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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?

Once available outside the chamber, the signals are typically routed to data-acquisition system, which often requires custom software to analyse and compare the signal information to allowable tolerances and decide if the if EUT meets the specified requirements. Unlike many sensors, ECUs (electronic control units) may have several signals to monitor and evaluate measurements to acceptance limits and the software needed can come at a high development cost. Instead, we use an array of oscilloscopes in place of a complex, custom data acquisition system. Because oscilloscopes are already equipped with mask testing and parameter limit test abilities, they can address many, if not all, of the test requirements directly, without any significant amount of software development time needed.

Figure 2 shows the open doorway to the reverberation chamber, which is to the right of the test bench. On the left side, fibre optic cables, receiver and an array of oscilloscopes for performing real-time analysis.

Figure 2: An array of oscilloscopes is used for real-time analysis of the DUT response to radiated electric fields.

We use waveform masks in the oscilloscope to compare the waveform shapes during exposure to a disturbance relative to the shapes with no disturbance present. The dimensions of the mask depend on the acceptance criteria defined in the test plan.

Figures 3, 4, and 5 show the output of a simulated ECU. For confidentiality reasons, simulated data is used which closely approximates what signals may be monitored with a typical ECU. Channels 1 and 2 show simulated PWM signals which control an output driver actuator signal. The simulated actuator signal is captured on Channel 3, and a CAN split voltage is displayed on Channel 4.

Figure 3 shows the acquisition with mask 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.

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