Block diagram of the instrumentation and data acquisition system used for automating soil water infiltration measurements. A) Pressure sensor, B) instrumentation amplifier, C) data logger including analogue to digital converter, internal memory, interface circuitry and power supply for transferring data to D) a PC. E) Power supply circuit for the analogue electronics section. 

Block diagram of the instrumentation and data acquisition system used for automating soil water infiltration measurements. A) Pressure sensor, B) instrumentation amplifier, C) data logger including analogue to digital converter, internal memory, interface circuitry and power supply for transferring data to D) a PC. E) Power supply circuit for the analogue electronics section. 

Context in source publication

Context 1
... which in turn, depends on a number of factors such as soil content and texture (Das Gupta et al., 2006), vegetation root hardness (Rachman et al., 2004; Seobi et al., 2005), soil preparation (Park & Smucker, 2005), chemical content (Schwartz & Evett, 2003), soil temperature and weather conditions (Prunty & Bell, 2005; Chunye et al., 2003), stability and continuity of the porous system (Soracco, 2003), including macro (Mbagwu, 1995), meso (Bodinayake et al., 2004) and microporosity (Eynard et al., 2004). Amognst the methods reported for studying the hydraulic properties of soils, the infiltrometer and permeameter are probably the most commonly used devices in field (Angulo-Jaramillo et al., 2000) and laboratory tests (Johnson et al. , 2005) respectively. Other methods used for characterizing soil hydraulic properties reported are heat-pulse soil water flux density measurements (Kluitenberg, 2001), electromagnetic measurements (Dudley et al., 2003; Seyfried & Murdock, 2004), radiation-based measurements (Simpson, 2006) image analysis (Gimmi & Ursino, 2004) and multimodal instruments (Pedro Vaz et al., 2001; Schwartz & Evett, 2003) that permit measurement of several variables simultaneously. The infiltrometer is a very popular instrument among researchers (Fig. 1A), because knowledge of soil hydraulic properties is a key factor in understanding their impact on hydrological processes such as infiltration (Esteves et al., 2005) the superficial flow and aquifer recharge. Basic infiltrometers are relatively simple devices, which essentially consist of a reservoir (fitted with a graduated scale), a metallic ring (single or double) partially inserted into the soil, and a stop valve. A test is conducted by allowing the liquid to exit the container, either directly or through a pipe into the ring, measuring the rate of water infiltration while maintaining a small positive pressure on the fluid. The infiltration process consists of two main parts: the transient and steady state (Fig. 1B). The transient state occurs from the beginning of the experiment up to the time when a constant rate of water infiltration is attained. Once the soil sample is saturated with water, the constant pressure maintains a constant infiltration rate. Hydraulic conductivity can then be calculated using the entire data set (Wu1 method) (Wu & Pan, 1997) or the data corresponding to the steady state phase (Wu2 method) (Wu & Pan 1999) by measuring the slope of the resulting curve. However, recording the infiltration process data from direct, visual measurements is a highly demanding task, both, in time and economic resources; data has to be recorded in time intervals between 1 to 5 minutes in elapsed times ranging from 0.5 to 4 hours. Many authors transducers with measurement range 0-5 PSI (Omega Engineering, Stanford, CT) and a 21X Campbell data logger (Campbell Scientific, Inc.). The resulting scheme using two transducers required precise timing, but minimized the variability generated by bubbling and reduced the standard deviation from 6.2 mm (single transducer) to 2.2 mm. Prieksat et al. (1992) used the two-transducer design in a single ring infiltrometer, to register data from multiple locations simultaneously, facilitating the characterization process. Casey and Derby (2002) used a differential pressure sensor (PX26-001DV, Omega Engineering, Stanford, CT) and evaluated the device in the field, achieving 0.05 mm standard deviation. The authors noted that the improvement in resolution might not change significantly the estimation of soil hydraulic properties, but could be useful when data are processed as exponential relations methods such as Ankeny (1992) or Reynolds and Elrick, (1991). Johnson et al. (2005) constructed six laboratory variable load permeameters, using pressure sensors PX236 (Omega Engineering) and perspex tubes, to work with undisturbed samples, using a data logger programmed to record readings at regular intervals. The comparison with the manual method showed no significant differences for texture analysis. Špongrová (2006), designed, built and tested a fully automated tension infiltrometer, that included both the measurement of water level and the control of the voltages applied, using a Honeywell differential pressure transducer with range 0 to 5 PSI (0 to 34.4 kPa), connected to a Campbell 21X datalogger (Campbell Scientific Inc.) and a laptop. The results showed that the equipment reduced the monitoring time, increasing the number of test trails per day. Although there are several commercial devices, such as manual or automated tension infiltrometers they generally depend on external data logger units. One of the preferred methods for measurement the height changes of the water column involves the use of pressure transducers. Therefore, it is necessary to implement an instrumentation and data acquisition system that can be used to gather information of the infiltration process for off-line signal processing. Fig. 2 shows the classic data acquisition scheme used. The instrumentation scheme consists of a pressure transducer, a signal conditioning and amplifier stage, and a digitizing unit with data storage capabilities for transferring the measurements to a host computer. To allow some level of autonomy, and ease of use, it is necessary to use low-power, versatile analogue and digital devices. Fortunately, the advances in electronics technology over the last two decades have resulted in a number of components that can be obtained from local and international distributors to build the analogue and signal conditioning circuitry. As to the digitizing section, a number of data logger units are commercially available with impressive operating characteristics. The case study presented in this section is based on the choice of a low-cost data acquisition unit. One particular low-cost, simple-to-use device is the EL-USB-3 data logger from Lascar Electronics (Fig. 3). The first step in developing the instrumentation circuitry consists of obtaining a little over +30V from a +9V battery, because interfacing with the data logger requires that the analogue instrumentation operate with a voltage slightly over 30V. The circuit must be small and must consume very little current from the battery. Fig. 5 shows the block diagram of the power supply. Typical current consumption values for the ICL 7660 are 80 μA (ICL7660A) which makes it suitable for this and other battery powered applications. In order to maintain the high efficiency of the CMOS voltage converters it is necessary to reduce the current consumption; therefore the analogue instrumentation must also be a low-power circuit. The water reservoir is built using an 80 – 100 cm perspex pipe with rubber stoppers on each end. The pressure at the bottom, when the container is full (100 cm H 2 O @ 4 o C) is 9.806 kPa. Therefore, it is necessary to use a differential pressure transducer with 10 kPa measurement range (Fig. 8). Recalling that the MPX201DP pressure transducer is a ratiometric device, it is necessary to provide a highly-stable voltage reference signal to achieve correct operation, regardless of voltage and temperature variations. It is common to find circuits that suggest the use of the voltage supply line to power up the pressure transducer (Fig. 9A). Unless the pressure transducer includes an internal voltage reference supply (i. e. it is a voltage compensated device), it is necessary to use a dedicated voltage reference circuit. (Fig. 9B). In terms of temperature variations, voltage reference circuits are specified in ppm/ o C (parts per million per degree centigrade). Consider a reference circuit specified to change at a rate of 100ppm/ o C. If the circuit output value is 10V @ 20 o C, exposing the integrated circuit to a 50 o C would change the output from 10V to 10.03 Volts ensuring the correct operation of the transducer. Some devices may also be specified to 10ppm/ o C increasing the stability of the overall instrumentation circuit. Instrumentation amplifiers are a type of differential amplifier with high input impedance and adjustable gain that constitute essential building blocks in analogue electronics. One of the classical configurations of instrumentation amplifiers uses three operational amplifiers to form a two-stage amplifying circuit (Figure ...

Citations

... van Genuchten (1980); Durner (1994); Durner and Flühler (2006)). Hydraulic conductivity can be considered as an indispensable parameter for soil characterization, simulation of water and mass transport in vadose and saturated zone, management of soil organic matter and sustainable development of regional water resources (Gutierrez Gnecchi et al., 2011). ...
... Empirical methods based on systematic data collection are used as to correlate K s with soil properties like particle size, soil texture, pore size and relative effective porosity (Gootman et al., 2020;Gupta et al., 2020;Huang et al., 2019;Hwang et al., 2017;Picciafuoco et al., 2019;Vereecken et al., 2010Vereecken et al., , 1992Wösten et al., 1999). Experimental methods are distinguished in laboratory and field methods (Durner and Flühler, 2006;Gutierrez Gnecchi et al., 2011;Morbidelli et al., 2017). However, the adequacy and cost-effectiveness of these methods can often be a limiting factor in soil-water modeling applications. ...
... However, the adequacy and cost-effectiveness of these methods can often be a limiting factor in soil-water modeling applications. In this concept, although the number of methods and apparatuses used is quite large, it is still a need to elaborate new methodological approaches and instrumentation technologies to enhance the quality and quantity of reliable information and to provide alternative options to address the uncertainty of hydraulic parameters estimations (Gamie and De Smedt, 2018;Gutierrez Gnecchi et al., 2011;Zhang et al., 2007). A physical analogue for soil water movement can be modelled with the Hele-Shaw (Hele-Shaw, 1898) apparatus. ...
Article
The estimation of saturated hydraulic conductivity is a key parameter for studying the water flow in the unsaturated zone of the soil. In this work, a combined modelling approach of the waterfront movement is elaborated, integrating a physical analogue type device with image analysis. A customized Hele-Shaw apparatus is designed for the wetting process visual inspection, while an optical flow algorithm is used for the numerical calculation of flow velocity and saturated hydraulic conductivity values at a pixel level of the image processing. Saturated hydraulic conductivity values estimated by the proposed method are in close agreement with values found in the literature under similar soil conditions. Also, the proposed method seems to be a useful tool for a comprehensive analysis of the waterfront movement in the vadose zone.
Article
Permeability is a vital parameter for the design and construction of structures involving ocean engineering. Based on the steady-state heat transfer theory and Darcy's law, a novel in-situ test method for permeability in saturated sandy porous media is introduced in this work. This approach aims to obtain permeability through the inversion of the measured temperatures. Temperatures measuring device with a constant heater was installed in an insulating experimental tank filled with sandy sediments of different permeability. Further, a numerical model based on the Finite Element method was simulated to validate the feasibility of the proposed method and accuracy of the experimental data. Besides, the results obtained by the constant head test were compared with those calculated by the novel in-situ test method, considering different surface temperatures of the heater and different sediments’ permeability. It shows that the permeability obtained by in-situ method are reliable and accurate (the accuracy is within one order of magnitude) in both numerical simulations and experimental tests. The effects of different surface temperatures of the heater and permeability of porous media on permeability calculation results were also discussed. The surface temperature was found that has little influence on permeability. And the proposed method is applicable when the permeability is higher than 10⁻¹² m². The findings can provide some reference to the in-situ measurement of submarine sediments' permeability.