Mar Joseph E. Edjan, Member, IEEEAbstract— Soils moisture content that are determined by traditional convection oven or microwave oven method.
The aim of this study is to apply automation in microwave oven drying method. Traditional convection method was considered to produce the right moisture content but for longer duration and using microwave oven with rapid duration but the method is still done manually. By applying automation, it will simplify the complexity of the procedure, accelerates the time duration of the process, measurement of moisture content based on initial and final weights will be automated, and power usage will be reduced and controlled. In addition, graphical data and other information will be displayed on the screen connected to the single board computer. A comparison of power consumption between the traditional convection oven and the microwave drying oven will be monitored during the testing procedure. Also, different types of soils of the same location will be used as test samples.
Index Terms—Force Sensors, Infrared Sensors, Microwave Ovens, Microcontrollers, Single Board Computer, Soil Moisture. I. INTRODUCTIONA. Background of the Study Soil testing is an important tool in developing efficient and suitable soil for the construction site. A soil test provides basic information on the composition of the soil and its ability to support a structure; as well as the absorption and drainage rate of the soil. Thus, a proper investigation prior to construction is highly recommended. One of the investigations to be made is to determine the properties of the soil to be able to have a safe and economic design to avoid any difficulties prior and during the construction. 1The properties of the soil which to be identified are clay, loam, and sandy.
Through the aide of the process known as oven drying method, the properties such as the moisture content of the soil can be determined. 2 Oven drying method is a method wherein sample soil is placed in a container then into the oven. The oven is turned on and in a few minutes or an estimated hour; the soil sample is removed and measure its weight, then reheat the soil sample again for few minutes.
If the weight of soil is almost constant, the test is done and the moisture content is now calculated based on its initial and final weight. However, doing this manually has a disadvantage like manual test cannot be simple in storing the data. Recording and storing data and results such as temperature, weight and moisture content are quite difficult when dealing with manual oven drying. Also, the use of power is inefficient due to reheating processes. Thus, adding some improvements that help the user should be implemented to compensate some shortcomings of the manual process. Graphical views of moisture and weight changes in the soil are done manually; plotting the numerical values of moisture before and after drying process with respect to its temperature.
This manual process takes time and not accurate because temperature changes when the soils under test are removed from the oven to be measured. B. Statement of the ProblemThe study aims to automate the drying process. Instead of using a conventional or industrial oven, a common household microwave oven will be modified to minimize the cost of constructing the device.
Adding temperature sensor, moisture content sensor and weight sensor will make a difference with a microwave oven for soil testing. By interfacing the sensors with a low-powered single board computer, graphical view of the process can be displayed on an external monitor.If the weight and/or soil moisture of the soil is almost constant, the oven will shut off as per controlled by the single board computer.Also, the power consumption will be monitored and controlled to minimize the use of excessive and unnecessary power usage or loses. C.
Significance of the Study This study will benefit the end users such as students in engineering courses for laboratory activities related to soil drying test; engineers in the construction industries for soil investigation prior to construction; and as general usage to help them simplify and automate the tasks in soil drying and testing, and also for the future researchers to develop the concept of automation with the applications of single board computer.D. Scope and Limitationsa. The system is limited only for monitoring the temperature, weight and moisture content of the soil.b. The system controls the on/off of the microwave system.c.
The test will be limited to one sample per test.d. The test would also be limited to the volume of the sample under test.E. Objectives of the Study The purpose of the study is to develop an automated soil drying oven to determine the temperature, weight and moisture content of the soil.
a. To design a system that monitors the temperature and weight of the soil sample inside the microwave oven.b. To develop hardware that automatically turns on/off the microwave oven system.c.
To interface the sensors to a single board computer.d. To display the data and results on an external display.
e. To construct a working prototype.f. To test the reliability and power consumption of the prototype.F. Novelty of WorksExisting works related to microwave soil drying oven are using manual technique in measuring the moisture content of the samples, hence, the data are manually recorded. The proposed study includes automation of measuring moisture content, records and displays a graphical data of the process.II.
REVIEW OF RELATED LITERATUREThe following articles and researches that are related in the study will be discussed in this chapter.Microwaves were used as early as 1939 during the Second World War to detect Nazi aircrafts. A chocolate bar in the pocket of a military officer melted when working near microwave radar and hence recognised the heating effect of microwaves.
The production of microwaves for domestic use by means of a magnetron was invented by a Japanese, Keishi Ogura in the early 1960s. Since then, the use of microwave ovens for heating purposes has become increasingly popular.3One research established that for most soils, the microwave oven drying method gives a precise result to within 0.4% moisture content4. However, the method is unfitting for soil containing gypsum or for materials with high carbon content. Further study used two different processes to dry soil samples. It was found that the two procedures yielded different moisture content values and required drying time increased with sample size and initial moisture content5.
Another study on soil drying by microwave oven method was introduced and noticed that soil with higher moisture content required longer microwave drying time6.One of the major concerns using this method is about the overheating problem of soil samples by microwave oven drying method and therefore developed some methods. The conclusion from the test results that the microwave oven drying method using the modified processes should be acceptable in soil quality control, mainly when the microwave oven results were adjusted against values obtained by use of conventional oven method.7 The standard drying time for the soil using traditional convection oven is around 20 to 24 hours with temperatures between 45oC to 105 oC depending on the type of soil under test is required. Hence, rapid but accurate measurement of moisture content is essential. 8A method is conducted by which exposing the soil samples inside the microwave oven in a rapid manner to determine the proper duration for soil drying, the result shows lower power consumption. But the process is done manually. 9The proposed study aims to provide automation in the process with rapid drying methods to be applied while maintaining low power consumptions than conventional ovens or air drying ovens.
Difference in moisture content = microwave oven result – convection oven result (i.e. the value shown is the actual difference in moisture content values between microwave oven and convection oven methods). The figure shown in parentheses is the normalized difference determined by the following equation:(m.c. from microwave oven – m.
c. from convection oven / m.c. from convection oven) x 100% (1) III. METHODOLOGY The design methodology will be discussing about oven drying process, sensors, data acquisition system, software overview, hardware overview, and test plan.A.
Conventional oven drying process This process is used to determine the water content of a soil by drying a sample to constant mass at a specified temperature. The water content of a given soil is defined as the ratio, expressed as percentage, of the mass of pure water to the mass of the solid material (or solids). The apparatus used in the in this test are weight device, drying device and container specifically a pan.Fig. 1. Block diagram of test procedure. Figure 1 shows the test procedures are as follows:a. Prepare the sample, particularly the soil to be tested.
b. Determine the mass of the test sample and record the mass as “wet mass”.c. Dry to constant temperature at about 110 +- 5 oC.d.
Remove the sample from the drying device, cool to room temperature.e. Determine the mass of the test sample and record this as “dry mass”.f. Determine the moisture content of the test sample as follows: Mass of water in sample = wet mass – dry mass (2) Percent moisture = (mass of water / Dry mass sample) x 100% (3) The drying rate of test samples will be affected by the moisture conditions and number of samples in the drying device. When wet samples are placed in the drying device with nearly dry samples, completion of the drying may be started.
10 The conventional oven drying process will be the guide for establishing an automated microwave oven drying method.B. Main ComponentsMicrowave Oven A common household microwave oven with approximate maximum power of 600W with voltage requirement of 220v AC at 60Hz will be used in this study.
Sensors A sensor is a device that produces a measureable response to a change in physical condition, such as temperature or to a change in chemical concentration. 11 For the automated oven drying method the sensors that are useful are temperature sensors, and a load cell.Temperature sensors Temperature sensors are devices that open and close a switch in response to changes in the temperature.
Might be a metal contact, or a thermocouple that generates minute electrical current proportional to the differences in heat, or a variable resistor whose value changes in response to changes in temperature and is also known as heat sensor. 12 For automated microwave oven drying method, an infrared sensor will be used to measure the temperature since exposure of metal inside a microwave oven may damage the microwave oven itself. Load Cell Load Cell uses strain gauges connected to a Wheatstone bridge circuit. The output of the bridge circuit is voltage that is proportional to the force on the load cell.
13 Load cells are force transducers that converts force or weight into electrical signal and is used in electronic weighing systems. For this study, the load cell to be used has a maximum capacity of 5Kg.C. Data Acquisition System Today, SBCs can be grouped into two main categories– proprietary and open source. Proprietary SBCs are generally designed for use in end applications or as a reference to be evaluated. They are often industrialized designs that have gone through the same type of testing that an end product requires and are often integrated into end product designs or installed in a rack mount configuration.
Open source SBCs on the other hand offer users access to both the hardware design and layout as well as access to the source code used on the board. This is ideal for all users as they can easily understand how the software and hardware operates and adopt the design to meet their end designs requirements or simply learn how a piece of hardware or software works. 14 Current SBCs come with a wide variety of processor types, most with GPUs on-board. These processors range from X86 based processors from the traditional PC space (AMD and Intel) to ARM processors which have traditionally been used in the industrial and more recently mobile spaces.
The most prevalent form of software used on SBCs is Linux with numerous derivations including Android, Ubuntu, Fedora, Debian and Arch Linux as well as FreeBSD and Windows CE. 14 SBC based system follows the typical data acquisition system starting with the sensor, signal conditioning, ADC, SBC, DAC, Control circuit, actuator, and load. 15 The Raspberry Pi 3 model B, the latest model of the raspberry pi single board computers, is a low power device that can be supplied with a 5v DC voltage and 1.5A current power supply. It can be interfaced with other device via IO, pwm, analog, SPI, UART and USB ports. Display and audio can be interfaced via HDMI ports and 3.
5mm audio jack. Wireless connectivity to this device is also possible with its built-in Bluetooth and WiFi module. The single board computer is powered by Broadcom BCM2387 ARM Cortex-A53 Quad Core Processor running at 1.2GHz with 1GB RAM so you can now run bigger and more powerful applications.Fig. 2. Block diagram of typical data acquisition system Sensors are devices used to sense and convert physical properties to electrical properties which have been discussed also in the previous part. Signal conditioning circuit is basically an operational amplifiers and bridge circuit.
Operational amplifier is a very high gain differential amplifier with high input impedance and low output impedance. 16 Bridge circuit is a circuit in which load is connected between two levels of potentials and are instruments for making comparison measurement in which resistance, inductance, capacitance and impedance can be measured.16 Analog to digital converter (ADC) accepts analog information and converts it to a digital information which can be done in three ways: digital ramp, successive approximation ADC and flash ADC.
16 Single board computer has its own microprocessor. Microprocessors are electronic devices used to implement direct digital control in the process using buses that consists of the data, address and control lines. 14 Digital to analog converter (DAC) is basically an R-2R ladder; it accepts digital information and transforms it into analog voltage. The output voltage can be computed as: Vout = Vref/2^n (resolution). 16 (4) Control circuit consist basically of thyristors and op-amps.
Thyristors are four (4) layered devices such as silicon controlled rectifier (SCR), silicon control switch (SCS), triac, diac, quadrac and gate turn off switch (GTO). A silicon controlled rectifier (SCR) has the following characteristics: Forward break-over voltage and holding current. Forward break-over voltage is the voltage above the SCR enters the conduction region. Holding current is the value of current at which the SCR switches from conduction to forward blocking region under stated conditions. 15 Actuators are usually machines that convert electric energy into mechanical energy by utilizing the forces exerted by magnetic fields produced by current flowing through conductors. And loads are the devices connected to actuator.
17D. Hardware Overview Fig. 7. Single Board Computer Based Microwave Drying Oven for Soil Testing Figure 7 illustrates the system concept of single board computer based microwave drying oven for soil testing. The system is powered by an AC source to supply the microwave and then be converted to DC supply for the power the single board computer and its sensors. The touch screen display interface will be used to operate the system by the user. Before, during and after the operation, the data will be displayed on the same screen, hence, minimizing the hassle of measuring the sample weight during the entire process.
E. Software Overview Figure 8 illustrates the system flowchart of the entire process. When the system started, it will automatically detect the presence of sample by measuring the weight of the base. If a sample is detected, the user will be prompt to choose between automatic and manual method. For automatic method, the system will initially measure the weight and temperature of the sample then display the data onto the screen. Proportional–integral–derivative or PID loop control will be next, a timer will start, followed by a duty cycle to activate the SCR that turns on the microwave system.
While doing this process, the measurement of the sample weight,Fig. 8. Software flowchart of the systemtemperature and power usage will be shown in the screen. Another prompt will be encountered if the weight of the sample doesn’t change after 2 minutes. If the weight changes, the microwave system will continue its function, otherwise, the deactivation of SCR that turns off microwave system will follow. And the display will show the final sample weight, temperature, moisture content, power consumed and total time of the entire process. If the manual method is selected, the user will be asked to enter the desired time of which the microwave system is turned on, desired temperature and maximum power to be consumed. Unlike the automatic method, the timer will do a count down and when started, duty cycle will activate the SCR to turn on the microwave system.
The temperature and power usage are monitored with respect to desired values and will be displayed onto the screen. When the countdown timer reached the specific time, it will be followed by the deactivation of SCR and turning of the microwave system. And the display will show the final sample weight, temperature, moisture content, power consumed and total time of the entire process. For the software, Raspbian operating system and Phyton programming language can be installed to this device 18.
And here’s the catch, all of the softwares are open source license making it free to use and can be used commercially. Graphical user interface (GUI) will be developed using Phyton and QtCreator softwares. 19F. Test Plan The test plan includes testing for accuracy of the weighing sensor, and reliability of the design that compares automation and manual processes. The configuration of the manual process will be based on the configuration generated by the automated process to compare the reliability of automation. The test will be conducted in five trials for each type of soil.Table 1.
Accuracy of weighing sensor in the microwave drying oven.# of trials Trial balance Load cell % difference1. 2. 3. 4. 5.
Table 2. Automated process of the microwave drying oven.# of trials Maximum Temperature (*C) Power Usage (Watts) Time (Sec.) Initial weight (grams) Final weight (grams) Moisture content1.
2. 3. 4. 5. Table 3. Manual process of the microwave drying oven.# of trials Maximum Temperature (*C) Power Usage (Watts) Time (Sec.
) Initial weight (grams) Final weight (grams) Moisture content1. 2. 3.
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Accessed: 15-Nov-2017.Mar Joseph E. Edjan (M’17) received the BSECE from La Salle University – Ozamiz City in 2012, and is currently working towards the master’s degree in engineering from the Mindanao State University – Iligan Institute of Technology, Iligan City.His research interests include inno-vations of existing technologies, renewable energies and power management systems for small and medium scale industries.