We needed a highly flexible, yet powerful monitoring system to accommodate the variety of sensors and communication protocols from the different subsystems.
We defined the following requirements:
• Continuous multichannel voltage sampling at >10,000 Hz to monitor six inputs for high-voltage transients
• At least three different configurable sampling rates to optimize each signal class data rate and minimize storage requirements
• A serial input using standard protocols to interface with the GPS antenna and provide location information for events
• Real-time calculations to provide output responses to interact with the sensors
• Pre- and post trigger (event) data recording without saving non-trigger data to optimize analysis and minimize storage needs
• Large storage capacity
• Video management
• Automatically synchronize all inputs regardless of data rate or format
• Automatic downloads for extended operation with minimal personnel interactions
• Vibration and temperature operating ranges acceptable for installation on a rail vehicle
• Small footprint for installation in an electrical compartment
We decided to instrument two light-rail vehicles with CompactRIO modules, which we were surprised to learn fulfilled all of our system requirements. We used two different vehicles to compare the collected data and monitor how the vehicles interacted. We installed high-voltage transducers and connected them to several train components, focusing on areas before and after the power input filters. This helped us determine if the transients were being generated from RTD's power network (pre filter), or if a subsystem of the train (post filter) was generating the transient.
Figure 1: Semi-permanent CompactRIO installation in Denver Car 321 propulsion/APS compartment
Figure 2: High-voltage transducers and fuse installation in Denver Car 321
Programming with NI LabVIEW
We programmed our system exclusively with NI LabVIEW system design software, using the LabVIEW Real-Time and LabVIEW FPGA modules. We programmed the FPGA to acquire high voltages, currents, and vehicle diagnostics. We programmed the processor to acquire GPS locations and vehicle speeds, to perform daily housekeeping, and to perform post processing which allowed us to erase non-trigger data and minimize storage requirements since we were recording about 1 GB of data every 30 minutes. With automated post processing, we stored only about 5 GB per day. NI has a great database of prewritten code. Plugging in GPS software modules and general templates for the FPGA and processor software layout saved us a significant amount of time. After attending LabVIEW Core 1 and Core 2 classes in San Diego, we progressed from first-time users to advanced programmers in only a few months. Due to the intuitive nature of LabVIEW and previous programming experience, we completed and tested the software in less than six months.