Developing an Auto-Synchronized Multiavionics Protocol Data Bus Acquisition System

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"We chose LabVIEW to program this system because of its excellent graphical capabilities and tight integration with NI PXI products using NI-DAQmx measurements services software. We easily and accurately incorporated features such as timestamp data, TCP/IP functions, UDP, self-test of the cards, and periodic tests. Additionally, NI-Sync, a strong and effective tool, helped us achieve the three-level time synchronization easily."

- Swati Poduval, Captronic Systems Pvt. Limited

The Challenge:
Designing a self-correcting multichassis synchronized system that acquires multiple protocol data simultaneously with a correct timestamp and synchronizes this system with local network time protocol (NTP) and the global positioning system (GPS) module.

The Solution:
Developing a custom, three-level solution using NI LabVIEW system design software, NI-Sync software, and the industry-standard PXI hardware platform, which included multiple interfaces with large I/O counts.

Author(s):
Swati Poduval - Captronic Systems Pvt. Limited
Premraj S. Moily - Captronic Systems Pvt. Limited
Omkar Nagendra - Captronic Systems Pvt. Limited

A modern aircraft includes a combination of multiple intelligent subsystems that aid in communication, navigation, and surveillance. These subsystems, called line replaceable units (LRUs), are modular and easy to replace on the field. Typically, independent teams design and develop LRUs. It is important to test the LRUs with a test rig on the ground before integrating them on the aircraft. A ground-based  LRU integration rig (LRUIR) facility uses state-of-the-art hardware and software in a distributed architecture to help completely integrate the process of verifying the functionality of the avionics subsystems. An LRUIR provides a platform to test the LRUs in an integrated environment on the ground. Real-time data acquisition of the test rig is important to ensure reliable testing of the LRUs. The data acquired provides insight into the behavior of the units and the communication between them. Captronic Systems, a National Instruments Platinum Alliance Partner, was privileged to design and develop such an important test facility.

System Implementation

A large number of LRUs connect to the data bus acquisition system. Figure 1 shows the block diagram of the system setup.

This system featured:

  • 730 I/O points from different LRUs
  • User-configurable data formats for acquisition
  • Different protocols for different data formats
  • Multiple chassis

This was a validation system, which made efficiency and calibration our top priorities. We used NI Measurement & Automation Explorer to first test the individual cards, applying the concept of self test to make sure the system checked all the cards as soon as the software ran. We used the following cards in our system:

  • NI PXI-6225 M Series DAQ board for analog acquisition
  • NI PXI-6511 module for digital acquisition
  • NI-8431 device for asynchronous RS422 measurements
  • NI PXIe-7962R NI FlexRIO module for synchronous RS422 measurements
  • NI PXIe-8234 gigabit Ethernet interface device
  • Avionics Interface Technologies (AIT) MIL-STD-1553 for MIL acquisition
  • AIT ARINC 429 module for ARINC acquisition

Next, the user could design each parameter from low-level to high-level configurations. Low-level configurations included sampling rates for analog or transistor-transistor logic and open source for digital, start bits, stop bits, RS422 baud rates, MIL real-time addresses and subaddresses, or port numbers in case of Ethernet. High-level configurations included encoding techniques such as non-return-to-zero, biphase, or even protocols like high-level data link control in which the user could configure for start of frame, end of frame, controls bits, or FCS.

The main challenge was to synchronize up to a millisecond among different cards using different protocols spread across three chassis. This was not a single-step process. We needed any event occurring during the acquisition process to be captured by all three PXI systems with the same timestamp so the event could be recognized during analysis. First, we synchronized our network with the GPS time. Next, we used network time protocol (NTP) to synchronize other systems within the network. Finally, we used precision time protocol (PTP) to synchronize the three chassis. N I-Sync helped us avoid traditional coding techniques for time stamping each event, which would not have been as precise, so we could achieve this task easily. Figure 2 shows a block diagram representing the three-level synchronization.

Inspired by NI Diadem data management software, we made our software user friendly so the user could view the acquired data as a graph or table or with special templates for MIL and ARINC data. We developed a customized coding format for synchronous RS422 by using the NI PXIe-7962R NI FlexRIO FPGA module. The FPGA Module offered extra flexibility so we could efficiently design the format per our client’s requirements.

We divided the application software into two modules—the real-time module and the host user interface module. We deployed the real-time module in the PXI controller and the host user interface module ran on the client PC. The TCP/IP Ethernet interface facilitated communication between these modules. Figure 3 shows the block diagram depicting our entire software.

The host system ran the LabVIEW application software, which featured:

  • Login—Only authorized users could access the software
  • Configuration—Users could configure parameters such as sampling rate, baud rate, or conversion parameters for the desired channels present in the hardware
  • Acquisition—Users could see the data acquired in real time
  • Diagnostic—Users could test the functionality of channels
  • Analysis—Users could convert the data stored during acquisition into .xls format so the user could open the files using Microsoft Excel

The real-time system used:

  • NI-VISA to acquire asynchronous RS422 data
  • NI LabVIEW FPGA Module to acquire synchronous RS422 data
  • AIT drivers to help acquire ARINC and MIL-1553 data
  • User Datagram Protocol (UDP) to acquire Ethernet data


Figure 4 shows the display panel of our software.

The post analysis of data was done using NI Diadem data management software.

Benefits of Using the NI Platform

We chose LabVIEW to program this system because of its excellent graphical capabilities and tight integration with NI PXI products using NI-DAQmx measurements services software. We easily and accurately incorporated features such as timestamp data, TCP/IP functions, UDP, self-test of the cards, and periodic tests. Additionally, NI-Sync, a strong and effective tool, helped us achieve the three-level time synchronization easily.

Author Information:
Swati Poduval
Captronic Systems Pvt. Limited
India
swati@captronicsystems.com

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