An alternating voltage and frequency and duty cycle measuring circuit

Abstract

The utility model relates to a kind of measurement circuit of alternating voltage and frequency and duty ratio, belong to electrical safety test circuit field, including front-end input signal measurement adjustment circuit, high pass filter circuit and digital multimeter chip circuit, wherein, front-end input signal measurement adjustment circuit is used to carry out voltage division attenuation to measured signal, make signal amplitude and the input range of subsequent analog-digital converter match;Digital multimeter chip circuit is comprehensively handled to measured signal by the circuit such as analog-digital converter, digital processor, comparator and microcontroller contained in it. The signal after voltage division is converted into digital signal by analog-digital converter on one hand, high-frequency signal is obtained by filtering low-frequency noise through high pass filter circuit on the other hand, comparator converts high-frequency signal into standard pulse signal, and digital processor obtains the voltage, frequency and duty ratio numerical value of measured signal in combination with digital signal and pulse signal. The measurement circuit structure is compact and comprehensive in function, effectively meet the electrical safety test demand.

Description

Technical Field

[0001] This utility model relates to the field of electrical safety testing tools, and in particular to a measuring circuit for AC voltage, frequency and duty cycle. Background Technology

[0002] When analyzing AC signals, in addition to measuring amplitude, measuring the signal frequency and duty cycle is also crucial. AC voltage signals have both AC and AC + DC modes in practical applications. AC mode is commonly used for power transmission, AC motor driving, and audio signal transmission; while AC + DC mode is mainly used for biasing in electronic circuits, communication systems, and sensor signal processing. Square wave or pulse signals can be further divided into unipolar and bipolar signals. Unipolar signals are commonly used in digital circuits to represent logic levels, such as high level representing logic "1" and low level representing logic "0." They are also common in some sensor output signals; for example, the current signal generated by a photodiode under illumination is usually a unipolar signal after conversion, used to represent the magnitude of the measured quantity. Bipolar signals are mainly used in the communication field, such as audio signals and radio frequency signals. Furthermore, in analog signal processing, many weak signals output by sensors are also bipolar. These different types and application scenarios of AC signals all require precise measurement of parameters such as frequency and duty cycle, placing high demands on the measurement circuitry.

[0003] However, in typical frequency and duty cycle measurement circuits in existing technologies, the PTC usually works in conjunction with a transistor for overvoltage protection. This measurement circuit has strict requirements on the input signal amplitude, normally not exceeding AC 30VRMS. If the input signal amplitude is too large, the thermistor and protective transistor will overheat and trigger protection mechanisms, accelerating product aging and affecting its lifespan. If the input test voltage exceeds the PTC's allowable withstand voltage, it may even lead to the risk of burning out the meter. Some frequency and duty cycle measurements use circuits shared with voltage measurements, adding a voltage divider resistor before the digital multimeter chip circuit to ensure effective attenuation of strong input signals and guarantee measurement safety. However, in this method, frequency measurement is only applicable to AC signals in AC mode and requires a strong input signal amplitude, greatly limiting its practicality.

[0004] In summary, there is an urgent need for a new type of measurement circuit that can adapt to different voltage measurement ranges, is unaffected by the DC component of the signal during measurement, enables the measurement of AC voltage, frequency, and duty cycle using a single circuit, and possesses high accuracy and sensitivity. Utility Model Content

[0005] To address the problems existing in the prior art, this utility model proposes a measurement circuit for AC voltage, frequency, and duty cycle.

[0006] The technical solution of this utility model is as follows: A circuit for measuring AC voltage, frequency, and duty cycle includes: a digital multimeter chip circuit, a front-end input signal measurement and adjustment circuit, and a high-pass filter circuit, wherein: The digital multimeter chip circuit includes an analog-to-digital converter, a digital processor, a comparator, and a microcontroller; The input terminal of the front-end input signal measurement and adjustment circuit is connected to the signal source under test, and is used to acquire the signal under test and perform voltage division. The output terminal of the front-end input signal measurement and adjustment circuit is connected to the input terminal of the analog-to-digital converter and the high-pass filter circuit. The analog-to-digital converter is used to convert the voltage-divided signal under test into an analog-to-digital signal, and its output terminal is connected to the input terminal of the digital processor. The high-pass filter circuit is used to filter out low-frequency noise signals in the voltage-divided signal under test to obtain a high-frequency signal, and its output terminal is connected to the input terminal of the comparator. The comparator is used to output a standard pulse signal based on the high-frequency signal, and its output terminal is connected to the input terminal of the digital processor. The digital processor is used to output measurement results based on the analog-to-digital converted signal under test and the standard pulse signal, including the voltage, frequency, and duty cycle values ​​of the signal under test, and its output terminal is connected to the input terminal of the microcontroller. The microcontroller is used to store the measurement results.

[0007] In a preferred embodiment of this utility model, the digital multimeter chip circuit further includes a multiplexer, a programmable gain amplifier, and an RC filter, wherein the input terminal of the analog-to-digital converter connected to the output terminal of the front-end input signal measurement and adjustment circuit is replaced with the input terminal of the multiplexer. The input terminal of the multiplexer is connected to the output terminal of the front-end input signal measurement and adjustment circuit, and is used to receive the type and range of the measured signal after voltage division for measurement channel selection. The output terminal of the multiplexer is connected to the input terminal of the programmable gain amplifier. The programmable gain amplifier is used to adjust the gain of the measured signal output from the multiplexer, and its output terminal is connected to the input terminal of the RC filter. The RC filter is used to filter the measured signal after gain adjustment. Its output is connected to the analog-to-digital converter, which converts the measured signal output by the RC filter into an analog signal.

[0008] In a preferred embodiment of this utility model, the front-end input signal measurement and adjustment circuit includes a voltage divider resistor R25, a positive input terminal INPUT, and a negative connection terminal COM. One end of the voltage divider resistor R25 is connected to the positive input terminal INPUT, and the other end is connected to the analog signal input terminal of the analog-to-digital converter. The negative connection terminal COM is grounded.

[0009] In a preferred embodiment of the present invention, the high-pass filter circuit includes a filter resistor R22 and a capacitor C32, wherein one end of the capacitor C32 is connected to the output terminal of the front-end input signal measurement and adjustment circuit, and the other end is connected to one end of the filter resistor R22 and the analog signal input terminal of the comparator, and the other end of the resistor R22 is grounded.

[0010] In a preferred embodiment of this utility model, the measurement circuit further includes an LCD liquid crystal display, the input terminal of which is connected to the output terminal of the microcontroller for displaying measurement results.

[0011] In a preferred embodiment of this utility model, the measuring circuit further includes a power supply circuit, which includes a battery and a blade switch. The positive terminal of the battery is connected to the power supply terminal of the digital multimeter chip circuit through the blade switch to provide operating power to the digital multimeter chip circuit.

[0012] This utility model has the following beneficial effects; 1. Compared with traditional AC voltage measuring multimeters, this utility model effectively prevents damage to subsequent circuit components caused by excessively high input voltage by designing and using a front-end input signal measurement and adjustment circuit, while ensuring that the signal amplitude matches the input range of the subsequent ADC. 2. Compared with traditional AC voltage measuring multimeters, this utility model makes full use of the characteristics of high-pass filters that pass high frequencies and suppress or attenuate low-frequency signals. Based on the fact that frequency and duty cycle measurements share the same circuit, it also improves the accuracy of frequency and duty cycle measurements. Attached Figure Description

[0013] Figure 1 The circuit block diagram provided for this utility model; Figure 2 This is a circuit diagram of Embodiment 3 of the present invention. Detailed Implementation

[0014] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0015] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0016] It should be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0017] The terms “comprising” and “including” indicate the presence of the described feature, whole, step, operation, element and / or component, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0018] The term “and / or” refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes these combinations.

[0019] Example 1: See Figure 1 This embodiment provides a measurement circuit for AC voltage, frequency, and duty cycle, including a front-end input signal measurement and adjustment circuit, a digital multimeter chip circuit, a high-pass filter circuit, an LCD display, and a power supply circuit. The digital multimeter chip circuit includes an analog-to-digital converter, a digital processor, a comparator, and a microcontroller. The measurement circuit of this embodiment will be described in detail below: A1. Front-end input signal measurement and adjustment circuit: The input terminal of the front-end input signal measurement and adjustment circuit is connected to the signal source under test, and is used to acquire the signal under test and perform voltage division. Furthermore, the front-end input signal measurement and adjustment circuit includes a voltage dividing resistor R25, a positive input terminal INPUT, and a negative connection terminal COM. The positive input terminal INPUT is the positive input terminal for all physical quantity measurements (i.e., the signal being measured in this embodiment), and the negative connection terminal COM is the negative input terminal for all physical quantity measurements, i.e., the common terminal, which is also the analog ground terminal. The positive input terminal INPUT is connected to one end of the voltage divider resistor R25. The measured signal from the signal source is proportionally attenuated by the voltage divider resistor R25 to a range suitable for subsequent circuit processing, preventing excessively high voltage from damaging subsequent circuit components. This also ensures that the amplitude of the measured signal matches the input range of the subsequent analog-to-digital converter (ADC). The other end of the voltage divider resistor R25 is connected to the analog signal input terminal of the ADC, used to transmit the proportionally attenuated measured signal to the ADC. Preferably, in this embodiment, the voltage divider resistor R25 has a value of 10MΩ; A2. High-pass filter circuit: The high-pass filter circuit includes a filter resistor R22 and a capacitor C32. One end of the capacitor C32 is connected to the output terminal of the front-end input signal measurement and adjustment circuit, and the other end is connected to one end of the filter resistor R22 and the analog signal input terminal of the comparator. The other end of the resistor R22 is grounded. The high-pass filter circuit receives the voltage-divided measured signal from the front-end input signal measurement and adjustment circuit. Through the filter resistor R22 and capacitor C32, it simultaneously suppresses or attenuates low-frequency signals. Its frequency response characteristics are determined by the cutoff frequency. The decision, expressed as a formula, is as follows: ; In the formula That is, the filter resistor R22. That is, capacitor C32; Based on the cutoff frequency, the corresponding capacitive reactance can be determined. Expressed as a formula: ; The lower the frequency of the measured signal after voltage division in the high-pass filter circuit, the larger the capacitive reactance. According to the voltage division principle, most of the voltage drops across capacitor C32, resulting in a very small amplitude of the low-frequency signal output to subsequent circuits, which is significantly attenuated. For example, if the measured signal is a DC signal (frequency 0Hz), capacitor C32 is essentially an open circuit, and the measured signal can hardly pass through, with the output voltage approximately zero. As the frequency increases, the capacitive reactance of capacitor C32 gradually decreases. When the frequency of the measured signal after voltage division in the high-pass filter circuit is higher than the cutoff frequency... At this time, the capacitive reactance of capacitor C32 is relatively small, and the voltage drop across resistor R22 gradually increases. The high-frequency signal in the measured signal can pass smoothly through the high-pass filter circuit and be transmitted to the subsequent processing part, thus achieving the screening of high-frequency components and allowing only high-frequency signals to enter the subsequent circuit.

[0020] A3. Digital multimeter chip circuit: A31. Analog-to-digital converter: The analog-to-digital converter is used to convert the voltage-divided test signal into an analog-to-digital signal to obtain the digital signal form of the test signal. The output terminal of the analog-to-digital converter is connected to the input terminal of the digital processor to transmit the analog-to-digital converted test signal to the digital processor. A32, Comparator: The input terminal of the comparator is connected to the output terminal of the high-pass filter circuit. In the digital multimeter chip circuit of this embodiment, the comparator receives a high-frequency signal from the output of the high-pass filter circuit. This high-frequency signal serves as one input of the comparator (assuming it is the non-inverting input terminal). At the same time, the other input terminal of the comparator (the inverting input terminal) is connected to a reference voltage source. The reference voltage source provides a fixed voltage value as a reference for comparison.

[0021] When the high-frequency signal voltage output by the high-pass filter circuit is higher than the reference voltage, the comparator outputs a high level; when the high-frequency signal voltage is lower than the reference voltage, the comparator outputs a low level. In this way, the comparator converts the continuously changing high-frequency analog signal into a series of high and low level pulse signals, i.e., standard pulse signals. Its output is connected to the input of the digital processor, outputting the standard pulse signals to the digital processor. A33, Digital Processor: The digital processor is used to output measurement results based on the analog-to-digital converted signal and the standard pulse signal, including the voltage, frequency and duty cycle values ​​of the measured signal, and its output terminal is connected to the input terminal of the microcontroller. A34, Microcontroller: The microcontroller is used to store the measurement results; Preferably, the measurement circuit further includes an LCD liquid crystal display, the input terminal of which is connected to the output terminal of the microcontroller for displaying measurement results.

[0022] Preferably, the measurement circuit further includes a power supply circuit, which includes a battery and a blade switch, wherein the positive terminal of the battery is connected to the power supply terminal of the digital multimeter chip circuit through the blade switch to provide working power to the digital multimeter chip circuit. Preferably, in this embodiment, the battery consists of two 1.5V batteries that directly power the digital multimeter chip circuit without the need for voltage regulation.

[0023] Example 2: The difference between this embodiment and Embodiment 1 is that the digital multimeter chip circuit further includes a multiplexer, a programmable gain amplifier, and an RC filter. Specifically, the input terminal of the analog-to-digital converter connected to the output terminal of the front-end input signal measurement and adjustment circuit is replaced with the input terminal of the multiplexer. B1. Multiplexer: The input terminal of the multiplexer is connected to the output terminal of the front-end input signal measurement and adjustment circuit. It is used to receive the type and range of the measured signal after voltage division and select the measurement channel. Since the measured signal has multiple types (such as signals corresponding to different physical quantities such as voltage, current, and resistance) and different ranges (such as different voltage values), the multiplexer determines which measurement channel to select based on the corresponding control signal. The control signal is issued by the digital processor according to the preset measurement mode. The output terminal of the multiplexer is connected to the input terminal of the programmable gain amplifier. B2. Programmable gain amplifier: The programmable gain amplifier is used to adjust the gain of the measured signal output by the multiplexer to meet the needs of different measurement scenarios, and its output terminal is connected to the input terminal of the RC filter. B3, RC filter: The RC filter is used to suppress noise in the measured signal after gain adjustment and improve the signal-to-noise ratio (SNR). Noise usually contains components of various frequencies, and the RC filter selectively attenuates signals of different frequencies according to its cutoff frequency. Its output is connected to the input of the analog-to-digital converter of the digital processor. The analog-to-digital converter converts the measured signal output from the RC filter into an analog signal.

[0024] Example 3: like Figure 2 As shown, this embodiment uses MXC53P63 as the digital multimeter chip circuit, based on embodiment two.

[0025] As shown in the figure, the analog signal input terminal of the analog-to-digital converter is port 10, A0, of the MXC53P63 digital multimeter chip circuit; the input terminal of the high-pass filter circuit is port 12, A7, of the MXC53P63 digital multimeter chip circuit; and the analog signal input terminal of the comparator is port 13, A8, of the MXC53P63 digital multimeter chip circuit.

[0026] The measured signal passes through voltage divider resistor R25 to the VMIP terminal. The VMIP terminal is then connected to port A7 (12th port) of the digital multimeter chip circuit MXC53P63 via a switch. A7 is then connected to port A8 (13th port) via a high-pass filter circuit. A8 is connected to VMIN via a switch. The VMIN signal is amplified by a programmable gain amplifier and then enters a comparator for comparison. The comparator outputs a square wave, which is then sent to a digital processor to process the frequency and duty cycle of the measured signal.

[0027] Preferably, the digital multimeter chip circuit MXC53P63 processes the frequency and duty cycle of the measured signal as follows: the frequency signal processed by the peripheral circuit (front-end input signal measurement and adjustment circuit, high-pass filter circuit) is passed through multiplexers such as DMM PMUX and DMM NMUX, and then transmitted to the digital processor after being selected by the corresponding control signal. The 16-bit Timer0 or 16-bit Timer1 inside the digital processor counts the input frequency signal; within a certain time period, the number of pulses of the input signal is recorded, thereby calculating the frequency and duty cycle of the signal; the digital processor calculates the frequency value of the measured signal based on the number of pulses recorded by the timer and the set counting time.

[0028] In summary, the working principle of this utility model is as follows: The AC signal under test is first input to the front-end input signal measurement and adjustment circuit for voltage attenuation, adjusting the signal amplitude to a suitable level to prevent damage to subsequent circuits due to high voltage. The adjusted signal is then fed into the analog-to-digital converter (ADC) within the digital multimeter chip circuit, where it is converted into a digital voltage value. Simultaneously, it passes through a high-pass filter circuit to filter out low-frequency interference (including DC components). The high-pass filtered AC signal is then fed into the comparator within the digital multimeter chip circuit, converting it into a standard pulse signal for frequency measurement. The digital processor receives the digital voltage signal from the ADC for processing, and also receives the standard pulse signal from the comparator. It captures signal edges (such as rising and falling edges) and uses high-frequency counting to calculate the frequency and duty cycle. The digital processor also controls the range switching of the front-end input signal measurement and adjustment circuit and works with its internal programmable gain amplifier to optimize signal accuracy. The processed measurement data (voltage, frequency, duty cycle) is sent by the digital processor to the microcontroller for calculation and storage. Finally, the microcontroller drives the LCD display to show the measurement results in real time. The entire process is supported by a stable power supply circuit.

[0029] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, A and B simultaneously, or B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of singular or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0030] The above description is merely an embodiment of this utility model and does not limit the patent scope of this utility model. Any equivalent structural or procedural transformations made based on the description and drawings of this utility model, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this utility model.

Claims

1. A circuit for measuring AC voltage, frequency, and duty cycle, characterized in that, include: The digital multimeter chip circuit, the front-end input signal measurement and adjustment circuit, and the high-pass filter circuit include: The digital multimeter chip circuit includes an analog-to-digital converter, a digital processor, a comparator, and a microcontroller; The input terminal of the front-end input signal measurement and adjustment circuit is connected to the signal source under test, and is used to acquire the signal under test and perform voltage division. The output terminal of the front-end input signal measurement and adjustment circuit is connected to the input terminal of the analog-to-digital converter and the high-pass filter circuit. The analog-to-digital converter is used to convert the voltage-divided signal under test into an analog-to-digital signal, and its output terminal is connected to the input terminal of the digital processor. The high-pass filter circuit is used to filter out low-frequency noise signals in the voltage-divided signal under test to obtain a high-frequency signal, and its output terminal is connected to the input terminal of the comparator. The comparator is used to output a standard pulse signal based on the high-frequency signal, and its output terminal is connected to the input terminal of the digital processor. The digital processor is used to output measurement results based on the analog-to-digital converted signal under test and the standard pulse signal, including the voltage, frequency, and duty cycle values ​​of the signal under test, and its output terminal is connected to the input terminal of the microcontroller. The microcontroller is used to store the measurement results.

2. The AC voltage, frequency, and duty cycle measurement circuit according to claim 1, characterized in that, The digital multimeter chip circuit also includes a multiplexer, a programmable gain amplifier, and an RC filter, wherein the input terminal of the analog-to-digital converter, which is connected to the output terminal of the front-end input signal measurement and adjustment circuit, is replaced with the input terminal of the multiplexer. The input terminal of the multiplexer is connected to the output terminal of the front-end input signal measurement and adjustment circuit, and is used to receive the type and range of the measured signal after voltage division for measurement channel selection. The output terminal of the multiplexer is connected to the input terminal of the programmable gain amplifier. The programmable gain amplifier is used to adjust the gain of the measured signal output from the multiplexer, and its output terminal is connected to the input terminal of the RC filter. The RC filter is used to filter the measured signal after gain adjustment. Its output is connected to the analog-to-digital converter, which converts the measured signal output by the RC filter into an analog signal.

3. The AC voltage, frequency, and duty cycle measurement circuit according to claim 1, characterized in that, The front-end input signal measurement and adjustment circuit includes a voltage divider resistor R25, a positive input terminal INPUT, and a negative connection terminal COM. One end of the voltage divider resistor R25 is connected to the positive input terminal INPUT, and the other end is connected to the analog signal input terminal of the analog-to-digital converter. The negative connection terminal COM is grounded.

4. The AC voltage, frequency, and duty cycle measurement circuit according to claim 1, characterized in that, The high-pass filter circuit includes a filter resistor R22 and a capacitor C32. One end of the capacitor C32 is connected to the output terminal of the front-end input signal measurement and adjustment circuit, and the other end is connected to one end of the filter resistor R22 and the analog signal input terminal of the comparator. The other end of the resistor R22 is grounded.

5. The AC voltage, frequency, and duty cycle measurement circuit according to claim 1, characterized in that, The measurement circuit also includes an LCD display, the input of which is connected to the output of the microcontroller to display the measurement results.

6. The AC voltage, frequency, and duty cycle measurement circuit according to claim 1, characterized in that, The measurement circuit also includes a power supply circuit, which includes a battery and a blade switch. The positive terminal of the battery is connected to the power supply terminal of the digital multimeter chip circuit through the blade switch to provide operating power to the digital multimeter chip circuit.

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