CN101216444A - Multi-point automatic monitoring device for soil pore water conductivity - Google Patents

Abstract

The invention discloses a multi-point automatic monitoring device for soil pore water conductivity. n sensors with the same structure are respectively connected to the coaxial multiplexer through the coaxial cable through the BNC connector, the coaxial multiplexer is excited by electromagnetic waves, and the receiver is connected to the PC; each of the sensors includes a coaxial cable Conductor, inner conductor of coaxial cable, epoxy resin box, first test probe, second test probe and third test probe; second test probe is connected with coaxial cable inner conductor; first test probe, The third test probes are equidistantly distributed on both sides of the second test probes, the first test probes and the third test probes are connected to the outer conductor of the coaxial cable, and the connection points are placed in the epoxy resin box. The PC software is used to monitor the pore water conductivity EC _ω in the soil to measure the pollution degree of the soil, especially for long-term monitoring under high corrosion conditions in sanitary landfills. It is fast, convenient and highly automated, and can be remotely controlled and monitored at multiple points for a long time.

Description

Multi-point automatic monitoring device for soil pore water conductivity

technical field

The invention relates to a detection device utilizing electromagnetic wave reflection, in particular to a multi-point automatic monitoring device for soil pore water conductivity.

Background technique

At present, in terms of pollution prevention and control measures, people pay more attention to technical measures such as engineering restoration, biological restoration, physical and chemical restoration, electrokinetic restoration, etc., and do not pay enough attention to the monitoring of soil pollution. Most of the soil pollution testing methods in engineering are indoor. Testing and pollution monitoring instruments are limited to complex testing instruments (HP network analyzers, HP impedance analyzers) used in indoor tests. The disadvantages are 1: it is difficult to prepare samples and require long-term indoor experiments; 2. It is impossible to conduct on-site testing. real-time monitoring.

In addition, the current soil pollution tester can measure the content of heavy metal ions in the soil on site, but it cannot realize multi-point testing and long-term monitoring on the test site.

Contents of the invention

The purpose of the present invention is to provide a multi-point automatic monitoring device for soil pore water conductivity, which can measure the pollution degree of the soil body by monitoring the pore water conductivity EC _ω in the soil body.

The technical scheme that the present invention adopts is as follows:

In the present invention, n sensors with the same structure are respectively connected to the coaxial multiplexer through the coaxial cable through the BNC connector, and the coaxial multiplexer is excited by electromagnetic waves, and the receiver is connected to the PC; each of the sensors includes the same Coaxial cable outer conductor, coaxial cable inner conductor, epoxy resin box, first test probe, second test probe and third test probe; second test probe is connected with coaxial cable inner conductor; first test Probes, the third test probes are equidistantly distributed on both sides of the second test probe, the first test probe and the third test probe are connected to the outer conductor of the coaxial cable, and the connection points are placed in the epoxy resin box middle.

The beneficial effects that the present invention has are:

The pollution degree of the soil can be measured by monitoring the pore water conductivity EC _ω in the soil. It can realize the rapid test of the EC _ω of the pore water conductivity in the soil and the multi-point remote monitoring and long-term monitoring of the pore water conductivity of the soil, especially the long-term monitoring under the high corrosion condition of the sanitary landfill.

Description of drawings

Figure 1 is a schematic diagram of the field test device.

Figure 2 is a schematic diagram of the structure of the self-made three-needle probe.

Fig. 3 is a graph of conductivity and permittivity tested by TDR method.

Figure 4 is a calibration diagram of soil parameters.

In the figure: 1PC, 2. Electromagnetic wave excitation receiver, 3. Coaxial multiplexer, 4. Coaxial cable, 5. Sensor, 5.1. Coaxial cable outer conductor, 5.2. Coaxial cable inner conductor, 5.3. Ring Oxygen resin box, 5.4 Test probe A, the first reflection point of the sensor in the TDR waveform B, the second reflection point of the sensor in the TDR waveform

Detailed ways

As shown in Fig. 1 and Fig. 2, in the soil pore water conductivity multi-point automatic monitoring device of the present invention, n sensors 5 with the same structure are respectively connected with the coaxial multiplexer 3 through the coaxial cable 4 by the BNC joint, and the same The multiplexer 3 is excited by electromagnetic waves, and the receiver 2 is connected to the PC 1; each sensor 5 includes a coaxial cable outer conductor 5.1, a coaxial cable inner conductor 5.2, an epoxy resin box 5.3, a first test probe Needle 5.4, the second test probe 5.5 and the third test probe 5.6; the second test probe 5.5 is connected to the inner conductor 5.2 of the coaxial cable; the first test probe 5.4 and the third test probe 5.6 are equidistantly distributed on the On both sides of the second test probe 5.5, the first test probe 5.4 and the third test probe 5.6 are connected to the outer conductor 5.2 of the coaxial cable, and the connection points are placed in the epoxy resin box 5.3.

The distance between the first test probe 5.4, the third test probe 5.6 and the second test probe 5.5 is 25-30 mm.

The first test probe 5.4, the second test probe 5.5 and the third test probe 5.6 should have the same diameter, which is 8-10mm, and the 10mm sections at the lower ends of the test probes are all conical.

The number of sensors 5 with the same n structure is n≤512.

The electromagnetic wave excitation, receiver 2, and coaxial multiplexer 3 are all products TDR100 of Campbell Scientific in the United States.

The coaxial cable 3 is a coaxial cable of model RG58A/U.

Working process of the present invention is as follows:

During the on-site test, run the TDR100 test software on the PC, set the test starting point and collection frequency, and start collecting test waveforms. For each test waveform, the apparent conductivity of the soil EC _a = 1/M(2V _s /V _f -1), where V _s is the voltage value at the beginning of the test waveform, and V _f is the voltage at the stable point of the test waveform Relative voltage values, as shown in Figure 3. M is the probe constant, which is obtained through calibration in the laboratory. The calibration method is: at room temperature of 25 degrees, use this probe to test the TDR waveform of the solution with known conductivity to obtain the values of V _s and V _f , and then reversely calculate the value of the probe constant M from the above formula.

At the same time, the dielectric constant of the soil between the probes can also be obtained: K _a = (v×t/2L _p ) ² , where t is the propagation time obtained from the test waveform, which is the first reflection point of the sensor in the TDR waveform and The distance between the second reflection points (as shown in Figure 3). V is the speed of light propagating in vacuum, and L _p is the length of the probe test section, which is obtained by indoor calibration. The calibration method is: at room temperature of 25 degrees, use this probe to test the TDR waveform of deionized water with known dielectric constant, get the t value from the test waveform, and then calculate the probe constant K _a value from the above formula.

Then the pore water conductivity EC _ω of the soil is:

${\mathrm{<span\; class="notranslate">\; EC</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; EC</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; bg</span>}<span\; class="notranslate">\; )</span>\sqrt{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; b\; f</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; ad</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; cd</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; m</span>}}}$

In the formula, K _a is the dielectric constant of the soil, and EC _a is the electrical conductivity of the soil, calculated from the above TDR test waveform. ω is the water content of the soil, ρ _w is the density of water, ρ _d is the dry density of the soil, and d _s is the particle specific gravity of the soil, which are obtained from indoor experiments according to the properties of the soil on site.

的线性拟合的斜率与截距，如图4(a)所示、c、d为曲线

的线性拟合的斜率与截距，如图4(b)所示，f和g为曲线

的线性拟合的斜率与截距，如图4(c)所示。它们与现场土体的电学性质有关，由室内标定得到，标定方法如下：a and b are curves

The slope and intercept of the linear fitting of , as shown in Figure 4(a), c and d are the curves

The slope and intercept of the linear fit, as shown in Figure 4(b), f and g are curves

The slope and intercept of the linear fit of , as shown in Figure 4(c). They are related to the electrical properties of the soil on site, and are obtained by indoor calibration. The calibration method is as follows:

、

和

图，如图4所示。对图中的数据进行线性拟合，线性拟合的斜率和截距分布是土体参数a、b、c、d、f、g。Take some undisturbed soil that needs to be tested, take an appropriate amount of soil sample and add a certain amount of deionized water to prepare a uniform sample with a certain density, then record the volume and mass of the sample, and test its dielectric strength with a TDR tester Constant and conductivity, test its water content by drying method. plot the test results as

,

and

Figure, as shown in Figure 4. Perform a linear fit to the data in the figure, and the slope and intercept distributions of the linear fit are the soil parameters a, b, c, d, f, g.

Claims (6)

1. soil pore water conductivity multi-point automatic monitoring apparatus, it is characterized in that: n the identical sensor (5) of structure is connected with coaxial Port Multiplier (3) by BNC connector through concentric cable (4) respectively, and coaxial Port Multiplier (3) is connected with PC (1) through electromagnetic wave excites, receptacle (2); Described each sensor (5) comprises coaxial cable outer conductor (5.1), inner conductor (5.2), epoxy resin box (5.3), first test probe (5.4), second test probe (5.5) and the 3rd test probe (5.6); Second test probe (5.5) links to each other with inner conductor (5.2); First test probe (5.4), the 3rd test probe (5.6) is equally distributed on the both sides of second test probe (5.5), first test probe (5.4), the 3rd test probe (5.6) all link to each other with coaxial cable outer conductor (5.2), and tie point all places epoxy resin box (5.3).

2. a kind of soil pore water conductivity multi-point automatic monitoring apparatus according to claim 1 is characterized in that: described first test probe (5.4), the 3rd test probe (5.6) are 25～30mm with second test probe (5.5) standoff distance.

3. a kind of soil pore water conductivity multi-point automatic monitoring apparatus according to claim 1, it is characterized in that: described first test probe (5.4), second test probe (5.5) should be identical with the 3rd test probe (5.6) diameter, be 8-10mm, test probe lower end 10mm section is coniform.

4. a kind of soil pore water conductivity multi-point automatic monitoring apparatus according to claim 1 is characterized in that: the identical sensor (5) of described n structure is n≤512.

5. a kind of soil pore water conductivity multi-point automatic monitoring apparatus according to claim 1 is characterized in that: described electromagnetic wave excites, receptacle (2), coaxial Port Multiplier (3) are the product TDR100 of U.S. CampbellScientific company.

6. a kind of soil pore water conductivity multi-point automatic monitoring apparatus according to claim 1 is characterized in that: described concentric cable (3) is the concentric cable of model RG58A/U.

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