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DIGISONDE-4D
SYSTEM MANUAL
VERSION 1.2.11
6-14 SECTION 6 - MAINTENANCE
6:49. Once you have entered a new value in the data2 field, press Enter to make “Apply” active at the bottom
of the window. Then click “Apply” to accept the new Data2 value.
6:50. Note that increasing data2 (or data1) will make the GPS 1 pps drift to the right on the screen if you are
triggering the oscilloscope with the TRIG 1/2 pps. Decreasing data2 will make the GPS 1 pps drift to the left on
the screen. A change to data2 (or data1) of one unit (one bit, or LSB and do remember that these are hexadeci-
mal values, 0 1 2 3 4 5 6 7 8 9 A B C D E F) is equivalent to approximately a change in the drift between the
GPS and R pulses of 7 ns (nanoseconds) /second or 0.1 µs per 17 seconds.
6:51. The following steps are generally not necessary but once you have the drift down to less than 200 ns /
17 seconds, it might be helpful to watch the drift for a longer period of time, perhaps as long as 4 or 5 minutes
in order to get down to the least significant bit of data2. To stop the automatic resynchronizing every 17 sec-
onds, disconnect the 1 pps BNC cable from the BNC Tee which you have temporarily installed in the chassis.
6:52. Be careful not to drop the cable so that the BNC connector short circuits anything in the chassis.
6:53. After making a change to data2 the GPS pulse will jump well off the screen of the oscilloscope. It will
be necessary to reconnect the 1 pps GPS cable back to the BNC Tee for as long as 17 seconds or until resyn-
chronization occurs and the GPS 1 pps signal is back to 7 µs after the TRIG 1/2 pps. Then disconnect the cable
again and watch the drift for 4 or 5 minutes.
6:54. Adjust data2 to achieve minimum drift in either direction. You should be able to get down to the LSB
of data2 so that the drift of the GPS 1 pps is very slow in one direction and a change in data 2 of one unit makes
the drift very slow in the other direction. This minimum drift should be on the order of 3 or 4 ns (nanoseconds)
/ second or 1 µs in 4 minutes (240 seconds).
6:55. It is possible, but unlikely that to achieve the minimum drift data2 would exceed the maximum possible
limits for its adjustment, i.e., 00 (0x00) or FF (0xFF). If that is the case it will be necessary to adjust data1 in
the same direction you are trying to go with data2. Data1 and data2 have equal weights. A change of one LSB
in data1 will have the same effect as a change of one LSB in data2.
6:56. When done with this tuning procedure return to the normal operational schedule and change back to
“normal” operation. To change DCART back to normal mode, navigate to the DCART Options menu and se-
lect General. Under General Appearance and Interface: click Normal Mode. Please remember to change back
to Normal Mode after completing this procedure. To return to the standard operational schedule first navigate
to PROGSCHED / SST, Rules, Campaigns tab. Within the CAMPAIGNS section of the page select the cam-
paign entered earlier in this procedure and click Del to delete the entry from the list of currently applied cam-
paigns. Click on Activate Changes to apply the new campaign settings, and click Auto to resume the normal
rule based scheduling.
MAINTENANCE SPARES RECOMMENDATION
6:57. A listing of recommended maintenance spares showing manufacturer’s part number, quantity fitted in
the system, recommended support sparing level, and recommended maintenance policy is provided in Table
6-4. It is recommended that spares be held in appropriate locations to support fielded systems in accordance
with the overall system maintenance support plan.
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