ashtech DG16 Reference Manual page 65

signal. The trigger signal can be set to the rising or falling edge using the
$PASHS,PHE command.
TTT synchronization message output
The precision of the measured time is 50 nanoseconds (ns) in differential mode
and 200 ns in stand-alone mode with SA off. This is based on GPS time, which is
output as day number, hours, minutes, seconds, and fractional seconds to 6 digits
past the decimal mark.
The photogrammetry time measures the event time relative to the receiver's GPS
time. It measures only the first event during the period between 2 GPS epochs
(Figure 3.1).
The DG16 measures only one event time per data collection period. If more than
one event time is measured within a data collection period, the receiver measures
only the first one. The event time record rate is dependent upon the setting of the
RCI parameter.
Because the 1 PPS signal is used to measure the photogrammetry events, the
period of the 1 PPS signal must be set to a value equal to or less than the period
of the event pulse.
The trigger pulse may be TTL-compatible or open collector. Minimum pulse
duration is 100 nanoseconds when the signal is not terminated at the receiver
input. The impedance is approximately 5 KW.
Use a coaxial cable with BNC connectors to connect the camera trigger output to
the photogrammetry input connector of the DG16.
Basic Operation
DEFAULT SETTINGS
—
synchronize with the rising edge
of the trigger signal
Figure 3.1. GPS Epochs
CAUTION
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