High-Speed In-Vehicle Data Acquisition System for ABS Testing

Author(s):
Arum Kumar - Apna Technologies & Solutions
Karthikeyan J - Apna Technologies & Solutions
Sriram Iyer - Apna Technologies & Solutions
Senthil Raj - Apna Technologies & Solutions

Industry:
Transportation, Automotive

Products:
CompactRIO, LabVIEW, DIAdem

The Challenge:
Developing a rugged, in-vehicle data acquisition system suitable for antilock brake system (ABS) testing

The Solution:
Acquiring signals from different sensors at a high sampling rate and performing data acquisition, processing, logging, trending, and analysis using the NI CompactRIO platform and NI LabVIEW software.

Due to new government regulations, all vehicles in India must be fitted with ABS in a few years. This makes ABS testing important, because the testing procedure must comply with the new standards and should test whether the brakes meet the requirements of the new regulations. Vehicles fitted with an ABS will be tested on tracks with different surface frictions and under various conditions of load. Braking ability will also be tested from a range of speeds. The signals acquired during testing include pressure, speed, steering angle, yaw, and temperature. Apart from the physical parameters, the system needs to calculate the distance traveled, speed, and deceleration of each wheel. 

During the test, the vehicle undergoes high deceleration and rapid change in the yaw. The data acquisition system used for ABS testing must be able to sustain high vibration and shock and be compact for easy placement inside the vehicle. It must also provide easy connectivity and a locking mechanism for connecting sensors. Other specifications include appropriate sensor signal conditioning, built in sensor excitation, and dust, oil, and moisture proofing. 

ABS Testing 

The ABS unit in a brake system prevents the locking of wheels, giving the driver greater control when braking. When the vehicle is stopped from a high speed, the wheels tend to lock due to the transfer of vehicle load (inertia of motion), which causes skidding and poor braking. The ABS unit controls the pressure distributed to each of the wheels, and when one or more wheels locks, pressure to this wheel is cut out and distributed equally to the other wheels avoiding locking of the wheels and skidding. 

Another important parameter is the angle of steering. The IS 11852 standard has stringent rules about the maximum angle of steering during braking. This regulation ensures that even at high speeds, the vehicle does not swing, but maintains its line of motion until it comes to a standstill. 

System Requirements 

The system requirements include: 

• High-speed data logging of speed, load, pressure, and temperature during testing 
• Interfaces with the sensors and transmitters providing the necessary 15 VDC or 5 VDC excitation to the sensors 
• Connects easily to the sensors through LEMO or D-type connectors 
• Powerable and operable by a 12 VDC car battery 
• Interfaces with Corrsys-Datron speed sensor to measure vehicle speed, acceleration, deceleration, and stopping distance 
• Measures the vehicle speed from a noncontact optical speed sensor or a fifth wheel speed sensor
• Measures the vehicle speed from a GPS device 
• Measures the speed of the vehicle as a function of analog frequency 
• Calculates the stopping distance, deceleration, and mean fully developed deceleration based on the wheel speed signal 
• Features configurable channels for calibration and for deriving additional pseudo channels from existing hardware and pseudo channels 
• Features configurable display in the software for viewing the parameters during acquisition that can be saved and loaded when required 
• Offers user-friendly configuration options like drag-and-drop 
• Displays test results and test summary in user-defined units that can be changed anytime Provides online X-Y trending for any parameter on either axis 
• Offers configuration for data logging speed; prelog and postlog time; pretrigger, start trigger, and stop triggers; and selecting which channels to log 
• Runs more than one test at a time independently 
• Offers modular hardware options to be adaptable to different test methods and future expansion for more channels or for adding vibration/sound 
• Features a high-end analysis module in the software to perform extensive research on test data taken during trials 
• Exports test data to NI DIAdem and Microsoft Excel formats for analysis and to generate custom defined test reports

apnaVDAS Description 

The NI CompactRIO platform, NI LabVIEW, LabVIEW Real-Time, and the LabVIEW FPGA Module were used to create the apnaVDAS vehicle data acquisition system to address the requirements of the ABS data logger application. The NI cRIO-9004 controller was used with the NI cRIO-9104 8-slot chassis. The NI cRIO-9201 analog input module, the NI cRIO-9411 digital input module, the NI cRIO-9211 thermocouple input module, and the NI cRIO-9237 strain input module were used for data acquisition. In this solution, the data is transferred to the laptop or hand-held display through a TCP/IP communication. 

apnaVDAS Software 

The apnaVDAS software is a versatile data acquisition system software that caters to the vehicle testing applications and the stringent usage conditions of ABS. The apnaVDAS software consists of three parts:

• The FPGA software that runs on the chassis, which is used for data acquisition, basic analysis, and filtering 
• The real-time software used for streaming the data to storage, setting calibration factors, configuration, and various analysis of data and data streaming to a laptop or hand-held display 
• The application software that provides the user interface on the laptop 

All the configuration modules in apnaVDAS can be accessed from one common screen called the control palette. The user can activate as many tests as required, each test independent of the others. Thus, a user can configure one test to continuously monitor the temperature at a low log rate and another test to log the pressure and speed values at a higher log rate when the brakes are applied. 

ABS Testing 

The apnaVDAS software was configured to acquire the four wheel speeds, vehicle speeds, brake line pressures, brake chamber temperatures, pedal efforts, steering angles, and brake trigger inputs at a 1kS/s acquisition rate to evaluate the dynamic performance of the vehicle under different braking conditions. Data is continuously acquired on all channels, which the user can view even when a test is not running. As apnaVDAS displays data, the configuration is dynamic and flexible, so the user can open and close as many indicators as required and use the drag-and-drop feature in the display configuration to visualize the parameter by dropping onto the selected indicator. The configured display settings are saved and loaded when required. 

With the help of the CompactRIO platform and LabVIEW 8.0, the apnaVDAS ABS data logger was built, meeting all the requirements of the vehicle test engineer. The ruggedness of the CompactRIO along with the durable enclosure built by ATS, which offers easy connectivity, makes the logger a perfect fit for all vehicle applications. The apnaVDAS software developed in LabVIEW provides all the features needed for vehicle testing in a simplified flow, which allows dynamic display configurations and multiple test handling, bringing together the world of measurement and an easy-to-use, flexible user interface.

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