CN208314071U - A kind of digital frequency meter - Google Patents
A kind of digital frequency meter Download PDFInfo
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- CN208314071U CN208314071U CN201820071345.XU CN201820071345U CN208314071U CN 208314071 U CN208314071 U CN 208314071U CN 201820071345 U CN201820071345 U CN 201820071345U CN 208314071 U CN208314071 U CN 208314071U
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Abstract
The utility model discloses a kind of digital frequency meters, single-chip microcontroller including being equipped with first timer and second timer, and display module, key module, indicating lamp module and the power module being connect respectively with single-chip microcontroller, single-chip microcontroller includes surveying all modules and frequency measurement module, is additionally provided with signal frequency split module and data selecting module, signal conditioning module and timing signal source module.The software of single-chip microcontroller insertion includes that parameter adjustment programme, frequency measurement program and LCD frequency show program.Compared with prior art, route is simple for the utility model, compact-sized, it is at low cost, stable system performance, strong antijamming capability, measurement accuracy are higher, intelligence degree is high, frequency division coefficient can be reasonably selected, be at the count value under optional frequency in more reasonable range, moreover it is possible to which the unit of display frequency is automatically adjusted, so that the display of frequency is accurate to one decimal place, can be widely applied to the measurement of the physical quantitys such as revolving speed, vibration frequency.
Description
Technical field
The utility model relates to frequency measurements, more particularly to a kind of digital frequency meter.
Background technique
Digital frequency meter is the instrument measured to frequency signal using digital circuit, be mainly used for measuring sine wave,
The frequency values of the periodic signals such as rectangular wave, triangular wave and sharp pulse.For improve measurement accuracy, measured signal frequency 10KHz with
Under, using cycle test method measurement frequency, between the two neighboring rising edge or failing edge for having carried out the measured signal of signal condition
Timing signal is counted, the frequency of measured signal is calculated further according to count value；Measured signal frequency is more than 10KHz, is used
Multi-period synchronous measuring method measurement frequency, the corresponding counter of timing signal is corresponding with measured signal under the control of signal strobe
Counter start simultaneously at and be simultaneously stopped counting, obtain two count values, further according to the two count values calculate measured signal
Frequency.Existing digital frequency meter because of manufacturing firm respectively complicated design scheme, different properties, be further improved with it is complete
It is kind.
Utility model content
Technical problem to be solved in the utility model is to make up the defect of the above-mentioned prior art, provides a kind of numerical frequency
Meter.
The technical issues of the utility model, is resolved by the following technical programs.
This digital frequency meter, including be equipped with first timer and second timer single-chip microcontroller, and respectively with it is described
Display module, key module, indicating lamp module and the power module of single-chip microcontroller connection, the single-chip microcontroller is system control core,
The display module for display counting process with as a result, the key module for function select and parameter setting, it is described
Indicating lamp module is used to indicate whether system powers on and current frequency measurement is cycle test method or Measuring Frequency Method, the power supply mould
Block is for providing 5V DC power supply and 3.3V DC power supply；
The characteristics of this digital frequency meter, is:
The single-chip microcontroller includes surveying all modules and frequency measurement module, and all modules of survey measure frequency using the method for measurement period
Rate, by one and the trapping module of door and the second timer of the universaling I/O port control single chip computer of single-chip microcontroller to measured signal one
Timing signal in a period is counted, and cycle timer number process is completed, and the frequency measurement module uses multi period testing frequency measurement rate
Method measurement frequency, determined under the signal strobe control of the universaling I/O port of the same single-chip microcontroller by first timer and second
When device counted to measured signal with timing signal respectively, the universaling I/O port respectively with the capture channel of first timer
0, the capture channel 0 of second timer is connected, and while corresponding capture channel captures signal strobe, completes to corresponding timing
The record of the count value of device completes frequency measurement counting process；
It is additionally provided with signal frequency split module and the data being connected among the signal frequency split module and single-chip microcontroller choosing
Module is selected, the signal frequency split module is used to divide the signal for being higher than upper frequency limit required by the single-chip microcontroller, institute
Data selecting module is stated to reasonably select the measured signal and timing signal of the measured signal and two divided-frequency not divided,
The square wave that is at the count value under optional frequency in more reasonable range, and will be suitble to signal frequency split module cooperation
Signal is sent into single-chip microcontroller and is counted；
It is additionally provided with the signal conditioning module being connected among measured signal and the signal frequency split module, and is connected to institute
The timing signal source module among single-chip microcontroller and the signal frequency split module is stated, the signal conditioning module is used for 0~5V's
Measured signal is converted into the square-wave signal that amplitude is 3.3V, and the timing signal source module includes timing signal data selector,
The crystal oscillating circuit of two clock signals MCLK, SMCLK selection 8MHz of single-chip microcontroller, third clock signal ACLK selection
The crystal oscillating circuit of 32.768KHz is exported by clock out pin P5.5, P5.6 of the single-chip microcontroller respectively, is surveyed as frequency
Timing signal during amount, the timing signal are generated by the signal frequency split of 8MHz or 32.768KHz, pass through modification of program
Corresponding register is realized.
The technical issues of the utility model, is resolved by technical solution further below.
The single-chip microcontroller is 16 single-chip microcontrollers of model MSP430F149, and the signal frequency upper limit that I/O mouthpiece is received is
10MHz, including 12 analog-digital converters, with capture, threshold function 2 16 digit counters and piece in comparator, it is embedding
The software entered includes that parameter adjustment programme, frequency measurement program and LCD frequency show program, and the parameter adjustment programme is in difference
The clock source and frequency division coefficient of the timing signal to match with the frequency of measured signal, the frequency measurement are selected under frequency range
By the reasonable selection of the frequency division coefficient of frequency division coefficient and timing signal to measured signal, realize makes under optional frequency program
Count value is in more reasonable range, and the LCD frequency shows program under the width that limited character is shown, by certainly
The unit of dynamic adjustment display frequency, realizes that the frequency for being accurate to one decimal place is shown.
The signal frequency split module is the two divided-frequency module for using chip as 74HC74.
The data selecting module is the data selector of model 74LS157, to the measured signal not divided and two points
The measured signal and timing signal SMCLK and ACLK signal of frequency are selected.
The signal conditioning module includes signal comparison module and signal shaping module.
The signal comparison module is the comparison module for using chip as MAX903, converts amplitude for measured signal and is
The square-wave signal of 3.3V, to adapt to the measurement amplitude range of 0.5V to 5V and the output amplitude of 3.3V.
The signal shaping module is the phase inverter with Schmidt trigger for using chip as 74HC14, to the letter
The square-wave signal that the amplitude of number comparison module output is 3.3V carries out shaping, keeps its rising edge and failing edge more precipitous.
The technical issues of the utility model, is resolved by following further technical solution.
The key module includes range key, refresh time key, for respectively to the range of measurement frequency and display
Refresh time is adjusted.
The display module includes the LCD5110 liquid crystal using three-wire system SPI interface, is made by the USART0 of the single-chip microcontroller
Its work completes the driving to LCD5110 liquid crystal in SPI mode.
The power module includes using chip for the voltage regulator circuit of LM1117, USB power supply interface, and digital signal is public
Ground is publicly linked by 0 Ω resistance with analog signal, is 3.3V by 5V power source transition, is generated 5V DC power supply and 3.3V direct current
Power supply.
The beneficial effect of the utility model compared with prior art is:
Route is simple, compact-sized, at low cost, and stable system performance, strong antijamming capability, measurement accuracy is higher, intelligence
Change degree is high, can reasonably select to frequency division coefficient, be at the count value under optional frequency in more reasonable range, also
The unit of display frequency can be automatically adjusted, so that the display of frequency is accurate to one decimal place, can be widely applied to
The measurement of the physical quantitys such as revolving speed, vibration frequency.
Detailed description of the invention
Fig. 1 is the structural block diagram of specific embodiment of the present invention；
Fig. 2 is the survey week module map of specific embodiment of the present invention；
Fig. 3 is the frequency measurement module map of specific embodiment of the present invention；
Fig. 4 is the main program flow chart of specific embodiment of the present invention；
Fig. 5 is the survey week program flow diagram of specific embodiment of the present invention；
Fig. 6 is the frequency measurement program flow diagram of specific embodiment of the present invention；
Fig. 7 is the parameter adjustment programme flow chart of specific embodiment of the present invention；
Fig. 8 is that the LCD frequency of present embodiment shows program flow diagram.
Specific embodiment
With reference to embodiment and compares attached drawing the utility model is illustrated.
A kind of digital frequency meter such as Fig. 1~8 shown in, for measuring amplitude as 0.5V~5V, frequency range 0.1Hz~
The sinusoidal signal or square-wave signal of 15MHz.
Present embodiment includes the single-chip microcontroller equipped with first timer and second timer, and respectively with single-chip microcontroller
Display module, key module, indicating lamp module and the power module (being not drawn into Fig. 1) of connection, single-chip microcontroller are system control core
The heart, display module include the Nokia LCD5110 liquid crystal using three-wire system SPI interface, make its work by the USART0 of single-chip microcontroller
In SPI mode, complete the driving to NokiaLCD5110 liquid crystal, for display counting process with as a result, key module includes
Range key, refresh time key, for the range of measurement frequency and display refresh time to be adjusted respectively, indicator light mould
Block is used to indicate whether system powers on and current frequency measurement is cycle test method or Measuring Frequency Method, and power module includes using core
Piece is voltage regulator circuit, the USB power supply interface of LM1117, and digital signal publicly passes through 0 Ω resistance and analog signal publicly
5V power source transition is 3.3V, for providing 5V DC power supply and 3.3V DC power supply by link.
Single-chip microcontroller is 16 single-chip microcontrollers of model MSP430F149, and the signal frequency upper limit that I/O mouthpiece is received is 10MHz,
Including 12 analog-digital converters, have capture, threshold function 2 16 digit counters and piece in comparator, insertion it is soft
Part includes that parameter adjustment programme, frequency measurement program and LCD frequency show program, is correspondingly provided with parameter adjustment module, frequency is surveyed
Amount module and system initialization module, parameter adjustment programme select the frequency phase with measured signal under different frequency scope
The clock source and frequency division coefficient of matched timing signal, frequency measurement program pass through frequency division coefficient and markers letter to measured signal
Number frequency division coefficient reasonable selection, realization is at the count value under optional frequency in more reasonable range, and LCD frequency is aobvious
Show program under the width that limited character is shown, by the unit of adjust automatically display frequency, after realization is accurate to decimal point
One frequency is shown.
Single-chip microcontroller includes surveying all modules and frequency measurement module, and measured signal frequency is in 10KHz hereinafter, measuring frequency using cycle test method
Rate counts timing signal between the two neighboring rising edge or failing edge for having carried out the measured signal of signal condition,
The frequency of measured signal is calculated further according to count value；Measured signal frequency is more than 10KHz, is measured using multi-period synchronous measuring method
Frequency, the corresponding counter of timing signal counter corresponding with measured signal starts simultaneously at and together under the control of signal strobe
When stop count, obtain two count values, further according to the two count values calculate measured signal frequency.
The method measurement frequency that all modules use measurement period is surveyed, by one there are four groups of identical two input terminals one to export
End with the trapping module of door 74HC08 and the second timer of the universaling I/O port control single chip computer of single-chip microcontroller to measured signal one
Timing signal in a period is counted, and cycle timer number process is completed, defeated using wherein one group two with door 74HC08 in Fig. 2
Enter to hold 1A, 1B and an output end 1Y, a universaling I/O port of input terminal 1A connection single-chip microcontroller inputs control gate signal
The universaling I/O port of period_ctrl, that is, a cycle measured signal, single-chip microcontroller is connected with second timer capture channel 1, phase
While the capture channel capture signal strobe answered, the record to the count value of corresponding second timer is completed.Fx_std is
By the timing signal after data selector, TBCLK is the counting clock input pin of second timer.
Frequency measurement module uses the method measurement frequency of multi period testing frequency measurement rate, in the universaling I/O port of the same single-chip microcontroller
Signal strobe control under counted to measured signal with timing signal respectively by first timer and second timer, it is general
I/O mouthfuls are connected with the capture channel 0 of the capture channel 0 of first timer, second timer respectively, corresponding to capture channel capture
While signal strobe, the record to the count value of corresponding timer is completed, completes frequency measurement counting process.In Fig. 3 with door
For 74HC08 using wherein two group of two input terminal 2A, 2B, 3A, 3B and output end 2Y, a 3Y, freq_ctrl is control gate signal,
Fx_std be by the timing signal after data selector, fx ' be by the measured signal after data selector, TACLK and
TBCLK is respectively the counting clock input pin of first timer and second timer.
The data selecting module for being additionally provided with signal frequency split module and being connected among signal frequency split module and single-chip microcontroller, letter
Number frequency division module is the two divided-frequency module for using chip as 74HC74, for the letter for being higher than upper frequency limit required by single-chip microcontroller
It number is divided, data selecting module is the data selector of model 74LS157, to the measured signal and two divided-frequency not divided
Measured signal and timing signal SMCLK and ACLK signal reasonably selected, be at the count value under optional frequency
In more reasonable range, and suitable square-wave signal is sent into single-chip microcontroller with the cooperation of signal frequency split module and is counted.
It is additionally provided with the signal conditioning module being connected among measured signal and signal frequency split module, and is connected to single-chip microcontroller
With the timing signal source module among signal frequency split module, signal conditioning module signal conditioning module include signal comparison module with
Signal shaping module, signal comparison module are the comparison modules for using chip as MAX903, for by the to be measured sinusoidal of 0~5V or
Square-wave signal is converted into the square-wave signal that amplitude is 3.3V, to adapt to measurement amplitude range and the output of 3.3V of 0.5V to 5V
Amplitude, signal shaping module is the phase inverter with Schmidt trigger for using chip as 74HC14, to signal comparison module
The square-wave signal that the amplitude of output is 3.3V carries out shaping, keeps its rising edge and failing edge more precipitous, timing signal source module
Including timing signal data selector, the crystal oscillating circuit of two clock signals MCLK, SMCLK selection 8MHz of single-chip microcontroller, third
The crystal oscillating circuit of a clock signal ACLK selection 32.768KHz, it is defeated by clock out pin P5.5, P5.6 of single-chip microcontroller respectively
Out, as the timing signal in frequency measuring process, timing signal is generated by the signal frequency split of 8MHz or 32.768KHz, is led to
The corresponding register of modification of program is crossed to realize.
The main program flow chart of present embodiment is as shown in figure 4, the major function of entire program is to carry out frequency
It measures and is shown, by key scan entered function interface, corresponding range, display refresh time are adjusted
It is whole.
Present embodiment is before carrying out frequency measurement, for the measured signal of different frequency, needs to letter to be measured
It number takes different frequency division coefficients to combine with timing signal, count value is made to maintain 1000~50000, to guarantee the accurate of measurement
Property.The timing signal source and frequency division coefficient surveyed under all states combine as shown in table 1, and fx ' is measured signal, and fx_std is markers letter
Number.
Table 1: all relevant parameters are surveyed
The all program flow diagrams of survey of present embodiment as shown in figure 5, using second timer capture register group 1
The number of the timing signal passed through between two neighboring failing edge to measured signal is captured, and count value is obtained: with it is to be measured
The corresponding count value temp2 of signal frequency.
The combination of timing signal source and frequency division coefficient under frequency measurement state and the opening time of gate are as shown in table 2,
Fx ' is measured signal, and fx_std is timing signal.
Table 2: frequency measurement relevant parameter
The frequency measurement program flow diagram of present embodiment is as shown in fig. 6, simultaneously by first timer and second timer
It is counted to measured signal with timing signal, and starts simultaneously at and be simultaneously stopped meter under the control of the same signal strobe
Number, obtains two count values: the temp1 of count value corresponding with measured signal frequency, corresponding with timing signal frequency
The temp2 of count value.
The parameter adjustment programme flow chart of present embodiment is as shown in Figure 7.In the case where surveying all states, count value maximum value
It is the maximum value of fx_std count value range shown in the count value i.e. table 1 under current frequency range, count value minimum value is to work as
The minimum value of fx_std count value range shown in count value, that is, table 1 under preceding frequency range.The core of parameter adjustment programme is
It determines the frequency range of measured signal, specifically carries out the count value range in obtained count value and original inquiry table
Compare and obtain, after the completion of the corresponding frequency range of determination matches, set match flag position, match flag position position shows
Reasonable count value corresponding with measured signal is obtained, is the display for carrying out frequency in next step.Frequency measurement state is then similar
Situation, what is only adjusted in the case where surveying all states is frequency range, and adjusted under frequency measurement state be gate opening time, table 1
Show to survey under all states with table 2 and be different frequency range corresponding to different count value ranges, and is different under frequency measurement state
The gate opening time correspond to different count value ranges.In view of actual conditions are there are the interference of noise, count value can go out
Count value range shown in Tables 1 and 2 is extended by now certain deviation in specific program, and maximum value increases
100, minimum value reduces 100, and anti-count value overflows range, to enhance anti-interference ability.
The LCD frequency of present embodiment shows that program flow diagram is as shown in Figure 8.In figure,
Flag: currently by character to be shown, whether there is or not display nonzero characters before, if so, being then 1；If nothing, for
0。
Tem: the current value of certain one-bit digital of the frequency obtained by operation, when calculated temp value non-zero, then
It will be shown on LCD, and flag at this time sets 1, even if showing first effective digital it has been shown that occurring temp below
The case where being 0, will also be shown on LCD.
(x, y+j): character is shown in xth row, y+j column, wherein j: the character that current frequency value is shown on LCD
Number, LCD frequency show program use j control character display position, if j be 0, illustrate that the integer part of freq1 is
0, i.e. the frequency of measured signal is less than 1Hz, needs to show one 0 integer part as measured signal in designated position.
Q: frequency range label, the corresponding unit of display are " Hz ", " KHz ", or " MHz ".
The LCD frequency of present embodiment shows that program passes through following three equatioies: temp=freq1/dec_
The cooperation of const, freq1=freq1%dec_const and dec_const=dec_const/10 can decompose freq1's
Kilobit, hundred, ten and a position are shown, after the numerical value of display frequency, then the unit of display frequency.
The measurement frequency range of present embodiment is 0.1Hz~15MHz, and span is big, takes different frequency scope
Different display modes.The frequency (including unit) that LCD5110 is shown is 8 characters (including number or letter and decimal
Point), the division of specific frequency range is as shown in table 3:
3 frequency range of table and its label
Table 3 illustrates the unit being shown on LCD5110 under the division of frequency range, current frequency range, and is used for
Show the frequency range label of not commensurate.Frequency range label only needs enquiry frequency range mark from parameter adjustment module
Number, the correct display of unit can be carried out.
Present embodiment is tested for the property using the square-wave signal of known different standard frequency, test knot
Fruit is as shown in table 4.The result shows that the measurement accuracy of the digital frequency meter of the design is higher.
Table 4: standard frequency and practical frequency Comparative result
It, cannot the above content is specific preferred embodiment further detailed description of the utility model is combined
Assert that the specific implementation of the utility model is only limited to these instructions.For the ordinary skill of the utility model technical field
For personnel, make several equivalent substitute or obvious modifications without departing from the concept of the premise utility, and performance or
Purposes is identical, all shall be regarded as belonging to the utility model scope of patent protection determined by the appended claims.
Claims (10)
1. a kind of digital frequency meter, the single-chip microcontroller including being equipped with first timer and second timer, and respectively with the list
Display module, key module, indicating lamp module and the power module of piece machine connection, the single-chip microcontroller is system control core, institute
Display module is stated for the process of display counting and as a result, the key module is used for function selection and parameter setting, the finger
Show that lamp module is used to indicate whether system powers on and current frequency measurement is cycle test method or Measuring Frequency Method, the power module
For providing 5V DC power supply and 3.3V DC power supply, it is characterised in that:
The single-chip microcontroller includes surveying all modules and frequency measurement module, the method measurement frequency surveyed all modules and use measurement period,
By one and the trapping module of door and the second timer of the universaling I/O port control single chip computer of single-chip microcontroller week to measured signal
Timing signal in phase is counted, and cycle timer number process is completed, and the frequency measurement module uses the side of multi period testing frequency measurement rate
Method measurement frequency, by first timer and second timer under the signal strobe control of the universaling I/O port of the same single-chip microcontroller
Counted to measured signal with timing signal respectively, the universaling I/O port respectively with the capture channel 0 of first timer,
The capture channel 0 of two timers is connected, and while corresponding capture channel captures signal strobe, completes to corresponding timer
The record of count value completes frequency measurement counting process；
It is additionally provided with signal frequency split module and the data being connected among the signal frequency split module and single-chip microcontroller selection mould
Block, the signal frequency split module are used to divide the signal for being higher than upper frequency limit required by the single-chip microcontroller, the number
It is reasonably selected according to measured signal and timing signal of the selecting module to the measured signal and two divided-frequency not divided, makes to appoint
Count value under meaning frequency is in more reasonable range, and the square-wave signal being suitble to signal frequency split module cooperation
Single-chip microcontroller is sent into be counted；
It is additionally provided with the signal conditioning module being connected among measured signal and the signal frequency split module, and is connected to the list
Timing signal source module among piece machine and the signal frequency split module, the signal conditioning module are used for the to be measured of 0~5V
Signal is converted into the square-wave signal that amplitude is 3.3V, and the timing signal source module includes timing signal data selector, monolithic
The crystal oscillating circuit of two clock signals MCLK, SMCLK selection 8MHz of machine, third clock signal ACLK select 32.768KHz
Crystal oscillating circuit, exported respectively by clock out pin P5.5, P5.6 of the single-chip microcontroller, as in frequency measuring process
Timing signal, the timing signal are generated by the signal frequency split of 8MHz or 32.768KHz, are deposited accordingly by modification of program
Device is realized.
2. digital frequency meter as described in claim 1, it is characterised in that:
The single-chip microcontroller is 16 single-chip microcontrollers of model MSP430F149, and the signal frequency upper limit that I/O mouthpiece is received is 10MHz,
Including 12 analog-digital converters, with capture, threshold function 2 16 digit counters and piece in comparator.
3. digital frequency meter as claimed in claim 1 or 2, it is characterised in that:
The signal frequency split module is the two divided-frequency module for using chip as 74HC74.
4. digital frequency meter as claimed in claim 3, it is characterised in that:
The data selecting module is the data selector of model 74LS157, to the measured signal and two divided-frequency not divided
Measured signal and timing signal SMCLK and ACLK signal are selected.
5. digital frequency meter as claimed in claim 3, it is characterised in that:
The signal conditioning module includes signal comparison module and signal shaping module.
6. digital frequency meter as claimed in claim 3, it is characterised in that:
The signal comparison module is the comparison module for using chip as MAX903, and converting amplitude for measured signal is 3.3V's
Square-wave signal, to adapt to the measurement amplitude range of 0.5V to 5V and the output amplitude of 3.3V.
7. digital frequency meter as claimed in claim 3, it is characterised in that:
The signal shaping module is the phase inverter with Schmidt trigger for using chip as 74HC14, to the signal ratio
The square-wave signal that amplitude compared with module output is 3.3V carries out shaping, keeps its rising edge and failing edge more precipitous.
8. digital frequency meter as described in claim 1, it is characterised in that:
The key module includes range key, refresh time key, for refreshing respectively to the range of measurement frequency and display
Time is adjusted.
9. digital frequency meter as described in claim 1, it is characterised in that:
The display module includes the LCD5110 liquid crystal using three-wire system SPI interface, makes its work by the USART0 of the single-chip microcontroller
Make to complete the driving to LCD5110 liquid crystal in SPI mode.
10. digital frequency meter as described in claim 1, it is characterised in that:
The power module includes using chip for the voltage regulator circuit of LM1117, USB power supply interface, and digital signal is publicly led to
It crosses 0 Ω resistance publicly to link with analog signal, is 3.3V by 5V power source transition, generates 5V DC power supply and 3.3V direct current
Source.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201820071345.XU CN208314071U (en) | 2018-01-16 | 2018-01-16 | A kind of digital frequency meter |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201820071345.XU CN208314071U (en) | 2018-01-16 | 2018-01-16 | A kind of digital frequency meter |
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| CN208314071U true CN208314071U (en) | 2019-01-01 |
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ID=64724825
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| CN201820071345.XU Expired - Fee Related CN208314071U (en) | 2018-01-16 | 2018-01-16 | A kind of digital frequency meter |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108333425A (en) * | 2018-01-16 | 2018-07-27 | 南昌大学 | A kind of digital frequency meter |
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2018
- 2018-01-16 CN CN201820071345.XU patent/CN208314071U/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108333425A (en) * | 2018-01-16 | 2018-07-27 | 南昌大学 | A kind of digital frequency meter |
| CN108333425B (en) * | 2018-01-16 | 2024-03-29 | 南昌大学 | Digital frequency meter |
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