LabVIEW-Based System Puts Dallas Transit on Track

Author(s):
Matt Jacobs - Dallas Area Rapid Transit (DART), Rail Transit Consultants, Inc.

Industry:
Transportation

Products:
LabVIEW

The Challenge:
Developing a portable system to test the performance of light rail vehicles.

The Solution:
Using LabVIEW, plug-in DAQ boards, and SCXI signal conditioning hardware to run performance, continuity, and system tests on each vehicle.

"Anyone who has driven in Dallas during rush hour," said Pedro Delgado, "knows this city needs a rapid transit system."In June 1996, when the 40 Dallas Area Rapid Transit (DART) light rail vehicles (LRVs) begin rolling on 22 miles of track, Dallas commuters can thank Delgado and his LabVIEW-based test and measurement system for helping ease congestion on the city’s streets.

Delgado, a Senior Electrical Engineer with Rail Transit Consultants, Inc. (Penn, PA), has developed a portable test and vehicle monitoring system for the rail transit industry. The new DART LRVs were the first site to implement the system. Each LRV can hold up to 190 people. The monitoring system uses LabVIEW, plug-in data acquisition (DAQ) boards, and SCXI signal conditioning hardware to run performance, continuity, and system tests on each LRV.

About the LabVIEW-Based Test System
Delgado began developing his system in January 1995. "I had no time to attend a training class," he said, "so I learned how to use LabVIEW by going through the demo and actually using the product." Delgado had a prototype system designed before the LRVs were ready for testing. "So, I used my Ford Explorer as a ‘beta site’ to test acceleration, braking, and so on," said Delgado. "The system worked fine."

The vehicle performance test and mon-itoring system is designed around LabVIEW running on a 486/66 industrial rugged PC with a touchscreen, an AT-AO-10 analog output board, and an AT-MIO-16F-5 multifunction plug-in board. The system also includes a 12-slot SCXI-1001 chassis containing three SCXI-1160 relay modules, three SCXI-1162HV high-voltage input mod-ules, and three SCXI-1120 isolation amplifier modules. Delgado has a smaller system built using a four-slot SCXI-1100 chassis that he uses to troubleshoot problems that occur away from the DART building.

With his system, Delgado has access to 24 analog channels and 96 digital channels. The system tests three basic requirements established by DART - LRV performance (acceleration and stopping distance), continuity line testing on the electrical lines on the LRV, and systems monitoring (brake pressure, line voltage, line current, and so on).

"We run checks to make sure that the LRVs provide a comfortable ride and stay within DART safety parameters," said Delgado. "For example, does the LRV accelerate and decelerate smoothly at a rate of 3 mph/s?"

Typical DART train configuration has three LRVs articulated together. Each LRV has three trucks, each with two axles. The trucks on each end of the LRV have traction motors and pneumatic disk brakes that power or brake each axle, while the center truck has only brakes. The LRVs weigh approximately 108,000 lb and travel at speeds up to 65 mph. One LRV has been loaded with approximately 26,000 lb when testing to simulate a crush or rush hour passenger load.

Delgado created more than 100 virtual instruments (VIs) on a Toshiba 4700 laptop, then transferred the completed VIs to the industrial PC using a tape drive. He has various sensors scattered throughout the test LRVs - accelerometers tell him how quickly the LRV accelerates and decelerates, while thermocouples on the wheels gather data on wheel temperature. Analysis routines in LabVIEW then calculate the acceleration and braking distance of the LRV to check the efficiency of the motors and brakes.

LabVIEW Delivers Productivity
An experienced C programmer, Delgado gravitated towards the benefits offered by LabVIEW. "Previous systems built using C had a crude user interface and regularly generated error messages," said Delgado. "LabVIEW is easy to use and the DAQ hardware is very reliable. We collect 300 KB of data on a typical test, and can view the data in real time."

"LabVIEW also helps us analyze the data," continued Delgado. "For example, I quickly built a VI to integrate a curve that calculates the antilock brake efficiency. We can run reports in one night from the data generated by a test " it would take us nearly two man-weeks to analyze the same data using conventional chart recorders. With LabVIEW, we can turn out lots of tests in a short amount of time."

LabVIEW Helps Generate New Customers
Delgado tells of an official from a California city who came to Dallas to see how Delgado and his crew were using off-the- shelf hardware and software to test the DART LRVs. "He couldn’t believe that we were that efficient with our testing," said Delgado. "He said, ‘Would you be able to do another system like this as quickly for us?’ I told him ‘Yup " here’s my card.’"

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