A TDR system and method suitable for extended high-saline soil moisture measurement

Abstract

The invention discloses time domain reflectometry (TDR) system and method applicable to expanded high saline soil moisture measurement. The system comprises a stainless steel probe, an organic glass packaging box, a PIN diode, a glue packaging box, a coaxial cable, a TDR tester, a first capacitor, a second capacitor, a third capacitor, a first resistor and a second resistor. The method comprises the following steps: judging whether the length of the coaxial cable exceeds the set value according to the propagation time of an electromagnetic wave in the coaxial cable, if not, carrying out weight calculation of considering conductance on the result by adopting a surface-reflexion method and a travel time method at the same time; if so, automatically controlling the diode circuit through a program; respectively obtaining an original waveform under a shutdown condition and a waveform under a channel condition; respectively adopting the surface-reflexion method and the waveform difference travel time method; finally outputting medium moisture content after weight calculation considering the coaxial cable length. By adopting the system and the method, the accuracy of a moisture salinity test of the high saline soil can be ensured, and a TDR probe can be expanded, so that more points can be simultaneously monitored.

Description

technical field [0001] The invention belongs to the field of soil physical characteristic monitoring, and relates to a system and method for measuring moisture in high-saline soil suitable for expansion, in particular to a system for automatically measuring moisture in high-saline soil by using a TDR (Time Domain Reflectometer) system It is mainly used in agriculture, forestry, geotechnical engineering and related fields that are closely related to soil and require continuous and accurate understanding of soil water and salt conditions. Background technique [0002] TDR (Time Domain Reflectometry, Time Domain Reflectometry) was first applied to cable fault detection. Canadian scientist Topp first realized the application of TDR to soil moisture measurement in 1980. After decades of development, TDR system measurement has become a A fast, accurate and safe on-site testing method, and can realize automatic monitoring. Although the TDR water content test method has been widely...

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Problems solved by technology

For the center coating method, the coating or heat-shrinkable sleeve is easy to wear or peel off during the repeated insertion and insertion of the probe, and the information of the conductivity of the medium cannot be obtained from the reflected waveform

The probe end short-circuit method needs to install a short-circuit device between the ends of the probes, so that the probes cannot be pulled out. When the value is high, it will cause a large test error due to the limited difference of the reflected waveform before and after the short circuit

For the surface reflection method, the key lies in the calculation of the reflection coefficient between the air section and the surface of the medium, but when the length of the coaxial cable connecting the probe is too long, most of the electromagnetic wave has been attenuated before reaching the air section, so the test reflection coefficient is relatively low. Disaster

At present, the coaxial cables of TDR probes are relatively short, no more than 15m, but this greatly limits our use, especially when we need to detect multiple points at the same time, the use of multi-layer expansion boards will increase the length of the coaxial cable. thus affecting the test results

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