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soil sample volumetric water content and apparent electrical conductivity (Fig. 22): − propagation time of the pulse in the parallel waveguide of the measurement TDR sensor, ie the time between the points A and B, for determination of volumetric water content of the soil sample (Dalton and van Genuchten [20], Malicki and Skierucha [59]), voltage ratio V2/V1, for determination of apparent electric conductivity, EC a , the soil sample (Giese and Tiemann [33]). The interface built on the base of the microcontroller PIC16F874 [65] is the interpretation of commands from PC compatible computer (the experiment control unit) by RS232C serial interface. The interface reacts on the following commands: − setting/resetting digital outputs of PORT1 for switching on/off the sampling oscilloscope HP54121T (by a semiconductor switch), − − setting/resetting the digital output of PORT2 for switching on/off the heater in the temperature chamber (by a semiconductor switch), setting/resetting the digital output of PORT3 for switching on/off the power to the temperature chamber to stop cooling it (by a semiconductor switch), − controlling the 1-Wire interface [18] by PORT3, for the reading of temperature in the containers with soil samples in the chamber, − selection and management of the serial RS232C multiplexer channel for the communication with the chosen probe, − management of communication between the interface and PC compatible control unit, − selection of the microwave multiplexer 2.4 GHz channel. For simultaneous automatic registration of a number of probes the system uses two multiplexers. The broad bandwidth 2.4 GHz multiplexer is the proprietary construction described by Skierucha [80] and briefly presented in this publication in the point 10.4.2. It uses an integrated circuit made of GaAs technology. This switching circuit mounted on specially designed PC board proved its superior performance over other type of high frequency signals switching. RS232C multiplexer communicates among the interface and the measurement probes. It is possible to omit the PIC16F874 interface and connect a single measurement probe directly to the RS232C computer interface. Then the measurement will be performed on the connected probe. The performance of the PIC16F874 interface is transparent from the point of view of a measurement probe. 49
The 1-Wire link uses Dallas DS18B20 semiconductor temperature sensors described in [18]. The sensors can be connected in parallel to limit the cable length and number of wires in a cable. The temperature conversion lasts about 700 ms and the analog to digital converter integrated in the sensor in connection with the applied digital signal transfer protocol make the sensor a smart device. Before taking measurement from a sensor it must be addressed, ie transmit a serial number in the form of digital signals to all the sensors connected in parallel. The next command activates only the addressed sensor, the other are not operating. The additional advantage of 1-Wire temperature sensors is small power consumption, supply current of the sensor is taken from the digital communication line. The only drawback of 1-Wire system is a complicated communication protocol for completing the commands in defined time sequence, which requires the application of a dedicated microcontroller. The schematic description of the TDR probe with integrated electronic circuitry for temperature and electrical conductivity measurement in is presented in Fig. 20. The digital and analog parts are integrated in one enclosure with the TDR probe. The commands coming from PIC16F874 interface or directly form the PC compatible computer (by RS232C serial link) are decoded and executed by the embedded microcontroller PIC16F872. It controls the 1-Wire link for temperature measurement, RS232C link for serial communication with higherlevel device and 16-bit analog to digital Sigma/Delta converter [4]. The measurement of the soil electrical conductivity consists in the measurement of the voltage drop on the reference resistor R1. The magnitude of this voltage drop depends on the apparent resistance of the soil located between the steel rods of the TDR probe. The analyzed voltage drop is forced by the rectangular signal of 0.5 duty cycle and frequency 100 kHz, generated by the PIC16F872 microcontroller. Application of alternate signal, symmetrical around the ground voltage enables to avoid electrical polarization of the electrodes-soil setup, which would produce measurement errors. The probe temperature measurement is necessary for temperature correction of electrical conductivity measured values and overall temperature correction of the electronics elements in the probe. The temperature sensor is placed inside the probe enclosure (filled with epoxy resin). The experiment for testing the temperature effect on the dielectric permittivity of soil uses also other temperature sensors, placed together with the TDR probe rods in the tested soils. They are applied due to the presence of temperature gradients between soil and the TDR probe enclosure (the temperature difference between the probe and soil reaches ±1 °C. This fact caused the application of additional sensors placed directly in the tested soil samples (the sensors T0, T1, .., T7 in Fig. 19). The advantage of the presented approach of the soil electrical conductivity measurement is that the measurement is performed in 50
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 52 and 53: close vicinity of the analyzed obje
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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