Oscilloscopes detect ECU disturbances from EMI: Page 4 of 5

November 16, 2015 //By Loren Dunn , Mike Hertz & Dan Steinken
Oscilloscopes detect ECU disturbances from EMI
Loren Dunn , Mike Hertz and Dan Steinken examine how to use oscilloscopes to detect ECU disturbances from EMI.
testing turned off, the wave shape of each signal is observed. The oscilloscope is Edge-triggered on Channel 2, and all four waveforms are captured synchronously.

Figure 3. Simulated ECU output signals include PWM signals on Channels 1 and 2, an Actuator Driver Output on Channel 3, and a CAN Split voltage on Channel 4.

Figure 4 shows mask testing. The mask shape verifies that the signal's high level, low level, frequency, duty cycle, and other criteria fit within tolerance limits described in the test plan. The mask thickness forms the specified tolerance band around a defined nominal value, which verifies that each acquired waveform doesn't deviate by more than a specified percentage beyond the defined nominal value. In this example, all waveforms meet all of the specified test criteria. Note that the oscilloscope, set for edge triggering, continuously monitors for deviations using the predefined mask criteria. The oscilloscope triggers on an edge occurring on Channel 2, and the scope is configured to identify and document each of the deviations as they occur.

Figure 4. Simulated ECU output signals show that the PWM signals on Channels 1 and 2, the Actuator Driver Output on Channel 3, and the CAN Split voltage on Channel 4 all fit within the defined tolerance masks, resulting in passing mask test criteria.

In Figure 5, the simulated ECU exhibits an out-of-tolerance response during exposure to an electric field, 1 kHz 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.

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