CN101458279B - Frequency measurement method by beat method capable of enhancing precision - Google Patents

Abstract

The invention relates to a beat method frequency measurement method capable of improving precision. The method is technically characterized by comprising the following steps: respectively inputting an actual frequency value fx of a frequency signal to be measured and a frequency fr taken as a reference frequency signal into two input terminals of a beater, solving cross-correlation of data of two interval-free sampling periods, then solving a mean of N cross-correlation function values, obtaining a decimal component value of a phase variance and a deviation value of the frequency signal to be measured, determining the deviation of the frequency signal to be measured according to the values, and obtaining the frequency value fx of the frequency signal to be measured by adding a known nominal value f of the frequency signal to be measured and a frequency deviation delta f of the frequency signal to be measured. The beat method frequency measurement method capable of improving precision can help reduce the effect of circuit noise of the beater on the frequency measurement precision and minimize cost of constructing a measurement system.

Description

A kind of frequency measurement method by beat method that can improve precision

Technical field

The present invention relates to a kind of frequency measurement method by beat method that can improve precision, relate to the precise frequency fields of measurement, particularly the method for beat method frequency measurement accuracy improvement.

Background technology

The beat method frequency measurement is one of main means of present precise frequency measurement, the main flow process of beat method frequency measurement at present is: will treat that measured frequency (fx) and reference frequency devious (fr) carry out mixing, obtain difference frequency through low-pass filter, difference frequency is a difference for the treatment of measured frequency and reference frequency, the difference frequency signal forms square wave after filtering, amplification integer, by the counter measures square wave frequency.The beat method frequency measurement is converted into low frequency measurement with high frequency measurement, and measuring accuracy has improved the beat factor doubly (ratio of frequency nominal value and difference frequency).

Because the circuit technology level, the beat circuit can produce The noise.Circuit noise relates to the choosing of components and parts, the design of circuit board level, making of circuit board etc.Owing to relate to the horizontal aspect of circuit technology, domestic technological level is not as developed countries, so same measuring method utilizes its measuring accuracy of domestic metering circuit still not reach the measuring accuracy of international metering circuit in addition.Even utilize external metering circuit, because the relative progress of the raising of circuit technology is slower, make the raising of frequency measurement accuracy also be limited, so the measurement level of precise frequency has lagged behind the precision level that atomic clock can reach at present.

Summary of the invention

The technical matters that solves

For fear of the deficiencies in the prior art part, the present invention proposes a kind of frequency measurement method by beat method that can improve precision, can reduce the influence of beat device circuit noise to frequency measurement accuracy, and reduces the cost that makes up measuring system as much as possible.

Technical scheme

Technical characterictic of the present invention is: with the actual frequency values fx of frequency signal to be measured with as the frequency f r with reference to frequency signal, import two input ends of beat device respectively, adopt following method that the signal of beat device output is handled, concrete steps are as follows:

Step 1: the signal of beat device output is sampled according to sampling rate N, obtain the sampling period that N data set forms

Wherein:

Be the initial phase of measured signal, g (n) is the random noise in the transmission course, and l (n) is equally distributed white noise, and the i value is 1～∞; The data v in first sampling period in two sampling periods intermittently will do not had _i(n) and the data v in second sampling period _I+1(n) ask simple crosscorrelation, obtain N cross correlation function $R\left(m\right)=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{v}_i\left(n\right)v_{i+1}(n+m),$ The arbitrary integer of m ∈ in the formula [0, N-1]; The value of described N is the arbitrary integer of 100K～1M;

Step 2: N cross-correlation function value averaged $C=\frac{1}{N}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}R\left(m\right),$ And the cross-correlation function value R (0) when extracting m=0;

Step 3: calculating phase changing capacity Φ=± (2 (R (0)-C)) are to obtain the decimal component value f of measured signal exemplary frequency deviation values for arccos _Dec=Φ/2 π;

Step 4: work as f _T/ 2-|f _r-f|＜1 o'clock, the amounts of frequency offset f of measured signal _Dec=Δ f; Work as f _T/ 2-|f _r-f|＞1, measured signal amounts of frequency offset Δ f=[N (2k π ± arccos (2R (1)-C)-Φ)/2 π]-f ₀Wherein said f is the nominal value of known frequency signal to be measured, f _TBe the upset of the signal waveform in each sampling period number of times, f _T/ 2 is the bigness scale value of fx and fr difference, $R\left(1\right)=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{v}_i\left(n\right)v_{i+1}(n+1);$

Step 5: known frequency signal nominal value f to be measured and measured signal amounts of frequency offset Δ f sum are the frequency values fx of frequency signal to be measured.

Beneficial effect

The frequency measurement method by beat method that can improve precision that the present invention proposes, (relation is arranged by some sampled points of analyzing each cycle of Beat Signal with sampling rate, usually each periodic sampling is o'clock more than 100) calculated rate, the measuring error of having avoided spot measurement to cause; Measuring accuracy brings up to 10 under the situation of primary circuit noise ^-7/ 10 ⁷=10 ^-14Magnitude.

Description of drawings

Fig. 1: sinusoidal wave beat device structured flowchart

Fig. 2: frequency measurement software flow pattern

Embodiment

Now in conjunction with the embodiments, accompanying drawing is further described the present invention:

The measuring system of present embodiment comprises three parts: the software of sinusoidal wave beat device, data acquisition equipment and operation measuring method of the present invention.

Sinusoidal wave beat device comprises front end circuit, phase detector, low-pass filter and amplifying circuit four parts, as accompanying drawing 1.Measuring-signal and reference signal are by front end circuit input beat device, sinusoidal wave beat device carries out mixing (realizing the mixing function by phase detector) to signal, obtain Beat Signal after the low-pass filtering, signal demand amplifies with impedance matching to be handled, and exports the Beat Signal of sinusoidal pattern then.

Data acquisition equipment mainly realized by data collecting card, and it comprises analog-to-digital conversion device and pci interface, communications portion, 6122 type data collecting cards of the pci interface of the American National instrument company (NI) that chooses.

Frequency measuring system software is the software of developing on the platform of LabWindows/CVI, and software flow as shown in Figure 2.

Be that the measured frequency for the treatment of of f=10MHz is that example is implemented this method now to measure nominal value:

With the actual frequency values fx of frequency signal to be measured with import two input ends of beat device respectively as frequency f r=9.999999MHz with reference to frequency signal, through the beat device signal is carried out obtaining Beat Signal after mixing, the low-pass filtering, signal demand amplifies with impedance matching to be handled, and exports the Beat Signal of sinusoidal pattern then; Utilize data collecting card that output signal is sampled, adopt following method that the signal of beat device output is handled then, concrete steps are as follows:

Step 1: the signal of beat device output is sampled according to sampling rate N=100KHz, obtain 10 * 10 ⁴The sampling period v that individual data set forms _i(n), 100K the data of putting in first sampling period in two sampling periods intermittently will do not had

100K the data of putting with second sampling period

Ask simple crosscorrelation, obtain 100K cross correlation function $R\left(m\right)=\frac{1}{N}\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}{v}_i\left(n\right)v_{i+1}(n+m),$ The arbitrary integer of m ∈ in the formula [0,100K-1]; The value of described N is 100K;

Wherein: Be the initial phase of measured signal, g (n) is the random noise in the transmission course, and l (n) is equally distributed white noise.These components all are eliminated in the method;

Step 2: N cross-correlation function value averaged $C=\frac{1}{N}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}R\left(m\right),$ And the cross-correlation function value R (0) when extracting m=0;

Step 3: calculating phase changing capacity Φ=± (2 (R (0)-C))=1.06193888E-5 are to obtain the decimal component value f of measured signal exemplary frequency deviation values for arccos _Dec=Φ/2 π=1.7E-6;

Step 4: work as f _T/ 2-|f _r-f|=1E-6＜＜1, the amounts of frequency offset f of measured signal _Dec=Δ f=1.7E-6;

Step 5: known frequency signal nominal value f to be measured and measured signal amounts of frequency offset Δ f sum are the frequency values fx=10MHz+1.7E-6 of frequency signal to be measured.

There is the foregoing description as can be seen, the principal feature that difference frequency is measured is that high frequency measurement is converted into low frequency measurement, with nominal value is the reference frequency mixing for the treatment of measured frequency and 9.999999MHz of 10MHz, produces the difference frequency of 1Hz, beat factor 10MHz/1Hz=10 ⁷, with resolution 10 ^-8Counter just the measuring accuracy for the treatment of measured frequency can be brought up to 10 ^-8/ 10 ⁷=10 ^-15

Though counter can reach 10 ^-8Precision, but final accuracy of measurement system can not reach 10 ^-15Precision, main cause is the influence of beat device circuit noise.The beat of beat device goes out square-wave signal, and when measuring with counter, the zero crossing flip-flop number of square wave carries out frequency measurement, since the influence of circuit noise, the restriction accuracy of measurement system.With top example is example, and according to present domestic technological level, the additional noise that beat goes out the 1Hz square wave is about 10 ^-5Even the counter measures precision reaches 10 ^-8, the measuring accuracy of last measuring system is also only 10 ^-5/ 10 ⁷=10 ^-12Magnitude.

The present invention proposes beat numerical frequency measuring method just for addressing this problem, the beat of beat device goes out sine wave, the sampling of offset of sinusoidal ripple, some points of can sampling in the one-period, utilize the frequency of a plurality of some associating estimated signal, like this, become traditional single-point and trigger to multiple spot triggers, it is effectively level and smooth to use multiple spot that circuit noise is carried out.Also be example with the previous example, the 1Hz sine wave is carried out the 10kH sampling, 10000 points of promptly sampling in the one-period are even the circuit noise of 1Hz signal is 10 ^-5, become with the level and smooth back of 10000 somes circuit noise ${10}^{-5}/\sqrt{10000}={10}^{-7},$ Measuring accuracy brings up to 10 under the situation of primary circuit noise ^-7/ 10 ⁷=10 ^-14Magnitude.Though domestic technological level lags behind developed country, use such method also can reach leading in the world measurement level.

As seen, beat numerical frequency measuring method can increase substantially measuring accuracy under current technological level condition, and measurement result computing machine easy to use shows in real time and preserve that back-end processing is more flexible.

Tradition beat measuring method and beat digital measuring method all need the beat device, both costs are suitable, but traditional beat measuring system needs a counter, the price of counter such as sr620 surpasses 30,000 Renminbi, and in the beat digital measuring method, only needing AD converter and computing machine, price can be controlled at below 10,000 yuan, as seen, the cost of the structure measuring system of beat digital measuring method is low.

Claims (1)

1. difference frequency measuring method that can improve precision, it is characterized in that with the actual frequency values fx of frequency signal to be measured with as frequency f r with reference to frequency signal, import two input ends of beat device respectively, adopt following method that the signal of beat device output is handled, concrete steps are as follows:

Step 1: the signal of beat device output is sampled according to sampling rate N, obtain the sampling period that N data set forms

Wherein:

Be the initial phase of measured signal, g (n) is the random noise in the transmission course, and l (n) is equally distributed white noise, and the i value is 1～∞; The data v in first sampling period in two sampling periods intermittently will do not had _i(n) and the data v in second sampling period _I+1(n) ask simple crosscorrelation, obtain N cross correlation function

The arbitrary integer of m ∈ in the formula [0, N-1]; The value of described N is the arbitrary integer of 100K～1M;

Step 2: N cross-correlation function value averaged

And the cross-correlation function value R (0) when extracting m=0;

Step 3: calculating phase changing capacity Φ=± (2 (R (0)-C)) are to obtain the decimal component value f of measured signal exemplary frequency deviation values for arccos _Dec=Φ/2 π;

Step 4: work as f _T/ 2-|f _r-f|＜1 o'clock, the amounts of frequency offset Δ f=f of measured signal _DecWork as f _T/ 2-|f _r-f|＞1, measured signal amounts of frequency offset Δ f=[N (2k π ± arccos (2R (1)-C)-Φ)/2 π]-f ₀Wherein said f is the nominal value of known frequency signal to be measured, f _TBe the upset of the signal waveform in each sampling period number of times, f _T/ 2 is the bigness scale value of fx and fr difference,

Step 5: known frequency signal nominal value f to be measured and measured signal amounts of frequency offset Δ f sum are the frequency values fx of frequency signal to be measured.

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