“By making efficient use of SCXI modules, we can build a cost-effective, high-channel-count data acquisition system with just one DAQ board.â€
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challenge:
Updated a dual dynamometer system to provide repeatable, reliable testing for heavy-duty tracked vehicles such as bulldozers or armored military vehicles such as tanks.
solution:
Develop a PC-based acquisition and control system using SCXI and DAQ systems controlled by LabVIEW.
Introduction
Engineers at the Southwest Research Institute (SWRI) are working on installing and upgrading an old-fashioned high-power dynamic vehicle test system from the 1980s that replicates road load conditions for tracked vehicles, including steering resistance loads. There has been an increasing demand for the detection of tracked vehicles for a long time, as most test equipment can only test individual components, such as the engine of the power section, the gearbox and the final drive. Due to different weather conditions or drivers and other factors, road test vehicles can produce non-repeatable results. It has become increasingly important to test the durability and performance of a vehicle under controlled environmental conditions.
The dynamic characteristics of a tracked vehicle are quite different from those of a wheeled vehicle. When a tracked vehicle has the same road conditions as other vehicles, it also needs to experience a "frictional" load—the friction encountered by the track when the vehicle turns. During a turn, as the track turns to propel the vehicle forward, the track slides along the ground. Many studies have established equations that predict the torque needed to overcome a "frictional" load based on vehicle geometry and ground conditions.
hardware
Our upgraded test system includes two 1250 hp DC dynamometers (dyno). It simulates road load conditions. For measuring the speed and cornering radius of the vehicle under test, we chose a LabVIEW-based data acquisition system to upgrade the system. We configured a system with 370 data acquisition channels to monitor the dynamometer while monitoring the measured vehicle and measuring its performance. Thanks to SCXI's multiplexing technology, the acquisition task can be done on a multi-function data acquisition board that is installed on an industrial PC.
We used SCXI to achieve 370 channels with some relatively simple setup. The SCXI accessory's terminal block has a wired interface that allows us to wire and troubleshoot with a handheld device. Although the company is unlikely to use all channels, they still want to have many options to configure different test tasks.
we provide:
• 48 K-type thermocouple inputs
• 48 J-type thermocouple inputs
• 96 analog inputs
• 32 isolated analog inputs
• 16 frequency inputs
• 42 analog outputs
• 24 SPDT relay outputs
• 32-bit digital input
• 32-bit digital output
Although some channels are used for fixed hardware test tasks (control dynamometers and their accessories), users can customize most channels on the setup interface, including renaming channels and providing zoom factors. Input channels provide error checking, upper/lower limit alarms and alarm thresholds, while output channels provide default values ​​that can be set. When the input exceeds the alarm threshold, all outputs are restored to the specified default values.
Fixed analog input channel sensors include left/right dynamometer torque, left/right dynamometer torque, and gearbox temperature. Fixed digital inputs include oil pressure limit switches, fire extinguisher limit switches, oil level switches, oil temperature limit switches, dynamometer air temperature limit switches, and dynamometer air flow switches.
Users may use a universal input channel to monitor various signals such as temperature, pressure, level and speed of the vehicle, as well as environmental conditions such as humidity, air pressure and temperature.
software
SwRI chose LabVIEW because it provides a sophisticated graphical user interface, simple integration with NI hardware, and a rapid development environment. With LabVIEW, we don't have to rely on more complex text-based programming languages ​​to efficiently implement the complex requirements of test systems.
We use LabVIEW controls to customize our graphical user interface with a large number of display properties. Since this application may design a large number of channels, it is not possible to display all channels simultaneously on the same screen; in addition, many channels do not need to be seen on the screen. Through the front panel display control's property node, the operator can display the channel that he needs to monitor on the specified position on the screen. We use array clusters in a scrollable form in the setup program, and the operator can define the name and characteristics of the channel. We use global variables to store all system constants and pass data from one subroutine to another.
The program also includes a calibration procedure that allows the technician to monitor and adjust the signal for each channel and then store the calibration parameters in a file. We use buffer acquisition to read the values ​​acquired by all defined input channels at 100 Hz. The main program loop runs at 10 Hz and performs an average of 10 points to help eliminate any noise signals. The program saves the data to the file once every two seconds. In addition, it saves the last 400 data points (10Hz rate) in the circular buffer. At the time of the alarm, the data in this buffer can help diagnose what went wrong.
to sum up
The development of this system is progressing smoothly. By making efficient use of the SCXI module, a single cost-effective, high-channel-count data acquisition system can be built with just one DAQ board. LabVIEW and these NI hardware products provide convenient software development and system integration. Our customers look forward to using this system to test new prototype test cars.
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