A circuit and device for detecting aluminum liquid level in a riser tube for differential pressure casting

Abstract

The present invention discloses a circuit and device for detecting the aluminum liquid level in a differential pressure casting riser tube, belonging to the field of aluminum liquid level detection equipment. An eddy current sensor is used to detect the aluminum liquid level signal in the riser tube. The liquid level signal is collected and converted by a signal conditioning circuit, a differential filter circuit, and an AD conversion circuit, and is sent to a processor for signal processing to obtain aluminum liquid level data.

Description

Technical Field

[0001] The invention relates to the field of aluminum liquid level detection equipment, in particular to a circuit and device for detecting the aluminum liquid level in a differential pressure casting riser, and specifically to aluminum liquid level detection in differential pressure casting of aluminum castings. Background Art

[0002] Aluminum castings are manufactured using differential pressure casting machines. Figure 1 The figure shows the schematic diagram of the principle structure of a conventional differential pressure casting machine. The differential pressure casting machine primarily comprises an upper pressure tank 1, a lower pressure tank 2, a crucible 3, a riser tube 4, and a mold 5. The lower pressure tank 2 houses the crucible 3, which contains molten aluminum. The bottom end of the riser tube 4 extends into the crucible 3, within the molten aluminum. The top end of the riser tube 4 is connected to the first cover 201 of the lower pressure tank 4, which seals the top of the lower pressure tank. The differential pressure casting machine operates as follows: A certain pressure is maintained in the upper and lower pressure tanks. The upper pressure tank is then depressurized (or the lower pressure tank is pressurized). Due to the slightly higher pressure in the crucible, the molten aluminum in the crucible is transported through the riser tube to the mold in the upper pressure tank under the pressure difference, filling the casting mold and crystallizing under the pressure. Differential pressure casting of aluminum castings is divided into six stages. 0~t1 is the inflation stage of the upper and lower pressure tanks, and the inflation pressure is P; t1~t3, the upper pressure tank is the pressure decreasing stage. Since the pressure of the lower pressure tank remains unchanged, the aluminum liquid rises along the rising pipe into the mold under the action of the pressure difference, so t3~t4 is the liquid rising and filling stage; t4~t5 is the pressure holding stage; t5~t6 is the intercommunication stage; t6 starts to be the exhaust and pressure relief stage.

[0003] The existing technology has the following problems: during the pressure relief phase, the aluminum liquid in the riser tube drops, causing the aluminum liquid hanging on the inner wall of the riser tube to cool and solidify. As the use time goes by, the aluminum liquid hanging on the inner wall of the riser tube will become thicker and thicker, so the existing technology requires frequent replacement of the riser tube. In order to solve the problem of high frequency of replacement of the riser tube caused by the aluminum liquid in the riser tube cooling and solidifying due to the drop of the aluminum liquid in the riser tube, the manufacturer hopes to improve the equipment to maintain the aluminum liquid in the riser tube at the upper part during the pressure relief phase. Figure 1 Position A in the center is near the interface between the riser tube and the mold. However, to maintain the molten aluminum at the top of the riser tube, it is necessary to first obtain information about the molten aluminum's position within the riser tube. Because the molten aluminum in the riser tube is hot, with detection temperatures reaching 500-600°C, and the riser tube is a sealed container, it is impossible to place sensors above the molten aluminum inside. This inability to obtain information about the molten aluminum's position within the riser tube makes it impossible to achieve pressure control, and thus, the technical goal of maintaining the molten aluminum in the riser tube at the top during the pressure relief phase cannot be achieved, becoming a major challenge that the industry urgently needs to solve. Summary of the Invention

[0004] The purpose of the present invention is to provide a circuit and device for detecting the aluminum liquid level in a differential pressure casting riser tube, which is used to obtain the position information of the aluminum liquid in the riser tube, and more specifically, to obtain the position information of the aluminum liquid near the interface between the riser tube and the mold.

[0005] The technical solution adopted by the present invention is as follows: First, the present invention provides an aluminum liquid level detection circuit in a differential pressure casting riser tube, comprising: an aluminum liquid level sensor, including an excitation coil and a detection coil, installed on the outside of the riser tube; a signal conditioning circuit, providing a sinusoidal wave excitation signal to the excitation coil, and receiving and synchronously demodulating the measurement signal output by the detection coil, filtering, shaping, and amplifying the demodulated signal to obtain a DC voltage that changes linearly with the change of the aluminum liquid level; a differential filter circuit, comprising a main circuit and a standard voltage circuit; wherein the standard voltage circuit is used to generate a reference voltage, and the main circuit is used to filter the DC voltage and the reference voltage generated by the signal conditioning circuit; an AD conversion circuit, wherein a subtraction operation module in the AD conversion circuit performs a subtraction operation on the DC voltage input by the differential filter circuit and the reference voltage, and converts the result into a digital quantity and sends it to a processor; a processor, filtering and scaling the digital signal to obtain liquid level data; and a power supply module, supplying power to the circuit.

[0006] Preferably, the aluminum liquid level sensor further comprises a coil support, and the excitation coil and the detection coil are thermocouples, and are wound on the coil support in a double-wire parallel spiral shape.

[0007] Preferably, the power supply module includes power supply module A and power supply module B, an external DC power supply is connected to power supply module A and power supply module B, the output end of power supply module A is connected to the power input end of the signal conditioning circuit, and the output end of power supply module B is respectively connected to the power input end of the differential filtering circuit, the AD conversion circuit and the processor.

[0008] Preferably, the signal conditioning circuit includes: an AD698 chip, which is provided with a sine wave generating circuit for generating a sine wave excitation signal; a sensor interface for connecting the excitation coil and the detection coil of the sensor; a bandwidth adjustment circuit, including capacitors C102, C103 and C104, which determines the bandwidth of the signal conditioning circuit;

[0009] The output voltage full-scale adjustment circuit includes resistor R102 and potentiometer W101, which are used to adjust the full-scale output range of the AD698 chip; the output voltage offset adjustment circuit includes the output voltage offset adjustment circuit composed of R103, W102 and R104, W103, which adjusts the positive and negative offsets of the output voltage by adjusting the resistance values ​​of W102 and W103.

[0010] Preferably, the standard voltage circuit is composed of R0, C0, and D0. The power output by the power module is connected to the standard voltage circuit composed of R0 and DO. The voltage is stabilized by the voltage regulator diode D0 and then output. C0 filters the stabilized output voltage.

[0011] Preferably, in the main circuit, R1_10 and C1_11 form a low-pass filter circuit to filter the output of the signal conditioning circuit; R1_11 and C1_12 form a low-pass filter circuit to filter the standard voltage; D1_1 and D1_2 are limiting diodes.

[0012] Furthermore, a frequency modulation capacitor switching circuit is added between the signal conditioning circuit and the processor, and the processor modifies the frequency of the sinusoidal wave excitation provided by the signal conditioning circuit to the excitation coil in the aluminum liquid level sensor through the frequency modulation capacitor switching circuit.

[0013] Preferably, the FM capacitor switching circuit includes: a multi-way switch CD4051, capacitors C201, C202, C203, C204, C205, and C206; the processor is connected to the multi-way switch CD4051 through the three terminals CA, CB, and CC, and sends different data to control one of the six capacitors to access the demodulation circuit.

[0014] Furthermore, it also includes a key interface circuit, a VFD display interface circuit, and an RS232 communication interface circuit connected to the processor.

[0015] The present invention also provides an aluminum liquid level detection device in a differential pressure casting riser tube, comprising a main unit, in which the aluminum liquid level detection circuit in the differential pressure casting riser tube is installed. The front panel of the main unit is provided with a digital display screen and at least four function keys, the four function keys being respectively: a function selection key, a + key and a - key, and a confirmation key for modifying parameter values.

[0016] The beneficial effects of the present invention are as follows: the present invention provides a circuit and device for detecting the aluminum liquid level in a differential pressure casting riser tube, which uses an eddy current sensor to detect the aluminum liquid level signal in the riser tube, collects and transforms the liquid level signal through a signal conditioning circuit, a differential filter circuit, and an AD conversion circuit, and sends the signal to a processor for signal processing to obtain aluminum liquid level data. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the principle structure of an existing differential pressure casting machine.

[0018] Figure 2 This is a structural block diagram of the aluminum liquid level detection circuit in Example 1 of the present invention.

[0019] Figure 3 It is a three-dimensional structural diagram of the aluminum liquid level sensor of the present invention after being cut apart.

[0020] Figure 4 This is a structural diagram showing that the aluminum liquid level sensor of the present invention is installed on the outer side of the upper part of the riser.

[0021] Figure 5 This is a specific circuit schematic diagram of the signal conditioning circuit in Example 1 of the present invention.

[0022] Figure 6 This is a specific circuit principle diagram of the differential filter circuit in Example 1 of the present invention.

[0023] Figure 7 This is a specific circuit principle diagram of the AD conversion circuit in Example 1 of the present invention.

[0024] Figure 8 This is a specific circuit schematic diagram of the processor in Example 1 of the present invention.

[0025] Figure 9 This is a specific circuit schematic diagram of the power supply in Example 1 of the present invention.

[0026] Figure 10 This is a structural block diagram of the aluminum liquid level detection circuit in Example 2 of the present invention.

[0027] Figure 11 This is a specific circuit principle diagram of the frequency modulation capacitor switching circuit in Example 2 of the present invention.

[0028] Figure 12 This is a structural block diagram of the aluminum liquid level detection circuit in Example 3 of the present invention.

[0029] Figure 13 This is a specific circuit schematic diagram of the key interface circuit and the VFD display interface circuit in Example 3.

[0030] Figure 14 This is a specific circuit schematic diagram of the RS232 communication interface circuit in Example 3.

[0031] Figure 1 、 Figure 3 、 Figure 4 Middle: upper pressure tank 1, lower pressure tank 2, first cover 201, crucible 3, riser tube 4, mold 5, excitation coil 6, detection coil 7, coil support 8, mounting base 9. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the prior art and the present invention are further described in detail below with reference to the accompanying drawings and specific embodiments. In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be internal communication between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] Example 1

[0035] See also Figure 2 , Figure 2 This is a structural block diagram of the first aluminum liquid level detection circuit of the present invention. As shown in the figure, the aluminum liquid level detection circuit provided in this embodiment mainly includes several parts such as an aluminum liquid level sensor, a signal conditioning circuit, a differential filter circuit, an AD conversion circuit, a processor, a power module A, and a power module B.

[0036] First, if Figure 3 The figure shows a three-dimensional structure diagram of the aluminum liquid level sensor after being cut open. The aluminum liquid level sensor includes an excitation coil 6, a detection coil 7, and a tubular coil support 8. The excitation coil 6 and the detection coil 7 can be wound using thermocouples. For example, the excitation coil 6 and the detection coil 7 are wound in parallel in a spiral shape on the coil support 8. The coil support 8 can be made of high-temperature resistant glue, and the excitation coil 6 and the detection coil 7 are directly solidified in the high-temperature resistant glue.

[0037] like Figure 4 The figure shows the structure of the aluminum level sensor installed on the outer side of the upper portion of the riser tube 4. The top of the riser tube 4 is mounted within a mounting seat 9 on the upper surface of the first cover 201. Specifically, a stepped circular hole is formed in the center of the mounting seat 9 for the riser tube 4 to pass through. The upper end of the riser tube 4 is engaged within the circular hole, leaving a gap between the inner wall of the hole and the aluminum level sensor for installation. During installation, the coil support 8, along with the excitation coil 6 and detection coil 7 thereon, is placed outside the upper end of the riser tube 4. The height range covered by the excitation coil 6 and detection coil 7 is the range of the aluminum liquid level to be detected. After obtaining the aluminum liquid level information at this location, the pressurization system of the differential pressure casting machine can be further controlled.

[0038] The aluminum level sensor operates as follows: a high-frequency sinusoidal excitation signal is applied to the excitation coil, inducing a measurement signal with the same frequency as the excitation signal in the detection coil. As the aluminum liquid level in the riser changes, the impedance of the excitation and detection coils changes, thereby altering the amplitude and phase of the measurement signal output by the detection coil. This measurement signal is then sent to the subsequent circuitry of the aluminum level detection circuit for processing. The following describes this subsequent circuitry in detail.

[0039] like Figure 2 As shown, the aluminum liquid level sensor is connected to a signal conditioning circuit, the output of the signal conditioning circuit is connected to the input of a differential filter circuit, the output of the differential filter circuit is connected to the input of an AD conversion circuit, and the output of the AD conversion circuit is connected to the input of a processor. In addition, the present invention also includes a power supply circuit, which includes a power supply module A and a power supply module B. An external 12V DC power supply is connected to power supply module A and power supply module B. The output of power supply module A is connected to the power input of the signal conditioning circuit, and the output of power supply module B is connected to the power input of the differential filter circuit, the AD conversion circuit, and the processor, respectively.

[0040] The operating principle of the detection circuit in this embodiment is as follows: First, the signal conditioning circuit provides sinusoidal excitation to the excitation coil of the aluminum liquid level sensor, and the detection coil induces and outputs a measurement signal with the same frequency as the excitation signal. When the aluminum liquid level in the riser changes, the impedance of the excitation coil and the detection coil changes, thereby changing the amplitude and phase of the measurement signal output by the detection coil. This measurement signal is output to the signal conditioning circuit for synchronous demodulation. The demodulated signal is filtered, shaped, and amplified to obtain a DC voltage that changes linearly with the aluminum liquid level. Next, this DC voltage is input to one end of the differential filter circuit, while the other end of the differential filter circuit is connected to the +2.5V reference voltage generated by the standard voltage circuit. The differential filter circuit sends the filtered differential voltage to the A / D conversion circuit. The subtraction module in the A / D conversion circuit subtracts the input DC voltage from the reference voltage and converts the result into a digital value, which is then sent to the processor. The processor filters and scales the digital signal to obtain liquid level data.

[0041] Further, if Figure 9 As shown in FIG, a specific circuit schematic diagram of the power supply of the present invention is shown; as shown in the figure, a 12VDC power supply is used in this embodiment, and the power supply module A includes a DW-12D12 power supply module, which isolates the input +12V power supply and converts it into stable +12V and -12V to provide power for the signal conditioning circuit.

[0042] Power module B mainly includes the IB1205S power module, the AMS1117-3.3 power module, and the filter capacitors composed of C47, C48, and C49. The input +12V power supply is converted into a stable +5V power supply by the IB1205S power module. The +5V power supply is filtered by C49 and sent to the AMS1117-3.3 power module to be converted into a stable +3.3V power supply. The +3.3V power supply is filtered by C47 and C48 to provide a stable DC power supply for the differential filter circuit, AD conversion circuit, processor, etc.

[0043] Further, if Figure 5 FIG. 1 is a schematic diagram of a specific circuit principle of the signal conditioning circuit of the present invention. As shown in the figure, the signal conditioning circuit mainly includes an AD698 chip, a sensor interface, a power supply filter circuit, a sine wave generating circuit, a bandwidth adjustment circuit, an output voltage full-scale adjustment circuit, and an output voltage offset adjustment circuit. The structure and principle of each sub-circuit are described one by one below:

[0044] (1) The sensor interface is used to connect the excitation coil and detection coil of the sensor. Specifically, the two ends of the excitation coil are connected to the +OSC1 and -OSC1 terminals of the sensor interface respectively, and the two ends of the detection coil are connected to the +LIN and -LIN terminals of the sensor interface respectively. The AGND of the sensor interface is connected to the shielding layer of the connecting line.

[0045] (2) Power filter circuit: The +12V output of power module A is filtered by C108 and C109 and then connected to the +Vs pin of AD698 chip. The -12V is filtered by C106 and C107 and then connected to the -Vs pin of AD698 chip.

[0046] (3) Sine wave generating circuit: The internal sine wave generator of the AD698 chip generates an excitation sine wave signal and outputs it through the EXC1 and EXC2 pins; the amplitude of the sine wave excitation is adjusted by the resistor R101. In this embodiment, R101 can be selected as 7.5KΩ, and the excitation amplitude is 5V; the frequency of the sine wave excitation is adjusted by the capacitor C101. Specifically, C101 can be selected as 1.8nF, and the excitation frequency is 20kHz.

[0047] (4) Bandwidth adjustment circuit: C102, C103 and C104 determine the bandwidth of the AD698 signal conditioning circuit. Specifically, C102=C103=C104=2μF can be selected. At this time, the system bandwidth is 50Hz.

[0048] (5) Output voltage full-scale adjustment circuit: R102 and W101 adjust the full-scale output range of the AD698 chip. Specifically, R102 = 30KΩ and W101 = 10KΩ can be selected. The full-scale output can be adjusted by adjusting the resistance value of W101.

[0049] (6) Output voltage offset adjustment circuit: R103, W102 and R104, W103 constitute the output voltage offset adjustment circuit. Specifically, R103=10KΩ, W102=1KΩ, R104=10KΩ, W103=1KΩ can be selected. By adjusting the resistance values ​​of W102 and W103, the positive and negative offsets of the output voltage can be adjusted.

[0050] Further, if Figure 6 FIG. 1 is a specific circuit schematic diagram of the differential filter circuit of the present invention; as shown in the figure, the differential filter circuit includes a main circuit and a standard voltage circuit, and the structure and principle are as follows:

[0051] (1) Standard voltage circuit: It is composed of R0, C0, and D0. The 5V power output by power module B is connected to the standard voltage circuit composed of R0 and DO. The voltage regulator diode D0 stabilizes the 5V voltage to 2.5V output, and C0 filters the 2.5V voltage.

[0052] (2) Main circuit: R1_10 and C1_11 form a low-pass filter circuit to filter the output of the signal conditioning circuit; R1_11 and C1_12 form a low-pass filter circuit to filter the standard voltage 2.5V; D1_1 and D1_2 are limiting diodes that limit the output of the differential filter circuit to within 5V to protect the subsequent AD conversion circuit.

[0053] Further, if Figure 7 FIG2 is a schematic diagram of a specific circuit principle of the AD conversion circuit of the present invention. As shown in the figure, the AD conversion circuit mainly includes a CS5524 chip. The output of the differential filter circuit is connected to the AIN1+ and AIN1- terminals of the CS5524 chip respectively, and the converted voltage is sent to the CS5524 chip. The CS5524 chip uses a serial communication method to exchange data with the processor, where SCLK is the serial clock, SDI is the serial data input terminal, and SDO is the serial data output terminal.

[0054] Further, if Figure 8 The figure shows a specific circuit schematic diagram of the processor of the present invention. As shown in the figure, the processor core circuit mainly includes an STM32 microprocessor, a reset circuit, a clock circuit, and a programming and debugging interface circuit. The reset circuit is composed of R10 and C8 to ensure that the system resets normally when powered on. The clock circuit is composed of an 8M crystal oscillator Y2 and capacitors C11 and C12, providing the basic clock signal for the system. The programming and debugging interface circuit is composed of R12, R13 and a terminal block pin J3, providing the system with an SWD programming and debugging interface.

[0055] Example 2

[0056] See also Figure 10 , Figure 10This is a block diagram of the structure of the second aluminum liquid level detection circuit of the present invention. As shown in the figure, the aluminum liquid level detection circuit provided in this embodiment mainly includes several components, namely an aluminum liquid level sensor, a signal conditioning circuit, a differential filter circuit, an AD conversion circuit, a processor, a frequency modulation capacitor switching circuit, power module A, and power module B. The difference from the first embodiment is that a frequency modulation capacitor switching circuit is further added between the signal conditioning circuit and the processor. Through the frequency modulation capacitor switching circuit, the processor can modify the frequency of the sinusoidal wave excitation provided by the AD698 signal conditioning circuit to the excitation coil in the aluminum liquid level sensor.

[0057] The sensor's measurement accuracy can be further improved by adding a frequency-modulated capacitor switching circuit. The excitation signal operates using a swept frequency method. High-frequency excitation offers a fast response speed but poor penetration, while low-frequency excitation offers a slow response speed but greater penetration. If there is no molten aluminum clinging to the riser tube during measurement, high-frequency excitation signals are primarily used. However, as production progresses, molten aluminum will gradually cling to the riser tube, and the clinging layer will become increasingly thick. At this point, the high-frequency excitation signal cannot penetrate the clinging layer, leading to increased measurement error. Switching to low-frequency excitation signals reduces measurement speed but maintains accuracy.

[0058] like Figure 11 The figure shows a schematic diagram of a specific structure of the frequency modulation capacitor switching circuit of the present invention. As shown in the figure, the frequency modulation capacitor switching circuit includes: a multi-way switch CD4051, capacitors C201, C202, C203, C204, C205, and C206. The processor is connected to the CD4051 through the three terminals CA, CB, and CC, and sends different data to control one of the six capacitors to connect to the AD698 demodulation circuit, thereby adjusting the excitation frequency. The specific adjustment range is shown in Table 1 below:

[0059] Capacitance (nF) 35 17.5 7 3.5 1.75 0.7 Frequency (kHz) 1 2 5 10 20 50

[0060] Example 3

[0061] See also Figure 12 , Figure 12 This is a block diagram of the structure of the third aluminum liquid level detection circuit of the present invention. As shown in the figure, this embodiment further adds a key interface circuit connected to the processor, a VFD display interface circuit, and an RS232 communication interface circuit based on the second embodiment. The key interface circuit is used to connect to a keyboard for inputting parameters, such as setting the instrument range, zero point, full scale calibration, and operating parameter settings. The VFD display interface circuit is used to connect to the VFD display module. The processor sends processed liquid level data to the display module for display. The RS232 communication interface circuit is used to connect to control devices and management equipment.

[0062] Further, if Figure 13 The figure shows a specific circuit schematic diagram of the above-mentioned key interface circuit and VFD display interface circuit. The key interface circuit includes 4 independent membrane keys.

[0063] like Figure 14 The figure shows a specific circuit schematic diagram of the RS232 communication interface circuit. The RS232 communication interface circuit includes an SP3232 communication interface chip, capacitors C1A, C1B, C1C, C1D, and a DB9 socket.

[0064] The present invention also provides a device for detecting the aluminum liquid level in a differential pressure casting riser tube. The device comprises a main unit, in which the aforementioned aluminum liquid level detection circuit for differential pressure casting is installed. The main unit's front panel is provided with a digital display (display module) and at least four function keys: a zero calibration key, a full calibration key, and "+" and "-" keys for modifying parameter values. Furthermore, the main unit's rear panel is provided with a power socket, a fuse, a measurement signal cable socket, and a power switch.

[0065] The method of using the detection device is as follows:

[0066] 1. Instrument Calibration

[0067] 1. System connection: Install the sensor on the differential pressure casting machine and connect it to the host machine. According to the measurement process requirements, the pressure system of the differential pressure casting machine is controlled to keep the aluminum liquid at different heights.

[0068] 2. Instrument adjustment

[0069] A: System zero point calibration: By controlling the pressurization system of the differential pressure casting machine, make the aluminum liquid at the height "0mm" position (the lower edge of the height range covered by the excitation coil and the detection coil or close to the lower edge), use the function key "F" on the measuring instrument panel to select the function "Zero", at this time, the digital display will flash to display the measurement result; press the "<" key, the digital display will change the measured value to 0000mm and the display will be always on, at this time the zero point calibration is completed; if the measured value does not return to zero, press the confirmation key several times until it returns to zero.

[0070] B: System full-scale calibration: By controlling the pressurization system of the differential pressure casting machine, make the aluminum liquid at the height "xxxmm" position (set by the user, specifically the upper edge or close to the upper edge of the height range covered by the excitation coil and the detection coil), use the function key "F" on the measuring instrument panel to select the function "full scale", the digital display will flash to display the full-scale value, use the "+" and "-" keys to adjust the required full-scale value, so that the digital display shows the value "xxxmm", press the "<" key, and the full-scale calibration is completed.

[0071] C: System re-inspection: By controlling the pressurization system of the differential pressure casting machine, the height of the molten aluminum returns to the "0mm" position. At this time, the digital display should show a value of 0000mm. Otherwise, it is necessary to repeat the adjustments of steps A and B.

[0072] 2) Display

[0073] To ensure operators can clearly see the measured height data, the measuring device uses a high-definition digital VFD display to display the measurement results and parameters during the setting process. The VFD display brightness can also be automatically adjusted according to the brightness of the external environment.

[0074] 3) Keyboard Operation

[0075] Panel Key Operation Instructions: The main panel of the differential pressure casting riser tube aluminum level detection device is equipped with four keys to complete system zero and full scale calibration, parameter setting, and other functions. The key response speed is 5 times / second. The following describes the function and operation of each key:

[0076] 1. "F" key: Function selection key, used to select a function number. The function number determines the operations that can be performed on the panel and the VFD display.

[0077] 2. "+" "-" key: Modify parameter value. The execution time is divided into three levels. When the key is pressed, the duration is:

[0078] 0~5 seconds, +1 each time

[0079] 5~10 seconds, +10 each time

[0080] When >10 seconds, +100 each time

[0081] 3. "<" key: Confirmation key / status conversion key when modifying parameters.

[0082] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A circuit for detecting the aluminum liquid level in a differential pressure casting riser tube, characterized in that: include: The aluminum liquid level sensor, including an excitation coil and a detection coil, is installed outside the vertical riser pipe; The aluminum liquid level sensor also includes a coil support body, and the excitation coil and the detection coil are thermocouples, and are wound on the coil support body in a double-wire parallel spiral shape; A high-frequency sinusoidal excitation signal is applied to the excitation coil; The signal conditioning circuit provides a sinusoidal excitation signal to the excitation coil, receives the measurement signal output by the detection coil and performs synchronous demodulation. It then filters, shapes, and amplifies the demodulated signal to obtain a DC voltage that changes linearly with the aluminum liquid level. The differential filter circuit includes a main circuit and a standard voltage circuit; wherein the standard voltage circuit is used to generate a reference voltage, and the main circuit is used to filter the DC voltage and the reference voltage generated by the signal conditioning circuit; AD conversion circuit, the subtraction operation module in the AD conversion circuit performs a subtraction operation on the DC voltage input by the differential filter circuit and the reference voltage, and converts the result into a digital value and sends it to the processor; The processor filters and scales the digital signal to obtain liquid level data; Power module, which provides power to the circuit.

2. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to claim 1 is characterized in that: The power supply module includes power supply module A and power supply module B. An external DC power supply is connected to power supply module A and power supply module B. The output end of power supply module A is connected to the power input end of the signal conditioning circuit, and the output end of power supply module B is respectively connected to the power input end of the differential filter circuit, the AD conversion circuit and the processor.

3. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to claim 1, characterized in that: The signal conditioning circuit comprises: AD698 chip, which has a built-in sine wave generating circuit for generating a sine wave excitation signal; Sensor interface, used to connect the excitation coil and detection coil of the sensor; The bandwidth adjustment circuit, including capacitors C102, C103 and C104, determines the bandwidth of the signal conditioning circuit; The output voltage full-scale adjustment circuit includes a resistor R102 and a potentiometer W101, which is used to adjust the full-scale output range of the AD698 chip; The output voltage offset adjustment circuit includes a resistor R103, a potentiometer W102, a resistor R104, and a potentiometer W103, and adjusts the positive and negative offsets of the output voltage by adjusting the resistance values ​​of the potentiometers W102 and W103.

4. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to claim 1, characterized in that: The standard voltage circuit is composed of a resistor R0, a capacitor C0, and a Zener diode D0. The power output by the power module is connected to the standard voltage circuit composed of a resistor R0 and a Zener diode DO. The Zener diode D0 stabilizes the voltage and outputs it, and the capacitor C0 filters the stabilized output voltage.

5. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to claim 1, characterized in that: In the main circuit, a low-pass filter circuit is formed by resistor R1_10 and capacitor C1_11 to filter the output of the signal conditioning circuit; a low-pass filter circuit is formed by resistor R1_11 and capacitor C1_12 to filter the standard voltage; D1_1 and D1_2 are limiting diodes.

6. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to claim 1, characterized in that: A frequency modulation capacitor switching circuit is added between the signal conditioning circuit and the processor. The processor modifies the frequency of the sinusoidal wave excitation provided by the signal conditioning circuit to the excitation coil in the aluminum liquid level sensor through the frequency modulation capacitor switching circuit.

7. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to claim 6, characterized in that: The FM capacitor switching circuit includes: a multi-way switch CD4051, capacitors C201, C202, C203, C204, C205, and C206; the processor is connected to the multi-way switch CD4051 through the three terminals CA, CB, and CC, and sends different data to control one of the six capacitors to access the demodulation circuit.

8. The aluminum liquid level detection circuit in the differential pressure casting riser tube according to any one of claims 1 to 7, characterized in that: It also includes a key interface circuit, a VFD display interface circuit, and an RS232 communication interface circuit connected to the processor.

9. A device for detecting the aluminum liquid level in a differential pressure casting riser tube, characterized in that: It comprises an aluminum liquid level detection circuit in a differential pressure casting riser tube and a main unit as described in any one of claims 1 to 8, wherein the aluminum liquid level detection circuit in a differential pressure casting riser tube is installed in the main unit, and a digital display screen and at least 4 function keys are provided on the front panel of the main unit, wherein the 4 function keys are: a function selection key, a + key and a - key, and a confirmation key; and are used to modify parameter values.

Images