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close vicinity of the analyzed object, which eliminates errors associated with the measured analog signal transmission along the wires. Now, the signal with the measurement results is digitally transmitted to the data processing unit (PC compatible computer or PIC16F874 interface) by means of the RS232C serial link. The temperature chamber is the specially adopted freezer. It has a heater and two vans installed inside, which ensure continuous air movement and minimization of temperature gradient inside. Remotely activated heater in the temperature chamber creates the danger of non-controlled temperature increase and eventually fire. This may happen when for example the controlling program hangs-up for some reason when the heater is on. An independent temperature measurement system in the chamber protects the whole system against this danger. The protection has the upper temperature limit set to the value which exceeded will reset the PIC16F874 microcontroller in the interface and set the digital outputs at PORT0, PORT1, PORT2 to the values corresponding to off state of the external devices, including the heater in the temperature chamber. 6.2. Summary The presented system automatically registers data from the complex setup consisting not only on the data measurement devices but also actuators that control the measurement conditions. The applied hardware and software are applied for testing the temperature effect of physical parameters of the tested materials as well as the performance of the electronic devices. The system has been designed for the analysis of temperature effect on the soil dielectric permittivity. The results of this research are not the subject of the above study. 51
7. TEMPERATURE PROPERTIES OF SOIL DIELECTRIC PERMITTIVITY Application of time domain reflectometry to monitor soil water content in long time periods revealed significant fluctuations of water content readings correlated with the soil temperature. The aim of the study is to determine the influence of temperature on soil bulk dielectric permittivity, ε b , measured by TDR method and indirectly on soil water content calculated from ε b . The end result is the verification of physical models describing the change of soil dielectric permittivity with temperature for soils of different type, water content and salinity. The presented models will help to interpret the influence of selected soil physical parameters on its electromagnetic properties and will improve the calibration procedure of the reflectometric soil water content meters. The measurements performed on mineral soils collected from Lublin region, Poland, by specially constructed experimental setup confirmed the temperature effect of ε b , causing the TDR soil water content measurement error. The experimental data confirm the theory of the soil dielectric permittivity, ε b , temperature effect as the result of two competing physical phenomena: ε b increases with temperature increase following the release of bound water from soil solid particles with soil temperature increase and ε b decreases with temperature increase following the temperature effect of free water molecules. However the applied four component dielectric mixing models do not fully reflect all examined soils temperature behaviour, and the temperature correcting formula based on model α does not work properly. The proposed temperature correcting formula is based on the observed temperature behaviour of ε b at a specific water content for each of the analysed soil, named equilibrium water content, θ eq . The temperature effect for this soil water content is not observed, which means that at θ eq the both competing phenomena mentioned earlier compensate each other. The equilibrium water content, θ eq , is correlated with the soil specific surface area. The temperature correcting formula, adjusting the TDR measured soil water content values of the analysed soils to the respective values at 25°C, decreases the standard deviation around the mean values about two times as compared to not corrected data. 7.1. Introduction Measurement of soil water content using time domain reflectometry (TDR) has become increasingly popular because of simplicity of operation, accurate and rapid measurement, usually there is no need for soil individual calibration, the 52
Page 2 and 3: TDR METHOD FOR THE MEASUREMENT OF W
Page 4 and 5: PREFACE The importance of water for
Page 6 and 7: CONTENTS 1. Status of water as an s
Page 8 and 9: 12.2. New prototype version of FOM/
Page 10 and 11: that stimulate the phenomena and pr
Page 12 and 13: The solution to the problem of elec
Page 14 and 15: 3. ELECTRICAL MEASUREMENTS METHODS
Page 16 and 17: v = c 1 2L = = ( θ ) n ∆t ε (2)
Page 18 and 19: The TDR probe consists of two waveg
Page 20 and 21: ε a =1 and φ=0.5 the Eq. (10) has
Page 22 and 23: The experiment description is given
Page 24 and 25: Results obtained with the discussed
Page 26 and 27: Notice that at C s = 0, ie when dis
Page 28 and 29: water orientation polarization [s],
Page 30 and 31: Fig. 8. Frequency dispersion of the
Page 32 and 33: The measurements were performed in
Page 34 and 35: 5. EVALUATION OF DIELECTRIC MIXING
Page 36 and 37: ε α = ∑V α iε i (29) i where
Page 38 and 39: where SAND and CLAY are percents of
Page 40 and 41: Below the transition value, the soi
Page 42 and 43: To verify the observations concerni
Page 44 and 45: 6. TEMPERATURE EFFECT ON SOIL DIELE
Page 46 and 47: chamber and the freezer, only one w
Page 48 and 49: The user interface on the main comp
Page 50 and 51: soil sample volumetric water conten
Page 54 and 55: process of measurement is non-destr
Page 56 and 57: dielectric permittivity change caus
Page 58 and 59: The values of the refractive index
Page 60 and 61: The relative, ∆n/∆T, and absolu
Page 62 and 63: Fig. 25. The temperature effect on
Page 64 and 65: The temperature effect of TDR soil
Page 66 and 67: The purpose of the above discussion
Page 68 and 69: ( ,25 + T )( 45 + T ) 49 9 f rel =
Page 70 and 71: 8. THE ACCURACY OF SOIL WATER CONTE
Page 72 and 73: gravimetric method and the soil ref
Page 74 and 75: where: a 0 ÷ a 6 are coefficients
Page 76 and 77: values of p F calculated for the re
Page 78 and 79: eason of this is the fact that wate
Page 80 and 81: 9 ∆θ = 0,2 ⋅10 ⋅ ∆t = 0.00
Page 82 and 83: values of θ rel for lower values o
Page 84 and 85: 9. COMPARISON OF OPEN-ENDED COAX AN
Page 86 and 87: ε" = EC ε d " + (82) 2π fε wher
Page 88 and 89: dielectric permittivity, the dielec
Page 90 and 91: The applied lumped capacitance mode
Page 92 and 93: stainless steel wires soldered to t
Page 94 and 95: ε’ Open Coax and ε b-TDR , exce
Page 96 and 97: − − The difference of the imagi
Page 98 and 99: Integrated Circuit) recently introd
Page 100 and 101: 10.2. Electromechanical microwave s
Page 102 and 103:
RF1. Two PIN diodes in series in ea
Page 104 and 105:
The significant aspect of the proto
Page 106 and 107:
visible for lower values of soil el
Page 108 and 109:
In the TDR method the signal propag
Page 110 and 111:
description of functional and techn
Page 112 and 113:
MASTER modules are wireless transce
Page 114 and 115:
time the Real Time Clock module wak
Page 116 and 117:
ase station distinguishes A SLAVE d
Page 118 and 119:
sensor, format the data received fr
Page 120 and 121:
12. SOIL WATER STATUS MONITORING DE
Page 122 and 123:
D-LOG/mpts is a moisture/pressure/t
Page 124 and 125:
For compatibility reasons it uses t
Page 126 and 127:
D-LOG/mts (Fig. 59) is a TDR (Time-
Page 128 and 129:
12.4. FP/m, FP/mts - Field Probe fo
Page 130 and 131:
inside of a separate polyethylene b
Page 132 and 133:
differential water capacity and the
Page 134 and 135:
− maximum number of LP/p probes t
Page 136 and 137:
12.7. LP/t - Laboratory Probe for s
Page 138 and 139:
From the collected data set, after
Page 140 and 141:
25. de Loor G.P.: Dielectric proper
Page 142 and 143:
TDR. Symposium on Time Domain Refle
Page 144 and 145:
100. Whalley W.R.: Considerations o
Page 146 and 147:
Fig. 14. Fig. 15. Fig. 16. Fig. 17.
Page 148 and 149:
Fig. 38. The three-rod TDR probe -
Page 150 and 151:
Fig. 67. A set of LP/ms and LP/p LO
Page 152:
Table 17. An example of the executa
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