Characteristic parameter synchronous test circuit of oil liquid sensor

Abstract

The utility model discloses a kind of characteristic parameter synchronous test circuit of oil sensor, including integrated circuit, excitation amplification circuit, piezoelectric ceramic and feedback conversion circuit;Integrated circuit includes chip of model AD5933;Excitation amplification circuit is used for basic excitation signal biasing translation and ac amplification;Piezoelectric ceramic is used to be connected with tuning fork component, to generate feedback current signal;Feedback conversion circuit is used to convert to feedback current signal.This characteristic parameter synchronous test circuit of oil sensor is cooperated by integrated circuit and excitation amplification circuit, piezoelectric ceramic can be driven to drive tuning fork component to vibrate stably in different viscosity, density oil, then cooperate feedback conversion circuit to convert signal, expand the application range of detection circuit, and AD5933 can be adjusted excitation parameter signal by program control, without modifying hardware can be adapted to wider range, without additional vibration piezoelectric ceramic, simplify hardware structure, reduce signal interference, improve circuit operation reliability.

Description

Technical Field

[0001] This utility model relates to a test circuit for characteristic parameters of an oil sensor, and in particular to a synchronous test circuit for characteristic parameters of an oil sensor. Background Technology

[0002] In fields such as industrial equipment operation, automotive power systems, and hydraulic circuits of construction machinery, the quality of oil directly affects the operating efficiency, service life, and safety stability of the equipment. Since the viscosity and density of oil are the core characteristic parameters reflecting its quality, real-time monitoring of oil viscosity and density is a key environment for equipment condition monitoring and maintenance. The characteristic parameter testing circuit of oil sensor is the core hardware foundation for realizing the oil monitoring function.

[0003] In existing technologies, a self-resonant oscillating circuit is typically used to monitor oil quality. After the self-resonant circuit is connected to a tuning fork in front of a sensor, it generates an oscillating waveform voltage signal with a specific frequency. When the tuning fork is immersed in the liquid, the frequency and amplitude of the oscillating voltage waveform output by the circuit and tuning fork combination will change due to the viscosity and density of the oil. Therefore, by monitoring the frequency and amplitude, these can be converted into the viscosity and density of the oil.

[0004] However, traditional self-resonant circuits, lacking program control, have limited testing ranges due to the inherent characteristics of their hardware circuitry. During use, different hardware circuit parameters need to be modified and adjusted for liquids with varying densities and viscosities, limiting the sensor's detection capabilities to a narrow viscosity and density range and restricting its applicability. Furthermore, traditional self-resonant circuits require a dedicated vibration-sensitive piezoelectric ceramic to separately acquire the vibration feedback signal from the tuning fork, forming an independent circuit with the piezoelectric ceramic driving the tuning fork. This necessitates multiple sets of leads between the sensor and the circuit, resulting in redundant hardware. Excessive leads and components increase assembly complexity and raise the risk of contact defects and signal interference. In addition, self-resonant circuits struggle to analyze signal phase changes and minute current fluctuations. When oil viscosity and density changes are small, the frequency and amplitude variations are weak and easily masked by circuit noise and environmental interference, leading to a low signal-to-noise ratio. The inherent drift of the hardware circuitry further amplifies errors, making it difficult to meet the demands of high-precision testing scenarios.

[0005] Therefore, it is necessary to improve the characteristic parameter testing circuit of the oil sensor in the prior art. Utility Model Content

[0006] The purpose of this invention is to overcome the defects in the existing technology and provide a synchronous test circuit for the characteristic parameters of an oil sensor that expands its applicability, enhances adaptability, reduces the complexity of the hardware structure, and ensures detection accuracy.

[0007] To achieve the above technical effects, the technical solution of this utility model is as follows: a synchronous test circuit for characteristic parameters of an oil sensor, comprising an integrated circuit, an excitation amplifier circuit, a piezoelectric ceramic and a feedback conversion circuit connected in sequence, wherein the output terminal of the feedback conversion circuit is connected to the integrated circuit; The integrated circuit includes a chip of model AD5933, which is used to generate a basic excitation signal and receive the feedback signal processed by the feedback conversion circuit and perform analysis and calculation. The excitation amplifier circuit is used to bias-shift and AC amplify the basic excitation signal output by the integrated circuit to output an excitation signal acting on the piezoelectric ceramic. The piezoelectric ceramic is used to connect with the tuning fork assembly to generate a feedback current signal through mechanical vibration under the action of an excitation signal; The output of the feedback conversion circuit is connected to the integrated circuit and is used to convert the feedback current signal into a feedback signal that conforms to the chip's detection range.

[0008] Preferably, in order to simplify the structure, reduce leads, and reduce assembly complexity, a sensor interface is also included. The sensor interface has an excitation output pin and a feedback input pin. The excitation output pin is connected to the output terminal of the excitation amplifier circuit, and the feedback input pin is connected to the input terminal of the feedback conversion circuit.

[0009] Preferably, in order to adapt to the characteristics of piezoelectric ceramics, cover the needs of oil detection, and balance circuit stability and detection accuracy, the basic excitation signal generated by the integrated circuit has an amplitude of 2Vp-p and a frequency of 100Hz to 10KHz.

[0010] Preferably, in order to ensure signal amplification accuracy, improve circuit anti-interference capability, and ensure multi-module collaborative stability, the integrated circuit is also used to output a master clock signal to provide synchronization timing for the excitation amplification circuit.

[0011] Preferably, in order to ensure the compatibility of the piezoelectric ceramic drive, guarantee signal stability and coverage of the detection range, the excitation signal output by the excitation amplifier circuit has an amplitude of 10Vp-p and a bias voltage of 6V.

[0012] Preferably, in order to achieve the bias shift and AC amplification functions of the basic excitation signal, the excitation amplification circuit includes a third operational amplifier. The inverting input terminal of the third operational amplifier is connected to a 6V reference voltage source through a seventh resistor, the non-inverting input terminal is connected to a 6V reference voltage source through a parallel circuit composed of a third resistor and a fifth capacitor, and the output terminal is connected to the inverting input terminal through a fourth resistor.

[0013] Preferably, in order to improve detection accuracy and ensure the correctness of parameter calculation, the feedback conversion circuit includes an IV conversion circuit and a VI conversion circuit connected in sequence. The IV conversion circuit is used to convert the feedback current signal into a voltage signal that is proportional to it, and the VI conversion circuit is used to convert the voltage signal into an input signal that conforms to the detection range of the integrated circuit.

[0014] Preferably, in order to realize the current-to-voltage conversion and preliminary amplification function of the feedback current signal, the IV conversion circuit includes a first operational amplifier. The non-inverting input terminal of the first operational amplifier is used to receive the feedback current signal, and the output terminal is connected to the non-inverting input terminal through a second resistor. The non-inverting input terminal is connected to a 6V reference voltage source.

[0015] Preferably, in order to achieve the bias adjustment and voltage-to-current conversion functions of the voltage signal, the VI conversion circuit includes a second operational amplifier. The inverting input terminal of the second operational amplifier is connected to a 1.65V reference voltage source through a sixth resistor, and the output terminal is connected to the inverting input terminal through a fourteenth resistor. The non-inverting input terminal is connected to a 1.65V reference voltage source through a parallel circuit composed of a thirteenth resistor and a sixth capacitor.

[0016] Preferably, in order to improve the overall integration of the circuit and ensure structural compactness, the first operational amplifier, the second operational amplifier and the third operational amplifier are all integrated into a four-channel operational amplifier chip of model OPA4170AIPW.

[0017] In summary, compared with existing technologies, the synchronous test circuit for the characteristic parameters of the oil sensor of this utility model, through the cooperation of integrated circuits and excitation amplification circuits, can drive the piezoelectric ceramic to drive the tuning fork assembly to vibrate stably in oils of different viscosities and densities. In addition, the feedback conversion circuit converts the signal, expanding the applicable range of the detection circuit. Moreover, the chip can be controlled by program to adjust the excitation parameter signal, adapting to a wider range without modifying the hardware, eliminating the need for additional vibration piezoelectric ceramics, simplifying the hardware structure, reducing signal interference, and improving the reliability of circuit operation. Attached Figure Description

[0018] Figure 1 This is the circuit schematic diagram of this utility model; Figure 2 This is a system block diagram of this utility model; In the diagram: U1, chip; P1, sensor interface; A1, first operational amplifier; A2, second operational amplifier; A3, third operational amplifier; C1, first capacitor; C2, second capacitor; C3, third capacitor; C4, fourth capacitor; C5, fifth capacitor; C6, sixth capacitor; C7, seventh capacitor; C16, sixteenth capacitor; R1, first resistor; R2, second resistor; R3, third resistor; R4, fourth resistor; R5, fifth resistor; R6, sixth resistor; R7, seventh resistor; R8, eighth resistor; R9, ninth resistor; R10, tenth resistor; R11, eleventh resistor; R12, twelfth resistor; R13, thirteenth resistor; R14, fourteenth resistor; R15, fifteenth resistor; R16, sixteenth resistor. Detailed Implementation

[0019] The specific embodiments of this utility model will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solution of this utility model and should not be construed as limiting the scope of protection of this utility model.

[0020] like Figure 1 and Figure 2 As shown, the present invention provides a synchronous test circuit for characteristic parameters of an oil sensor, comprising an integrated circuit, an excitation amplifier circuit, a piezoelectric ceramic, and a feedback conversion circuit connected in sequence, wherein the output terminal of the feedback conversion circuit is connected to the integrated circuit. The integrated circuit includes a chip of model AD5933, which is used to generate basic excitation signals and receive feedback signals processed by feedback conversion circuits and perform analysis and calculations. The excitation amplifier circuit is used to bias-shift and AC amplify the basic excitation signal output by the integrated circuit to output the excitation signal acting on the piezoelectric ceramic. Piezoelectric ceramics are used to connect with tuning fork components to generate a feedback current signal through mechanical vibration under the action of an excitation signal; The output of the feedback conversion circuit is connected to the integrated circuit to convert the feedback current signal into a feedback signal that conforms to the chip's detection range.

[0021] This invention's synchronous test circuit employs a characteristic impedance testing method. By testing the amplitude-frequency and phase-frequency characteristics of the characteristic impedance of the front tuning fork assembly, it detects the viscosity and density parameters of the liquid. The circuit generates a basic excitation signal through an AD5933 chip in an integrated circuit. This basic excitation signal undergoes bias shifting and AC amplification by an external excitation amplifier circuit, resulting in an excitation signal acting on the piezoelectric ceramic. This excitation signal excites the tuning fork assembly through the piezoelectric ceramic, causing it to vibrate mechanically due to voltage excitation. In different liquids, the resonant frequency and amplitude change due to the varying viscosity and density, synchronously affecting the operating current of the piezoelectric ceramic and generating different feedback current signals. These feedback current signals are processed by a feedback conversion circuit, converted into current signals within the chip's detection range, and transmitted to the chip's input pin. By calculating the excitation voltage and return current, the characteristic impedance information at different frequency points can be obtained. Through program control and communication, the amplitude-frequency and phase-frequency characteristics of the impedance at that moment can be read. Using these characteristics, the resonant frequency and amplitude information can be obtained, thus yielding the viscosity and density parameters of the liquid.

[0022] Since the chip can adjust the excitation parameter signal through program control, it can adapt to a wider range without modifying the hardware, thus expanding the applicability of the detection circuit and enhancing its adaptability. Furthermore, it eliminates the need for additional vibration piezoelectric ceramics, simplifying the hardware structure of the entire detection circuit, which helps reduce signal interference and improve the stability and reliability of circuit operation.

[0023] Specifically, chip U1 has fourteen pins. Pins 1, 2, 3, and 7 are unused and have no external electronic components connected to them. Pin 6 is the excitation voltage signal output pin, corresponding to VOUT in the diagram. Pin 5 is the input pin for receiving feedback current signals, corresponding to VIN in the diagram. The current signal related to the oil characteristics after feedback conversion circuit is input to this pin for subsequent analysis and calculation. Pin 8 is the system master clock input pin provided by the user, corresponding to MCLK in the diagram. It provides a synchronous clock signal for the digital and analog circuits inside chip U1, ensuring that the functional modules can work in coordination. Pin 9 is the digital power supply pin, corresponding to DVDD in the diagram. It provides the operating power for the digital circuits inside chip U1, connected to an external 3.3V positive power supply voltage, and grounded through the 100nF seventh capacitor C7. Pins 10 and 11 are two analog power supply pins, corresponding to AVDD1 and AVDD2 in the diagram, respectively. They provide stable power for the analog circuits inside chip U1. A fixed power supply ensures the accuracy of analog signal processing. Both are externally connected to a 3.3V voltage and grounded through the sixth capacitor C6 (10uF). Pins 13, 14, and 12 are two analog ground pins and one digital ground pin, corresponding to AGND1, AGND2, and DGND in the diagram. They provide reference potentials for the analog and digital circuits, ensuring a unified reference for signals in the circuit, reducing signal interference, and ensuring normal circuit operation. Pins 15 and 16 are the data input pin and clock input pin, corresponding to SDA and SCL in the diagram. They are used for communication between chip U1 and external devices and are externally connected to a 3.3V power supply through the 12th resistor R12 and the 16th resistor R16 (20kΩ) respectively. Pin 4 is the external feedback resistor connection pin, corresponding to RFB in the diagram. It is connected to the fifth resistor through the eighth resistor R8 (20kΩ) and is used to set the gain of the receiver feedback conversion circuit, thereby adjusting the amplification factor of the input signal to adapt to different measurement requirements.

[0024] A further improvement includes a sensor interface with an excitation output pin and a feedback input pin. The excitation output pin connects to the output of the excitation amplifier circuit, and the feedback input pin connects to the input of the feedback conversion circuit. This sensor interface facilitates connection between the output of the excitation amplifier circuit and the input of the feedback conversion circuit to the piezoelectric ceramic and tuning fork components, reducing leads and simplifying the structure.

[0025] Further improvements include the integrated circuit generating a basic excitation signal with an amplitude of 2Vp-p and a frequency of 100Hz to 10KHz; the integrated circuit also outputs a master clock signal to provide synchronization timing for the excitation amplifier circuit; the excitation signal output by the excitation amplifier circuit has an amplitude of 10Vp-p and a bias voltage of 6V.

[0026] In this invention, the chip U1 is model AD5933. The output amplitude range of its internal analog circuit is limited by the power supply voltage (usually 3.3V). The 2Vp-p sine wave signal is within the safe output range of chip U1, which can avoid saturation distortion of the internal amplifier circuit of chip U1 due to excessive amplitude, or poor signal-to-noise ratio due to excessive amplitude. Compared with higher voltage amplitude, 2Vp-p can ensure signal linearity and stability; compared with lower voltage amplitude, 2Vp-p can reserve sufficient signal margin for subsequent circuits and reduce noise interference to subsequent processing.

[0027] Furthermore, the subsequent excitation amplifier circuit amplifies the basic excitation signal to 10Vp-p (the required amplitude to drive the piezoelectric ceramic). The initial amplitude of 2Vp-p corresponds to a 5x amplification factor, which falls within the conventional linear amplification range of operational amplifiers. This eliminates the need for complex multi-stage amplification circuits and can be achieved through a single-stage amplification. This reduces circuit complexity, the number of components, and potential failure points, while also avoiding issues such as signal phase shift and noise superposition caused by multi-stage amplification.

[0028] The basic excitation signal frequency is 100Hz to 10kHz, mainly for the precise matching of "oil viscosity and density detection requirements" and "tuning fork component-piezoelectric ceramic combination characteristics". For low viscosity and low density oils, the damping of vibration is small, and a higher frequency is required to show obvious changes in vibration characteristics. For high viscosity and high density oils, the damping of vibration is large, and the deviation of vibration amplitude and frequency is more significant at lower frequencies. Therefore, the frequency range of 100Hz to 10kHz can cover the damping characteristic sensitive frequency band of different types of oils, realizing accurate detection of a wide range of oils. In addition, it can also avoid high frequency interference and low frequency noise, ensuring signal quality.

[0029] Chip U1 also provides synchronization timing for the excitation amplifier circuit by outputting a master clock signal, ensuring the amplitude and phase accuracy of the excitation signal amplification process and avoiding signal distortion; improving the circuit's anti-interference capability and reducing the impact of external noise on the excitation signal; and facilitating the collaborative work of multiple circuit modules, ensuring the stability and scalability of the overall test circuit system.

[0030] The excitation signal output from the excitation amplifier circuit has an amplitude of 10Vp-p, which meets the driving requirements of the piezoelectric ceramic, ensuring stable vibration of the tuning fork assembly and providing a clear signal basis for oil parameter calculation. As a polarity-sensitive element, the piezoelectric ceramic is protected from reverse breakdown by using a 6V bias voltage, thus extending its lifespan and ensuring stable vibration characteristics, avoiding detection errors caused by component damage or performance drift. In summary, the combination of a 10Vp-p amplitude and a 6V bias voltage allows the piezoelectric ceramic to maintain a detectable vibration response when faced with oils of different viscosities and densities, ensuring that the piezoelectric ceramic operates within a safe voltage range. This guarantees the stability and compatibility of the entire detection chain, facilitating "wide-range, high-precision" detection.

[0031] A further improvement is that the excitation amplifier circuit includes a third operational amplifier A3. The inverting input of the third operational amplifier A3 is connected to a 6V reference voltage source through a 20kΩ seventh resistor R7. The non-inverting input is connected to a 6V reference voltage source through a parallel circuit consisting of a 100kΩ third resistor R3 and a 10nF fifth capacitor C5. The output is connected to the inverting input through a 20kΩ fourth resistor R4. One end of the circuit consisting of a 10uF first capacitor C1 and a 10uF third capacitor C3 connected in parallel is connected to the sixth pin of chip U1, and the other end is connected to the non-inverting input of the third operational amplifier A3 through a 1kΩ fifth resistor R5.

[0032] The third operational amplifier A3, as the core unit of the excitation amplifier circuit, processes the fundamental excitation signal by using the synergistic effect of bias shift and AC amplification to convert the fundamental excitation signal output by chip U1 into a signal that meets the requirements of piezoelectric ceramic driving. The third operational amplifier A3 receives the 2Vp-p, 100Hz~10KHz sine wave fundamental excitation signal output by chip U1, and connects a 6V reference voltage through its non-inverting input to achieve bias shift, raising the DC reference of the original signal from near 0V to 6V, thus making the voltage of the sine wave signal... The range is adjusted to 5V~7V to avoid the piezoelectric ceramic drive failure caused by the negative half-cycle of the signal; at the same time, through the amplification circuit composed of an external resistor network, the shifted AC signal is amplified by a fixed factor (5 times in this utility model), increasing the signal amplitude of 2Vp-p to 10Vp-p, and finally outputting a 10Vp-p, 6V biased sine wave voltage signal. The excitation signal A_FORK is transmitted to the piezoelectric ceramic through the output terminal, meeting its requirements for the driving voltage amplitude and reference, and ensuring that the key ceramic generates mechanical vibration.

[0033] A further improvement is that the feedback conversion circuit includes an IV conversion circuit and a VI conversion circuit connected in sequence. The IV conversion circuit is used to convert the feedback current signal into a voltage signal that is proportional to it, and the VI conversion circuit is used to convert the voltage signal into an input signal that conforms to the detection range of the integrated circuit.

[0034] With the above structure, the IV conversion circuit can receive the feedback current signal (corresponding to B_FORK in the figure) generated by the piezoelectric ceramic, convert it to current and voltage, and simultaneously amplify the converted voltage to provide a clear voltage signal source for the subsequent VI conversion circuit. After receiving the voltage signal, the VI conversion circuit performs bias adjustment and then converts the voltage signal into a current signal within the detection range of chip U1. This current signal is then input to the fifth pin to detect the density and viscosity parameters of the oil.

[0035] A further improvement is that the IV conversion circuit includes a first operational amplifier A1, the non-inverting input of which is used to receive the feedback current signal, and the output is connected to the non-inverting input through a 20kΩ second resistor R2. The non-inverting input is connected to a 6V reference voltage source. The VI conversion circuit includes a second operational amplifier A2, the inverting input of which is connected to a 1.65V reference voltage source through a 20kΩ sixth resistor R6, and the output is connected to the inverting input through a 100kΩ fourteenth resistor R14. The non-inverting input is connected to a 1.65V reference voltage source through a parallel circuit consisting of a 1MΩ thirteenth resistor R13 and a 10nF sixth capacitor C6.

[0036] The first operational amplifier A1, the second operational amplifier A2, and the third operational amplifier A3 are all integrated into a four-channel operational amplifier chip of model OPA4170AIPW to ensure the compactness of the test circuit. Specifically, the first, second, and third pins of the four-channel operational amplifier chip are the output, inverting input, and non-inverting input of the first operational amplifier A1, respectively. The fifth, sixth, and seventh pins of the four-channel operational amplifier chip are the non-inverting input, inverting input, and output of the second operational amplifier A2, respectively. The twelfth, thirteenth, and fourteenth pins of the four-channel operational amplifier chip are the non-inverting input, inverting input, and output of the third operational amplifier A3, respectively. In addition, the output of the first operational amplifier A1 is connected to the non-inverting input of the second operational amplifier A2 in sequence through a 10uF fourth capacitor C4 and a 10kΩ eleventh resistor R11.

[0037] With the above structure, in the IV conversion circuit, the core function of the first operational amplifier A1 is to convert the feedback current signal of the piezoelectric ceramic into a processable voltage signal. Affected by the characteristics of the oil, the piezoelectric ceramic generates a feedback current signal B_FORK with the same frequency as the excitation signal. Based on the transimpedance amplification principle, that is, output voltage = input current * feedback resistance, the small current signal is linearly converted into a voltage signal. At the same time, the amplification factor is set through the resistor network to achieve preliminary signal amplification and improve the signal-to-noise ratio.

[0038] The converted voltage signal is transmitted to the second operational amplifier A2 for processing. A 1.65V reference voltage is connected to the non-inverting input terminal to complete the bias adjustment, calibrating the current reference of the voltage signal to 1.65V to match the optimal input reference of chip U1. The VI conversion circuit is constructed using operational amplifiers and sampling resistors to linearly convert the adjusted voltage signal into a current signal, ensuring that the output current is within the detection range of chip U1. Finally, the converted current signal is transmitted to the fifth pin of chip U1 through the output terminal of the second operational amplifier A2 for chip U1 to perform digital-to-analog conversion and analysis calculations.

[0039] In summary, compared with the prior art, the synchronous testing circuit for the characteristic parameters of the oil sensor of this utility model has the following advantages: First, the circuit adopts a design that uses a single loop for excitation and detection, requiring only two leads to connect to the piezoelectric ceramic. Compared with traditional self-resonant circuits, it does not require additional vibration-sensitive piezoelectric ceramics, greatly simplifying the structure and reducing the number of leads, which helps to reduce signal interference and improve the stability and reliability of circuit operation. Secondly, in this test circuit, the AD5933 chip of the integrated circuit can be controlled by a program to adjust the excitation parameter signal, which can cover liquid testing with a large viscosity and density range, thus expanding the detection range and enhancing applicability. Finally, the feedback conversion circuit in this circuit converts the feedback current signal into a current signal within the detection range of the AD5933 chip through signal conversion, preliminary amplification, and bias adjustment, thereby improving the signal detection accuracy.

[0040] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A synchronous testing circuit for characteristic parameters of an oil sensor, characterized in that, It includes an integrated circuit, an excitation amplifier circuit, a piezoelectric ceramic, and a feedback conversion circuit connected in sequence, with the output terminal of the feedback conversion circuit connected to the integrated circuit; The integrated circuit includes a chip of model AD5933, which is used to generate a basic excitation signal and receive the feedback signal processed by the feedback conversion circuit and perform analysis and calculation. The excitation amplifier circuit is used to bias-shift and AC amplify the basic excitation signal output by the integrated circuit to output an excitation signal acting on the piezoelectric ceramic. The piezoelectric ceramic is used to connect with the tuning fork assembly to generate a feedback current signal through mechanical vibration under the action of an excitation signal; The output of the feedback conversion circuit is connected to the integrated circuit and is used to convert the feedback current signal into a feedback signal that conforms to the chip's detection range.

2. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 1, characterized in that: It also includes a sensor interface, which has an excitation output pin and a feedback input pin. The excitation output pin is connected to the output of the excitation amplifier circuit, and the feedback input pin is connected to the input of the feedback conversion circuit.

3. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 1, characterized in that: The basic excitation signal generated by the integrated circuit has an amplitude of 2Vp-p and a frequency of 100Hz to 10KHz.

4. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 1, characterized in that: The integrated circuit is also used to output a master clock signal to provide synchronization timing for the excitation amplifier circuit.

5. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 3, characterized in that: The excitation signal output by the excitation amplifier circuit has an amplitude of 10Vp-p and a bias voltage of 6V.

6. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 5, characterized in that: The excitation amplifier circuit includes a third operational amplifier. The inverting input terminal of the third operational amplifier is connected to a 6V reference voltage source through a seventh resistor, and the non-inverting input terminal is connected to a 6V reference voltage source through a parallel circuit composed of a third resistor and a fifth capacitor. The output terminal is connected to the inverting input terminal through a fourth resistor.

7. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 6, characterized in that: The feedback conversion circuit includes an IV conversion circuit and a VI conversion circuit connected in sequence. The IV conversion circuit is used to convert the feedback current signal into a voltage signal that is proportional to it. The VI conversion circuit is used to convert the voltage signal into an input signal that conforms to the detection range of the integrated circuit.

8. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 7, characterized in that: The IV conversion circuit includes a first operational amplifier, the non-inverting input of which is used to receive the feedback current signal, and the output is connected to the non-inverting input through a second resistor. The non-inverting input is connected to a 6V reference voltage source.

9. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 8, characterized in that: The VI conversion circuit includes a second operational amplifier. The inverting input terminal of the second operational amplifier is connected to a 1.65V reference voltage source through a sixth resistor, and the output terminal is connected to the inverting input terminal through a fourteenth resistor. The non-inverting input terminal is connected to a 1.65V reference voltage source through a parallel circuit consisting of a thirteenth resistor and a sixth capacitor.

10. The synchronous test circuit for characteristic parameters of the oil sensor according to claim 9, characterized in that: The first operational amplifier, the second operational amplifier, and the third operational amplifier are all integrated into a four-channel operational amplifier chip of model OPA4170AIPW.

Images