A major automobile manufacturer encountered a problem with their antilock brake or ABS
modules. During final automobile assembly, the ABS warning light on the dashboard was
coming on. After some research, the engineers discovered that as the power connector was
slid on to the battery post, intermittent power was briefly applied to the ABS module, causing
the ABS light to erroneously to come on. This caused quality engineers to realize that they
needed a way to simulate intermittent power to the ABS module to test it on the bench.
To simulate this waveform, the quality engineers needed to generate a DC voltage that bounces
between zero volts and 14.4 volts. The voltage must change between 50 milliseconds, 100 milliseconds,
and 200 milliseconds. These on times and off times are encountered as the terminal is slipped
onto the battery post. Generating a power waveform that can quickly switch between zero
volts and 14.4 volts is a test challenge. The quality engineers considered using two
common instruments, a power supply and an arbitrary waveform generator, but typical
power supplies can’t change fast enough to generate this waveform and typical function
generators can generate the waveform, but can’t provide enough drive current to power
the ABS module. The only solution would be to design some form of custom-built power
amplifier. If the quality engineers custom built a power amplifier, it will need to be
designed, mounted, and controlled. Agilent Technologies has developed the DC power analyzer
which is a new category of test equipment for R&D work. The Agilent N6705A DC Power Analyzer
is a highly integrated instrument that combines up to four advanced DC power supplies, DMM,
oscilloscope, arbitrary waveform generator and data logger. The DC power analyzer eliminates
the need for multiple pieces of equipment and complex test set-ups. It provides an easy
to use interface with all sourcing and measuring functions available from the front panel.
The N6705A can be used to generate the battery voltage waveform. The N6705A’s arbitrary
waveform generator can create a variety of power dropouts to look for problems and evaluate
margins after design changes are made. Let’s see how easy it is to set up the DC power
analyzer to generate this waveform. The arbitrary waveform generator function will be used to
create this waveform. The N6705A has several built in waveforms including sine, step, ramp,
and pulse. But for this application the user defined voltage waveform is selected. On the
user defined voltage properties screen, you can enter the values to define the waveform.
To generate the power waveform, you enter 14 volts as the first step in the waveform.
And the time duration to stay at 14 volts in this case, for 100 milliseconds. Then you
press the add button to add the next step. This step will be two volts for 50 milliseconds.
You can continue to add steps manually up to 512 steps, however, to simplify setup,
the N6705A permits the ability to import a waveform. The user-defined waveform can be
stored on an external USB memory device. The waveform data is imported from a comma separated
value or CSV file. This file can easily be generated in a text editor, spreadsheet, or
mathematic software. The CSV file is easily loaded and the waveform is now ready to be
generated. To confirm that the DC power analyzer will generate the desired waveform, you can
use the built in scope to show that the desired voltage waveform is being generated. In scope
mode, the N6705A can directly measure the voltage versus time flowing out of its power
supply into the ABS module. Press properties to configure the scope measurement, select
view of voltage on channel two. Since this is a non-repetitive waveform. Set the trigger
mode to triggered. Select the trigger source to trigger when you press the ARB run stop key.
With the integrated instrument, it is very easy to configure the trigger source
as when you start the wave form by pressing the ARB run button, then go back to scope
screen. Next, you set the time base to show the waveform, 200 milliseconds per division.
Finally, arm the scope by pressing the run stop button. Now, the scope is ready to show
the waveform. To start generating the waveform, press the ARB run stop button, this both starts
the ARB and triggers the scope. The desired waveform appears on the scope. The DC power
analyzer has a fast rise time with voltage transitions as fast as 160 microseconds per
step change. This allows the DC power analyzer to directly generate a power waveform with
sharp edges just like those that are applied to the ABS module when the battery cable is
connected. To review, Agilent Technologies has developed the DC power analyzer, which
is a new category of test equipment for R&D work. The Agilent N6705A DC Power Analyzer
is a highly integrated instrument that combines up to four advanced DC power supplies, DMM,
oscilloscope, arbitrary waveform generator, and data logger. The DC power analyzer eliminates
the need for multiple pieces of equipment and complex test set-ups. It provides an easy
to use interface with all sourcing and measuring functions available from the front panel.