CN108333425B - Digital frequency meter - Google Patents
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- CN108333425B CN108333425B CN201810042192.0A CN201810042192A CN108333425B CN 108333425 B CN108333425 B CN 108333425B CN 201810042192 A CN201810042192 A CN 201810042192A CN 108333425 B CN108333425 B CN 108333425B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
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Abstract
The invention discloses a digital frequency meter, which comprises a singlechip provided with a first timer and a second timer, and a display module, a key module, an indicator lamp module and a power module which are respectively connected with the singlechip, wherein the singlechip comprises a Zhou Mokuai and frequency measuring module, and is also provided with a signal frequency dividing module, a data selecting module, a signal conditioning module and a time signal source module. The software embedded by the singlechip comprises a parameter adjusting program, a frequency measuring program and an LCD frequency display program. Compared with the prior art, the invention has the beneficial effects that: the circuit is simple, the structure is compact, the cost is low, the system performance is stable, the anti-interference capability is high, the measurement accuracy is high, the intelligent degree is high, the frequency division coefficient can be reasonably selected, the count value under any frequency is in a more reasonable range, the unit of the display frequency can be automatically adjusted, the display of the frequency is accurate to the position behind the decimal point, and the frequency measuring device can be widely applied to measurement of physical quantities such as rotating speed, vibration frequency and the like.
Description
Technical Field
The present invention relates to frequency metering, and more particularly to a digital frequency meter.
Background
The digital frequency meter is an instrument for measuring frequency signals by adopting a digital circuit and is mainly used for measuring frequency values of periodic signals such as sine waves, rectangular waves, triangular waves, spike pulses and the like. In order to improve the measurement accuracy, the frequency of a signal to be measured is below 10KHz, the frequency is measured by a week measurement method, a time mark signal is counted between two adjacent rising edges or falling edges of the signal to be measured, which is subjected to signal conditioning, and then the frequency of the signal to be measured is calculated according to the count value; the frequency of the signal to be measured exceeds 10KHz, the frequency is measured by adopting a multi-period synchronous frequency measurement method, the counter corresponding to the time scale signal and the counter corresponding to the signal to be measured start to count simultaneously and stop to count simultaneously under the control of the gate signal, two count values are obtained, and then the frequency of the signal to be measured is calculated according to the two count values. The existing digital frequency meter has different performances due to respective complex design schemes of manufacturers, and needs to be further improved and perfected.
Disclosure of Invention
The technical problem to be solved by the invention is to remedy the defects of the prior art and provide a digital frequency meter.
The technical problems of the invention are solved by the following technical proposal.
The digital frequency meter comprises a singlechip provided with a first timer and a second timer, and a display module, a key module, an indicator lamp module and a power module which are respectively connected with the singlechip, wherein the singlechip is a system control core, the display module is used for displaying counting processes and results, the key module is used for function selection and parameter setting, the indicator lamp module is used for indicating whether a system is electrified or not and whether the current frequency measurement is a Zhou Fa or frequency measurement method, and the power module is used for providing a 5V direct current power supply and a 3.3V direct current power supply;
the digital frequency meter is characterized in that:
the single chip microcomputer comprises a measurement Zhou Mokuai and a frequency measurement module, the frequency measurement module measures the frequency by adopting a method of measuring the period, a capture module of a second timer of the single chip microcomputer is controlled by a general I/O port of the single chip microcomputer through an AND gate and the single chip microcomputer, the time scale signal in one period of the signal to be measured is counted, the frequency measurement module measures the frequency by adopting a method of measuring the frequency synchronously in multiple periods, the signal to be measured and the time scale signal are respectively counted by a first timer and the second timer under the control of a gate signal of the general I/O port of the same single chip microcomputer, the general I/O port is respectively connected with a capture channel 0 of the first timer and a capture channel 0 of the second timer, the corresponding capture channel captures the gate signal, the count value of the corresponding timer is recorded, and the frequency measurement counting process is completed;
the signal frequency division module is used for dividing the frequency of a signal higher than the upper frequency limit required by the singlechip, and the data selection module reasonably selects an undegraded signal to be detected, a signal to be detected with two frequency divisions and a time signal, so that the count value at any frequency is in a reasonable range, and is matched with the signal frequency division module to send a proper square wave signal to the singlechip for counting;
the signal conditioning module is used for converting a signal to be detected with 0-5V into a square wave signal with the amplitude of 3.3V, the time scale signal source module comprises a time scale signal data selector, two clock signals MCLK and SMCLK of the singlechip select 8MHz crystal oscillator circuits, a third clock signal ACLK select 32.768KHz crystal oscillator circuits, the clock signals are output through clock output pins P5.5 and P5.6 of the singlechip respectively and serve as time scale signals in the frequency measurement process, and the time scale signals are generated by 8MHz or 32.768KHz signal frequency division and are realized by program modification of corresponding registers.
The technical problems of the invention are solved by the following further technical proposal.
The single chip microcomputer is a 16-bit single chip microcomputer with the model of MSP430F149, the upper limit of the signal frequency born by an I/O port is 10MHz, the single chip microcomputer comprises a 12-bit analog-to-digital converter, 2 16-bit counters with capturing and threshold functions and an on-chip comparator, embedded software comprises a parameter adjusting program, a frequency measuring program and an LCD frequency display program, the parameter adjusting program selects clock sources and frequency dividing coefficients of time scale signals matched with the frequency of signals to be detected in different frequency ranges, the frequency measuring program reasonably selects the frequency dividing coefficients of the signals to be detected and the frequency dividing coefficients of the time scale signals to enable count values at any frequency to be in a reasonable range, and the LCD frequency display program automatically adjusts the unit of display frequency to achieve frequency display of the next decimal point accurately under the limited character display width.
The signal frequency division module is a frequency division module with a chip of 74HC 74.
The data selection module is a data selector with the model number of 74LS157, and selects the undegraded signal to be detected and the clock signals SMCLK and ACLK.
The signal conditioning module comprises a signal comparison module and a signal shaping module.
The signal comparison module adopts a comparison module with a chip MAX903 to convert a signal to be detected into a square wave signal with the amplitude of 3.3V so as to adapt to the measuring amplitude range of 0.5V to 5V and the output amplitude of 3.3V.
The signal shaping module adopts an inverter with a schmitt trigger and a chip of 74HC14 to shape the square wave signal with the amplitude of 3.3V output by the signal comparison module, so that the rising edge and the falling edge of the square wave signal are steeper.
The technical problems of the invention are solved by the following further technical proposal.
The key module comprises a range key and a refresh time key, and is used for adjusting the range of the measurement frequency and the display refresh time respectively.
The display module comprises LCD5110 liquid crystal adopting a three-wire SPI interface, and USART0 of the singlechip enables the display module to work in an SPI mode to finish driving the LCD5110 liquid crystal.
The power module comprises a voltage stabilizing circuit and a USB power supply interface, wherein the voltage stabilizing circuit and the USB power supply interface adopt a chip of LM1117, and digital signals are commonly connected with analog signals through 0 omega resistors, so that a 5V power supply is converted into 3.3V, and a 5V direct current power supply and a 3.3V direct current power supply are generated.
Compared with the prior art, the invention has the beneficial effects that:
the circuit is simple, the structure is compact, the cost is low, the system performance is stable, the anti-interference capability is high, the measurement accuracy is high, the intelligent degree is high, the frequency division coefficient can be reasonably selected, the count value under any frequency is in a more reasonable range, the unit of the display frequency can be automatically adjusted, the display of the frequency is accurate to the position behind the decimal point, and the frequency measuring device can be widely applied to measurement of physical quantities such as rotating speed, vibration frequency and the like.
Drawings
FIG. 1 is a block diagram of an embodiment of the present invention;
FIG. 2 is a block diagram of a perimeter measurement module according to an embodiment of the present invention;
FIG. 3 is a diagram of a frequency measurement module according to an embodiment of the present invention;
FIG. 4 is a main program flow chart of an embodiment of the present invention;
FIG. 5 is a flowchart of a cycle measurement procedure according to an embodiment of the present invention;
FIG. 6 is a flow chart of a frequency measurement procedure according to an embodiment of the present invention;
FIG. 7 is a flow chart of a parameter adjustment procedure according to an embodiment of the present invention;
fig. 8 is a flowchart of the LCD frequency display program of the present embodiment.
Detailed Description
The invention will now be described with reference to the following detailed description and with reference to the accompanying drawings.
A digital frequency meter as shown in fig. 1-8 for measuring sinusoidal signals or square wave signals having amplitudes of 0.5V-5V and frequencies in the range of 0.1 Hz-15 MHz.
The specific implementation mode comprises a single chip microcomputer provided with a first timer and a second timer, and a display module, a key module, an indicator lamp module and a power module (not shown in fig. 1), wherein the display module, the key module, the indicator lamp module and the power module are respectively connected with the single chip microcomputer, the single chip microcomputer is a system control core, the display module comprises Nokia LCD5110 liquid crystal adopting a three-wire SPI interface, the Nokia LCD5110 liquid crystal is enabled to work in an SPI mode by USART0 of the single chip microcomputer, driving of the Nokia LCD5110 liquid crystal is completed, a counting process and a counting result are used for displaying, the key module comprises a range key and a refreshing time key and is used for respectively adjusting the measuring range of measuring frequency and the refreshing time of displaying, the indicator lamp module is used for indicating whether a system is electrified and the current frequency measurement is Zhou Fa or a frequency measurement method, the power module comprises a voltage stabilizing circuit adopting a chip LM1117, a USB power supply interface, and digital signals are commonly connected with an analog signal through a 0 omega resistor to convert a 5V power supply into 3.3V direct current power supply and a 3.3V direct current power supply.
The single chip microcomputer is a 16-bit single chip microcomputer with the model of MSP430F149, the upper limit of the signal frequency born by an I/O port is 10MHz, the single chip microcomputer comprises a 12-bit analog-to-digital converter, 2 16-bit counters with capturing and threshold functions and an on-chip comparator, embedded software comprises a parameter adjusting program, a frequency measuring program and an LCD frequency display program, a parameter adjusting module, a frequency measuring module and a system initializing module are correspondingly arranged, the parameter adjusting program selects clock sources and frequency dividing coefficients of time scale signals matched with the frequency of signals to be detected in different frequency ranges, the frequency measuring program reasonably selects the frequency dividing coefficients of the signals to be detected and the frequency dividing coefficients of the time scale signals, so that count values in any frequency are in a reasonable range, and the LCD frequency display program realizes frequency display to the next decimal point by automatically adjusting the unit of display frequency under the limited character display width.
The singlechip comprises a Zhou Mokuai and a frequency measuring module, the frequency of a signal to be measured is below 10KHz, the frequency is measured by adopting a cycle measuring method, a time mark signal is counted between two adjacent rising edges or falling edges of the signal to be measured which is subjected to signal conditioning, and then the frequency of the signal to be measured is calculated according to the count value; the frequency of the signal to be measured exceeds 10KHz, the frequency is measured by adopting a multi-period synchronous frequency measurement method, the counter corresponding to the time scale signal and the counter corresponding to the signal to be measured start to count simultaneously and stop to count simultaneously under the control of the gate signal, two count values are obtained, and then the frequency of the signal to be measured is calculated according to the two count values.
The frequency measurement module measures the frequency by adopting a method of measuring the period, the capture module of the second timer of the singlechip is controlled by an AND gate 74HC08 with four groups of same two input ends and one output end and the general I/O port of the singlechip, the time scale signal in one period of the signal to be measured is counted, the period measurement counting process is completed, the AND gate 74HC08 in FIG. 2 adopts one group of two input ends 1A and 1B and one output end 1Y, the input end 1A is connected with one general I/O port of the singlechip, the input gate control signal period_ctrl is a signal to be measured in one period, the general I/O port of the singlechip is connected with the capture channel 1 of the second timer, and the corresponding capture channel captures the gate signal and simultaneously completes the recording of the count value of the corresponding second timer. fx_std is a time scale signal after passing through the data selector, and TBCLK is a count clock input pin of the second timer.
The frequency measurement module measures the frequency by adopting a multi-period synchronous frequency measurement method, the first timer and the second timer count the signal to be measured and the time mark signal respectively under the control of the gate signal of the universal I/O port of the same singlechip, the universal I/O port is connected with the capture channel 0 of the first timer and the capture channel 0 of the second timer respectively, the corresponding capture channel captures the gate signal, the count value of the corresponding timer is recorded, and the frequency measurement and counting process is completed. The and gate 74HC08 in fig. 3 employs two sets of two input terminals 2A, 2B, 3A, 3B and one output terminal 2Y, 3Y, freq_ctrl is a gate control signal, fx_std is a time scale signal after passing through the data selector, fx' is a signal to be measured after passing through the data selector, and TACLK and TBCLK are count clock input pins of the first timer and the second timer, respectively.
The signal frequency division module is a frequency division module with a chip of 74HC74 and is used for dividing the frequency of signals higher than the upper frequency limit required by the single chip microcomputer, the data selection module is a data selector with a model of 74LS157 and is used for reasonably selecting the signals to be detected which are not divided and the signals to be detected which are divided by two and the time signals SMCLK and ACLK, so that the count value of any frequency is in a reasonable range, and the signal frequency division module is matched with the signal frequency division module to send the proper square wave signals into the single chip microcomputer for counting.
The signal conditioning module comprises a signal comparing module and a signal shaping module, wherein the signal comparing module is a comparison module with a chip MAX903 and is used for converting a sinusoidal or square wave signal to be measured with the amplitude of 3.3V into a square wave signal with the amplitude of 3.3V so as to adapt to a measuring amplitude range of 0.5V to 5V and an output amplitude of 3.3V, the signal shaping module is an inverter with a Schmitt trigger with a chip 74HC14 and is used for shaping the square wave signal with the amplitude of 3.3V output by the signal comparing module so that rising edges and falling edges of the square wave signal are steeper, the time scale signal source module comprises a time scale signal data selector, two clock signals MCLK and SMCLK of the single chip microcomputer select 8MHz crystal oscillator circuits, and a third clock signal ACLK selects 32.768KHz crystal oscillator circuits to be respectively output through clock output pins P5.5 and P5.6 of the single chip microcomputer and is used as a frequency measuring signal, and a time scale signal is generated by a corresponding time scale register of 32.768KHz in a frequency measuring process.
The main program flow chart of the embodiment is shown in fig. 4, and the main function of the whole program is to measure and display the frequency, and enter the function interface through key scanning, so that the corresponding measuring range and the display refresh time can be adjusted.
Before the frequency measurement is carried out, the specific embodiment needs to adopt different frequency division coefficient combinations for the signals to be measured and the time scale signals to ensure the count value to be maintained at 1000-50000 so as to ensure the accuracy of the measurement. The combination of the time scale signal source and the frequency division coefficient in the cycle measurement state is shown in table 1, fx' is the signal to be measured, and fx_std is the time scale signal.
Table 1: measuring relevant parameters of the week
As shown in fig. 5, a flowchart of a cycle measurement procedure in this embodiment includes capturing the number of time scale signals passing between two adjacent falling edges of a signal to be measured by using a capture register group 1 of a second timer, to obtain a count value: count value temp2 corresponding to the frequency of the signal to be measured.
The combination of the time scale signal source and the frequency division coefficient in the frequency measurement state, and the opening time of the gate are shown in table 2, fx' is the signal to be measured, and fx_std is the time scale signal.
Table 2: frequency measurement related parameter
As shown in fig. 6, the flow chart of the frequency measurement procedure in this embodiment is that the first timer and the second timer count the signal to be measured and the time scale signal at the same time, and start and stop counting at the same time under the control of the same gate signal, so as to obtain two count values: temp1 of count value corresponding to frequency of signal to be measured, temp2 of count value corresponding to frequency of time scale signal.
A flowchart of the parameter adjustment program of this embodiment is shown in fig. 7. In the cycle measurement state, the maximum value of the count value is the maximum value of the count value range of fx_std shown in table 1, which is the count value in the current frequency range, and the minimum value of the count value is the minimum value of the count value range of fx_std shown in table 1, which is the count value in the current frequency range. The core of the parameter adjusting program is to determine the frequency range of the signal to be measured, specifically, the obtained count value is compared with the count value range in the original lookup table, when the corresponding frequency range is determined, namely, the matching is completed, a matching flag bit is set, the matching flag bit indicates that the reasonable count value corresponding to the signal to be measured is obtained, and the next step is to display the frequency. The frequency measurement state is similar, but the frequency range is adjusted in the frequency measurement state, and the time for opening the gate is adjusted in the frequency measurement state, and tables 1 and 2 show that the frequency range is different in the frequency measurement state and corresponds to the different count value range, and the gate opening time is different in the frequency measurement state and corresponds to the different count value range. In consideration of noise interference in actual situations, certain deviation of the count value can occur, in a specific procedure, the count value ranges shown in the table 1 and the table 2 are expanded, the maximum value is increased by 100, the minimum value is reduced by 100, and the count value overflow range is prevented, so that the anti-interference capability is enhanced.
The flow chart of the LCD frequency display program of this embodiment is shown in fig. 8. In the drawing the view of the figure,
and (3) flag: whether a non-zero character is displayed before the character to be displayed currently or not, and if yes, the character to be displayed currently is 1; if not, 0.
And (3) Tem: when the calculated temp value is non-zero, the current value of a certain digit of the frequency obtained through operation is displayed on the LCD, and the flag at the moment is set to 1, which indicates that the first significant digit is already displayed, and then even if temp is 0, the current value is displayed on the LCD.
(x, y+j): displaying characters in an x-th row, a y+j-th column, wherein j: the number of characters displayed on the LCD at the current frequency value, the LCD frequency display program adopts j to control the display position of the characters, if j is 0, the integer part of freq1 is 0, that is, the frequency of the signal to be detected is less than 1Hz, and a 0 needs to be displayed at a designated position as the integer part of the signal to be detected.
q: the frequency range labels, the corresponding display units are "Hz", "KHz", or "MHz".
The LCD frequency display program of this embodiment is represented by the following three equations: the coordination of temp=freq1/dec_const, freq1=freq1% dec_const and dec_const=dec_const/10 can decompose kilobits, hundred bits, ten bits and bits of freq1 to display the frequency values, and then display the frequency units.
The measuring frequency range of the specific embodiment is 0.1 Hz-15 MHz, the span is large, and different display modes are adopted for different frequency ranges. The LCD5110 displays 8 characters (including numbers or letters, and decimal points) in frequency (including units), and the specific frequency ranges are divided as shown in table 3:
table 3 frequency ranges and labels therefor
Table 3 shows the division of the frequency ranges, the units displayed on the LCD5110 at the current frequency range, and the frequency range numerals for displaying the different units. The frequency range label is from the parameter adjustment module, and the correct display of the unit can be performed only by inquiring the frequency range label.
The performance of this embodiment was tested using known square wave signals of different standard frequencies, the test results are shown in table 4. The result shows that the digital frequency meter of the design has higher measurement accuracy.
Table 4: comparison of standard frequency with measured frequency results
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. Several equivalent substitutions or obvious modifications will occur to those skilled in the art to which this invention pertains without departing from the spirit of the invention, and the same should be considered to be within the scope of this invention as defined in the appended claims.
Claims (9)
1. The utility model provides a digital frequency meter, includes the singlechip that is equipped with first timer and second timer, and respectively with display module, button module, pilot lamp module and the power module that the singlechip is connected, the singlechip is the system control core, display module is used for showing the process and the result of count, button module is used for function selection and parameter setting, the pilot lamp module is used for instructing whether the system is on electricity and current frequency measurement is survey Zhou Fa or frequency measurement method, power module is used for providing 5V DC power supply and 3.3V DC power supply, its characterized in that:
the single chip microcomputer comprises a measurement Zhou Mokuai and a frequency measurement module, the frequency measurement module measures the frequency by adopting a method of measuring the period, a capture module of a second timer of the single chip microcomputer is controlled by a general I/O port of the single chip microcomputer through an AND gate and the single chip microcomputer, the time scale signal in one period of the signal to be measured is counted, the frequency measurement module measures the frequency by adopting a method of measuring the frequency synchronously in multiple periods, the signal to be measured and the time scale signal are respectively counted by a first timer and the second timer under the control of a gate signal of the general I/O port of the same single chip microcomputer, the general I/O port is respectively connected with a capture channel 0 of the first timer and a capture channel 0 of the second timer, the corresponding capture channel captures the gate signal, the count value of the corresponding timer is recorded, and the frequency measurement counting process is completed;
the signal frequency division module is used for dividing the frequency of a signal higher than the upper frequency limit required by the singlechip, and the data selection module reasonably selects an undegraded signal to be detected, a signal to be detected with two frequency divisions and a time signal, so that the count value at any frequency is in a reasonable range, and is matched with the signal frequency division module to send a proper square wave signal to the singlechip for counting;
the system is characterized by further comprising a signal conditioning module connected between a signal to be detected and the signal frequency division module and a time scale signal source module connected between the singlechip and the signal frequency division module, wherein the signal conditioning module is used for converting a signal to be detected with the amplitude of 0-5V into a square wave signal with the amplitude of 3.3V, the time scale signal source module comprises a time scale signal data selector, two clock signals MCLK and SMCLK of the singlechip select 8MHz crystal oscillator circuits, a third clock signal ACLK selects 32.768KHz crystal oscillator circuits, the clock signals are respectively output through clock output pins P5.5 and P5.6 of the singlechip and are used as time scale signals in the frequency measurement process, and the time scale signals are generated by 8MHz or 32.768KHz signal frequency division and are realized by program modification of corresponding registers;
the single chip microcomputer is a 16-bit single chip microcomputer with the model of MSP430F149, the upper limit of the signal frequency born by an I/O port is 10MHz, the single chip microcomputer comprises a 12-bit analog-to-digital converter, 2 16-bit counters with capturing and threshold functions and an on-chip comparator, embedded software comprises a parameter adjusting program, a frequency measuring program and an LCD frequency display program, the parameter adjusting program selects clock sources and frequency dividing coefficients of time scale signals matched with the frequency of signals to be detected in different frequency ranges, the frequency measuring program reasonably selects the frequency dividing coefficients of the signals to be detected and the frequency dividing coefficients of the time scale signals to enable count values at any frequency to be in a reasonable range, and the LCD frequency display program automatically adjusts the unit of display frequency to achieve frequency display of the next decimal point accurately under the limited character display width.
2. The digital frequency meter of claim 1, wherein:
the signal frequency division module is a frequency division module with a chip of 74HC 74.
3. The digital frequency meter of claim 2, wherein:
the data selection module is a data selector with the model number of 74LS157, and selects the undegraded signal to be detected and the clock signals SMCLK and ACLK.
4. The digital frequency meter of claim 2, wherein:
the signal conditioning module comprises a signal comparison module and a signal shaping module.
5. The digital frequency meter of claim 2, wherein:
the signal comparison module adopts a comparison module with a chip MAX903 to convert a signal to be detected into a square wave signal with the amplitude of 3.3V so as to adapt to the measuring amplitude range of 0.5V to 5V and the output amplitude of 3.3V.
6. The digital frequency meter of claim 2, wherein:
the signal shaping module adopts an inverter with a schmitt trigger and a chip of 74HC14 to shape the square wave signal with the amplitude of 3.3V output by the signal comparison module, so that the rising edge and the falling edge of the square wave signal are steeper.
7. The digital frequency meter of claim 1, wherein:
the key module comprises a range key and a refresh time key, and is used for adjusting the range of the measurement frequency and the display refresh time respectively.
8. The digital frequency meter of claim 1, wherein:
the display module comprises LCD5110 liquid crystal adopting a three-wire SPI interface, and USART0 of the singlechip enables the display module to work in an SPI mode to finish driving the LCD5110 liquid crystal.
9. The digital frequency meter of claim 1, wherein:
the power module comprises a voltage stabilizing circuit and a USB power supply interface, wherein the voltage stabilizing circuit and the USB power supply interface adopt a chip of LM1117, and digital signals are commonly connected with analog signals through 0 omega resistors, so that a 5V power supply is converted into 3.3V, and a 5V direct current power supply and a 3.3V direct current power supply are generated.
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| CN112730977B (en) * | 2020-12-14 | 2024-09-20 | 陕西天行健车联网信息技术有限公司 | Device and method for improving frequency measurement sensitivity |
| CN112611913B (en) * | 2020-12-24 | 2024-01-30 | 哈尔滨工业大学 | Time and frequency measuring device for teaching |
| CN115356532B (en) * | 2022-08-26 | 2024-07-09 | 北京自动化控制设备研究所 | Multi-channel frequency measuring system of microprocessor and frequency measuring method thereof |
| CN116908537B (en) * | 2023-09-13 | 2023-12-19 | 西安西电高压开关有限责任公司 | Current voltage frequency calculation circuit and method |
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| CN108333425A (en) | 2018-07-27 |
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