Using LabVIEW and PXI Modular Instruments to Build a Supervision and Acquisition System for a Full-Scale Train Traction Test Rig


"The design takes advantage of NI PXI modular instruments with the overall architecture split into two main subsystems."


The Challenge:

Coordinating different devices of a full-scale test rig for train traction equipment to supervise the test rig motors and manage the different types of installed sensors.

The Solution:

Developing a multilayer system based on two NI PXI modules and the NI LabVIEW Real-Time Module to supervise the machine-embedded controllers.




We designed an experimental full-scale test rig to monitor train traction equipment and implement efficient condition-based maintenance (CBM) techniques, focusing on the traction components. We can use the test rig to investigate detail failures in the main mechanical components such as bearings, gears, and motors.


We installed a traction motor and a traction gearbox from a real train in a special test rig with a braking motor to simulate actual train operating conditions. To correctly reproduce the environmental noise due to rugged operating conditions in train applications, such as bogie suspensions, we installed the traction motor and the traction gearbox on vibrating platforms driven by four brushless motors.


We equipped the gearbox, bearing seats, and motor with accelerometers, thermocouples, a torque meter, and other sensors. Due to the complexity of the test rig, as well as the safety concerns over a high-power, high-speed, heavy-payload application, we needed a sophisticated system to supervise, monitor, measure, and register the state of the test rig and its components. Therefore, we developed a double-intelligence, multilayer system and installed part of it in the test room close to the test rig and part of it in a separate control room.


The design takes advantage of NI PXI modular instruments with the overall architecture split into two main subsystems:

• The supervision system (SUSY) manages the test sessions and related tasks
• The data acquisition system (DASY) handles and stores data measured by the installed sensors




Architecture of the Supervision and Acquisition System

We structured the SUSY in a three-layer architecture. At the first level, a LabVIEW application running on a host PC manages the graphical user interface, displaying the status of the actuators (such as speed and torque) and storing user inputs. The user-accessible PC in the control room also controls the macroschedule of the test rig activities, such as triggering the execution of warm ups, transitions, and tests.


Each activity is interpreted, coordinated, and translated into commands for the single devices by the second layer, represented by a NI PXI-1042 8-slot chassis with a real-time embedded processor and several I/O modules, including the following:

• 1 PXI-8512 CAN/HS
• 2 PXI-6143 multifunction data acquisition (DAQ) modules
• 1 PXI-6521 8-channel insulated relay and 8-channel digital input module
• 1 PXI-6238 M Series multifunction DAQ module


This device is placed physically close to the PC in the control room. The LabVIEW application running on this device monitors the system in real time with a time cycle of 2 ms as well as the conditions of the single devices on the bench. Also, the application elaborates signals to report the status of the test rig to the first layer. In addition, the PXI module is responsible for safety and emergency management. With the deterministic loop in the real-time software, LabVIEW Real-Time can quickly detect warnings or fault signals from the motor and autonomously solve emergency situations without waiting for inputs from the host PC.


The application communicates with the network of motor control units and represents the third layer through different channels:
• We chose the CANopen protocol to deliver messages to and from the drives handling the vibrating platforms using a shielded serial cable. We used this protocol due to the distance that the signals have to cover because these motor control units are placed directly in the test room, about 50 m away from the PXI module.
• We selected a combination of analogue and digital signals for traction components located in the control room.


We based the data acquisition system on another PXI-1042 module without a real-time processor, which we placed in the test room close to the bench. We connected this PXI module to a PC using a long fiber-optic cable and a remote controller. We chose a fiber-optic cable because large electric train motors create an electrically disturbed environment, the signal has to cover a long distance, and a large amount of signals are conveyed to this cable.


We installed several NI DAQ devices on the PXI platform, providing 24 analogue input channels for accelerometer signals (24-bit at 102 kS/s/ch), four analogue input channels for audio signals (24-bit at 204.8 kS/s/ch), 16 analogue input channels (16-bit at 1 MS/s/ch), 24 digital input/output, and two counters (32-bit). We have used these channels to handle the signals measured by the different types of sensors installed on the test rig, including:

• 1 torque meter
• 1 tachometer
• 4 triaxial accelerometers (1 placed on chassis of the motor and 3 on the one of the gearboxes)
• 4 dual industrial piezoelectric accelerometers that can read the temperature and 16 simple piezoelectric accelerometers, all placed on the bearing housing
• 2 microphones
• 2 environment temperature/humidity sensors and 2 thermistors


The application running on the DASY PC programmed in LabVIEW is based on a producer-consumer architecture that acquires and stores the 46 signals with a sample frequency of 20 kHz. The acquisition is triggered by a digital signal sent out by the SUSY PXI module and detected by the DASY PXI module using one of the digital inputs.


Author Information:

P. Borghesani