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IOTA-VTI Operation Manual
The Time Screen - Hour Glass:-
If the backup battery voltage is not maintained since previous use, due to battery
discharge or removal, an hourglass symbol will be displayed next to the satellite number.
This is to alert the user that the GPS has lost its backup power and it's almanac has
reverted to the default status, thereby perhaps losing the correct offset between GPS-time
and Universal Time, therefore time displayed can not be guaranteed.
The absence of the hourglass symbol in the third character position means that the time
displayed is correct to Universal Time.
For information on Almanac Updates and Battery Maintenance, see sections below.
The Time Screen - Loss of GPS fix:-
In normal circumstances, once started IOTA-VTI's sensitive GPS should keep good
reception to the GPS constellation of satellites. However, if the number of satellites in the
GPS fix falls to 3 or less, the GPS will stop outputting 1pps signals, and so IOTA-VTI will
stop displaying time and will display 'x' shown above.
IOTA-VTI will display plenty of warning that loss of fix might be imminent by;
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the F, X and N code (see above)
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the reduction of the satellite count
Should loss of fix appear likely, and an event is imminent, the user should make a brief
recording of the time screen display, thereby calibrating the field counter to UT, then the
event timing can be salvaged by use of the field counter, which will keep working at all times
the device has power.
Note-1: this condition is unlikely in normal circumstances because, once the GPS has
started, it is very difficult to prevent the GPS from receiving signals. During testing the
IOTA-VTI had to be wrapped in aluminium foil AND placed in a metal toolbox to prevent
GPS reception.
Note-2: If IOTA-VTI is to be used in difficult conditions, e.g. in an observatory with a metal
dome, then the purchase and use of an external antenna that is sited outside the metal
dome is recommended. See External GPS Antenna section for more information.
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Video Timers
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