Automating the San Francisco Bay Model with LabVIEW

Author(s):
Dave Weisberg - Cal-Bay Systems

Industry:
Research

Products:

The Challenge:
Automating one of the only physical hydraulic models in the U.S. to simulate precise tidal conditions and acquire large amounts of data.

The Solution:
Cal-Bay Systems, Inc. and National Instruments products provided a cost effective, cutting edge, fully networked closed loop systems with full flexibility and expandability for the future.

Introduction
The San Francisco Bay Model is a physical model of the bay that we use to simulate tidal conditions and river flows and measure hydraulic conditions. Sensors and transducers placed around the model gather velocity (flow) and salinity readings every two seconds. We analyze the data to determine the environmental impacts of dredging new shipping channels and constructing new levees and dams.

Various Project Requirements
We undertook three areas of automation on the bay model:
• Tidal Control - precise water levels at the Golden Gate Bridge must be reproduced to within 0.01 in.
• High Channel Count Data Acquisition - more than 150 sensors located around the model acquire information and make it available on the Internet.
• Distributed Control - flow controllers located around the model simulate river flows from the Sacramento Delta.

System Configuration
The tide control system is comprised of a 75 hp, three-phase pump used to drive water into the model at a constant flow rate. In the Pacific Ocean area, the model has three butterfly valves that control the flow of water out of the model and three ultrasonic level sensors to monitor the water level at three different locations.
The system monitors the water level, filters the data, and determines the proper outflow for the desired tide. Using National Instruments motion control technology, LabVIEW converts the desired outflow to motor positions on the servo-controlled butterfly valves. We fed the PID controller a setpoint profile that represented the desired tide; LabVIEW handled the rest.

The data acquisition portion of the system is housed in a server machine containing data acquisition and signal conditioning hardware. LabVIEW scans 256 channels at a rate of 30 Hz (once every two seconds), collects the data, scales it appropriately, and stores it in an MS-Access database. We also wrote an application using National Instruments ComponentWorks to post the data on the Internet.
We used 166 MHz Pentium laptops equipped with portable DAQ hardware to perform the calibrations and send back to the server via wireless Ethernet. LabVIEW controlled the data collection and relayed the calibration information back to the data acquisition server.
Because the simulated river flows are located in distant locations around the model, they are excellent applications for National Instruments FieldPoint distributes I/O. Analog input modules monitor the flow rates and feed the data through multiple PID loops controlled with LabVIEW. FieldPoint varies the flow controllers to achieve the desired flow rates.

Design Challenges
The biggest challenge of the entire project was the tide control system. In this large hydraulic system, controllers tend to oscillate as waves bounce off walls and reverberate throughout the system. With the analysis features of LabVIEW, integrated with the PID and motion control features, we applied digital finite impulse response (FIR) filtering to the data to eliminate undesired frequencies before feeding the data into the PID control loop.
We were all new at tidal control and LabVIEW was invaluable in performing rapid prototyping and quick modifications of algorithms and parameters to assist us in converging on our solution. The options were abundant and easily implemented.

For more information, contact:

 Cal-Bay Systems, Inc.

3070 Kerner Blvd., Suite B

San Rafael, CA 94901

Tel: (415) 258-9400

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