Developing a Distributed Emissions Test Bench Using NI Software and Hardware

Author(s):
Leon Grossman - DMC, Inc.

Industry:
Automotive

Products:
PXI/CompactPCI, LabVIEW

The Challenge:
Developing an application to gather emissions data on various vehicle platforms, from experimental hybrid vehicles to production gasoline vehicles, using disparate hardware in a four-wheel drive dynamometer facility.

The Solution:
Creating a distributed application using National Instruments LabVIEW, the NI SCXI and PXI hardware platform, and third-party instrument hardware.

Laboratories run tests on vehicles with front- and rear-wheel drive as well as hybrid, gasoline, diesel, and experimental power train options. A test range for such different configurations requires an extremely flexible system. Channel counts change from vehicle to vehicle, and some vehicles use serial-controlled instruments. Each of these data sources must be combined into a single data stream and processed for results.

Hardware

At DMC, Inc., we developed a system capable of testing multiple vehicle types using National Instruments SCXI and PXI hardware and third-party instrument hardware. The system consists of a four-wheel drive dynamometer, an emissions bench, a fuel cart for measuring fuel during testing, and other serial instruments that we can add as necessary. A PXI chassis handles control and data collection for all the hardware devices.

The vehicle data collection hardware includes an NI PXI-8336 Optical MXI-4 Card plus matching PCI board in a PC connected to a PXI-1052 PXI/SCXI chassis. With this setup, we can place the data acquisition hardware near the vehicle with minimal signal complications. We can also set up vehicles more quickly with this configuration because the placement of the PXI/SCXI chassis minimizes excess wiring.

Software

We developed the system software in NI LabVIEW. It currently runs across four computers, but we could operate the system from a single processor with minimal code change, if necessary. With the single processor option, we could tailor computing power to the application without overloading the hardware.

We use a host computer during operation for test setup and monitoring and at the end for data synchronization and processing. Operation is easier with this single source for test setup than with previous multiple-computer applications. The data processing engine combines all the data streams and synchronizes them to produce a coherent test picture. In addition, we created a post-processing, plug-in architecture for users to implement automated data-processing code on a test-by-test basis. The post-processing system provides instant results from routine tests and still gives us the flexibility of manually analyzed custom tests.

The facilities data server provides timing for the application and controls all serial devices, including triggering test phase changes in the emissions bench and sending data to the drive trace in real time to guide the driver through the test. The facilities data server also functions as the master clock when matching data at the end of a test.

The drive trace computer displays a rolling chart of current and expected speed. This chart contains a window that documents speed, current and next shift points, time information, and a test overview. Drive trace requires real-time communication to properly direct the operator, so we preloaded the drive trace application with the test profile via fault-tolerant TCP/IP communications.

The vehicle server collects the data related to each acquisition channel. We synchronize the channels to the facilities server master timer and later combine the data with the timing when the data is transmitted to the host computer. The vehicle server also can run independently of the host computer to calibrate sensors during setup.

The main challenge we faced in working with all of these disparate modules was maintaining adequate integration among the components. We met this challenge with a messaging architecture designed to pass flexible data types through a minimal number of communications paths, and by transmitting only high-speed data at test completion. Each component then performed its assigned task with minimal overhead and interruption risk.

Summary

Using NI hardware coupled with NI software, we easily created a flexible architecture for testing various vehicles. With PXI and SCXI hardware, we had the channel count and channel type flexibility we needed to accommodate our laboratory’s changing needs. And with LabVIEW, we were able to create an application that we can quickly modify to support additional instruments for individual tests.

For more information, contact:

Leon Grossman, Senior Product Engineer

DMC, Inc.

1333 N. Kingsbury St.

Suite 110

Chicago, IL 60647

Tel: (312) 255-8757

Leon.grossman@dmcinfo.com

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