Tuesday, March 18, 2014

Quickly implementing several automotive electrical disturbances based on the ISO 16750-2 standard

In my previous posting “Upcoming software release unleashes the N7900 APS’s potential without any programming” <click here to review> I shared that we are updating our 14585A Control and Analysis software to now work our N7900A Advanced Power System (APS) so that one can quickly implement complex power-related testing without resorting to programming. One of many things the N7900A APS is very well suited for is performing a variety of automotive electrical disturbances, due to its higher power output, relatively fast output slew rates, and ability to store and run 64,000 point ARB waveforms. Offsetting this, until now, is it required a bit of programming effort to create, load, and run such ARB waveforms on an N7900A APS. In comparison, the 14585A has a pretty comprehensive library of ARB waveforms, lets you import and edit ARB files (for example, you capture an actual crank waveform profile with an oscilloscope), as well as create a mathematical expression for an ARB waveform. On top of that individual ARB waveforms can be tied together to create larger, much more complex ARB sequences. This is excellent for creating a variety of automotive electrical disturbances.

My first project here was to see how well I could do with implementing a number of electrical disturbances for testing automotive electrical and electronic equipment, based on the ISO 16750-2 standard.   I figured I would start with something easy and work my way up to more challenging ones from there. The first one was “4.5.1 Momentary drop in supply voltage”. This simulates a 0.1 second drop due to an electrical load suddenly short-circuiting followed by its fuse blowing open. In this case I used the pre-defined pulse ARB waveform, set up as shown in the 14545A ARB configuration screen in Figure 1.



Figure 1: Setting up ISO 16750-2 4.5.1 Momentary Drop in Supply Voltage in 14585A Software

The standard calls for under 10 milliseconds fall and rise times. The N7951A 20 volt APS provided about 0.4 millisecond fall and rise times and I was able to also use the slew control to set it slower if I desired.  Alternately I could have used ramp ARBs and enter the ramp times there. The resulting momentary drop was captured in the 14585A’s scope mode of operation, shown in Figure 2.



Figure 2: Capturing ISO 16750-2 4.5.1 Momentary Drop in Supply Voltage in 14585A Software

Next I decided to see how well I could do with implementing “4.5.2 Reset behavior at voltage drop”. This consists of a series of 5 second-long voltage drops spaced 10 seconds apart, increasing by an additional 5% drop in amplitude each time. This tests the DUT to see at what voltage drop level it takes to cause the DUT to reset due to low voltage. For this I linked 20 voltage drop ARB waveforms together in a longer sequence, in the 14585A software. Due to the longer duration the results of running this ARB sequence were instead captured in the 14585A’s data logging measurement mode, shown in Figure 3.



Figure 3: Capturing ISO 16750-2 4.5.2 Reset Behavior at Voltage Drop in 14585A Software

OK, I think I am up for a bigger challenge, and the ISO 16750-2 ”4.5.3 starting profile” looked to be just right to take on. This is a combination of a series of voltage ramps slewing milliseconds to 10’s of milliseconds at the beginning and end with a seconds-long period of a sine wave superimposed on DC embedded in the middle, to emulate the actual steady-state cranking portion.  As there are multiple versions of this starting profile, I selected one with an extended cranking period, as I figured that one would be the more challenging for fast details to be reproduce accurately. I implemented this in the 14585A ARB generation screen, using a combination of two ramps, a sine wave, and another ramp, as shown in Figure 4.



Figure 4: Setting up ISO 16750-2 4.5.3 Starting Profile in 14585A Software

I captured the results of the ISO 16750-2 ”4.5.3 starting profile” I created in the 14585A’s oscilloscope measurement mode, which is shown in Figure 5.



Figure 5: Capturing ISO 16750-2 4.5.3 Starting Profile in 14585A Software

Overall it appears to be good in Figure 5. The cranking sine wave superimposed on the DC is as it should be. I expanded the time scale to check to see if the fast slewing ramps at the beginning and end were also as expected, the beginning transient portion of the profile shown in Figure 6.



Figure 6: Capturing ISO 16750-2 4.5.3 Starting Profile in 14585A Software, Beginning Details

I was really pleased to see the timing of these milliseconds-long events were spot-on even when being just a small part of a seconds-long total ARB sequence. And because the ARB sequences are constructed with high level models it is an easy matter to make changes as well as quickly construct new or non-standard disturbances. This software took the challenge out of me trying to manually program these complex arbitrary automotive electrical disturbances.  While I like taking on challenges, with how quick and easy the 14585A software made this task become, in this case I didn’t mind it haven taken the challenge out one bit!

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