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Original Authors: Ing. Alejandro Sarabia, Continental Automotive
Edited by Cyth Systems
Designing and developing an automated test system for automotive sensors that is easy to maintain and minimizes hardware costs.
Using NI LabVIEW system design software and PXI modular instrumentation to build a custom end-of-line test system in a short time that has the capacity to increase the number of products that can be simultaneously tested.
The reliability of variable reluctance (VR) speed sensors is critical. These sensors must be able to operate in the hardest conditions and be highly compatible with all parts of the system. They need to be resistant to external factors such as temperature, humidity, dirt, and some chemicals. Additionally, the sensors must give reliable information without the results being affected by electromagnetic fields and the vicinity of other sensors.
Left: The system was replicated to create two parallel testing environments.
Right: The graphical user interface shows the values for resistance, inductance, and voltage, as well as the pass/fail values.
For this project, we needed to design a complete test system for all the different electrical and mechanical aspects, ranging from the creation of the feeler gauge to the programming of the software that verifies the different speed sensors.
The system carries out the following two main tests on the VR sensor:
Measurement of the nominal resistance and inductance of the coil, including checking that the values for the resistance and the inductance of the sensor’s coil are within normal working parameters.
Measurement of the induced voltage. We can use the NI PXI-6515 module to control the servomotor of a cogwheel that simulates a tire rotation. The rotation excites the sensor’s coil to generate a voltage signal. We can use the NI PXI-4072 digital multimeter (DMM) and the NI LabVIEW Advanced Signal Processing Toolkit to measure and analyze the signal to obtain its shape, amplitude, and phase angle. We can also use a signal from the servomotor to transmit the data from the DMM and to measure the induced voltage, always on the same wheel cogs. We used this measurement method for each VR sensor, otherwise, we would have different voltage measurements for each pin and the potential cost of the R&R analysis would increase by 100 percent.
One of the benefits of using the NI PXI-4072 DMM together with the NI PXI-2503 digital I/O module was that we could carry out multiple measurements such as resistance, inductance, and voltage using a single instrument. This provided significant cost savings. Also, using the NI PXI-6515 digital I/O card meant we could directly control the servomotor and the feeling gauge’s rotation without the need for additional hardware, which resulted in additional savings over using a programmable logic controller just for this task. Finally, implementing the tester in the PXI industrial platform led to a small and modular system. Therefore, we could fit all the testing equipment for the digital signals, analog measurements, and commutation, as well as the equipment for processing and mathematical analysis, in a small rack, which reduced the size of the testing cabinet.
Ing. Alejandro Sarabia, Continental Automotive
Edited by Cyth Systems