Using LabVIEW and SCXI to Develop a Vehicle Bridge-Crossing Test System

Author(s):
Namdoo Moon - VI Engineering Inc.

Industry:
Aerospace/Avionics

Products:
LabVIEW

The Challenge:
Generating a data acquisition and control system that applies a strain profile to a transportable vehicle bridge.

The Solution:
Using a LabVIEW application with the SCXI-1520 module to provide reliable data acquisition and closed-loop control of a hydraulic system.

User-Friendly Simulation of Military Vehicle Crossings
Our company, Tank-Automotive and Armaments Command (TACOM), contracted VI Engineering to integrate a bridge test system that simulates military vehicle crossings by controlling up to eighteen 100 klb hydraulic cylinders. An 11th order polynomial simulated strain data file of a vehicle driving across a bridge. VI Engineering used the simulated data for controlling servo controllers to generate the required load on the bridge in a closed-loop cycle by monitoring the strain then generating the required load via analog signals. They easily configured and multiplexed 18 strain gages and 18 load cells with the new NI SCXI-1520 modules.

Easy Integration of a Vehicle Bridge Crossing Test
We contracted VI Engineering Inc., a National Instruments Alliance Program Select Integrator, to integrate a vehicle bridge crossing test system. We use the system to test a portable bridge by simulating the required load on the bridge. We do this by controlling the servo controllers and acquiring data from up to 18 strain gages and load cells. We can place up to nine pairs of hydraulic cylinders along the length of the bridge. A strain gage sits at each cylinder location and other areas of concern. We use a data file of a vehicle previously driven across a bridge to simulate vehicle crossings with an 11th order polynomial.

VI Engineering designed the software interface as a user-friendly LabVIEW application to control servo controllers based on feedback from strain gages and load cells. They designed the Setup Editor screen to set initial values for strain gages and load cells along with warning setup for monitoring measurement limitations of the strain gages and the load cells. For debugging and diagnostics purposes, they used a manual test code. The system can control multiple pairs of cylinders to apply an incremental static load from a ramp generator for a certain time period. We use run test mode to generate multiple times of constant or incremental loads on the bridge by a flexible number of servo controllers for a certain time interval to simulate vehicle crossing.
The Setup Editor sets up initial SCXI values and calibrations for the strain gages and the load cells. We edit and save initial conditions in a file from the designated directory and select the number of the strain gages and the load cells.

The system uses warning setups to notify us and monitor readings of strain gages more than five percent of requested strains for warning, and more than 10 percent of requested strain for stopping the program. When the shutdown or emergency stop occurs, the program sends the last value of analog output (AO) signal to the servo controller to hold the cylinders in position.

Controlling Multiple Pairs of Cylinders
The manual test mode uses the initial conditions from the setup editor screen to debug or diagnose individual or multiple components of the strain gages and the load cells. The system also can control multiple pairs of cylinders to apply an incremental static load from the ramp generator for a certain time period. In this mode, constant, cosine type, and sawtooth type ramps use the ramp generator to generate static loads on the bridge. These ramps feed into the PCI-6713 DAQ card. The DAQ card converts the signals to engineering units (EU) and displays them as load. SCXI-1520 modules measure the signals from the strain gages and the load cells and multiplexes them into a PCI-6052E card. This converts these strain gage signals to EU and displays graphically on the screen.

Straightforward Configuration and Calibration
The program runs automatically by loading a strain data file from the designated directory with the initial conditions set in the Setup Editor. An 11th order polynomial simulates the strain data from a file of a vehicle driven previously on the bridge within an error of less than 10 percent of the data. The simulated signal is provided into the setpoint of proportional, integral and derivative (PID) control loop to generate smooth AO signals via the PCI-6713 card to the servo controllers. The determined strain gage signals remain the process variables of the PID. The load cells monitor the generated load, display them graphically on the screen, and save a load profile in a file. Using the load profile file, the operator creates multiple cycles of simulation on the bridge. A typical test consists of 5,000 crossing simulations. The system checks the strain gage signals with warning and shutdown limits of five and 10 percent of the previous strain data, respectively, to maintain accuracy of the strain gages in the measurement. When an emergency stop occurs during the test, the program automatically shuts down and notifies the operator.

VI Engineering developed a vehicle bridge-crossing test system that controls 100 klb hydraulic system, strain gages and load cells. The project takes full advantage of the new SCXI-1520 strain gage modules, maximizing user flexibility in selecting strain gages. The SCXI-1520 module provides operators with straightforward configuration and calibration of strain gages and load cells within the LabVIEW programming environment.

For more information, contact:
Namdoo Moon

VI Engineering, Inc.

Tel: 248-489-1200

E-mail: nmoon@vieng.com

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