Developing a Data Acquisition System for Railway Turnout Inspection

challenge:

In order to perform an on-site acquisition and analysis of physical quantities, such as pressure and forces generated by railway switches during operation and/or train passage, we create easily transportable systems in order to verify and analyze their behavior during motion.

Solution:

Integrating NI CompactDAQ hardware with the USB interface and developing applications using the NI LabVIEW development system installed on a portable computer creates an easily transportable system that is not only compact and easy to use, but also flexible, configurable, and rugged enough to interact with different types of sensors installed on the railway turnout system to collect physical quantities in real time.

Operation display interface

“Because of the small size of NI CompactDAQ system devices, we created a lightweight, compact, sealable box that also includes the necessary functions to condition and acquire electrical signals from sensors installed in the field to perform analysis for our customers’ applications.”

We designed the system and tested it for a while, during which time interference phenomena appeared, such as peak interference - interference even reaching several hundred volts, which was caused by the electromagnetic fields caused by the passing trains. We created the system not only to perform simple tests of the system, but also to study what happens when the turnout is repeatedly stressed.

System Components

The complete system consists of the NI CompactDAQ acquisition system, electrical interface components that condition the field electrical signals and protect the acquisition system from field interference, and a portable computer with data acquisition and processing applications installed and connected to the NI CompactDAQ system via a USB port.

We also assembled the electrical system, including the electrical signal conditioning and acquisition system, in a military-approved, sealable box on wheels, which is ideal for field use. [page]

app

We have designed dedicated applications for entering acquisition parameters such as sampling channels, sampling frequency, triggering and sampling duration; for managing data during testing, such as graphical visualization and saving of data; and for managing and analyzing acquired data in post-processing, with graphical visualization of data, application of mathematical functions and export of data in .csv format.

Compact hardware

Because of the compact size of NI CompactDAQ system devices, we created a lightweight, compact, sealable box that includes the necessary functions to condition and acquire electrical signals from sensors installed in the field to analyze the customer's application.

Due to the limited amount of hardware, users must provide the box with a 220-volt AC power supply to power all system components, sensor systems, and acquisition systems; use appropriate cable connectors to connect sensor cables to the wiring terminals inside the box; and use a USB cable to connect the NI CompactDAQ hardware device to the portable computer.

software

The software design separates the test acquisition module from the post-processing analysis module, allowing different types of acquisition methods to be used based on the different tests performed, and then analyzing the saved data during post-processing.

Flexible, configurable system

We structured the acquisition module so that the user can select the sampling channels and sampling frequency for the test - the maximum frequency that the user can select depends on the number of channels specified by the user. The user can also select a digital trigger to start the acquisition module. With this special feature, the user can define that the acquisition will only start under certain circumstances, thus optimizing the actual acquisition duration and the maximum acquisition duration implemented.

For each analog channel, the user can define the graphical representation of the curve, define the name associated with the analog channel, and define the linear parameter values ​​that convert the electrical signal into an engineering signal to represent the amplitude monitored by the single analog channel. The user can save these parameter values ​​in a file with a specific structure so that these values ​​can be reused as parameter configurations for different tests.

When the user starts data collection, the development application will dynamically configure the collection engine according to the user's selection, collect data, display the data on the graph in a dynamic collection manner, save the collected data, and display the collection status on the monitor.

We designed a post-processing module so that users can analyze the data stored through field acquisition again. With this module, users can reload previously saved test data, display these data graphically and manage the displayed data curves, and use mathematical functions, such as applying filter functions to eliminate interference on the frequency, to process the acquired data; obtain new charts that can be exported in .csv format, which is compatible with other mathematical analysis software, such as NI DIAdem; or save new test data in image format.