Series 3700A System Switch/Multimeter Reference Manual
Section 5: Switching and scanning
3700AS-901-01 Rev. D/June 2018
5-41
UTC suffers from discontinuities because of nonperiodic adjustments known as “leap seconds."
These adjustments present problems because they can make events that occurred at different
periods of time appear to occur at the same time. PTP is a time standard that does not have any
discontinuities and has no adjustments for local time (that is, it is not time-zone aware). PTP is
presented as the number of seconds since January 1, 1970.
The Series 3700A offers two versions of time for most IEEE-1588-related commands,
.seconds
and
.ptpseconds
, representing UTC and PTP respectively. IEEE-1588 requires that devices are
synchronized using UTC or PTP time, not local time. The Series 3700A does not distinguish UTC,
PTP, and local time; it is not time-zone aware. You must be aware of this when synchronizing with
devices that are time-zone aware.
When IEEE-1588 selects a time-zone aware device to be the master clock, the Series 3700A accepts
the time of that clock. This time may not agree with the local time of the Series 3700A, especially
when a network spans multiple time zones. If you schedule events on the Series 3700A to occur
according to your local time, events will not occur at the time you expect.
You can avoid confusion by setting the time on the Series 3700A to UTC time instead of local time.
Manage the conversion from UTC to local time in your software application. For example, assume
local time is Eastern Standard Time in the United States (EST), which is equivalent to GMT-5 (hours).
Therefore, if the current local time is 3:00 PM, the UTC time is 8:00 PM. Set the time of the Series
3700A clock to 8:00 PM. If it is then synchronized with a time-zone aware master clock, its time will
not change significantly.
The Series 3700A does not differentiate UTC and PTP time. The
ptp.utcoffset
(on page 11-307)
attribute is zero unless a master clock that is aware of the difference between UTC and PTP time
populates this value. This value is volatile and does not persist through a power cycle.
Configuring and enabling IEEE-1588
To configure IEEE-1588, connect the Series 3700A to the LAN, along with any other IEEE-1588
enabled devices that you want to synchronize to the Series 3700A. Refer to the
Series 3700A User
Manual
for information on connecting the Series 3700A to the LAN. If you want to synchronize
multiple Series 3700A instruments on a LAN, each instrument must have the same PTP subdomain
name.
The default PTP subdomain name is
_DFLT
for all Series 3700A devices. Use the
page 11-303) attribute to change the subdomain name for any Series 3700A on the LAN. After
changing the subdomain name, you must power cycle the Series 3700A to restart its clocks. If you
have changed the subdomain name of any third-party IEEE-1588 enabled device in that subdomain,
you must also restart its clock.
Cycling the power to the Series 3700A does not return the IEEE-1588-related parameters to factory
default state. To return these to factory defaults, perform a LAN configuration reset. This can be
done using the
(on page 11-265) function on the remote command interface. You can also
perform a reset through the front-panel interface by entering the Main menu, selecting LAN, and
selecting Reset.
