Grantee Research Project Results
2011 Progress Report: Development of Mobile Self-Powered Sensors for Potable Water Distribution
EPA Grant Number: R834868Title: Development of Mobile Self-Powered Sensors for Potable Water Distribution
Investigators: Banks, M. Katherine , Porterfield, Marshall , Pekarek, Steve
Current Investigators: Banks, M. Katherine , Brovont, Aaron D , Salim, Amani , Porterfield, Marshall , Wu, Ruoxi , Pekarek, Steve , Jefferson, Travis
Institution: Purdue University
EPA Project Officer: Page, Angela
Project Period: January 1, 2011 through December 31, 2013 (Extended to December 31, 2014)
Project Period Covered by this Report: January 1, 2011 through December 31,2011
Project Amount: $599,997
RFA: Advancing Public Health Protection through Water Infrastructure Sustainability (2009) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Progress Summary:
A mobile sensor system is being designed and fabricated for water quality monitoring in a potable water distribution system. The research being conducted is focused on the areas of (1) sensor research and device fabrication, (2) application testing of water quality sensors and (3) wireless mobile sensor networking. Significant progress has been made in all three areas.
In sensor research and device fabrication, a multi-analyte biochip (MAB) system has been designed that consists of multiple ion-selective electrodes that are microfabricated on a silicon substrate. Potentiometric measurements in the millivolt range are recorded. The sensor is calibrated based upon lab experiment, and the concentrations of target analytes are determined from calibration curves taken for a respective sensor. To date, ion-selective electrodes have been made that are selective for H+, NH4+, Ca2+, Cl- and CO32- ions, which are the key ions for pH, water hardness, and disinfectant. A MAB is shown in Figure 1.
Figure 1. Multi- analyste biochip (MAB) for water quality measurement
For application in water testing, the MAB is part of an integrated system that also includes a micropump, an electronic control system and an energy source. For water testing, a miniaturized (Bartels mp6) micropump was selected to provide samples to the MAB. It has a pumping rate of 160 uL per minute at a power of 200 mW. Samples are collected through microchannels that are fabricated via soft-lithography. A flow-cell chamber used to hous the MAB was designed using clear polycarbonate material so that it will not interact with the chemicals in the water sample. The sensing chip is sealed at the center of the flow cell with a gasket, where all working and reference electrodes are immersed in the sample liquid. In addition, the microfluidic system consists of a passive microvalve cell chamber, and MAB are shown in Figure 2.
Figure 2. MAB, micropump, and flow cell chamber. designed and fabricated for water quality monitoring
The electronic control system has been designed to coordinate all device activity, read measurements from the MAB, and transmit data to remote base stations with the lowest possible energy consumption. A Texas Instruments (TI) CC430 microcontroller with integrated RF transceiver was selected for this purpose. Its suite of peripheral devices, ultra-low power consumption, and minute footprint make it an ideal choice for the MAB-based water sensing application. The dimensions of the device are shown in Figure 3. A 3V battery cell was initially selected to provide system power. An energy harvesting system is being designed to replace the battery in future designs. A printed circuit board integrating all of the electronic control system components and the energy source has been designed and constructed. It is shown within Figure 4. Details are provided in subsequent sections.
Figure 3. Texas Instruments CC430 Microcontroller with Integrated RF Transceiver provides electronic backbone
Figure 4. Electronic Control System and Pump
A complete prototype of an integrated MAB-based sensor device, which contains all components needed for sensing, data collection, and transmission, has been designed and constructed. The outside structure was selected to be spherical to reduce the frictional resistance on the device surface and to gain maximum volumetric space for component placement. The dimension of the sensor shell is based on the size of common water distribution pipes. Depending on the length and quantity of water flow, most distribution systems range in size from 4-inch to 36-inch nominal diameters. This sensor shell is 2.76 inches in diameter, and thus will fit into the smallest distribution pipes. Half of the sphere contains the sensing unit and microfluidics, while the other half contains the electronics. The electronics portion is completely sealed from moisture. Pogopins provide electrical connection from the electrochemical sensing unit to the data-acquisition (DAQ) and power system. A picture of the complete package is shown in Figure 5.
Figure 5. Integrated MAB-based water testing device.
For wireless mobile sensor networking, a network base station has been designed to receive data from the mobile sensors and relay the data back to a control network or PC for monitoring and data logging. A base station prototype has been designed and constructed as shown in Figure 6. Details are provided in subsequent sections.
Figure 6. Network Base Station
To date, ion-selective electrodes for the MAB have been made for H+, NH4+, Ca2+, Cl-, and CO32- ions, which are the key ions for pH, water hardness, and disinfectant. Representative calibration slopes are shown in Figure 7. All calibration slopes are Nernstian, meaning the sensor is able to detect concentration of selected analytes.
Figure 7. The MAB calibration results for pH, C1-, NG4+, and Ca2+. The correlation between concentration and electromotive force
for the mentioned ions follows the Naernstian equation. The sensor detection ranges for target analytes covered the posssible ion
concentrations in drinking water.
As mentioned previously, mobile sensor electronic control system and network base station prototypes have been designed and constructed. The main design considerations for both prototypes are presented in greater detail in the following paragraphs along with the results of the initial hardware validation.
The mobile sensor electronic control system has three main objectives: data acquisition temporary data logging, coordination of pump activity, and wireless transmission of data to a base station. The primary design challenge for data acquisition in the mobile sensors is the interface of the MAB with analog to digital converter (ADC) on the microcontroller. The design objective for this interface is to maximize the resolution of the MAB output while satisfying the input requirements for the ADC, which is complicated by the unusual electrical characteristics of the MAB. The MAB has a very large output impedance, which makes the choice of amplifer critical. Therefore, three different circuits were designed based on Texas Instruments INA333 instrumentation amplifier to properly condition the output of the MAB.
It was desirable that all three circuits be implemented in the first prototype to compare the results from each circuit and investigate the impact of the interface circuit on the data collected. The INA333 was chosen for its very high input impedance, low power consumption, rail-to-rail operating range, and small footprint. The operation of the three signal conditioning circuits has been tested and verified. A simple DC input to the circuits was supplied, and the output was recorded and compared to expected results. The results are displayed in Figure 8.
Figure 8. Signal Conditioning Circuits DC Test Results
In the results shown above in Figure 8, all three signal conditioning circuits on the mobile sensor prototype board were connected to a floating DC source. The source voltage was then stepped from -100 mV to 100 mV by 10 mV intervals. The input and output voltages of each circuit were recorded at each operating point. Expected results were calculated from the voltage transfer function of each circuit using the nominal component values. Error was calculated at each point by the following equation.
The average error for the circuit was expected to be less than or equal to 5% as those are the manufacturing tolerances for the resistors that set the amplifier gain. The slopes of the trend lines in Figure 7 correspond to the amplifier gains. The gain for circuits represented by S1 and S2 was expected to be 14.02, and the gain for the circuit represented by S3 was expected to be 17.54. Thus, we have concluded that the three potential amplifiers for the MAB are capable of converting the mV output to that required for data collection and analysis.
Data logging by the electronic control system is limited by the relatively small amount of dynamic memory natively available to the microcontroller. To avoid the necessity of incorporating additional memory on board the mobile sensor, data logging is restricted to the temporary storage of data between base station transmissions—clearing all memory after each transmission to make room for new readings.
The electronic control system coordinates pump activity by enabling/disabling the pump controller through a single control signal. This control signal is specified in software; thus, the pump can be set to operate on any desired timing schedule.
Wireless communication is integrated on the CC430 microcontroller and therefore handled by software. Software demonstrating the basic functionality of the mobile sensors and wireless communication between devices has been implemented on CC430 evaluation modules. Currently, this software is being ported over to the actual mobile sensor and base station prototypes.
The network base station has two main objectives: wireless communication with the mobile sensors and the relaying of data to a network PC or other external controller. As stated for the mobile sensors, wireless communication is handled natively on the CC430 microcontroller. The main challenge to wireless communication will be to determine the effective distance over which the mobile sensors and base stations will be able to consistently communicate due to water, metals, and other unknown conductive media obstructing the path of communication. This challenge will be addressed in the next stage of testing, once basic system functionality has been confirmed.
The main design consideration for the base station was the interface with a PC or other external controller. To facilitate thid interface, the circuit incorporates an FT232R USB to UART converter, which will allow communication with the base station through a standard USB connection. Permanant data logging may then be handled by the netwrok PC, enabling a simple interface for monitoring and analyzing data.
Future Activities:
For sensor design and development, the plan for 2013 is to focus on the applications shown in Table 1. For application in water testing, future work will focus on four main issues: confirming compatibility of the signal conditioning circuits and MAB sensor, investigating the impact of the signal conditioning circuits on data obtained, development of a control algorithm for the mobile sensor electronic control system, and development of an optimal energy harvesting system. To confirm compatibility between the signal conditioning circuits and the MAB, all three signal conditioning circuits will be connected to the MAB, and a baseline test will be performed. The outputs of the signal conditioning circuits will be monitored and compared against expected results.
Once the compatibility of the signal conditioning circuits and MAB sensor has been verified, the results of each circuit design will be compared against the others to determine which signal conditioning circuit best suits our purposes. The criteria for selection will be signal integrity, long-term stability, and ease of calibration.
Table 1: 2013 Sensor Development Plan.
Year of 2013 | January, February | March, April | May, June | July, August | September, October | November, December | |
---|---|---|---|---|---|---|---|
Sensor Fabrication | X | X | X | X | |||
Sensor Functionalization | Mg2+ and Ca2+ | X | |||||
CO32- | X | ||||||
Cl- | X | ||||||
HClO | X | X | |||||
Sensor Calibration | H+ and NH4+ | X | |||||
Mg2+ and Ca2+ | X | X | |||||
CO32- | X | X | |||||
CL- | X | X | |||||
HClO | X | X | |||||
Sensor Package | Incorporate chip with energy system and micropump | X | X | ||||
Incorporate with data aquisition and transmitter | X | X | X | ||||
System adjustment | X | X | X | ||||
Distribution System Test-Bed | X | X | |||||
Data Analysis | X | X | X |
To demonstrate the performance of the completely integrated mobile sensor in its intended use, a control algorithm is to be developed for the microcontroller. The control algorithm will coordinate all of the mobile sensor’s activities to ensure valid data collection and transmission.
Finally, our goal is to design an energy harvest system that can harness the kinetic energy of the water to provide power for the electronic sensing and transmission systems. The design of the energy harvest system will facilitate the capture of energy from both impacts and random motion. It will eliminate the need for batteries, thus reducing maintenance costs and downtime. To date, design code has been developed to maximize energy harvest due to impact with pipe walls. This cde generated an initial design as shown in Figure 9.
Figure 9. Initial Design of Energy Harvest System
Presently, a mechanical model is under development to fully characterize the rotational behavior of the device as it flows through the distribution system. This will enable the design code to maximize the energy harvest due to impact and random motion. The mechanical model of the device is nearly complete. Once this is complete, a final energy harvest system will be designed and its usefulness in replacing the battery evaluated. If there is significant promise that the energy harvest system will provide sufficient energy,it will be constructed and integrated into the sensor system.
For wireless mobile sensor networking, future work will center on two main issues:establishing a consistent RF link between the base station and mobile sensor and developing a data-logging algorithm on a control PC. Currently, work is underway to tune the RF operation of the mobile sensor and network base station in software, to permit consistent and valid data transmission. This is being done through TI’s debugging software in combination with spectrum analysis. A data-logging algorithm will be developed on a Windows PC to receive data from the network base station and store it in a spreadsheet for ease of storage and monitoring.
Journal Articles:
No journal articles submitted with this report: View all 15 publications for this projectSupplemental Keywords:
Contamination, drinking water, sensors, water distribution system, potable water distribution, security of drinking water system;Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.