T801-4 Installation and Operation Manual
System Configuration
71
© Tait Electronics Limited September 2007
Monitoring Other
Alarms
Although the Satsync 7 GPS alarms will not be activated if the 1PPS
signal(s) becomes invalid, we still recommend that you monitor one of the
GPS alarm outputs. This alarm will be raised in the unlikely event that the
1PPS signal disappears while the 1PPS VALID signal is indicating “valid”.
This could occur, for example, if only the 1PPS signal path was somehow
broken.
We also recommend that you monitor the Satsync 7 oscillator alarms in case
a Satsync 7 module develops a fault.
You can also monitor the GPS RX IND output line to indicate which RSU
GPS receiver is in use.
All alarm outputs are available on the
I/O PORT
on the rear panel and are
summarised in the following table. Refer to
“Alarms” on page 32
for more
details about alarms. Detailed specifications for the
I/O PORT
are provided
in
“I/O PORT” on page 18
.
Table 4.9
Summary of alarms available with dual QS
2
RSU receivers
Pin
Signal Name
Notes
1
OSC ALRM OSC1
Activated by the Satsync 7 module(s) when the master oscillator accuracy is
below the ±1 part in 10
8
threshold. For example, when:
■
the T801-4 is first powered up and the oscillator has not yet stabilised
■
the 1PPS signal is drifting because it is invalid
■
the 1PPS signal is lost and the 24 hour “frozen” period has elapsed
■
the Satsync 7 oscillator circuitry has a fault.
The front panel
MASTER OSCILLATOR
LED is red when this alarm is activated.
2
OSC ALRM OSC2
3
GPS ALRM OSC1
Activated by the Satsync 7 module(s). This alarm is
not
activated when the
1PPS signal from the RSU becomes invalid. It is activated only when the 1PPS
signal is missing, for example when the 1PPS signal path is broken.
The front panel
GPS
LED is red when this alarm is activated.
4
GPS ALRM OSC2
5
GPS RX IND
This output indicates which GPS receiver is selected. It is an open collector
output. The output states are as follows:
■
high = primary RSU GPS receiver selected
■
low = secondary RSU GPS receiver selected.
9
1PPS VALID OUT
Activated (high) when one or both 1PPS signals become invalid. It also reflects
the state of the applied RSU 1PPS VALID signal.
