Design And Implementation Of High Precision Time Interval Calibration System

As one of seven international standard physical quantities,time is one of the key parameters in measure calibration.The high-precision measurement of time interval has significance in scientific research and national defense.It is a rigid index in many fields such as radar detection,Atomic Physics,precision measuring instrument and so on.With the improvement of modern technology,the precision of time interval measurement has been required higher and higher.Now there are large amounts of researches in time interval measurement and calibration at home and abroad.How to calibrate time interval measurement has become a scientific and key problem to be solved.Based on the national metrological verification regulation of time interval,we designed a high-precision and high-stability method to measure time interval using different length of wires in this article.This method is based on the principle of sine wave signal phase measurement.Because of the character of electric signal which has a stable transmission delay in the wire,we can delay the transmission time of proceed signal of sine signal which can be output by PLL and transmitted in wires.Using ADC with two channels,we can take samples of delayed signal and the other signal that isn't delayed by the wire at the same time.the data acquired is sent to SRAM cache,then it can be read by FPGA and be transmitted by USB controlling chip.As the data stream,the data is sent to the PC.Analysing the data acquired using Maximum likelihood estimation algorithm,we can get the delayed transmission time of signal in the wire.With measuring the delayed transmission time in different length of wires many times,errors can be eliminated by the way that one minus another.Then we can get high-precision and stable Electric pulse string on time interval through data analysis.In the average of 20ns,repetitiveness of Electric pulse string is better than that in 6ps,and uncertainty of measurement is better than that in 30ps.It provides technical basis for high-precision measurement calibration of time interval.In this article we introduce many details of hardware and software of different wires.First of all,we prove the feasibility of design in theory,analyse all factors which influence the system comprehensively,and put forward the relevant improved step.Secondly,through the repeatability tests of the system,we calibrate the specified performance index of time interval measuring instrument that we made:resolution of measurement is better than lps,uncertainty of measurement is better than that in 30ps,and it can trace to source efficiently.Besides,the system has characters of working stability,easy structure,high precision and high stability.What's more,test indicators have reached the leading domestic level,and it can provide calibration for other precision instrument s that measure time interval.