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Keysight Technologies
Reducing Device-Failure Risk
with a Black-Box Recorder

Application Note
Introduction

Protecting against damage in test for aerospace/defense and automotive devices -- or any
devices that are time consuming and costly to replace -- is essential to meeting delivery and
budget objectives. When the risk of device failure is of signiicant concern, test planning should
include strategies and equipment that can help you reduce the risk.

Even after planning carefully, taking extensive precautions, and executing a test plan step by
step, DUTs may still fail. DUTs may fail for a variety of reasons beyond DUT laws, among them
human error, test equipment failure, and controller failure. When a failure occurs, you need to
identify and understand the failure mechanism to avoid a repeat. Better still is to detect con-
ditions that can lead to DUT failure and to act to prevent damage. The Keysight Technologies, Inc.
N7908A black-box recorder (BBR) can provide the necessary functionality. As in commercial
aviation, and increasingly in automobiles and other high-value equipment, a BBR can provide
critical failure-mode insight and can play an important role in test strategy development aimed
at reducing the risk of failure. You can gain insight about the operation and health of a DUT from
examining the power source output and status data captured during a test cycle. The N7908A
BBR is a user-installable accessory available for the Keysight Advanced Power System N6900
and N7900 Series DC power supplies.

Keysight black-box recorder
The Keysight BBR runs in the background to continuously log the power supply's measured param-
eters and various other events. Logging starts automatically when the unit is turned on. Logging
does not interfere with any source or measurement features of the power supply. It never stops, and
data is preserved after a power cycle. Data logging can be performed every 10 ms or every 100 ms.
At the 10-ms logging rate, you can log 24 hours of continuous data, and at the 100-ms rate, you
can log 240 hours of data. Recorded measurements include average, minimum, and maximum
voltage, current, and power. Logged events include system status bits that might affect sourcing,
two user-deined status bits, front-panel keys pressed, SCPI command received, and trigger events.
Examining and analyzing recorder data to understand DUT failures
BBR data can help you analyze DUT failures by providing time-stamped records of events
and measurements of voltage, current, and power levels, as well as power-supply status
-- both leading up to the point of DUT or test-equipment failure and after the failure. When
the BBR clock is synchronized with the test-system controller and events external to the
power source are also recorded and time stamped, examining and analyzing the data may
provide a crucial link that can help you reconstruct the problem and determine the failure
mechanism. Voltage, current and power data coupled with power supply status captured
every 10 or 100 ms compared with expected values and conditions can help you discover
if a failure was the result of a test configuration error, test equipment malfunction, or an
isolated DUT failure. When a failure is not caused by test error or equipment malfunction,
BBR data such as higher- or lower-than-expected voltage, current or power as well as
short duration surges may help to uncover DUT flaws.

When a DUT fails or an unexpected event occurs during test, you can examine BBR voltage,
current, and power entries along with a broad array of status bits for anomalous values
and conditions. In addition to power-source output measurements, the BBR can record 31
status/event items. Recorded status states range from power-supply output operating mode
to power-supply programming to fault conditions to user-defined status events (see Figure
2). You can view up to 12 user-selectable status items with the Power Assistant software
(see Figure 1). Figure 1 shows the PC-based Keysight N7906A Power Assistant software
interface to the BBR. To facilitate a review of BBR data while testing is in progress, you can
use the software to capture and view snapshots with a specified time range.

Figure 1: Keysight N7906A Power Assistant software interface to the BBR

1. The area on top of the display indicates the total time period of the snapshot.
2. The yellow line is the output voltage.
3. The green line is the output current.
4. The green portion of the window displays the status states.
5. The vertical red lines indicate when power was cycled on or off.
6. The pale blue dots on the timeline indicate where a user-defined message was placed into the log.

3
Using BBR capability to establish and execute DUT test strategy
When it is critical that a test strategy includes a measured approach to the application of
power and loading on a DUT, the BBR can provide a useful record of events for each stage
of testing. When test-result expectations are not fully determined or understood prior to
test execution, you may need to use a cautious, incremental test approach to confirm the
DUT is operating within a safe range in each stage. For DUTs early in the development
cycle, test-result expectations may be preliminary. For DUTs in final stages of development,
test-result expectations will generally be firm. For either situation, the examination of BBR
data for appropriate or inappropriate source output levels or surges of current, voltage
and power and power supply status for each test stage may help you determine if testing
should continue, or if you need to modify the test or the DUT before proceeding.

For some DUTs, testing involves the application of a range of voltages and a range of
loads. Here, too, the BBR can be helpful and can provide useful information as you adjust
test conditions. In some cases, the testing of a multifaceted, multisubsystem DUT must
be done on a subsystem-by-subsystem basis, the results of which become a determining
factor for continuing on to each additional subsystem. For some subsystems or for an
entire DUT, it may be advisable to apply power to and/or loading on the DUT in measured
increments. Recorded power supply status and output levels during each incremental test
may help you determine the response of the DUT to additional changes in DUT stimulation
and loading. Examining the data may provide insight into device performance and whether
moving to higher stress levels of testing is appropriate.

Using BBR data to augment quality assurance measures
When a DUT is a finished product you intend to deliver to an end customer, quality assur-
ance plays an important role in ensuring product performance and life, and is most critical
when the product, such as a satellite, cannot be serviced once deployed. Inappropriate
and unexpected stress levels may not cause immediate DUT failure, but may cause or
contribute to the weakening of components in the DUT, potentially leading to early failure.
You can examine BBR recordings for anomalies to help verify that a DUT was operated
within safe parameters. For example, some devices require multiple bias voltages that
must be applied and removed in a specific order. Deviation may result in immediate failure,
but worse would be an undetected misapplication of voltage resulting in a potentially
shortened product life. Other potentially product-life-shortening events could result from
operator error, test-equipment malfunction or software glitches. The BBR records test-
system conditions that affect power-source status and output levels.

4
Status Status Status
/event Description /event Description /event Description
CV Regulating in CV mode Trans A Step or List transient is active USTAT2 User-defined status 2
(voltage priority only) Active
LIM+ Output is in +current limit in VPRI Instrument is set to voltage priority CP Negative over-power protection
voltage priority mode tripped

Output is in +voltage limit in
current priority
IPK Output is in positive peak CP+ Positive over-power protection CSF Current sharing fault has
current tripped occurred
IPK- Output is in negative peak CC Regulating in CC mode PCHG Programming DAC setting has
current (current priority only) changed
UNR Output is unregulated LIM Output is in