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Tracking down ECU disturbances from EMI

Posted: 25 Nov 2015 ?? ?Print Version ?Bookmark and Share

Keywords:EMC? oscilloscope? electrostatic discharge? ESD? pulse-width modulation?

In figure 5, the simulated ECU exhibits an out-of-tolerance response during exposure to an electric field, 1kHz amplitude modulated. Amplitude of the PWM signals is reduced and their duty cycles increase. Additionally, the modulation frequency superimposes onto the signal during their high state. The Driver Output waveform suggests an indirect effect from the disturbance as it merely responds to the PWM input signals. Unlike the other three signals, the CAN Split signal is not affected by the EMI and continues to produce a compliant result. This type of mask testing allows for multiple criteria to be rapidly tested in real time.

Figure 5: When subject to EMI, the simulated ECU PWM and Actuator Driver Output signals each exceed the tolerance mask test criteria and the scope notifies the operator that a deviation has occurred.

In addition to waveform mask testing, pass/fail limits are also applied to the parametric data to ensure that the numerical measurement results also comply with specified limits. Note that on the screen image in figure 5, the scope has indicated the three deviations which have occurred denoted with the red "Fail" message on the screen under the test criteria. In the event of a mask failure or parameter limit failure, an oscilloscope can also automatically execute actions, such as saving the waveform data to be used for direct comparison and documentation, saving a screen image to be used for documentation and evaluation, generating a pulse out of the oscilloscope to assist with test automation, and sounding an alarm to inform the test operator when a deviation occurs.

Although oscilloscopes are well equipped to perform the rapid parametric measurements required for detecting deviations in EMC immunity testing, they have been often overlooked, mainly due to lack of awareness and lack of sufficient oscilloscope channel count. Using an array of oscilloscopes is potentially the most efficient and cost effective method to qualify ECU signal and actuator outputs during immunity tests, since most of the functionality using pass/fail mask and parameter limit testing has already been implemented, saving design engineers significant cost and time for functional testing compared with the costly software development time needed to implement custom data acquisition systems to perform the same rigorous test requirements of EMC deviation detection.

About the author
Loren Dunn, Mike Hertz and Dan Steinken contributed this article.

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