Go with the flow

DN Staff

November 4, 2002

4 Min Read
Go with the flow

COMPANY: Cal-Bay Systems is a National Instruments Alliance member and a full-service systems integrator.

PROJECT LOCATION: San Francisco Bay.

PROJECT DESCRIPTION: The San Francisco Bay and Sacramento/San Joaquin Delta are the West Coast's largest estuary, encompassing some 1,600 square miles of waterways and draining over 40% of California's fresh water. In the warehouse district of Sausalito, CA there is a building that houses a miniaturized version of the estuary. It is known as the San Francisco Bay Model. It encompasses over 13,000 ft2. Built to scale (1,000:1 in the horizontal plane and 100:1 in the vertical plane) by the Army Corps of Engineers, the model is used to simulate tidal conditions, currents, and river flows around the San Francisco Bay and to examine changing hydraulic conditions. The original data acquisition in the model was done manually. Operators would visually inspect the instruments and log the data manually into a logbook. Tides were controlled manually using cam systems that controlled inflow and outflow valves to allow the correct amount of water to be introduced into the model. The project was to replace the old system with a PC-based system.

ENGINEERING CHALLENGES: There were three areas of automation and integration to tackle for the upgrade:

  1. Tidal Control-Precise tidal conditions at the Golden Gate Bridge must be reproduced in the model to within .01 inch of corresponding actual data collected by the Army Corps of Engineers for that location.

  2. High Channel Count Data Acquisition-Over 150 sensors are located around the model to acquire information, and data must be collected and archived every 2 seconds. All sensors must be calibrated before every test. And, all data is to be made available on the Internet.

  3. Distributed Control-Flow controllers are used to simulate river flows from the Sacramento Delta and are located at several distant places around the model. These needed to be controlled from a single central source.

PROJECT SOLUTION: The Tide Control system is comprised of a 75 hp, three-phase pump which is used to drive salt water into the model at a constant flow rate. There are three butterfly valves positioned in the Pacific Ocean area of the model, each controlled by a servo motor, which allow water to flow out of the model at a varying rate.

Three ultrasonic level sensors, placed in different physical locations, are used to monitor the water level in the model. The actual water level is derived by averaging the three, therefore filtering out any oscillations caused by high frequency ripples or waves. A National Instruments DAQ-Card, LabVIEW, and the LabVIEW PID (proportional-integral differential) toolkit are used to acquire, monitor, and filter the water level data and determine 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. A setpoint profile, representing 3.6 years of tide-level data, is fed into the PID controller as the desired tide signal.

Tuning the tide control system was the most difficult part of the application. Software techniques were implemented by Cal-Bay Systems that allowed a further understanding of the dynamics of the hydraulic system. Frequency analysis was done to determine the harmonics of the oscillations and the data was used to help tune the PID tide control algorithm.

The Data Acquisition portion of the application consists of a National Instruments SCXI Chassis housing eight SCXI 1100, 32 channel multiplexer modules.

PROJECT RESULTS: Using LabVIEW, Cal-Bay Systems implemented a data acquisition program that scans all 256 channels at a rate of once every two seconds. LabVIEW collects the data and scales it appropriately using 3rd order calibration equations that are generated by the calibration software. The data is stored to a MS-Access database and an Internet application, using Microsoft's Internet Information Server, was written to serve up the data on the Internet for viewing and analyzing in a web browser. ComponentWorks Active X technology from National Instruments is used as part of the Internet application for analysis of the data and presentation in the web browser.

Calibration of the sensors used to collect salinity and velocity information is critical before every test is run. Laptops are used for their portability, around the model, to perform the calibrations and send calibration information back to the server via wireless Ethernet. Cal-Bay authored a LabVIEW application that interfaces to National Instruments' PC-DAQ Cards for data collection on the laptops and relays the calibration information back to the main data acquisition server.

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