residual vibration with an amplitude greater than a set threshold.

[0008] S3 calculation determination: using the calibration coefficients of the current and / or adjacent multiple detection of the residual vibration parameters obtained to calculate the current material to be measured parameters;

[0009] S4. Delay: 0~600 seconds as needed;

[0010] S5. Repeat the above steps until the stopping condition is reached.

[0011] The stop conditions include receiving a manual stop instruction and completing the collection of data required for the current detection.

[0012] In a further embodiment, in the energizing step, at least one cycle of driving power is supplied to the LC network, wherein the driving power has a constant amplitude, cycle, and duty cycle;

[0013] In the detecting step, the detected aftershock parameter is the number of aftershock cycles with an amplitude greater than a set threshold, or the duration of aftershock with an amplitude greater than a set threshold. Correspondingly, in the calculating and determining step, the current substance and its parameters to be measured include but are not limited to:

[0014] The material level or liquid level of solid powder or liquid substance with known density;

[0015] The pressure and / or intensity of the solid powder or liquid substance applied to the ultrasonic transducer;

[0016] whether a solid or liquid substance is in contact with the ultrasonic transducer;

[0017] The density and / or viscosity of the fluid material in contact with the ultrasonic transducer is highly constant.

[0018] The method for detecting material parameters of the present invention works as follows:

[0019] When an inductor and capacitor are connected to form a loop, they form an LC network. When excitation energy is input into the LC network and then removed, this energy can repeatedly convert between magnetic energy and electric potential energy in the form of residual vibrations between the inductor and capacitor of the LC loop, forming a free oscillation until the energy is gradually consumed in the loop impedance in the conversion path and radiates electromagnetic energy into space.

[0020] As one of the components of the LC network, the ultrasonic transducer forms free oscillations after being excited, converting the electrical energy excited into the LC circuit into ultrasonic energy, and releasing it to the material in contact with it until the energy in the LC circuit is completely released.

[0021] When the properties (such as conductivity, viscosity, pressure, shape, etc.) of the material in contact with the ultrasonic transducer are different, the rate at which the ultrasonic transducer releases ultrasonic energy to it (the energy consumed per unit time) will be different. After receiving the same excitation energy, the residual oscillation parameters in the LC circuit will be different.

[0022] The present invention provides a method for detecting material parameters, using an ultrasonic transducer as one of the components of an LC circuit. After inputting a known energy excitation into the LC circuit, the residual vibration parameters of the LC circuit are detected to obtain the following parameters of the material in contact with the ultrasonic transducer, for example:

[0023] 1. Is there any substance in contact with the ultrasonic transducer, such as powdered solid material or liquid?

[0024] 2. The amount of material in contact with the ultrasonic transducer, such as material level, liquid level, etc.

[0025] 3. The properties of the material currently in contact with the ultrasonic transducer, such as conductivity, viscosity, pressure, morphology, etc.

[0026] A material parameter detection circuit using the above method is composed of an enabling circuit, an LC network, a residual oscillation extraction circuit, a shaping / post-processing circuit, a central processing unit, etc.

[0027] The enabling circuit is an excitation circuit for the LC network, and is controlled by the central processing unit to intermittently provide periodic electrical energy to the LC network to put the LC network into an oscillation state. The enabling circuit includes power devices and their driving circuits, etc. The power devices include but are not limited to transistors, MOSFETs, IGBTs, etc.;

[0028] The LC network is an inductor-capacitor combination network including an ultrasonic transducer;

[0029] The residual oscillation extraction circuit is a high-impedance coupling circuit connected between the LC network and the shaping / post-processing circuit, coupling the oscillation state of the LC network to the shaping / post-processing circuit. The residual oscillation extraction circuit includes, but is not limited to, an inductor winding coupled to the inductor in the LC network, or a capacitor or resistor connected to the LC network.

[0030] The shaping / post-processing circuit is a circuit that shares a common ground with the central processing unit and provides the central processing unit with a sampled signal, and is composed of a rectifier element, a clamping element, a filter element, etc.

[0031] One of the digital output terminals of the central processor is connected to the enabling circuit for controlling the intermittent operation of the enabling circuit, and the input port thereof is connected to the output terminal of the shaping / post-processing circuit for detecting the residual vibration parameters.

[0032] As a preferred solution, the ultrasonic transducer is a piezoelectric ceramic transducer; and the LC network is formed by connecting an inductor and the ultrasonic transducer.

[0033] As a further solution, the LC network is formed by connecting an inductor and a piezoelectric ceramic transducer in parallel; one end of the inductor is connected to the positive electrode of the power supply, and the other end is connected to the power device, or the center tap of the inductor is connected to the positive electrode of the power supply, and one of the other two ends is connected to the power device;

[0034] The enabling circuit is a circuit with an N-type MOSFET as its core, and forms an oscillation circuit with the LC network. The oscillation circuit includes the LC network, the N-type MOSFET, and the gate circuit of the MOSFET, and is either a separately excited oscillation circuit or a self-excited oscillation circuit.

[0035] The N-type MOSFET in the separately excited oscillator circuit has its drain connected to the LC network, its source connected to the negative electrode of the power supply, and its gate connected to one of the digital output ports of the central processing unit via a separately excited gate circuit. The central processing unit sends intermittent high-frequency switching signals to the N-type MOSFET via the separately excited gate circuit via the digital output port, causing the oscillator circuit to intermittently enter an oscillation state under the stimulation of the central processing unit. The separately excited gate circuit includes a resistor connected between the gate and source of the N-type MOSFET, and a resistor connected between the gate of the N-type MOSFET and the digital output terminal of the central processing unit.

[0036] The self-excited oscillation circuit is an inductive three-point LC oscillation circuit or a capacitive three-point LC oscillation circuit, or a variant of these two oscillation circuits. The gate or base of the power device of the self-excited oscillation circuit is also provided with a control circuit connected to the central controller, including a control transistor or MOSFET and a driving element for the control transistor or MOSFET. The base or gate of the control transistor or MOSFET is connected to the digital output port of the central controller via a bias resistor, and the collector or drain of the control transistor or MOSFET is connected to the gate of the power device. The central controller controls the gate bias voltage of the power device by driving the control transistor or MOSFET on / off, thereby controlling the self-excited oscillation circuit to stop / start oscillation, thereby achieving the purpose of controlled intermittent operation of the self-excited oscillation circuit.

[0037] As a further solution, the residual oscillation extraction circuit is an inductor winding having a magnetic coupling loop with the inductor in the LC network, one end of which is connected to the negative electrode of the power supply and the other end is connected to the shaping / post-processing circuit;

[0038] The shaping / post-processing circuit includes a rectifier diode, a clamping element, a resistor, a capacitor, etc. The anode of the rectifier diode is connected to the inductor winding of the residual vibration extraction circuit, and the cathode is connected to a network consisting of a clamping element, a resistor, and a capacitor in parallel. The other end of the network consisting of the clamping element, the resistor, and the capacitor in parallel is connected to the negative electrode of the power supply. The clamping element includes but is not limited to a unidirectional TVS diode, a unidirectional ESD, a Zener diode, a voltage reference chip, etc. The connection between the clamping element and the diode also serves as the output of the shaping / post-processing circuit and is connected to the central processing unit.

[0039] As a further solution, in the LC network, the parameters of the LC network are compensated by connecting a capacitor in series and / or in parallel with the piezoelectric ceramic transducer;

[0040] The inductance of the inductor and the equivalent capacitance of the ceramic transducer after compensation conform to the formula ,in:

[0041] f is the resonant frequency of the piezoelectric ceramic transducer;

[0042] L is the equivalent inductance of the inductor in the LC network;

[0043] C is the equivalent capacitance of the piezoelectric ceramic transducer after compensation.

[0044] As a further solution, the residual oscillation extraction circuit is indirectly connected to the LC loop, and is connected to a current sensor in the main power supply loop, including but not limited to a current detection resistor.

[0045] As a further solution, filtering elements are provided in the power supply circuit and the piezoelectric ceramic transducer circuit to prevent radiation into space and conduction of excessive high-frequency signals along the power supply circuit and the piezoelectric ceramic transducer circuit.

[0046] As a further solution, the after-oscillation extraction circuit is a capacitor connected between the LC network and the shaping / post-processing circuit.

[0047] The benefits of implementing the present invention are:

[0048] 1) Provide a feasible method for detecting material parameters;

[0049] 2) Through calibration, multiple parameters of the same substance can be detected simultaneously, or different substances can be distinguished;

[0050] 3) In ultrasonic atomization applications, the ultrasonic transducer can have both atomization and liquid level detection functions, which is conducive to simplifying the structure and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a flowchart of the material parameter detection method of the present invention;

[0052] Figure 2 is a functional block diagram of a circuit using the material parameter detection method of the present invention;

[0053] Figure 3 1 is a schematic diagram of a first embodiment of a circuit for a material parameter detection method according to the present invention;

[0054] Figure 4 This is a schematic diagram of a second embodiment of a circuit using the material parameter detection method of the present invention. DETAILED DESCRIPTION

[0055] The technical solution of this patent is further described in detail below in conjunction with specific implementation methods.

[0056] The following describes in detail embodiments of the present invention, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0057] Example 1

[0058] See also Figure 3 This embodiment provides a material parameter detection circuit. The working power is input from the P1 port. C1, L1, and C2 form a filter network, which can not only provide a stable power supply for the subsequent circuit, but also suppress the high-frequency harmonics generated by the subsequent circuit from leaking out from P1 and causing electromagnetic pollution.

[0059] L2_1, Co, and T1 form an LC network, and L3 and L3 are connected in series in the LC network to suppress high-frequency harmonics in the LC circuit;

[0060] N-channel field effect transistor (MOSFET) Q1 is connected between the LC network and the negative pole of the power supply to form an enabling circuit for the LC network. R3 and R4 are bias resistors for Q1, where R3 is connected to the gate of Q1 and the digital output port O of the central controller U1. When the O port of U1 outputs a high level, Q1 is turned on.

[0061] L2_2 is an inductor winding coupled to L2_1 and serves as a residual oscillation extraction circuit. The state of the LC loop is synchronously reflected at both ends of L2_2.

[0062] D1, R1, R2, D2, and C3 form the shaping / post-processing circuit, where D1 rectifies the signal from L2_2. R1 and R2 divide the voltage of the rectified pulse signal, while increasing the impedance of the shaping / post-processing circuit and reducing the impact of the shaping / post-processing circuit's power consumption on the LC loop. D2 is a voltage regulator diode, a unidirectional TVS diode, or a unidirectional ESD diode, which acts as a limiter to prevent high-voltage pulses from damaging subsequent circuits. C3 is a filter capacitor used to filter out possible interference in the signal.

[0063] U1 is the central controller (CPU), which controls the operation of the enabling circuit through its digital output port O and receives the residual vibration signal obtained by the shaping / post-processing circuit through the input port I.

[0064] When the capacity of C3 is small, the shaping / post-processing circuit outputs a pulse signal synchronized with the residual oscillation of the LC circuit. The characteristics of digital circuits determine that U1 has a recognition threshold for the signal at its digital input terminal. That is, signals with an amplitude greater than its high-level threshold are recognized as high levels, and signals with an amplitude less than its low-level threshold are recognized as low levels. U1 can obtain the residual oscillation status of the LC network by detecting the number of high-level pulses received at the I port.

[0065] When the capacity of C3 is large enough, the amplitude of the output signal of the shaping / post-processing circuit reflects the amplitude of the residual oscillation of the LC loop. U1 can also obtain the residual oscillation of the LC network by performing ADC conversion on the voltage of the I port.

[0066] During operation, U1 first outputs at least one enabling pulse to Q1 through port O, causing Q1 to conduct for one end of the time to charge the LC network with electrical energy. Then, port O is set to a low level, Q1 is turned off, and the LC network enters the residual vibration state. The residual vibration extraction circuit L2_2 synchronously obtains the residual vibration information, which is rectified by D1, divided by R1 and R2, clamped by D2, and filtered by C3 before being input into U1. U1 can obtain the residual vibration situation by detecting the information of port I, and can obtain the relevant parameters of the detected substance by calculation using the calibration parameters.

[0067] For example, in liquid level / material level detection applications, the pressure applied by the material or liquid to the ultrasonic transducer T1 is different, the efficiency of the external work done during vibration is different, and the residual vibration amplitude and maintenance time are also different. By detecting the residual vibration, the liquid level / material level information can be obtained.

[0068] Since parameters such as density and viscosity of materials / liquids affect the residual vibration of the LC network, under this design concept, the relevant parameters of the material in contact with the ultrasonic transducer can be detected by measuring the residual vibration.

[0069] In particular, in the ultrasonic atomization device, the ultrasonic transducer is responsible for atomizing the liquid (U1 continuously outputs a high-frequency signal through the digital output port O, driving the self-excited oscillation circuit to operate, so that the ultrasonic transducer continuously sends ultrasonic vibration energy to the liquid to atomize the liquid). At the same time, at intervals, U1 stops outputting the high-frequency signal and sets the digital output port O to a low level, which allows the LC network to enter a residual vibration state. U1 detects the residual vibration and can determine the liquid level and the presence or absence of liquid. When the liquid to be atomized is consumed, U1 stops outputting the atomization drive signal (U1's digital output port O stops outputting) to avoid damage to the ultrasonic transducer due to "dry burning". It can also send an alarm signal (the specific circuit is not shown) to remind the user to add liquid to be atomized.

[0070] Example 2

[0071] See also Figure 4A material parameter detection circuit, wherein an enabling circuit and an LC network form a self-excited oscillation circuit, wherein the source of Q1 is connected to the negative electrode of the power supply through a parallel source resistor Re and a high-frequency bypass capacitor Ce; R3 and R4 divide the fixed voltage V+ and connect it to the gate of Q1 to stabilize the gate potential of Q1; the drain of Q1 is connected to the positive electrode of the power supply through the LC network; an oscillation capacitor Cc is also provided between the drain and source of Q1; the collector and emitter of the transistor Q2 are connected across the gate of Q1 and the negative electrode of the power supply, the current limiting resistor R5 and the pull-down resistor R6 are connected to the base of Q2, and the other end of R5 is connected to the digital output port O of the central processing unit U1.

[0072] During operation, CPU U1's digital output port O outputs a high level, turning on Q2. Since Q1's gate potential is low, the self-oscillation circuit stops. During a detection cycle, CPU U1 first turns output port O low, turning off Q2 and bringing Q1's gate potential high. The self-oscillation circuit starts oscillating, inputting energy into the LC network. Then, CPU U1 again turns digital output port O high, turning on Q2 and bringing its gate potential low, stopping the self-oscillation circuit. The LC network then enters a residual oscillation state, and the residual oscillation extraction circuit and shaping / post-processing circuit transmit the residual oscillation information to U1, allowing it to complete the detection task.

[0073] Compared with Example 1, in this embodiment, since the vibration circuit is self-excited vibration, it is not necessary for U1 to control each vibration cycle. Therefore, it is not necessary to occupy a large amount of U1 time to generate a high-frequency drive signal. U1 can have more time to process other tasks, and the control accuracy of U1 can also be improved.

[0074] The above describes in detail the preferred embodiments of this patent, but this patent is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the purpose of this patent.

Claims

1. A method for detecting material parameters, characterized in that: The detection method is based on an LC network comprising an ultrasonic transducer, and the ultrasonic transducer is in direct or indirect contact with the substance to be detected; The detection method utilizes the influence of material properties on the rate at which an ultrasonic transducer releases ultrasonic energy into a material. It can simultaneously detect multiple parameters of the same material or distinguish different materials. It includes the following steps: S1. Energizing: delivering at least one excitation cycle of driving power to the LC network to cause it to enter a stable oscillation state, wherein the energy of each cycle of the driving power is consistent or known or measured; S2 detection: stop delivering the drive signal to the LC network, and detect the residual vibration parameters of the LC network, the residual vibration parameters include amplitude, period and / or amplitude greater than the set threshold value of the residual vibration period number and / or amplitude greater than the set threshold value of the residual vibration duration; S3 calculation determination: using the calibration coefficients of the current and / or adjacent multiple detection of the residual vibration parameters obtained to calculate the current material to be measured parameters; S4. Delay: Delay 0 to 600 seconds as needed; S5. Repeat the above steps until the stopping condition is reached; The stop conditions include receiving a manual stop command and completing the collection of data required for the current test; The material parameters include: whether there is material in contact with the ultrasonic transducer; and the properties of the material currently in contact with the ultrasonic transducer, including conductivity, viscosity, pressure, and morphology.

2. The method for detecting material parameters according to claim 1, characterized in that: In the energizing step, at least one cycle of driving power is supplied to the LC network, wherein the driving power has a constant amplitude, cycle and duty cycle; In the detecting step, the detected aftershock parameter is the number of aftershock cycles with an amplitude greater than a set threshold, or the duration of aftershocks with an amplitude greater than a set threshold. Correspondingly, in the calculating and determining step, the current substance and its measured parameters include: The material level or liquid level of solid powder or liquid substance with known density; The pressure and / or intensity of the solid powder or liquid substance applied to the ultrasonic transducer; whether a solid or liquid substance is in contact with the ultrasonic transducer; The density and / or viscosity of the fluid material in contact with the ultrasonic transducer is highly constant.

3. A material parameter detection circuit, characterized in that: Including enabling circuit, LC network, residual vibration extraction circuit, shaping / post-processing circuit and central processing unit, The enabling circuit includes a power device and a driving circuit thereof, is connected in series with the LC network to a power supply, and is controlled by the central processing unit; the power device includes a transistor, a MOSFET, or an IGBT; The LC network is an inductor-capacitor combination network including an ultrasonic transducer; The residual oscillation extraction circuit is a high-impedance coupling circuit connected between the LC network and the shaping / post-processing circuit to couple the oscillation state of the LC network to the shaping / post-processing circuit. The residual oscillation extraction circuit includes an inductor winding coupled to the inductor in the LC network, or a capacitor and a resistor connected to the LC network; The shaping / post-processing circuit is a circuit that shares a common ground with the central processing unit and provides the central processing unit with a sampled signal, and is composed of a rectifier element, a clamping element, and a filter element; One of the digital output terminals of the central processor is connected to the enabling circuit for controlling the intermittent operation of the enabling circuit, and the input port thereof is connected to the output terminal of the shaping / post-processing circuit for detecting the residual vibration parameters.

4. A material parameter detection circuit according to claim 3, characterized in that: The ultrasonic transducer is a piezoelectric ceramic transducer; The LC network is formed by connecting an inductor and the ultrasonic transducer.

5. A material parameter detection circuit according to claim 4, characterized in that: The LC network is formed by connecting an inductor and a piezoelectric ceramic transducer in parallel; The inductor has one end connected to the positive electrode of the power supply and the other end connected to the power device, or the inductor has a center tap connected to the positive electrode of the power supply and one of the other two ends connected to the power device; The enabling circuit is a circuit with an N-type MOSFET as its core, and forms an oscillation circuit with the LC network. The oscillation circuit includes the LC network, the N-type MOSFET, and the gate circuit of the MOSFET, and is either a separately excited oscillation circuit or a self-excited oscillation circuit: The N-type MOSFET in the separately excited oscillation circuit has a drain connected to the LC network, a source connected to the negative electrode of the power supply, and a gate connected to one of the digital output ports of the central processing unit via a separately excited gate circuit. The central processing unit sends an intermittent high-frequency switching signal to the N-type MOSFET via the digital output port through the separately excited gate circuit, so that the oscillation circuit intermittently enters an oscillation state under the stimulation of the central processing unit; The separately excited gate circuit includes a resistor connected between the gate and source of the N-type MOSFET, and a resistor connected between the gate of the N-type MOSFET and a digital output terminal of the central processing unit; The self-excited oscillation circuit is an inductive three-point LC oscillation circuit or a capacitive three-point LC oscillation circuit, or a variant of these two oscillation circuits; The gate or base of the power device of the self-excited oscillation circuit is further provided with a control circuit connected to the central processing unit, including a control transistor or MOSFET and a driving element for the control transistor or MOSFET. The base or gate of the control transistor or MOSFET is connected to the digital output port of the central processing unit via a bias resistor, and the collector or drain of the control transistor or MOSFET is connected to the gate of the power device. The central processing unit controls the gate bias voltage of the power device by driving the control transistor or MOSFET on / off, thereby controlling the self-excited oscillation circuit to stop / start oscillation, thereby achieving the purpose of controlled intermittent operation of the self-excited oscillation circuit.

6. A material parameter detection circuit according to claim 5, characterized in that: The residual oscillation extraction circuit is an inductor winding that forms a magnetic coupling loop with the inductor in the LC network, one end of which is connected to the negative electrode of the power supply, and the other end is connected to the shaping / post-processing circuit; The shaping / post-processing circuit includes a rectifier diode, a clamping element, a resistor and a capacitor. The anode of the rectifier diode is connected to the inductor winding of the residual oscillation extraction circuit, and the cathode is connected to a network consisting of a clamping element, a resistor, and a capacitor connected in parallel. The network consists of a clamping element, a resistor, and a capacitor connected in parallel, with the other end connected to the negative pole of the power supply. The clamping components include unidirectional TVS diodes, unidirectional ESD, voltage regulator diodes and voltage reference chips. The connection end between the clamping element and the diode also serves as the output end of the shaping / post-processing circuit and is connected to the central processing unit.

7. A material parameter detection circuit according to claim 5, characterized in that: In the LC network, the parameters of the LC network are compensated by connecting a capacitor in series and / or in parallel with the piezoelectric ceramic transducer; The inductance of the inductor and the equivalent capacitance of the ceramic transducer after compensation conform to the formula 2πf(LC) 0.5 ≈1, where: f is the resonant frequency of the piezoelectric ceramic transducer; L is the equivalent inductance of the inductor in the LC network; C is the equivalent capacitance of the piezoelectric ceramic transducer after compensation.

8. The material parameter detection circuit according to claim 3, characterized in that: The residual oscillation extraction circuit is indirectly connected to the LC network and is a current sensor connected to the main power supply circuit, including a current detection resistor.

9. The material parameter detection circuit according to claim 3, characterized in that: Filter elements are also provided in the power supply circuit and the piezoelectric ceramic transducer circuit to prevent radiation into space and conduction of high-frequency signals with excessive amplitude outward along the power supply circuit and the piezoelectric ceramic transducer circuit.

10. The material parameter detection circuit according to claim 3, characterized in that: The after-oscillation extraction circuit is a capacitor connected between the LC network and the shaping / post-processing circuit.

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