Cooper SMP 4 - About GPS, IRIG-B and SNTP

SMP Gateway User Manual • 197
come from another SMP 16 equipped with the GPS clock option that distributes IRIG-B to
your SMP Gateway.
 Directly from an SNTP server. SNTP stands for Simple Network Time Protocol, and is briefly
presented in section “About GPS, IRIG-B and SNTP”, below.
 Using a SCADA protocol, such as DNP3.
Here is a list of the possible time adjustment solutions that are available for the different Cybectec
SMP Gateway types:
SMP Gateway model Protocol SNTP
Modulated
IRIG-B
Demodulated
IRIG-B GPS
SMP 4-20
√ √
O O -
SMP 8-40
√ √
O O -
SMP 4
√ √ -
- -
SMP 16/CP
√ √ √ √
G
SMP 16/SG
√ √ √ √
G
Legend: O = With the SIOM option, G = with the SMP 16 GPS clock option.
Note: Only one time adjustment solution should be implemented at a time for an
SMP Gateway.
These different solutions are presented in the next sections.
21.3.1 About GPS, IRIG-B and SNTP
Global Positioning System (GPS) is a satellite-based navigation system operated and maintained
by the U.S. Department of Defense (DoD). GPS uses a constellation of satellites to calculate the
exact position and altitude of GPS receiver stations.
GPS technology requires a very accurate time source in order to calculate the orbital position of
the satellites and determine the position of the receiver. To ensure the required level of accuracy,
each GPS satellite is equipped with 4 atomic clocks that are kept in synchronization with the U.S.
Naval Observatory's Master Clock. Each satellite continuously transmits its current position and a
time code. This time code can be used to synchronize the SMP Gateway, if equipped with the
appropriate hardware.
IRIG-B is a military standard of the Inter Range Instrumentation Group. The best known IRIG
standard is the IRIG Timecode standard used to timestamp video, film, telemetry, radar, and other
data collected at test ranges. The main difference between the codes that are classified in letters
from A to H is their bit rate, which varies between 1 pulse per second and ten thousand pulses per
second. The IRIG-B standard operates at 100 pulses per second.