Digitalization Mnlti-frequency Point Frequency Standard Comparison Measurement System

The frequency standard refers to the equipment which has high accuracy and single frequency sine wave signal output function,their frequency values are mostly 10MHz or 5MHz.At present,the demand for frequency standard's using is more ample than before.It mainly reflects in the field of science and technology such as geodesy,satellite navigation,post and telecommunications,high-speed railway transportation and so on.In these domains,the frequency standard stability and accuracy requirements are getting higher and higher.Therefore,it is of great practical significance to study the measurement method of frequency scale ratio and its system development.At present,the high precision frequency standard comparison measurement system usually adopts the dual mixer time difference method,which makes it difficult to avoid the technical error caused by the counter and the measurement error caused by the noise interference at the zero crossing detection.At the same time,it can't measure the frequency standard signal of multiple frequency point flexibly due to the limit of the common oscillator which has fixed frequency point.In this thesis,we put forward a digital multi-frequency frequency standard comparison system design scheme,which can which uses the frequency source of the variable frequency point instead of the common oscillator with the fixed frequency in the traditional double-mixing time difference system,which uses the frequency source of the variable frequency point instead of the common oscillator with the fixed frequency in the traditional dual mixer time difference method system.In that case,the system has the function of multi-frequency comparison measurement.And under the premise of realize the synchronous sampling through the host computer drive acquisition card,it makes the two low-frequency string signal dispersing and digitalizing.By using digital correlation method measure the phase difference to avoid the traditional dual-mixing time difference method due to use counters caused by± 1 count error.In this thesis,a variable frequency point frequency source and a sinusoidal beat-frequency device are developed.The hardware platform of the system is realized with the high precision multi-channel synchronous data acquisition card.At the same time,based on Lab windows/CVI design and development system software,realizing the real-time accurate measurement,display and save of phase difference between frequency standard to be measured and reference frequency standard.In this thesis,the system test scheme is designed and the experimental platform is designed to measure the channel delay of the system and verifier the function of the multi-frequency system and the measurement accuracy.Using the Allan variance of continuous saved data for stability analysis,it turns out that the system background noise is typically 2.81E-12/s.The resolution of the phase difference measurement system reaches psec level,the index has reached the domestic more advanced equipment level,and it has a certain technical reference significance on the frequency standard ratio measurement engineering.