External Sync Input; Principle Of Operation - Pacific Power Source LMX Series Operation Manual

7.5 External Sync Input

The phase sync input can be used to synchronize in frequency and phase the internal
waveform generation of the LMX to an external sync reference. The reference must be
within the specified frequency range of the power source and zero phase offset calibration
for phase A may be required to compensate for any phase shifts. Note than Phase B and C
are still referenced to phase A as programmed by B and C phase angles.
7.5.1

Principle of Operation

In External sync mode, the LMX uses the external sync input to synchronize phase A. The
goal of the phase sync is to provide precise frequency synchronization, and consistent phase
at a given operating point, but the phase shift between sync input and AC output is not
automatically zero. A phase adjustment for Phase A must be made by the user to time-align
the power source's phase A output voltage to the external sync input signal.
A couple of factors affect the phase shift:
• There can be a phase shift that depends on the output load because of the finite
bandwidth of the output inverter stages. This is particularly visible at higher
frequencies. At 50Hz or 60Hz, the phase shift will be pretty small.
Note: When the sync input is enabled, the LMX output frequency must be set to a value
similar to the external sync signal. This minimizes the synchronization time and
improves the stability of the generated frequency.
After the sync input is activated, or the external signal frequency/phase is changed, the Sync
circuit's Phase Lock Loop (PLL) requires a short time to "lock" to the external source. The
LMX reports the status of the PLL in the external interfaces (front panel and webpage) by
showing a "Synced" or "Unsynced" message in the status bars. (See section 0 for details).
The status can also be queried with the SCPI command "SOURce:SYNChronize:STATe?".
The sync circuit is able to synchronize to any signal with a frequency if F
where F
SETPOINT
10Hz)
The following specifications apply to the phase sync input at the DB25 port:

Entire Contents Copyright 2018 by Pacific Power Source, Inc. (PPS) • All Rights Reserved • No reproduction without written authorization from PPS.
LMX Series Power Source Operation Manual
Figure 7-2: External Trigger Input Timing
is the normal frequency set point and F
LMX SERIES™ OPERATION MANUAL
SECTION 7: Auxiliary I/OError! Reference source not found.
is a configurable value (default is
RANGE
+/- F ,
SETPOINT RANGE
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