GPS16X-HVS GPS Receiver
12
The resolution of accuracy for the clock set is typically 10 microseconds. Some
older CR3000, CR800-series, and CR1000 data loggers (hardware revision
number less than or equal to 007 in RevBoard field in the data logger Status
table) have a resolution of 10 milliseconds. The clock set relies on information
from the GPRMC sentence. If this sentence is not returned, a clock set will not
occur.
By default, the instruction expects the GPS unit to be set up at 38400 baud,
outputting the GPRMC and GPGGA sentences once per second. The data
logger expects the start of the second to coincide with the rising edge of the
PPS signal. If there is no PPS signal or if the required sentences come out at
less than once per second, the data logger will not update its clock.
GPS units with lower baud rates can be used with the
GPS()
instruction but the
baud rate has to be set for the relevant Com port it is to be connected to either
in the data logger settings or by including a
SetStatus()
command after the
BeginProg()
instruction in the program (for example,
SetStatus
(
"BaudrateCOM4",19200
)).
Baud rates of 2400 bps or lower will not work as the GPS unit will not transmit
the two GPS sentences once per second reliably. Similar problems can be
encountered even at higher baud rates if too many optional GPS strings are
selected to be output.
The
GPS()
instruction has the following syntax:
GPS
(GPSArray,ComPort,TimeOffset,MaxTimeDiff,NMEAStrings)
Description of the parameters follows:
GPSArray
The
GPSArray
parameter is the variable in which to store the
information returned by the GPS. Fifteen values are returned.
If this array is not dimensioned to 15, values will be stored to
fill the array and no error will be returned. If no values are
available, NAN will be returned. The following values are
returned by the GPS:
Array(1) = Latitude, degrees
Array(2) = Latitude, minutes
Array(3) = Longitude, degrees
Array(4) = Longitude, minutes
Array(5) = Speed over ground, knots
Array(6) = Course over ground, degrees
Array(7) = Magnetic variation (positive = East, negative =
West)
Array(8) = Fix Quality (0 = invalid, 1 = GPS, 2 = differential
GPS, 6 = estimated)
Array(9) = Number of Satellites
Array(10) = Altitude, meters
Array(11) = Pulse per second (PPS) length, microseconds
Array(12) = Seconds since last GPRMC sentence
Array(13) = GPS Ready, 10 = ready
Array(14) = Maximum clock change, milliseconds (10 msec
resolution)
Array(15) = Clock change count
