Using real-time data acquisition tools benefits automotive test engineers
Engineers should consider the developments in DAQ systems and sensors to maximize potential benefits for mobile testing.
Reducing the time it takes for products to reach market is important and the automotive industry is looking at methods of making its testing programmes more efficient to achieve this goal. One possibility is the use of applications based on telematics to give engineers a comprehensive picture covering all tests.
Telematics combines information from data acquisition (DAQ), global positioning system (GPS), computer, digital video and telecommunications technologies. By using standard wireless application protocols (WAP) in the 2.4, or 5.8 GHz bands, test vehicles can send detailed information directly to the engineering office where it can be analysed in real-time.
The key to using these techniques is to supplement sensors and systems built in to a vehicle with specialist devices to get the additional data needed for a detailed analysis. When combined with a modern DAQ system they ensure accurate analysis of all the data.
European manufacturers have used Controller Area Network (CAN) bus data exchange networks in their vehicles for a number of years and automobile makers in both the USA and Japan are now also increasingly using this technology.
From a data acquisition standpoint, much of the data needed to measure a vehicle's operating characteristics is already built into the vehicle's computer system. The ability to tap into the CANbus system greatly reduces the number of additional sensors needed in a test set-up. Even comfort control functions, like switches for electric windows, can be included to give a total operational view of the vehicle.
In the past much of this information was often overlooked because of the complicated wiring schemes required. With the vehicle's dedicated CANbus, every motor and switch can have its own network address. This allows a DAQ system connected to the CANbus to receive information on both critical and secondary functions.
The DAQ system collects digitised information from selected devices on the CANbus and stores them as if they were measurement data from conventional sensors. Additionally, a CANbus loop can use semi-smart transducers to send data back to the engine management unit and to the DAQ system.
Modern vehicle tests use many types of force transducers, strain gauges, pressure transducers, displacement sensors, and accelerometers for gathering data when in service. Many of the sensors, especially for life-cycle estimation will be based on strain gauge and inductive measurement principles.
Strain gauges offer inexpensive, proven technology, and are easy to mount and adapt for mobile applications. However, as with stationary data acquisition, certain mobile measurements requiring great accuracy and precision need high-end sensors. Sensors for mobile applications must also be very robust, and protected from environmental factors such as temperature extremes, dust, and water.
The DAQ system is very important to the success of mobile real-time test analysis. This needs an amplifier system with a large number of input channels able to accommodate a wide range of transducers and sensors rather than those from a single manufacturer. During a test programme the DAQ will receive information from all of the sensors including the GPS and digital video. It should be easy to configure and adaptable for different test programs.
To provide maximum benefit the DAQ must feature CANbus measuring capability and, ideally, it should be part of the complete system covering the entire measuring chain. Another important consideration when choosing the DAQ system is the need for a high-resolution analogue to digital (A/D) converter for each channel. This allows the equipment to handle a wide range of dynamic signals without requiring any adjustment of the measuring range.
The DAQ system should have a memory format able to store a continuous stream of data and fully use all the digitised data sources. Equally, expandability can be important since it allows engineers to add extra amplifier module for more comprehensive tests. To provide additional benefits the DAQ system should be able to export data in a wide range of options and allow data compression for handling large data files.
All of these considerations should be contained in a single, integrated housing since space is often at a premium. Other features, such as a central processing unit (CPU) for standalone operation might be desirable, but are not essential.
The correct choice of DAQ system, along with any additional sensors, can ensure that the maximum amount of information can be gained from the vehicle’s CANbus and analysed in real-time using telematics.
