Test-rig design for automated evaluation of automotive electro-chemical sensors
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Examensarbete för masterexamen
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The main aim of this project is the design and development of an automated test-rig
for testing automotive electro-chemical sensors. The main targeted sensor is NOx
(Compounds of Nitrogen oxide), which is one of the most critical and failure-prone
components of exhaust after-treatment system. Based on the gas concentration
measurements from these sensors, several actions are taken to reduce the vehicle
emissions and comply with required emission guidelines by government. An automated
test-rig can perform various combinations of temperature and gas variations
on multiple sensors simultaneously while reducing the operating test time compared
to manual one. Added to the advantage is the scope of detailed analysis of faulty
field sensors thereby increasing the overall productivity.
A cRIO (Compact Re-configurable Input Output) is used as the main embedded
controller to carry out test command and control, data logging and saving, and communication
with sensors and other test-rig hardware components. The test software
is developed in LabVIEW (Laboratory Virtual Instrument EngineeringWorkbench).
To reduce operating complexity, script-based command files are made to control various
test-rig equipment. Finally, a GUI (Graphical User Interface) is developed for
user interaction and real-time monitoring during on-going test.
A working automated test-rig is successfully developed and its performance is compared
to manual operation through a series of tests. The final testing was carried
out in a test cell (gas-sealed box) with provision to mount sensors and other accessories
like gas inlet/ outlet valves, gas flow controller and pressure sensor. Several
test cases were conducted to evaluate three NOx sensors in three different gas environment
- air, nitrogen and NOx (489 ppm concentration). The sensors under
test corresponded well to the gas variations resulting in NOx and O2 measurements
within the expected range of 467 ppm and 20% respectively.
The aim of the project is successfully met with around 50% of active operator/
operating time saved by automated test-rig over manual one. In addition, this
test-rig removes the intermittent delays of manual maneuvers resulting in better
repeatability performance. Due to limitation of resources, some features and test
cases could not be incorporated and their implications are further discussed. As a
further improvement, additional safety features can be added and the test-rig can
be extended for testing other types of sensors.
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Automotive sensors, Test automation, NOx, Test-rig, cRIO, LabVIEW