Academic Company Events NI Developer Zone Support Solutions Products & Services Contact NI MyNI

Customer Solutions

Canadian National Railways Selects a PAC Solution with PXI to Control Classification Process

Author(s):

Shahzad Sarwar, Averna Technologies

Industry:

Transportation

Product:

LabVIEW, LabVIEW FPGA, LabVIEW Real-Time, PXI/CompactPCI, Programmable Automation Controllers (PACs)

The Challenge:

Upgrading the process control system for the Canadian National Railways classification yard operations.

The Solution:

Using a National Instruments PXI platform controlled by LabVIEW Real-Time and reconfigurable I/O modules with onboard FPGA technology to meet challenging control system requirements.


Managing a Demanding Industrial Process
The Canadian National Railways classification yard operation is managed by a redundant, mission-critical automated control system. As the train wagons are dropped in the yard, their weight, speed, and location are all monitored by the control system that manipulates the wagon speed and sorts them into outgoing tracks, per operations strategy. Sensors and actuators distributed throughout the yard feed process data to a very comprehensive redundant conditioning and data acquisition system. Local acquisition nodes process the data and feed it to central control computers. Detailed control software running on central nodes decides wagon speed, and redirects and sorts the wagons accordingly. Because of this powerful industrial process and capable actuators, the control decision is based on numerous inputs – some as sensitive as ambient air speed and wind direction.

PXI and Signal Conditioning Provide Powerful System Control
The system operates in an industrial environment with demanding signal conditioning requirements that include:

  • Transient protection up to 2000 V or more and isolation of all inputs
  • Programmatically adjustable debouncing for digital inputs
  • Programmatically adjustable deadband, hysteresis, and filtering for analog inputs
  • Zero crossing for a large variation on input signal amplitude


A combination of 5B Series and SSR Series signal conditioning modules with many of the programmable adjustments, embedded in a reconfigurable I/O module with onboard FPGA, provide a signal conditioning solution that meets these very specific needs with off-the-shelf hardware. The system provides conditioning hardware for a channel count exceeding 3,000, back-planes, and standard cables for signal connectivity between PXI and signal conditioning modules,, resulting in a significant cost reduction for such a high-channel-count solution.

The unique, innovative solution uses reconfigurable I/O and a LabVIEW FPGA Module, along with 5B Series and SSR Series signal conditioning modules, to provide programmable, specific signal conditioning. Using the LabVIEW FPGA Module, we program debouncing period, zero crossing detection, dead band, hysteresis, and filtering with provisions for parametric adjustments through a host CPU. An interrupt and event-driven real-time application running on PXI embedded controllers acquires sensor information, performs engineering conversions and other local computing, formulates the transmit buffer, and sends it to central computers over the serial link. The same application, while responding to commands from the central control, activates field actuators and generates output waveforms on analog channels.

A custom protocol for serial communication with central host computers that adapts to previous standards uses LabVIEW Real-Time to provide CRC validation, communication (running status and statistics), and complete message parsing and formulation.

The PXI system also implements watchdog-based local data acquisition and control monitoring and reporting. In case of signal conditioning or acquisition hardware failure, the system switches from active to a standby set of identical hardware while maintaining full functionality. Both active and standby sets of PXI hardware simultaneously and continuously process the inputs, but only the active system influences the outputs.

Using LabVIEW synchronization, notification, and interrupt-driving capabilities, the embedded real-time application does not have to poll all inputs for acquiring data. As the wagon passes through the field sensors, only certain segments of the acquisition system are triggered, and the event-based application architecture leaves the host CPU largely free without any resource polling requirements.

NI Solution Exceeds System Requirements
Making extensive use of the LabVIEW FPGA Module for this demanding signal conditioning, data acquisition, and deterministic control application, along with using LabVIEW Real-Time on a PXI platform, we have implemented a challenging mission-critical system with National Instruments cost–effective, versatile technology. The NI solution meets and exceeds the present system requirements, and remains promising for future performance enhancements.

For more information, contact:
Shahzad Sarwar
Director of Industrial and Real-Time Solutions
Averna Technologies, Inc
700 Wellington, Ste. 1400
Montreal, PQ H3C 1T4 Canada