User manual

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Time Synchronization
19. Time Synchronization
The XL2 Analyzer may synchronize the start time precisely with
the GPS signal. The measurement start matches the GPS time
with an accuracy of +/- 0.7 ms (+/- 32 samples @ 48 kHz).
This requires
a txt-file named “gpssync.txt” stored on the SD card•
a specially adapted GPS Receiver, NTi Audio # 600 000 357•
Concept
The measurement start follows these concept:
Relative Time•
The GPS Receiver generates a square signal with a frequen-
cy of 0.1 Hz. The rising edge is exactly synchronized to full
10 seconds. In other words, the positive edge of the signal
indicates the following: 00 – 10 – 20 – 30 – 40 – 50.
The square wave signal is available at the RCA input of the
XL2 Analyzer. The instrument architecture offers two chan-
nels, so it can simultaneously process the microphone signal
on the XLR input and the time signal on the RCA input.
Thanks to the GPS signal, the XL2 may precisely start every
10 seconds.
Absolute time•
The XL2 receives the absolute time from the connected
NetBox, which synchronizes to the NTP service. The XL2
time is synced every 60 seconds. The communication be-
tween XL2 and NetBox causes an uncertainty in the timing
in the two-digit milliseconds range.
The combination of the relative and absolute timing allows the
XL2 to start the measurement accurately. The GPS time signal
does not have to be permanently present on the XL2 during
the measurement, which accommodates the operation in case
of unfavorable GPS reception. It is important that the time sig-
nal was detected by the XL2 at least once before the start of
the measurement, the XL2 then retains this time information
with an accuracy of typically 0.5 ms per hour.
After repositioning the GPS receiver, the sys-
tem takes about an hour to initialize for the first
time.
After rebooting the XL2, or after changing the
measurement function, the XL2 needs to syn-
chronize with GPS time again.