Carlson Merlin LT, Руководство пользователя

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6 Merlin LT time-tagging
The Merlin LT laser data is time-tagged by aligning an NMEA ZDA message to an accurate 1 pulse per second
(PPS) timing pulse. Merlin LT has the ability to receive PPS and ZDA timing messages from certain external GPS
receivers. This timing information is then integrated into the header of the UDP packet that contains the laser
measurement data that is interpreted by the navigation software.
Time-tagging enables data from the Merlin LT to be accurately associated with corresponding position, heading and
motion data collected from other sensors on the vessel.
6.1.1 ZDA input options
GPS manufacturers implement the ZDA and PPS signal slightly differently. Therefore, when inputting a timing
source into Merlin LT from an external source the correct option must be selected from the GPS Receiver Type
drop-down list in the
Configuration
window of the Merlin diagnostic tool software: see section 7.4.
The options in the GPS Receiver Type drop-down list are outlined below. These options may apply to equipment
other than that specified by each label.
Trimble UTC : Trimble UTC data only; a valid string contains 26 characters. The laser expects the UTC string
approximately 700 ms before the 1 PPS signal:
UTC 09.11.03 23:01:52 56<cr><lf>
Novatel Span
: the laser will expect a valid data string to contain a 34-character string after the 1 PPS signal is
active:
$GPZDA,043342.00,08,12,2009,,*64<cr><lf>
Novatel Coda : the laser will expect a 35-character string after the 1 PPS signal is active. The falling edge of the 1
PPS signal denotes the GPS time crossing the second boundary:
$GPZDA,043342.000,08,12,2009,,*64<cr><lf>
Merlin (Trimble ZDA) : the laser will expect a 39-character string after the 1 PPS signal is active:
$GPZDA,161508.025,26,10,2010,00,00*5C<cr><lf>
Trimble Applanix
: the laser will expect a 36-character string after the 1 PPS signal is active. The rising edge of the
1 PPS signal denotes the GPS time crossing the second boundary:
$GPZDA,212649.0039,31,08,2011,,*6E<cr><lf>
In the above examples <cr> represents the carriage return character and <lf> the linefeed character.
The time-tagged ZDA message coming from the external timing source needs to be correctly interfaced to the Merlin
LT. When connecting the ZDA cable to the external source, the supplied cable configuration needs to be carefully
considered in relation to the pins of the external source.
The supplied ZDA cable is designed to connect directly to industry-standard receivers. The expected connector on
the external timing source is detailed in section 6.1.2 below.
6.1.2 External timing source: expected pin-outs
The external timing source should output the ZDA message through a serial cable with a m ale 9-pin, D-type
connector (standard RS232 protocol).
Figure 23 and Table 5 show a serial connector and the expected pin-out schematic of the external timing source.