BBR Clock Setup
The real-time clock is used to time-stamp the BBR, which is its only function. When shipped, the real-
time clock is set to Greenwich mean time. To set the clock:
Front Panel Menu Reference SCPI Command
Select System\Preferences\Display\Clock.
Enter the date in the Month, Day and Year fields.
Enter the time in the Hour, Minute, and Second fields.
Press Select to setthe date and time.
To setthe date:
SYSTem:DATE
To setthe time:
SYSTem:TIME
There will be a slight gap/discontinuity of less than 1 second in the BBR record when
the clock is set.
BBR Alignment
If the BBR option is installed, it is recommended that you align the real-time clock in the power supply
with the clock on your computer/controller before you perform any critical activity or test. This will
remove any error due to long term clock drifting.
Clock Drift
The real-time clock’s time base has a tolerance of ±100 ppm. This causes the time base to steadily
drift in relation to a perfect time reference. The following table illustrates this effect on long term BBR
measurements. Note that drift times apply to both 10 ms and 100 ms logging rates.
Logging Time Drift
1 hour ±0.36 seconds
1 day ±8.64 seconds
10 days (requires 100 ms logging rate) ±86.4 seconds
BBR Alignment Methods
Method 1- Set the real-time clock using the front panel or SCPI command as described above under
Real Time Clock Setup. Note that there is no automated way to synchronize the RTC to NIST,
TIME.GOV, or other internet clock sources. There is no external clock input to set the real-time clock.
Once the real time clock has been set on multiple units, mis-alignment of the BBR records between
units will be minimized.
Method 2- Send a text message (event tag) into the BBR record using the SCPI SYSTem:BBR:EVENt
“message” command. With this command, you can write a text record into the BBR log to mark a
particular time in the record. For example, you can send the following text message into the event log
“Starting Test ABC at 10:05:02”. Each BBR record is logged every 10 ms (or 100 ms), so the message
alignment should be within 1-2 records or 10-20 ms of the logged data, depending on how fast you
Keysight N6900/N7900 Series Operating and Service Guide 165
4 Using the Advanced Power System
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