Development Of TDR Device For Large Deformation Distributed Measurement Using Helical Sensing Cable

Geological disaster has always been an important part of national natural disaster prevention and control,and landslide disaster is a serious category in geological disaster.Therefore,it is very important to carry out monitoring and early warning for landslide disaster.While most of the domestic monitoring and scientific research of landslides use imported instruments,such as Tek-Tronix’s characteristic impedance tester DSA8300.At the same time,when using imported equipment,it is sometimes necessary to purchase additional supporting modules,which are expensive.So these imported equipment can only be used in large landslide monitoring and research,but in small and medium-sized landslides cannot be widely used.This paper aims at the monitoring of surface and underground deformation in landslide monitoring,a device for large deformation distributed measurement is developed by combining helical sensing cable and time domain reflection technique.The main research contents are as follows:(1)Several main methods of deformation monitoring and early warning are studied,and their respective characteristics are analyzed,while the helical sensing cable used in this subject can be bent and stretched to a large extent,so it has some advantages in the field of distributed measurement.(2)The measurement principle of this subject mainly lies in the conversion of tensile quantity,characteristic impedance and reflection voltage on the helical sensing cable.By combining with the TDR technology,the position of the stretching point of the helical sensing cable and the magnitude of the reflection voltage can be measured,realizing the distributed measurement of large deformation.(3)The part of the hardware circuit mainly includes narrow pulse generation circuit,echo conditioning circuit(amplitude limiting circuit and transistor amplifier circuit),ADC circuit(three ADC chips configuration circuit design),power module and communication module.(4)Design of high-speed sampling module based on FPGA,first verify the feasibility of the sequential equivalent sampling scheme,then carry out the actual sampling,at the same time,realize the buffer and storage of the sampling data,and upload the data through the serial port.(5)Design of waveform display based on Lab VIEW’s serial port data.(6)The stretching experiment of helical sensing cable is carried out on the stretching platform,and the sampled experimental data are analyzed and processed.The design of the pulse source and echo conditioning circuit for the TDR device in this paper enables a clearer observation of the change of the reflected wave.At the same time,it verifies the feasibility of the sequential equivalent sampling scheme and realizes the cross-clock domain reading and writing of the data.These lay a foundation for further optimization and the formation of a perfect large deformation distributed measurement system.