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EYPAD
4.3.6.1 Bit 7: 3D / Position-fix Time Evaluation (2 Options)
Validity: GPS systems
Bit 7 in the system byte is used to switch between 3D and Position-fix evaluation:
• Bit 7 = 0
• Bit 7 = 1
The accuracy of the time evaluation is defined by the exact calculation of the installation po-
sition. In order to carry out this calculation (3D evaluation) it is necessary to receive informa-
tion from at least 4 satellites. The signal runtime to several satellites is determined from the
calculated position and the precise second mark is produced from their mean value. The ac-
curacy of the second mark in this 3D evaluation mode is specified in the technical data.
In many cases for stationary installations a less precise evaluation of the second mark suf-
fices, e.g. this can be inaccurate by up to several milliseconds. In Position-fix mode the accu-
racy fundamentally depends on the exact input of the installation position. The second mark
is then calculated from the data from one received satellite and the input position. When in-
putting the position to minute accuracy, the accuracy of the second mark is already better
than ± 20 µsec. When the input is even more precise values can be achieved in accordance
with the technical specifications.
The advantage of the Position-fix mode is that the clock can be synchronised using the data
from only one received satellite. The antenna can also be installed in locations where less
than ¼ of the sky is visible.
In many cases the antenna can be mounted internally at the window (short cable, no light-
ning protection). If 4 satellites are available in this mode then the evaluation switches auto-
matically into 3D mode and calculates the exact position. In this case, the accuracy with one
satellite also increases to the value given in the technical data.
The accuracy data refer to the comparison with the 3D evaluation:
The second marks of a system in Position-fix mode deviate by max. ±1 µsec.
4.3.6.2 Bit 6: Recognition of Time Leaps during the Synchronisation Process
Bit 6 controls the status of the system during the synchronisation process.
Bit 6 = 0 normal synchronisation process, no recognition of time leaps
When a valid synchronisation signal is available ("R" status) the system clock is synchro-
nised every minute. If synchronisation fails but is reinstated within 9 hours then the system
clock is adjusted smoothly when synchronisation takes place again. This means that the mil-
liseconds are adjusted slowly and there is no erroneous system time change. When syn-
chronisation takes place after more than 9 hours then the system clock is synchronised fully
including the millisecond range. An erroneous system time change is possible if the deviation
is too great.
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hopf Elektronik GmbH
Nottebohmstr. 41 • D-58511 Lüdenscheid • Tel.: +49 (0)2351 9386-86 • Fax: +49 (0)2351 9386-93 • Internet: http://www.hopf.com • E-Mail: info@hopf.com
Position-fix evaluation
3D evaluation
When synchronisation takes place after a lengthy failure of the synchronisa-
tion source (> 9 hours) an erroneous system time change can occur. In the
normal synchronisation process (Bit 6 =0) no error message is output in this
case. It is therefore not possible for connected systems to detect whether
an erroneous system time change has taken place.
7001GPS Satellite Clock System - V08.00
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