TDC-Time-Interval Measurement Ement Applied To Absolute Gravimeter

Absolute gravimeter is an important instrument for measuring the earth’s gravitational value.As the performance of the instrument increases and the cost decreases,the application becomes more and more extensive.Domestic and foreign related industries are competing for research.In 2012,we also developed a small-scale micro-gamma absolute gravimeter.This paper takes the time measurement of absolute gravimeter as the background,takes the time digital conversion chip as the core,and sets up a high-precision time measurement system with the single-chip microcomputer technology,and conducts test experiments and comparative experiments.The thesis first briefly introduces the development history and status quo of absolute gravimeters and related time measurement techniques.According to the basic principles of the free fall absolute gravimeter,the basic principles of several time interval measurement methods are listed,including electronic counting method,analog interpolation.Method,delay line interpolation method,vernier method and other measurement methods,analysis of its characteristics and performance indicators,according to the research objectives of this article,compared to determine the timing method more suitable for the instrument.The third chapter is a detailed introduction to the key technologies used: STM32 control core technology,SPI communication principle,and the core chip TDC7200’s function of measurement time.It mainly describes the two working modes and measurement principle of TDC7200.The fourth chapter makes a detailed analysis of the overall structure of the time measurement system,including external interface circuit design,system software design and so on.SPI communication is used between the two chips,and USB is used to communicate between the STM32 and the PC.In addition,a test platform was built for the designed time measurement system.The event counter A032 and the time interval counter SR620 were used to control the temperature,control the comparison of measured values,and analyze the experimental results.The preliminary experimental test results show that the measurement accuracy of the two measurement modes in the time measurement system measurement module reaches 80 ps and 60 ps respectively,and the standard deviation variation with temperature is within 30 ps.Repeated experimental measurements show good stability and reliability.The overall system has the characteristics of compact structure,small size,low power consumption and low cost.As a relatively independent sub-time measurement system,it is easily integrated into the overall system of the gravimeter.