To measure the number of rotations of the peristaltic pump through digital pin of the Arduino using the Hall effect sensor, two small rare earth magnets were attached to the pump rotor with opposite pole directions. The Hall effect sensor was attached to the backside of the Peristaltic pump at 5 mm distance from the magnets. The Hall effect sensor readings were calibrated in the laboratory to detect accurate cumulative volume of water correspond to each number of pump rotor rotations. The Adafruit Data-logging shield, which stacked to Arduino, enabled storing of the flow data on a micro-SD card. The information of the cumulative water flow and time was stored in real-time on a micro-SD card in standard column format.
In the designed system, the test and flow measurements continued until the steady state infiltration rate was reached. This usually happens after 1 to 2 h in most soils (Maheshwari, 1996). The system stops working whenever the infiltration rate changes are less than 10% for an interval of 30 min (Amer, 2011). This is done by comparing the maximum and minimum values of the infiltration rates recorded every second in the last 30 min of the test. The test is terminated whenever the difference is not exceeding 10%.
The Arduino code loaded to the Arduino board from computer and stored on it for later use of the system. The set-up with continuous water level sensor could be also applied to run a single ring infiltrometer with falling head method (using only the inner ring). This could be done by simply adopting the code to turn on the pump after full seepage of water and turn it off when the required height was reached.
Besides the cost effective final price of the proposed system, it has the following advantages compared to previous proposed automating systems:
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Unlike some of the proposed systems, the current system does not require using a laptop computer in the field. In the current set-up, the digital data of the water flow are stored in a real-time on a micro-SD card in standard column format and can be used later for retrieval and easy import into conventional processing and plotting software like Excel.
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The designed set-up can be used for both single ring falling head and double ring constant head DRI by simply adopting the Arduino coding for each method.
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Since we measure the flow of water that passes through the pump, unlike other methods, a single reservoir can supply the water for both inner and outer rings.
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Automated pump shut downs when no water needs to be added to the inner ring extend battery life well enough to survive for the test duration.
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Compared to the complication of adding additional water to Mariotte systems due to their requirement of being “sealed”, water can be easily added to the current system.
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As the measurements of flow are done using the Hall effect sensor attached to the pump, adding water to the reservoir does not affect the calculations. To provide continuous supply of water to both rings, water can be added to the reservoir, whenever its level drops, without a need of correcting the measurements.
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Using the Hall effect sensor and counting the number of pump rotations to measure the flow of water also has the benefit of constant measurements in different temperatures. Unlike some other methods that require precautions and calibrations for temperature or sunlight effect, measurements of this set-up is not a factor of temperature or barometric pressure.
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Using the Hall effect sensor also enables precise measurements of low infiltration values. Since any rotation of pump corresponds to specific volume of water, even small volumes can be detected and measured at high precision by the sensors.
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The system can detect when the steady state infiltration has happened. This way, the test automatically stops and concludes data recording.
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This system can easily be stored in a waterproof, ruggedized storage container. This is very desirable for remote data logging in an outdoor environment.
4. System testing and results
In order to check the accuracy of the automated system, three sets of tests were conducted at different locations with different soil materials. For comparison purposes, at each test location, a manual and an automated DRI test were performed. In each location, we ran the automated and manual tests with enough of a separation distance to avoid interference of the wet fronts. The DRI field experiments, as shown in Fig. 7, had 20 cm inner and 40 cm outer ring diameters with ring depths of 10 cm. The measured steady state infiltration rates and initial infiltration values for both methods were measured afterwards using the recorded results of the flow. The values were compared for each set of tests. These data are plotted in Table 2. The automatic test results showed no irregularity in the infiltration from the pump response. After each experiment, granulometric analyses were performed on the field soil samples according to ASTM D 422-02 (ASTM, 2007).