NI PXI Architecture Combines Flexibility and Real-Time Performance in Networked Auto Component Test Systems

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Schematic Representation of the System

Author(s):
P. Kannan - Soliton Technologies Pvt. Ltd.
S. Venkatakrishna - Soliton Technologies Pvt. Ltd.
K. Arul Murugan - Soliton Technologies Pvt. Ltd.
Anand P Chinnaswamy - Soliton Technologies Pvt. Ltd.

Heavy vehicles have complex braking systems with many functions to ensure fail-safe operation, including shifting of braking between front and rear wheels, and hand and foot brake operation. This complex system is made of seven different types of components. Our customer, a leading manufacturer of such braking systems worldwide, needed automated test rigs to test all seven components. The tests involved measuring the leakage in the component, testing component characteristics and simulating fail conditions, and checking the response of the component.

The requirements of the test rig included:

• Flexibility – The customer wanted their test engineer to modify the entire test sequence without any involvement from the programmer because the models were new and the sequence could not be precisely determined during the purchase of these rigs. They also anticipated release of new models, which they wanted their test engineers to quickly configure.
• Cost-effective system – Our customer had the option of purchasing the test system from their European parent company’s vendor. However, the cost of that system was high due to a proprietary architecture and the cost of implementation in a different location (India).
• Performance – Requirements called for control loops to deterministically execute while at the same time servicing the user interface and Ethernet communications.
• Open architecture – Our customer preferred open hardware architecture and an industry-standard programming environment.
• Compact footprint – The customer needed efficient use of valuable manufacturing floor space.

We proposed the NI PXI real-time system along with the NI LabVIEW Real-Time programming environment. The customer accepted our proposal because of the openness of both the hardware and software platforms along with the ability to quickly meet the system requirements.

Auto Component System Description

We designed the system with the objective of meeting the main requirements of flexibility and providing a hard, real-time response. To achieve these requirements, we divided the system into two main blocks – the real-time system (RTS) and the monitoring PC (MPC).

The RTS system consists of the PXI real-time controller, data acquisition, digital I/O, and a motion controller. The system feeds the conditioned signals of the transmitters to the data acquisition module. The digital output and input lines are optically isolated to safeguard the cards. The MPC with a 2.6 GHz Pentium 4 processor provides the user interface.

The UUT is clamped in a corresponding fixture in the test rig. The pneumatic system consisting of the compressors, regulators, and valves supplies the pressurized air to test the UUT. Instrumentation on the test rig consists primarily of pressure and load transmitters and temperature sensors. Actuators activate the UUT. For example, in the hand brake test rig, an actuator simulates movement of the hand brake lever.

The RTS functions include:

• Run critically timed loop of 1 mSec (maximum allowed asynchronous jitter from MPC for data through Ethernet is 100 µSec every 100 mSec) to acquire data and control the outputs.
• Acquire the signals from various pressure, load, and temperature sensors. Average the data and store in a shared memory location.
• Provide hard, real-time control the solenoid valves and servo drive.
• Run the safety logic in parallel to ensure system and human safety.
• Data transfer to MPC for displaying, logging, and analysis.

The MPC provides the user interface to the testing system. The following are some of the MPC functions:

Test Sequence Editing

The customer can edit the sequence of testing and have full control of the test of the component. The sequence editor generates a script file that is transferred to the RTS. The integrity of the script file is checked before transferring to RTS.

Manual Test

The user can manually operate all the valves individually to test the component and test rigs. This gives the customer flexibility to troubleshoot the system. Logging of data during manual testing helps the customer understand their product better. This is useful during the product development phase.

Auto Test

The user sees the auto test screen during the actual testing of the component. The screen shows data as it is acquired by the RTS and displays descriptive graphs and text that help the user understand and follow the test.

The NI-DAQmx driver for real-time systems offered us greatly improved performance compared the previous driver. With this new driver’s advanced multithreading capabilities, we effortlessly met the system requirements.

Development Advantages with NI Products

NI hardware and software gave us many benefits during the development of the test rig, including:

• The multithreaded operation of the analog and digital lines of the data acquisition device (with NI-DAQmx)
• We could achieve the time criticality in the order of microseconds with LabVIEW Real-Time
• The Ethernet driver was robust enough for transferring the data between the RTS and MPC and logging the data in a database server.
• The easy configuration and reliability of the motion controller card reduced our effort even more than we estimated.
• We designed an attractive and self explanatory user interface that reduced the learning time for the customer to operate the system.

The entire set of seven test rigs for the different components was networked through a LAN, which provided centralized storage in a database. This ensured data traceability and easy access. Through the network, the customer could view information from any other computer in the LAN.

System Benefits

Besides meeting all the requirements, the test rigs developed using NI products offered the advantages compared a similar system used by our customer’s parent company in Europe.

Timely Development, Successful Implementation

We created seven custom test rigs in a period of eight months that met the challenging requirements of flexibility and real-time performance. Our choice of the NI hardware and software platform for these test rigs was the major contributor to the success of the systems. Continuing innovation from NI helped us comfortably achieve our goals.

Author Information:
P. Kannan
Soliton Technologies Pvt. Ltd.
#683, 15th Cross Road, 2nd Phase, JP Nagar
Bangalore 560078
India
Tel: +91 -80- 51208600
Fax: +91 -80- 51208700
kannan@solitontech.com