Multiparametric Probe for Real-Time Groundwater Monitoring

Author(s):
G. Conte - Diiga - Universita Politecnica Delle Marche
D. Scaradozzi - Diiga - Universita Politecnica Delle Marche
S. Franca - Diiga - Universita Politecnica Delle Marche
D. Luccarini - Digga - Universita Politecnica Delle Marche
M. Rosettani - Diiga - Universita Politecnica Delle Marche

Industry:
Research

Products:
PID Control Toolkit, Internet Toolkit, LabVIEW, PDA Module

The Challenge:
Creating a prototypical probe with an operator friendly interface for in situ groundwater analysis. The probe must enter small wells, reach low depths, and integrate with a number of sensors.

The Solution:
Developing the WTProbe, a prototype of a multiparametric probe with innovative structural features and an efficient data supervisory control system designed with NI LabVIEW software. The solution uses a DSP microcontroller main board that provides data collection, processing, and Ethernet communication for remote internet browsing and more complex data analysis.

Ground-water is an important freshwater resource, but it is plagued by some critical problems such as pollution from agriculture, manufacturing, and marine water infiltration. Today, groundwater is monitored by ex situ chemical and physical analysis. In this process, analysis technicians collect water samples, carry them to a laboratory, and then analyze them. We designed the WTProbe at the Lab MACS (Laboratory of Modeling, Analysis, and Control of Dynamical Systems) at the Università Politecnica delle Marche to offer innovative features for the in situ analysis of water that improves upon today’s standard approach. The probe is based on the standard oceanographic CTD model, so it measures the electrical conductivity, temperature, and pressure of the liquid in which it is submerged. When assessing ground-water quality, the probe also measures the dissolved oxygen concentration and pH level. When we designed the probe, we developed features that accommodated for the possibility of collecting water samples at different depths and built in options for investigating other variables, including biological variables such as pathogenic bacteria. 

Structural Architecture

The probe’s structural components are made from stainless steel to provide resistance to corrosion and pressure. To facilitate modularity and versatility, we engineered an individual case for each sensor.

Dedicated microcontrollers manage specific sensors on the probe. A Microchip dsPIC unit controls the power supply, converts signals, and acts as the logical interface between the remote unit and the various sensors and devices connected through its bus. Power and data flow through a cable attached to the probe in the well to the host device to exchange commands, status, and measurements in real-time.  

The probe can be used in one of two configurations: the S (slim) configuration and the W (wide) configuration. In the S configuration, the sensor cases are mounted in a row under the head case, so the probe assumes a slim form that can enter wells with a 3 in. diameter. In the W configuration, the sensor cases are mounted in tiers under the head case. The advantage of the W configuration with respect to the S configuration is the reduced vertical dimension that makes it more manageable and less fragile.

Software Architecture 

We designed the software architecture to facilitate simple interactions between human operators and the probe. Using an elementary M/M interface developed in the LabVIEW graphical programming environment, the operator can program and control the probe’s behaviors, such as starting and stopping data acquisition and activating the water sampler. The software interface also automatically performs the operations required for data logging, processing, and displaying data.

We implemented a software architecture with two levels. The low level is based on a dsPIC unit that integrates the features of a DSP for signal processing and an MCU for governing the data acquisition process, the filtering operations, and the communications process. Communications at the low level between the dsPIC unit, sensors, and memory devices is based on the I2C communication protocol.
The high-level architecture is responsible of the user interface, including data recovery, graphical visualization, and supervision and control of the low-level architecture.

The probe user interface is realized in three forms: through an HTML page included in the dsPIC main program to ensure a low level of interaction, through a PC with a LabVIEW VI for high-level, real-time data analysis and manipulation, and through a PDA or rugged tablet PC using the LabVIEW PDA Module.
The HTML user interface is designed to deal with a large amount of information. The navigation is organized in sections, so the data is displayed in real time and buttons implement controls and survey logs in ASCII files. With this simple browser interface, the user can control the probe, monitor data, and modify the status by simply clicking buttons.

The HTML interface offers simplicity, but the LabVIEW interface provides a set of tools for data manipulation and review, such as LED controls, graphs, and complex routines unavailable in the HTML browser. Thus, the LabVIEW interface is useful for the WTProbe user who wants maximum performance on real time tasks. There are also two additional interfacing options: the PDA interface using the LabVIEW PDA Module, and the Tablet PC interface that substitutes for the classic PC unit and also uses the LabVIEW PDA Module.

Using intelligent control strategies, the main control system monitors the probe to detect faults and notify the user. Faults are identified by incoherent sensor behaviors or by behavior that contradicts a given model. In addition, using a fuzzy inference motor developed by LabVIEW, the control system can compare the measured ground-water quality to suitable models developed by the department of Marine Sciences at the Università Politecnica delle Marche. Based on this comparison, the program then detects specific situations of interest. 

Results

The WTProbe is a good measuring instrument that performs reliable and accurate real-time measurements of chemical and physical water parameters. With LabVIEW, we rapidly prototyped the software implemented in PC and PDA units and created a versatile interaction system between the human operator and the onboard system. Using VIs provided by the LabVIEW Internet Toolkit, we built a software platform where the dsPIC mainboard and remote unit communicate and interact. The LabVIEW interface provides sensor calibration, system monitoring, data gathering, I2C bus control, and error reporting. Finally, with the LabVIEW PID Control Toolkit, we developed a fuzzy inference system that detects functioning anomalies and derives further information from acquired data.

Author Information:
For more information on this Case Study, contact:
D. Scaradozzi
Diiga - Universita Politecnica Delle Marche
d.scaradozzi@univpm.it

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