User Manual

SGD-SB2025NT-TUM, Part 2
Jan 12 Page 24 NI ET
Losing the 1PPS timing signal will cause the frequency and phase error reports to show zero. On
resumption of the timing signal and, depending upon the period of time that the timing signal was
lost, a ‘Freq Error’ may be seen, however, a ‘Phase Error’ is the most likely result together with the
‘Status’ indication being lit Red . Errors will be corrected as described above. If the 1PPS timing
signal is lost for a long period, control of the PLL may be taken on by the Traffic Manager – see
Section 2.4.5.2 – Ref .
A PLL ‘Status’ failure may be assigned to “Alarm” status – see Section 12 – Alarms .
2.4.2.2 Ref
The clock reference for the PLL is normally the 1PPS timing signal as indicated by the text report
‘PPS’. Loss of the timing signal will result in a slow drift of the clock and, over an extended period
of time, will result in the timing being too inaccurate and packets will be lost, which will ultimately
cause the NI to cease operating.
In order to mitigate this situation, the TM can assume control of the PLL and adjust the PLL so that
the packet arrival times are maintained. When operating in this mode, the report will show ‘TM
(+x)’ where “x” is a number used by the internal process of frame alignment (normally zero unless
the power has been interrupted). The ‘Freq Error’ and ‘Phase Error’ counts will remain at zero
whilst the PLL is being controlled by the TM.
2.4.2.3 Offset
This is the report of the ‘Offset delay’ that may be applied to each Station NI – see Section 5.2.1.7
Offset Delay . Delay offset has no effective meaning or use on a NI operating in Central mode.
2.4.2.4 DSP
This report confirms that the DSP is operating correctly. If a problem occurs the report will show
‘Error’ and the text in the PLL area will no longer rotate.
2.4.2.5 DAC
This is the reading of the internal control of the PLL. The reading will vary during normal operation.
2.4.3 Timing – PPS
A Green PPS indication shows that the selected source of 1PPS timing signal (see Section
5.2.3.2 – GPS Module ) is present; a Red indication shows no input. If the timing signal source is a
GPS receiver with NMEA data output, the number shown alongside the indicator is the number of
satellites (Space Vehicles) being used to acquire a fix or the number in use once the fix has been
obtained. Loss of timing signal input may be assigned to “Alarm” status – see Section 12 –
Alarms .
2.5 E NVIRONMENT I/O I NTERFACE
The ‘Environment I/O’ interface is an independent sub-module within the Solar 2 unit. It is
accessible from and available to any of the main modules that are fitted to the unit. Although the
description of the operation of the I/O is presented here under the NI ET it is just the same for the
TM ET if the TM module is installed in the unit. Consequently, any action or setting applied
through one module is visible to and open to change through another module.
2.5.1 Environment Status
The status of each of the sixteen connection points that comprise the ‘Environment I/O’ are
displayed on the Environment page shown in Figure 13 overleaf. To open this page, select the
‘Environment’ tab.