Lxi Class B And C Triggering (Ieee-1588) - Keithley 3700A Series Reference Manual

Section 5: Switching and scanning Series 3700A System Switch/Multimeter Reference Manual

LXI Class B and C triggering (IEEE-1588)

Introduction to IEEE-1588 based triggering
The Series 3700A uses IEEE-1588 precision time protocol (PTP) to implement synchronized
measurements and initiate time-triggered events over the LAN (ethernet) interface. IEEE-1588 is a
requirement of the LXI B and C Functional Classes. Using IEEE-1588, you can schedule instrument-
driven actions, such as measurements, to occur at a specific date and time and synchronize
timebases between instruments on the same network. You can only access these capabilities through
the remote command interfaces.
You can find detailed information on the syntax and usage of each remote command presented in
this section in Command reference.
IEEE-1588 implementation in the Series 3700A
When you enable IEEE-1588 on a Series 3700A on a local network, the Series 3700A communicates
with other IEEE-1588 enabled devices on the network through a dedicated network port called the
PTP port. A predetermined algorithm then automatically selects the network device with the most
accurate clock. This network device becomes the IEEE-1588 master. If multiple devices have the
same clock accuracy, the protocol arbitrarily chooses one device to be the IEEE-1588 master.
When the protocol selects the Series 3700A as the master clock, the Series 3700A uses the time
value stored in its battery-backed real-time clock and updates the time in all subordinate devices.
When the protocol selects another networked device as the master clock, the Series 3700A is
subordinate to the more accurate device and adjusts its time to that of the master clock. Additionally,
the Series 3700A updates its battery-backed clock so that the time is "remembered" if the master
clock is removed from the network.
At periodic intervals, the master clock synchronizes to all subordinate clocks through timestamped
messages over the PTP port. This allows IEEE-1588 to maintain time synchronization between
multiple devices on a network.
Program the synchronization interval in the Series 3700A using the ptp.syncinterval attribute. The
default synchronization interval is two seconds. Increasing the synchronization interval to values of
more than two seconds increases the amount of time that it takes devices on the LAN to synchronize.
If you change the synchronization interval, you must restart the clock of the Series 3700A by cycling
its power.
Synchronization of timestamps between IEEE-1588 enabled devices to within 150 ns can take as
long as two minutes.
Correlating PTP to Coordinated Universal Time (UTC)
To ensure synchronization across networked devices, you must be aware of the time protocol used
by those other devices on the network.
The most widely accepted time scale is Coordinated Universal Time (UTC); in many places, it is
considered standard time. UTC is nearly the same time as Greenwich Mean Time (GMT), another
very familiar time scale, and for the purposes of the Series 3700A, UTC and GMT are the same.
Local time is offset from UTC according to time zones; additional offsets can occur due to Daylight
Savings Time adjustments.
5-40 3700AS-901-01 Rev. D/June 2018