ISO 16750 is an international standard for environmental testing of the electrical and electronic equipment in road vehicles. ISO 16750-2 (i.e. part 2) addresses electrical loads. Basically, this describes a series of tests depicting subjecting automotive electrical and electronic equipment to variety of standardized electrical disturbances that exist within the electrical system of an automobile. These disturbances are a variety of transient events, some due to normal operation while others are caused by fault conditions within the electrical system. Either way the electrical and electronic equipment must be able to withstand these disturbances.
The electrical disturbance tests in ISO 16750-2 tend to be complex waveforms in most cases having relatively low speed rise and fall times of about a millisecond or slower, created by events such as the crank starting of the engine, for example. In comparison, the standardized tests in ISO 7637-2 tend to be electrical disturbances that are less complex but having much faster rise and fall times, down to nanosecond levels in some cases. This is because ISO 7637-2 tests are typically based on events such as switching inductive loads which results in very fast inductive voltage spikes.
There are several challenges with conducting the ISO 16750-2 tests. One challenge is recreating the complexity of many of the electrical disturbances. This calls for the solution to have an arbitrary waveform generator (ARB) as the basis for the signal generation and then a suitable power stage to bring the signal up to appropriate voltage, current, and power levels needed to both power the device under test (DUT) as well as drive the levels considerably higher in many cases, to apply the overload disturbance described by the test standard. Yet mores challenges are good ways to easily create, save, recall, and modify these electrical disturbances as required without having to resort to extensive programming to do so.
It turns out the Keysight N7900A Advance Power System (APS) is very well suited for is performing a variety of automotive electrical disturbances. This is due to its higher power output of 1 or 2 KW depending on model, provide greater power when paralleled, relatively fast output slew rates, and ability to store and run 64,000-point ARB waveforms. The N7900A APS family pictured in Figure 1.
Figure 1: Keysight N7900A Advanced Power System, 1 and 2 KW family
Complementing the N7900A APS family is the 14585A Control and Analysis software, with enables the user to create and manage complex waveforms and disturbances that can be run on the N7900A APS without needing to perform any programming. The 14585A has a 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. Together they form an excellent solution for implementing and running many of the electrical disturbances defined by ISO 16750-2.
To see how well I could do on implementing several electrical disturbances defined in ISO 16750-2, 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 from the 14585A library, set up in the 14545A ARB configuration screen as shown in Figure 2.
Figure 2: 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 oscilloscope mode of operation, shown in Figure 3. This solution lets you verify your waveform is what you were expecting to get with the digitizing readback built into the N7900A, instead of having to connect up a separate oscilloscope.
Figure 3: 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 4.
Figure 4: 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 from 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, due to more memory being dedicated to the extended cranking period. 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 5.
Figure 5: 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 6.
Figure 6: Capturing ISO 16750-2 4.5.3 Starting Profile in 14585A Software
Overall it appears to be good in Figure 6. The cranking sine wave superimposed on the DC is as it should be. I then expanded the time scale on the captured waveform 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 7.
Figure 7: 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. The 14585A 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 most of the challenge out of the task one bit!
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