Automated Control and Data Acquisition with LabVIEW in a Geotechnical Engineering Laboratory

Author(s):
Charles Aubeny - Texas A&M University

Industry:
University/Education

Products:
LabVIEW,

The Challenge:
Acquiring experimental data for the study of soil strengths by direct shear tests.

The Solution:
Using a PC-based system with a DAQ board controlled by LabVIEW to improve the study of soil properties.

The geotechnical engineering program at Texas A&M University constantly researches ways to improve the study of soil properties and characteristics. Determination of strength and behavior of soils is particularly important. Traditionally, laboratory experiments, such as a direct shear test or the triaxial confined compression test, required manual operation of the equipment. This limits the full potential of the testing device and results in poor data sampling resolution.

Automating the Direct Shear Machine
At the Texas A&M University geotechnical program, we recently decided to automate undergraduate and graduate laboratory facilities. After considering cost, service, reliability, user friendliness, and system flexibility, we selected LabVIEW software and MIO-16E DAQ boards for instrument control and acquisition. We installed these components on a Pentium desktop PC and Pentium III 500 MHz laptop PCs.
Experiments in the geotechnical engineering laboratory require measurement of short and long-term displacement, temperature, and load. We can control most of the lab equipment manually or with LabVIEW through a serial RS-232 communication routine. Often, the control adjusts automatically as a function of an input. The first piece of equipment we chose to automate was an ELE D-300A series direct/ residual shear machine. This machine allows us to characterize the shear strength of a soil sample.

Program Functionality
The basic foundation of the program used has three major sections: setup and initialization, instrument control, and data acquisition. Setup and initialization must be accessible throughout the entire experiment. This section controls options, such as the location and frequency of writing a file and facilitates instrument calibration. Instrument control and data acquisition interlink to allow the input to influence the control. A semi-hardware timed buffered input with real-time data processing provides the basis of data acquisition. By using pull-down menus on the screen, we can monitor up to eight inputs and control accordingly.
Some of the particular control features for the direct shear apparatus are:

1. Move forward/backward at a given speed - we can change both speed and direction during operation of the hardware
2. Set a datum point and automatically return to that point
3. Program a series of movements where we input a series of speeds and corresponding time to run at that speed

Some of the data acquisition features include:
1. Continuous DAQ at a set single-sampling rate (high speed to relatively slow sampling rates - 20 KS/s to ~1 sample every five seconds)
2. Finite DAQ at a set single-sampling rate for a given number of samples
3. Finite DAQ at specified times (arbitrary times - not a constant sampling rate) for a set number of samples.

Results
The most advantageous feature of LabVIEW is the flexibility it provided our lab. Programming a modular data acquisition procedure, enables us to build different programs for controlling multiple pieces of equipment with only minor modifications to the original code. This results in more efficient use of laboratory time and equipment and increases functionality from different instruments.

For more information, contact:

Dr. Charles Aubeny

Department of Civil Engineering, Texas A&M University

College Station, TX 77843

Tel: (409) 845-4478

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