© Valeport Limited 2003
MIDAS Surveyor Operating Manual
Page 26
0420805d.doc
4.2.11
TIME SETUP
GPS transmissions contain time as well as position data. However the MIDAS surveyor also requires an on board clock
to control its operating sequences, and it is more practical to use this to maintain instrument time on a second by second
basis. The clock used in the system has a stated accuracy of 20ppm, which equates to better than 2 seconds per day.
Note however that each time the instrument is switched on, it corrects the on board clock to the GPS time (if available),
ensuring that no significant timing errors can occur.
The part of the GPS time data that is used is simply "number of seconds past the hour". For this reason, the user must
set the clock to the correct date and approximate local time before use.
The sub-menu functions allow the user to individually set the year, month, date, hour, minute and second. It is advised
that the correct year, month, date and hour are entered, together with approximately correct minute and second values.
The system will correct these final two values to GPS time as soon as a valid fix is obtained. If no fix is available when
the clock is set, the entered values for minutes and seconds will be used instead, and corrected as soon as there is a fix.
The assumption is that surveying will not begin until a valid GPS fix is achieved anyway.
Use the Up and Down keys to scroll the values up and down, and the Enter key to set.
4.2.11.1 1/2 Hour Time Zones
Some locations use 1/2 hour time zones rather than the standard 1 hour increments. Since GPS timings are given as
time past the hour, the MIDAS Surveyor must include a feature to allow it to correct the time to the nearest 1/2 hour. If
the local time zone is a 1/2 hour zone, go to the last function in the Time Setup sub-menu, labelled "Time Zone 1/2hr".
Use and or down key to toggle between "Normal Time Zone" and "1/2hr Time Zone", and Enter to confirm.
4.2.11.2 Set Time
Once the date, time and appropriate time zone have been entered, the user must confirm the entry.
Under the Set Time function, use up or down to scroll between "Set Time Now" and “Do Not Set Time”. Note that for the
time to be set, you must scroll through the options to “Set Time Now”,
even if it already says this when you enter the
menu
. This is to ensure that the time is not set accidentally. Use the Enter key to confirm.
The MIDAS Surveyor will immediately adjust the internal clock to the values set, or to match the GPS time signal if it is
available.
