T801-4 Installation and Operation Manual
System Configuration
65
© Tait Electronics Limited September 2007
4.6
T801-4 with Dual QS
2
RSU Receivers
In this configuration the T801-4 would not normally be fitted with the
internal or external GPS receivers, as these are either disabled or redundant.
The T801-4 is supplied with two 1PPS RS-485 signals from the QS
2
RSUs
with GPS receivers, which provides a level of GPS redundancy.
The T801-4 DIP switches and links are used to configure this system. Either
of the RSU GPS receivers can be set as the primary 1PPS signal, while the
other then becomes the standby (secondary). The system is set to
“changeover” to the standby receiver when the primary 1PPS signal
becomes invalid. The validity of the 1PPS signal is determined by the state
of the 1PPS VALID line associated with each 1PPS input.
The changeover process is described below:
■
The primary RSU GPS receiver becomes faulty and its associated 1PPS
VALID line goes high.
■
If the RSU has firmware earlier than version 3.00.00.00, the changeover
is triggered immediately. If the RSU has version 3.00.00.00 and later
firmware, the changeover is triggered after approximately 28 seconds.
■
The standby RSU GPS receiver supplies the 1PPS signal to the T801-4.
■
The accuracy of the 1PPS outputs and reference frequency outputs is
restored.
The changeover to a functional standby RSU receiver ensures continuity of
supply of the 1PPS pulse to the T801-4, thus maintaining the accuracy of
the TTL 1PPS outputs and Satsync 7 reference frequency outputs.
