Circuit and method for checking tachometer

Abstract

The invention discloses a tachometer verification circuit and method, and relates to the technical field of airplane tachometer verification. The verification circuit comprises a control unit, a crystal oscillator unit, a digital waveform generation amplification circuit, a power amplification circuit, a frequency detection circuit, a voltage measurement circuit, a current measurement circuit and a motor driving unit. According to the invention, a closed-loop control system composed of a control unit, a digital waveform generation amplification circuit, a power amplification circuit, a frequency detection circuit, a voltage measurement circuit and a current measurement circuit generates a three-phase power waveform with variable frequency and voltage amplitude, outputs a rotating speed signal output by an analog rotating speed sensor, and provides the rotating speed signal to a tachometer; and verification of the tachometer is completed. According to the invention, the influence of the precision of the driving motor and the output precision of the rotating speed sensor on the testing precision of the tachometer is eliminated, the potential safety hazard caused by the difference of the rotating speed sensor is ensured, and the tedious operation steps are reduced.

Description

Technical Field

[0001] The invention relates to the technical field of aircraft tachometer calibration, and in particular to a tachometer calibration circuit and method. Background Art

[0002] At present, the aircraft tachometer calibration method uses the drive motor to rotate, drive the speed sensor matched with the tachometer to rotate and output a three-phase AC speed frequency signal, which is sent to the tachometer to indicate the speed function. The speed sensor speed frequency is changed by adjusting the speed of the drive motor, thereby realizing the measurement calibration of different ranges of the tachometer. However, this method has several disadvantages: a. The indication accuracy of the tachometer is affected by the speed accuracy of the drive motor and the speed signal output by the speed sensor; b. A speed sensor needs to be installed every time the tachometer is calibrated, which is cumbersome; c. The output voltage amplitude of the speed sensor changes with the speed change. When there are individual differences, the output voltage amplitude may be too high and exceed the tolerance range of the tachometer, thus damaging the tachometer. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a tachometer calibration circuit and method.

[0004] The objective of the present invention is achieved through the following technical solutions: In a first aspect, a tachometer calibration circuit includes a DC servo motor and a speed sensor, wherein the DC servo motor is connected to the speed sensor, and the speed sensor is connected to the tachometer, and further includes: a control unit, a crystal oscillator unit, a digital waveform generation and amplification circuit, a power amplification circuit, a frequency detection circuit, a voltage measurement circuit, a current measurement circuit, and a motor drive unit; The first input terminal and the second input terminal of the control unit are respectively connected to the output terminals of the frequency detection circuit, the voltage measurement circuit and the current measurement circuit, and the first output terminal and the second output terminal of the control unit are respectively connected to the first input terminals of the digital waveform generation and amplification circuit and the power amplification circuit; The first output terminal and the second output terminal of the crystal oscillator unit are respectively connected to the third input terminal of the control unit and the second input terminal of the digital waveform generating and amplifying circuit; The output end of the digital waveform generating and amplifying circuit is connected to the second input end of the power amplifying circuit; The output end of the power amplifier circuit is connected to the input end of the frequency detection circuit, the voltage measurement circuit, the current measurement circuit and the tachometer; The input end of the motor drive unit is connected to the control unit, and the output end of the motor drive unit is connected to the DC servo motor.

[0005] Furthermore, it also includes a human-machine interaction unit connected to the control unit and the motor drive unit, and the human-machine interaction unit uses a touch LCD screen for manually inputting settings and displaying parameters of the tachometer calibration circuit; the parameters include the operating status of the drive motor, the set speed, the output speed, the phase-to-phase voltage and the tachometer pointer.

[0006] Furthermore, it also includes a power supply unit for providing power supply to the human-machine interaction unit, the control unit, the digital waveform generation and amplification circuit, the motor drive unit and the tachometer; The power supply unit includes a power supply, an AC-DC power module, a DC-DC power module and a step-down module; the power supply is an externally introduced 220V±10% / 50Hz±5% power supply, the AC-DC power module is a UHP-350-24 switching power supply, and the AC-DC power module is used to convert the 220VAC power supply into a 24VDC±10% power output, with an output current of ≤14A; the DC-DC power module is a TPS54360 switching power supply, which is used to convert the input 24V power supply into +15VDC / 1A and –15VDC / 1A power outputs; the step-down module includes a SY8303AIC step-down chip and peripheral circuits, which convert the 24V power supply into a 3.3VDC / 2A power output.

[0007] Further, the digital waveform generation and amplification circuit includes a first waveform generator, a second waveform generator, a third waveform generator, a first shaping filter circuit, a second shaping filter circuit and a third shaping filter circuit; The first waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 0° phase sine wave signal, and the output terminal of the first waveform generator is connected to the input terminal of the first shaping filter circuit; The second waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 120° phase sine wave signal, and the output terminal of the second waveform generator is connected to the input terminal of the second shaping filter circuit; The third waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 240° phase sine wave signal, and the output terminal of the third waveform generator is connected to the input terminal of the third shaping filter circuit; The output ends of the first shaping filter circuit, the second shaping filter circuit and the third shaping filter circuit are all connected to the output end of the digital waveform generating and amplifying circuit, and are used to shape and filter the sinusoidal wave signal.

[0008] Further, it is characterized in that: the power amplifier circuit includes a first amplifier branch, a second amplifier branch and a third amplifier branch, which are used to output the frequency-adjustable 0° phase, 120° phase and 240° phase sine wave signals with adjustable voltage and power according to the voltage amplitude value output by the control unit, and output the three-phase sine voltage with adjustable frequency, voltage and power after filtering as the analog speed signal of the tachometer; The first amplifying branch, the second amplifying branch and the third amplifying branch each include a multiplication digital-to-analog converter, a power amplifier and an isolation filtering protection circuit connected in sequence, the first input end and the second input end of the multiplication digital-to-analog converter serve as the first input end and the first output end of the power amplifier circuit respectively, and the output end of the isolation filtering protection circuit serves as the output end of the power amplifier circuit.

[0009] Further, the frequency detection circuit includes a first detection branch, a second detection branch and a third detection branch, which are used to sample and shape the frequency of the 0° phase, 120° phase and 240° phase sine wave signals with adjustable frequency, voltage and power, respectively; The first detection branch, the second detection branch and the third detection branch all include a frequency isolation sampling module and a frequency shaping module, the input end of the frequency isolation sampling module serves as the input end of the frequency detection circuit, and the output end of the frequency shaping module serves as the output end of the frequency detection circuit; The frequency isolation sampling module isolates the input AC signal by using an optocoupler isolator to complete the isolation conversion from high-voltage signal to low-voltage signal. The frequency shaping module shapes and outputs the isolated signal.

[0010] Further, the voltage measurement circuit includes a first measurement branch, a second measurement branch and a third measurement branch, which are used to sample the effective voltage of the 0° phase, 120° phase and 240° phase sinusoidal wave signals with adjustable frequency, voltage and power, respectively; The first measurement branch, the second measurement branch and the third measurement branch all include a voltage isolation sampling module and an analog-to-digital conversion module, the input end of the voltage isolation sampling module serves as the input end of the voltage measurement circuit, and the output end of the analog-to-digital conversion module serves as the output end of the voltage measurement circuit; The voltage isolation sampling module converts the AC voltage signal into a DC voltage signal by using a voltage sensor, and the analog-to-digital conversion module converts the analog signal into a digital signal by using a 12-bit AD acquisition chip.

[0011] Further, the current measurement circuit includes a first sampling branch, a second sampling branch and a third sampling branch, which are used to sample the effective current of the 0° phase, 120° phase and 240° phase sinusoidal wave signals with adjustable frequency, voltage and power, respectively; The first sampling branch, the second sampling branch and the third sampling branch all include a current AC transformer, a current conversion circuit and a collection circuit, the input end of the current AC transformer serves as the input end of the current measurement circuit, and the output end of the collection circuit serves as the output end of the current measurement circuit; The current AC transformer is used to convert a large current of 5A into a small current signal of 2.5mA, the current conversion circuit is used to convert the small current signal into a voltage signal, and the acquisition circuit is used to realize digital conversion of the voltage signal.

[0012] Furthermore, data is transmitted between the control unit and the digital waveform generating and amplifying circuit, the power amplifying circuit, the frequency detecting circuit, the voltage measuring circuit, and the current measuring circuit via a serial bus.

[0013] In a second aspect, a tachometer calibration method is applied to the tachometer calibration circuit according to any one of the first aspects, and is characterized by comprising: Step 1: The motor drive unit drives the DC servo motor according to the motor output speed setting value. The DC servo motor is connected to the speed sensor through a coupling. The speed sensor collects the speed of the DC servo motor and outputs a three-phase signal to drive the tachometer. Step 2, the digital waveform generating and amplifying circuit generates a sine wave signal of any frequency according to the stable frequency source output by the crystal oscillator unit, and generates three sine wave signals with a phase difference of 120° between each other and adjustable frequency according to the waveform, frequency, phase and voltage amplitude setting values ​​output by the control unit; Step 3, the power amplifier circuit performs adjustable amplification output of the voltage and power of the three sinusoidal signals to provide the tachometer with an analog speed signal for calibration; Step 4: The control unit completes the frequency, AC phase-to-phase voltage and current acquisition and measurement of the analog speed sensor output signal according to the sampling feedback signals output by the frequency detection circuit, the voltage measurement circuit and the current measurement circuit; Step 5. Compare the frequency and AC phase-to-phase voltage of the output signal with the corresponding preset values. If they do not meet the settings, adjust the voltage or frequency proportionally until they meet the preset values. Determine whether the circuit is short-circuited or over-current based on the current of the output signal, and cut off the output analog speed signal when the output is short-circuited or over-current occurs.

[0014] The beneficial effects of the present invention are: The present invention generates a three-phase power waveform with variable frequency and voltage amplitude through a closed-loop control system composed of a control unit, a digital waveform generating and amplifying circuit, a power amplifying circuit, a frequency detecting circuit, a voltage measuring circuit, and a current measuring circuit, and outputs a speed signal simulating the output of a speed sensor to provide the speed meter, thereby completing the calibration of the speed meter. The present invention eliminates the influence of the drive motor accuracy and the speed sensor output accuracy on the speed meter test accuracy, while ensuring the safety hazards caused by the differences in the speed sensors, and also reduces the cumbersome operation steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A system structure diagram of a tachometer calibration circuit provided by an embodiment of the present invention; Figure 2 A display interface of a touch liquid crystal screen provided by an embodiment of the present invention; Figure 3 A circuit schematic diagram of a power supply unit provided in one embodiment of the present invention; Figure 4 A circuit schematic diagram of a voltage reduction module provided in one embodiment of the present invention; Figure 5 A schematic diagram of a waveform generator circuit provided by an embodiment of the present invention; Figure 6 A schematic diagram of a multiplication digital-to-analog converter circuit provided by an embodiment of the present invention; Figure 7 A schematic diagram of a power amplifier circuit provided by an embodiment of the present invention; Figure 8 An internal circuit schematic diagram of a frequency detection circuit provided by an embodiment of the present invention; Fig. 9 An internal circuit schematic diagram of a voltage measurement circuit provided by an embodiment of the present invention; Fig.10 A circuit schematic diagram of a current AC transformer provided by an embodiment of the present invention; Fig.11 A circuit schematic diagram of a current conversion circuit provided by an embodiment of the present invention; Fig.12 The present invention is a flowchart of a closed-loop control method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0017] See also Figure 1-Figure 12 , the present invention provides a technical solution: Embodiment 1, a tachometer calibration circuit, such as Figure 1 As shown, it includes a DC servo motor and a speed sensor, the DC servo motor is connected to the speed sensor, the speed sensor is connected to the tachometer, and also includes: a control unit, a crystal oscillator unit, a digital waveform generation and amplification circuit, a power amplifier circuit, a frequency detection circuit, a voltage measurement circuit, a current measurement circuit and a motor drive unit; The first input terminal and the second input terminal of the control unit are respectively connected to the output terminals of the frequency detection circuit, the voltage measurement circuit and the current measurement circuit, and the first output terminal and the second output terminal of the control unit are respectively connected to the first input terminals of the digital waveform generation and amplification circuit and the power amplification circuit; The first output terminal and the second output terminal of the crystal oscillator unit are respectively connected to the third input terminal of the control unit and the second input terminal of the digital waveform generating and amplifying circuit; The output end of the digital waveform generating and amplifying circuit is connected to the second input end of the power amplifying circuit; The output end of the power amplifier circuit is connected to the input end of the frequency detection circuit, the voltage measurement circuit, the current measurement circuit and the tachometer; The input end of the motor drive unit is connected to the control unit, and the output end of the motor drive unit is connected to the DC servo motor.

[0018] The tachometer calibration circuit also includes a human-machine interaction unit connected to the control unit and the motor drive unit. The human-machine interaction unit uses a touch LCD screen for manually inputting settings and displaying parameters of the tachometer calibration circuit; the parameters include the operating status of the drive motor, the set speed, the output speed, the phase-to-phase voltage and the tachometer pointer.

[0019] Taking into account the operating temperature and environment of the speed comprehensive test equipment, the display in the human-machine interface of this embodiment uses Jinpeng's industrial-grade 5-inch serial port wide-temperature touch LCD screen OCM800480T500-2D. The display interface of the touch LCD screen is as follows: Figure 2As shown, it is designed as a multi-page display to meet the setting and display of multiple parameters such as speed, output speed, phase-to-phase voltage, and tachometer pointer of the speed comprehensive test equipment. At the same time, the built-in touch function can complete the parameter input setting and parameter selection functions. This serial port touch LCD screen adopts ARM+FPGA dual-core control, comes with ASCⅡ characters and GBK fonts, and uses register operation. When the value of the main register changes, all related controls will change accordingly. It adopts serial port control, with few lines, simple control, and convenient operation. It can be conveniently and simply interfaced with various MCUs; users only need to write some simple instructions to realize drawing and display functions, and there is no need for tedious calculations and operations in the user code. This touch LCD screen has the following functions and characteristics: (1) built-in drawing function; (2) built-in display function; (3) built-in ASCⅡ encoding and GBK encoding; (4) UART serial port timing; (5) working temperature: -40℃~+80℃; (6) resolution: 800*480.

[0020] The tachometer calibration circuit also includes a power supply unit for providing power supply to the human-machine interaction unit, the control unit, the digital waveform generation and amplification circuit, the motor drive unit and the tachometer; The power supply unit includes a power supply, an AC-DC power module, a DC-DC power module and a step-down module; Figure 3 The power supply is an external 220V±10% / 50Hz±5% power supply, the AC-DC power supply module is a UHP-350-24 switching power supply, and the AC-DC power supply module is used to convert the 220VAC power supply into a 24VDC±10% power output, with an output current of ≤14A; the DC-DC power supply module is a TPS54360 switching power supply, which is used to convert the input 24V power supply into +15VDC / 1A and –15VDC / 1A power output; the voltage schematic diagram of the step-down module is as follows Figure 4 As shown, it includes SY8303AIC step-down chip and peripheral circuits to convert 24V power supply into 3.3VDC / 2A power output.

[0021] Considering the use environment, frequency of use and safety factors of the product, and the fact that the test circuit requires a variety of power supplies with high precision, this embodiment combines the actual situation of the workplace and focuses on the principle of convenient operation and use. Therefore, the power supply unit introduces 220V±10% / 50Hz±5% power from the outside as the power supply for the whole machine. The unit modules inside the test circuit require the use of: 24VDC, 3.3VDC, ±15VDC power supplies. Among them, the 24VDC power supply is converted from 220VAC power supply to 24VDC±10% power output by UHP-350-24 switching power supply, and the output current is ≤14A, which can meet the working test requirements. Other power supplies use TPS54360 switching power supply to convert the input 24V power supply into +15VDC / 1A and –15VDC / 1A power output through a high-reliability DC-DC power supply module to provide power supply for the power amplifier circuit. The SY8303AIC step-down chip and peripheral circuits convert the 24V power supply into a 3.3VDC / 2A power output to provide power supply for the microprocessor and control circuit. The entire power supply unit has no dangerous high voltage source, ensuring the two-way safety of operators and the equipment under test.

[0022] In a specific embodiment, the digital waveform generation and amplification circuit includes a first waveform generator, a second waveform generator, a third waveform generator, a first shaping filter circuit, a second shaping filter circuit and a third shaping filter circuit; The first waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 0° phase sine wave signal, and the output terminal of the first waveform generator is connected to the input terminal of the first shaping filter circuit; The second waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 120° phase sine wave signal, and the output terminal of the second waveform generator is connected to the input terminal of the second shaping filter circuit; The third waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 240° phase sine wave signal, and the output terminal of the third waveform generator is connected to the input terminal of the third shaping filter circuit; The output ends of the first shaping filter circuit, the second shaping filter circuit and the third shaping filter circuit are all connected to the output end of the digital waveform generating and amplifying circuit, and are used to shape and filter the sinusoidal wave signal.

[0023] In this embodiment, the three waveform generators all use a DDS circuit (waveform generation circuit) with AD9833 as the core to generate three sine wave signals with a phase difference of 120° between each other and adjustable frequency. The circuit schematic diagrams of the first waveform generator, the second waveform generator and the third waveform generator are shown in FIG. Figure 5 shown.

[0024] In a specific embodiment, the power amplifier circuit includes a first amplifier branch, a second amplifier branch and a third amplifier branch, which are used to output the frequency-adjustable 0° phase, 120° phase and 240° phase sine wave signals with adjustable voltage and power according to the voltage amplitude value output by the control unit, and output the three-phase sine voltage with adjustable frequency, voltage and power after filtering as the analog speed signal of the tachometer; The first amplifying branch, the second amplifying branch and the third amplifying branch each include a multiplication digital-to-analog converter, a power amplifier and an isolation filtering protection circuit connected in sequence, the first input end and the second input end of the multiplication digital-to-analog converter serve as the first input end and the first output end of the power amplifier circuit respectively, and the output end of the isolation filtering protection circuit serves as the output end of the power amplifier circuit.

[0025] In a specific embodiment, the circuit schematics of the multiplying digital-to-analog converter and the power amplifier are as follows: Figure 6 and Figure 7 As shown, the multiplication digital-to-analog converter circuit mainly uses a multiplication digital-to-analog converter with a chip model of DAC7811, and the power amplifier circuit mainly uses a power amplifier with a chip model of LM1875.

[0026] In a specific embodiment, the frequency detection circuit includes a first detection branch, a second detection branch and a third detection branch, which are used to sample and shape the frequency of the 0° phase, 120° phase and 240° phase sine wave signals with adjustable frequency, voltage and power, respectively; The first detection branch, the second detection branch and the third detection branch all include a frequency isolation sampling module and a frequency shaping module, the input end of the frequency isolation sampling module serves as the input end of the frequency detection circuit, and the output end of the frequency shaping module serves as the output end of the frequency detection circuit; The internal circuit diagram of the frequency detection circuit is as follows: Figure 8 As shown, the frequency isolation sampling module isolates the input AC signal by using an optical coupler isolator to complete the isolation conversion from the high voltage signal to the low voltage signal, and the frequency shaping module shapes and outputs the isolated signal.

[0027] The microprocessor in the control unit counts and calculates the pulse width of the input signal from the frequency detection circuit through the timer and timer functions, and finally calculates the frequency output (calculation formula: F (frequency) = 1 ÷ T (pulse width time)), which can achieve accurate acquisition within the frequency range of 0Hz to 6000Hz. It can complete the acquisition of the output frequency signal of the analog speed sensor, thereby realizing closed-loop control.

[0028] In a specific embodiment, the voltage measurement circuit includes a first measurement branch, a second measurement branch and a third measurement branch, which are used to sample the effective voltage of the 0° phase, 120° phase and 240° phase sinusoidal wave signals with adjustable frequency, voltage and power, respectively; The first measurement branch, the second measurement branch and the third measurement branch all include a voltage isolation sampling module and an analog-to-digital conversion module, the input end of the voltage isolation sampling module serves as the input end of the voltage measurement circuit, and the output end of the analog-to-digital conversion module serves as the output end of the voltage measurement circuit; The internal circuit diagram of the voltage measurement circuit is as follows: Fig. 9 As shown, the voltage isolation sampling module converts the AC voltage signal into a DC voltage signal by using a voltage sensor, and the analog-to-digital conversion module converts the analog signal into a digital signal by using a 12-bit AD acquisition chip. Specifically, the voltage isolation sampling module is mainly composed of a voltage sensor WBV411D01 and peripheral circuits, and the analog-to-digital conversion module is mainly composed of an acquisition chip ADS1115 and peripheral circuits.

[0029] The microprocessor in the control unit calculates the input signal from the voltage measurement circuit and displays the output. The voltage measurement circuit realizes three-phase AC voltage acquisition and completes the measurement of the AC phase-to-phase voltage output by the analog tachometer sensor, thereby realizing closed-loop control.

[0030] In a specific embodiment, the current measurement circuit includes a first sampling branch, a second sampling branch and a third sampling branch, which are used to sample the effective current of the 0° phase, 120° phase and 240° phase sinusoidal wave signals with adjustable frequency, voltage and power, respectively; The first sampling branch, the second sampling branch and the third sampling branch all include a current AC transformer, a current conversion circuit and a collection circuit, the input end of the current AC transformer serves as the input end of the current measurement circuit, and the output end of the collection circuit serves as the output end of the current measurement circuit; The circuit diagram of the current AC transformer and current conversion circuit is as follows Fig.10 and Fig.11 As shown, the current AC transformer is used to convert a large current of 5A into a small current signal of 2.5mA, the current conversion circuit is used to convert the small current signal into a voltage signal, and the acquisition circuit is used to realize digital conversion of the voltage signal.

[0031] The microprocessor in the control unit calculates the digital input signal from the current measurement circuit and displays the output, thereby completing the acquisition and measurement of the analog speed output signal.

[0032] In a specific embodiment, the control unit and the digital waveform generating and amplifying circuit, the power amplifying circuit, the frequency detecting circuit, the voltage measuring circuit, and the current measuring circuit transmit data via a serial bus. The control unit adopts a control circuit with an STM32F103VET6 microprocessor as the core, which has the characteristics of fast processing speed, stable and reliable operation, and has multiple functional peripherals to meet the working logic control and test process control of the speed comprehensive test equipment.

[0033] In this embodiment, a servo drive simulator of model MCDS4850L is selected as the motor drive unit to drive the DC servo motor to work. In combination with the DC servo motor and the speed acquisition circuit, the motor speed signal output of 0r / min to 6000r / min can be realized. The main functions of the servo drive simulator include: 1) input pulse and direction signals for step mode control; 2) real-time parameter adjustment and online monitoring through RS232; 3) digital storage of PID parameters; 4) overcurrent, overload, overvoltage, and undervoltage protection; 5) overshoot, misalignment protection, and dynamic tracking error protection.

[0034] The DC servo motor drives the speed sensor through the coupling. The speed sensor outputs the corresponding speed signal to drive the tachometer to indicate the corresponding speed value, thereby completing the tachometer calibration.

[0035] Embodiment 2, a tachometer calibration method, applied to the tachometer calibration circuit described in any one of Embodiment 1, comprises: Step 1: The motor drive unit drives the DC servo motor according to the motor output speed setting value. The DC servo motor is connected to the speed sensor through a coupling. The speed sensor collects the speed of the DC servo motor and outputs a three-phase signal to drive the tachometer. Step 2, the digital waveform generating and amplifying circuit generates a sine wave signal of any frequency according to the stable frequency source output by the crystal oscillator unit, and generates three sine wave signals with a phase difference of 120° between each other and adjustable frequency according to the waveform, frequency, phase and voltage amplitude setting values ​​output by the control unit; Step 3, the power amplifier circuit performs adjustable amplification output of the voltage and power of the three sinusoidal signals to provide the tachometer with an analog speed signal for calibration; Step 4: The control unit completes the frequency, AC phase-to-phase voltage and current acquisition and measurement of the analog speed sensor output signal according to the sampling feedback signals output by the frequency detection circuit, the voltage measurement circuit and the current measurement circuit; Step 5. Compare the frequency and AC phase-to-phase voltage of the output signal with the corresponding preset values. If they do not meet the settings, adjust the voltage or frequency proportionally until they meet the preset values. Determine whether the circuit is short-circuited or over-current based on the current of the output signal, and cut off the output analog speed signal when the output is short-circuited or over-current occurs.

[0036] The closed-loop control method flow chart implemented by the closed-loop control system is as follows: Fig.12 As shown, the present invention generates a three-phase power waveform with variable frequency and voltage amplitude through a closed-loop control system composed of a control unit, a digital waveform generating and amplifying circuit, a power amplifying circuit, a frequency detecting circuit, a voltage measuring circuit, and a current measuring circuit, and outputs a speed signal simulating the output of a speed sensor to provide the speed meter, thereby completing the calibration of the speed meter. The present invention eliminates the influence of the drive motor accuracy and the speed sensor output accuracy on the speed meter test accuracy, while ensuring the safety hazards caused by the differences in the speed sensors, and also reduces the cumbersome operation steps.

[0037] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A tachometer calibration circuit, comprising a DC servo motor and a speed sensor, wherein the DC servo motor is connected to the speed sensor, and the speed sensor is connected to the tachometer, characterized in that: Also includes: Control unit, crystal oscillator unit, digital waveform generation and amplification circuit, power amplification circuit, frequency detection circuit, voltage measurement circuit, current measurement circuit and motor drive unit; The first input terminal and the second input terminal of the control unit are respectively connected to the output terminals of the frequency detection circuit, the voltage measurement circuit and the current measurement circuit, and the first output terminal and the second output terminal of the control unit are respectively connected to the first input terminals of the digital waveform generation and amplification circuit and the power amplification circuit; The first output terminal and the second output terminal of the crystal oscillator unit are respectively connected to the third input terminal of the control unit and the second input terminal of the digital waveform generating and amplifying circuit; The output end of the digital waveform generating and amplifying circuit is connected to the second input end of the power amplifying circuit; The output end of the power amplifier circuit is connected to the input end of the frequency detection circuit, the voltage measurement circuit, the current measurement circuit and the tachometer; The input end of the motor drive unit is connected to the control unit, and the output end of the motor drive unit is connected to the DC servo motor.

2. A tachometer calibration circuit according to claim 1, characterized in that: It also includes a human-machine interaction unit connected to the control unit and the motor drive unit. The human-machine interaction unit uses a touch LCD screen to manually input, set and display parameters of the tachometer calibration circuit; the parameters include the operating status of the drive motor, the set speed, the output speed, the phase-to-phase voltage and the tachometer pointer.

3. A tachometer calibration circuit according to claim 2, characterized in that: It also includes a power supply unit for providing power supply to the human-machine interaction unit, the control unit, the digital waveform generation and amplification circuit, the motor drive unit and the tachometer; The power supply unit includes a power supply, an AC-DC power module, a DC-DC power module and a step-down module; the power supply is an externally introduced 220V±10% / 50Hz±5% power supply, the AC-DC power module is a UHP-350-24 switching power supply, and the AC-DC power module is used to convert the 220VAC power supply into a 24VDC±10% power output, with an output current of ≤14A; the DC-DC power module is a TPS54360 switching power supply, which is used to convert the input 24V power supply into +15VDC / 1A and –15VDC / 1A power outputs; the step-down module includes a SY8303AIC step-down chip and peripheral circuits, which convert the 24V power supply into a 3.3VDC / 2A power output.

4. A tachometer calibration circuit according to claim 1, characterized in that: The digital waveform generation and amplification circuit includes a first waveform generator, a second waveform generator, a third waveform generator, a first shaping filter circuit, a second shaping filter circuit and a third shaping filter circuit; The first waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 0° phase sine wave signal, and the output terminal of the first waveform generator is connected to the input terminal of the first shaping filter circuit; The second waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 120° phase sine wave signal, and the output terminal of the second waveform generator is connected to the input terminal of the second shaping filter circuit; The third waveform generator is connected to the first input terminal and the second input terminal of the digital waveform generation and amplification circuit, and is used to receive the waveform, frequency and phase setting value output by the control unit, and the stable frequency source output by the crystal oscillator unit, and output a frequency-adjustable 240° phase sine wave signal, and the output terminal of the third waveform generator is connected to the input terminal of the third shaping filter circuit; The output ends of the first shaping filter circuit, the second shaping filter circuit and the third shaping filter circuit are all connected to the output end of the digital waveform generating and amplifying circuit, and are used to shape and filter the sinusoidal wave signal.

5. A tachometer calibration circuit according to claim 4, characterized in that: The power amplifier circuit includes a first amplifier branch, a second amplifier branch and a third amplifier branch, which are used to output the frequency-adjustable 0° phase, 120° phase and 240° phase sine wave signals with adjustable voltage and power according to the voltage amplitude value output by the control unit, and output the three-phase sine voltage with adjustable frequency, voltage and power as the analog speed signal of the tachometer after filtering; The first amplifying branch, the second amplifying branch and the third amplifying branch each include a multiplication digital-to-analog converter, a power amplifier and an isolation filtering protection circuit connected in sequence, the first input end and the second input end of the multiplication digital-to-analog converter serve as the first input end and the first output end of the power amplifier circuit respectively, and the output end of the isolation filtering protection circuit serves as the output end of the power amplifier circuit.

6. A tachometer calibration circuit according to claim 5, characterized in that: The frequency detection circuit includes a first detection branch, a second detection branch and a third detection branch, which are used to sample and shape the frequency of the 0° phase, 120° phase and 240° phase sine wave signals with adjustable frequency, voltage and power respectively; The first detection branch, the second detection branch and the third detection branch all include a frequency isolation sampling module and a frequency shaping module, the input end of the frequency isolation sampling module serves as the input end of the frequency detection circuit, and the output end of the frequency shaping module serves as the output end of the frequency detection circuit; The frequency isolation sampling module isolates the input AC signal by using an optocoupler isolator to complete the isolation conversion from high-voltage signal to low-voltage signal. The frequency shaping module shapes and outputs the isolated signal.

7. A tachometer calibration circuit according to claim 5, characterized in that: The voltage measurement circuit comprises a first measurement branch, a second measurement branch and a third measurement branch, which are used to sample the effective voltage of the 0° phase, 120° phase and 240° phase sine wave signals with adjustable frequency, voltage and power respectively; The first measurement branch, the second measurement branch and the third measurement branch all include a voltage isolation sampling module and an analog-to-digital conversion module, the input end of the voltage isolation sampling module serves as the input end of the voltage measurement circuit, and the output end of the analog-to-digital conversion module serves as the output end of the voltage measurement circuit; The voltage isolation sampling module converts the AC voltage signal into a DC voltage signal by using a voltage sensor, and the analog-to-digital conversion module converts the analog signal into a digital signal by using a 12-bit AD acquisition chip.

8. The tachometer calibration circuit according to claim 5, characterized in that: The current measurement circuit comprises a first sampling branch, a second sampling branch and a third sampling branch, which are used to respectively sample the effective current of the 0° phase, 120° phase and 240° phase sinusoidal wave signals with adjustable frequency, voltage and power; The first sampling branch, the second sampling branch and the third sampling branch all include a current AC transformer, a current conversion circuit and a collection circuit, the input end of the current AC transformer serves as the input end of the current measurement circuit, and the output end of the collection circuit serves as the output end of the current measurement circuit; The current AC transformer is used to convert a large current of 5A into a small current signal of 2.5mA, the current conversion circuit is used to convert the small current signal into a voltage signal, and the acquisition circuit is used to realize digital conversion of the voltage signal.

9. A tachometer calibration circuit according to claim 1, characterized in that: The control unit and the digital waveform generating and amplifying circuit, the power amplifying circuit, the frequency detecting circuit, the voltage measuring circuit, and the current measuring circuit perform data transmission via a serial bus.

10. A tachometer calibration method, applied to the tachometer calibration circuit according to any one of claims 1 to 9, characterized in that: include: Step 1: The motor drive unit drives the DC servo motor according to the motor output speed setting value. The DC servo motor is connected to the speed sensor through a coupling. The speed sensor collects the speed of the DC servo motor and outputs a three-phase signal to drive the tachometer. Step 2, the digital waveform generating and amplifying circuit generates a sine wave signal of any frequency according to the stable frequency source output by the crystal oscillator unit, and generates three sine wave signals with a phase difference of 120° between each other and adjustable frequency according to the waveform, frequency, phase and voltage amplitude setting values ​​output by the control unit; Step 3, the power amplifier circuit performs adjustable amplification output of the voltage and power of the three sinusoidal signals to provide the tachometer with an analog speed signal for calibration; Step 4: The control unit completes the frequency, AC phase-to-phase voltage and current acquisition and measurement of the analog speed sensor output signal according to the sampling feedback signals output by the frequency detection circuit, the voltage measurement circuit and the current measurement circuit; Step 5. Compare the frequency and AC phase-to-phase voltage of the output signal with the corresponding preset values. If they do not meet the settings, adjust the voltage or frequency proportionally until they meet the preset values. Determine whether the circuit is short-circuited or over-current based on the current of the output signal, and cut off the output analog speed signal when the output is short-circuited or over-current occurs.

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