488HS GPS satellite time synchronisation
for master clocks, clock systems and individual digital
clocks |
 |
The Wharton 488HS GPS time synchronisation receiver
is designed to provide an extremely accurate, yet simple to install
and maintenance free, time reference for the 4850 system master clock
and 4860 NTP master clock and may also be used to synchronise
individual digital clocks, calendar clocks and timezone clocks.
The 488HS GPS receiver is housed in a rugged, IP65 rated, enclosure
with an integeral stainless steel post mounting bracket and is supplied
with a 25m (80ft) long four core cable for connection to the clock or
master clock.
| what is GPS? |
 |
| GPS is a system of satellites in six orbits,
each orbital plane equally spaced about the equator
and inclined at 55 degrees. The satellites transmit
highly accurate, real time, worldwide navigation
information at a frequency of 1575.42 MHz that
anyone with a suitable GPS receiver can use to
identify their position, together with a precise
local time. The GPS system was developed by the
US government initially for military use and is
now available for unlimited commercial access.
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| how GPS time
synchronisation works |
|
| GPS satellites travel in nearly circular
orbits every 12 hours at an altitude of 20,200km
(10,900 nautical miles). The exact position of
each satellite can be determined at all times.
Each satellite continuously transmits a unique
code sequence, derived from atomic clocks, which
is tracked by the GPS receiver. |
| The transmitted information includes current
orbital data for each satellite. The GPS receiver
is able to identify each satellite by its code
and is able to calculate the satellite's exact
position in space. The GPS receiver uses the calculated
information to determine its distance from several
satellites. The receiver then uses a process called
triangulation to compute its own position together
with a precise utc time. |
| |
| active antenna |
|
| The 488HS receiver has an integeral active antenna.
GPS signals are received by the antenna, amplified within the antenna
assembly and then relayed to the GPS signal processing module for
processing. The gain pattern of the antenna is designed for full
upper hemispherical coverage with the gain diminishing at low elevations.
This cross-section is consistent through 360 degrees and so the
3-dimensional gain pattern is a symmetrical spheroid surface. |
| The 488HS receiver should be horizontally mounted
with a clear view of 75% of the sky. If the sky view is reduced,
the interval between 'switch-on' and system time synchronisation
will be considerably increased. The post mounting clamp fitted enables
the receiver to be fixed to a suitable horizontal or vertical post
of up to 20mm diameter. The receiver may also be mounted on the
roof of a building or under a suitable skylight. |
| |
| receiver/decoder |
|
| The GPS receiver/decoder module contains an advanced
12 Channel parallel receiver and a microprocessor based communications
interface. |
| The 488HS GPS receiver is designed to self initialise
without the necessity of operator data input. On power-up the receiver
will automatically begin to search the sky for all available satellites.
After three satellites have been acquired a precise date and time
will be calculated from the satellite data transmissions. When accurate
satellite time information is available synchronising time signals
are transmitted from the receiver/decoder module to the 4850 or
4860 series master clock or individual clock unit. |
| The connection between the 488HS receiver and the
4850 or 4860 master clock or individual clock unit is by a four
core, screened twisted pair cable. A 25m length of cable is supplied
connected to the 488HS receiver. The cable length may be extended
to 50m using 7/0.2 screened twisted pairs cable or 200m using 16/0.2
cable. This cable also provides low voltage power to the receiver
from the master clock or individual clock unit. When the 4850/4860
master clock is synchronised with the GPS receiver/decoder module
all transmitted signals are accurate to within +/- 50uS. |
| |
| environment |
|
| Power supply |
The 488HS GPS system is powered via the master clock or individual
clock unit at 12v 100mA dc. |
| Operating temperature |
-25°C to +45°C (ambient) |
| MTBF |
›50,000 hours |
| Accuracy |
- Antenna/receiver +/- 1uS
- Master clock outputs +/- 50uS (100uS for 4850)
|
| EMC |
The 488HS GPS receiver, when installed and used in accordance
with our recommendations, complies European Community Electromagnetic
Compatibility Directive 89/336/EEC (as amended by 91/263/EEC, 92/31/EEC
and 93/68/EEC) and Low Voltage
Directive 73/23/EEC (as amended by 93/68/EEC) and conforms to the following standards:
- EN 61000-6-1
- EN 61000-6-3
- EN 60950
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| special
designs |
|
| If you have a special GPS, master clock,
ethernet NTP time synchronisation or time reference requirement that is not
covered by our standard range of products please
do not hesitate to contact our technical department. |
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