64
System Configuration
T801-4 Installation and Operation Manual
© Tait Electronics Limited September 2007
Alarms and
Monitoring
If the 1PPS pulse from the QS
2
RSU becomes invalid, the Satsync 7 module
will
not
activate its GPS alarms and front panel
GPS
LEDs. This is because
the invalid input signal (1PPS VALID I/O) is not available to the Satsync 7
modules, and the 1PPS pulse (although invalid) is still running (the RSU
GPS receiver does not disable its 1PPS pulse when it loses GPS tracking).
The maximum drift of the invalid 1PPS pulse from the RSU could be quite
large, and will consequently affect the accuracy of the T801-4 reference
frequency outputs. This drift will activate the Satsync 7 OSC alarms and
front panel LEDs whenever the accuracy threshold drops below ±1 part in
10
8
. The Satsync 7 will not apply the 24 hour delay and “freeze” the
OCXO, because it still considers the 1PPS to be valid.
Important
In this configuration you should monitor the 1PPS VALID
OUT line, and
not
the GPS alarm, to receive notification
that the 1PPS signal has become invalid.
The 1PPS VALID OUT line will be activated (high) when the 1PPS signal
becomes invalid. This line essentially follows the state of the 1PPS VALID
signal from the RSU. Although it is most important to monitor the 1PPS
VALID OUT line, we still recommend that you monitor the Satsync 7 GPS
and OSC alarms. They will provide notification of other faults (refer to
Table 4.5
below).
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 4.5
Summary of alarms available with a single QS
2
RSU receiver
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 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
9
1PPS VALID OUT
Activated (high) when the 1PPS signal becomes invalid. It also reflects the state
of the applied RSU 1PPS VALID signal.
