This wiki is not maintained! Do not use this when setting up AuScope experiments!

Differences

This shows you the differences between two versions of the page.

--- operations:monitoring_hb [2011/07/20 13:05]
cehotan
+++ operations:monitoring_hb [2014/12/17 09:53] (current)
Warren Hankey [FS time is out by several seconds]
@@ Line 46: / Line 46: @@
 ==== FS time is out by several seconds ====
 The origin of this problem is presently unknown but the FS time can get seriously out of step. To fix this, **while not recording** start the ''fmset'' program from an ''oper@pcfshb'' terminal and issue the "+" and "-" commands, then quit from fmset (ESC). Restart fmset and the FS time should now be correct. You may need to resync the mark5B pps after this procedure.
+Be sure to check that FHG=off.  Sometimes if there is a power glitch while the Mark5 is still recording, it can get 'stuck' in record mode.  This will need to be stopped with disk_record=off, then run fmset again.
 ==== clkoff reading is drifting or far from the maser-GPS offset ====
-This usually is caused by the DBBC. First, go around the back of rack 14 and move the cable from the DOTMON output of the Mark5B to the "1 PPS Mon" output of the DBBC (left hand side, sixth SMA from the top). If the same offset is seen on the counter, then the problem in in the DBBC. A temporary fix can be achieved with ''pps_sync'' in DBBC Control but this did not reliably fix the problem on 13/10/10. Instead, try reconfiguring the DBBC with ''reconf'' - this will take ~two minutes in total and you will need to re-issue the ''dbbcifa=...'' commands, and resynch the mark5B with ''fmset''.
+The clkoff command measures the difference in the 1 PPS (pulse per second) signal coming from the GPS with the 1PPS from the Mark5. The Mark5 1PPS has travelled through both the DBBC and Mark5 and is a good diagnostic of a timing problem in our hardware.
+There are occasionally timing glitches (clock jumps) that cause the clkoff value to change. There are several possible causes:
+  - Spurious signals on the 1 PPS signal. For example at Yarragadee we sometimes see a clock jump when the antenna drives are powered on. We also sometimes see it as a result of poor earthing or a bad connection in the cable between the DBBC or Mark5
+  - DBBC problem. Sometimes the DBBC (which uses the 1PPS from the maser and passes it's timing on to the Mark5) can become unstable and the 1PPS signal will start to drift.
+The easiest way to check for clock stability is to compare the clkoff and maserdelay values. The difference between these two should remain stable at around 0.3 us. The Log Monitor software calculates the difference and logs it as the "Delay difference". If this value exceeds abs(0.5) us, an alarm is sounded (by default).
+=== So what do I do if there's a clock jump? ===
+The first thing to do is not panic. If the new delay remains constant and less than abs(20) us, the correlator can handle it. Re-setting the delay introduces another clock jump which makes the correlation more difficult. So the first thing to do is in the Log Monitor:
+  - Press "Acknowledge alarm"
+  - Under the "Configure" menu, select either:
+    - "Delay monitoring -> Audible warning" which will make the monitor software beep every time it sees a > abs(0.5) us offset, rather than sound the alarm, or...
+    - "Delay monitoring -> Silent warning" which will log that the offset is large but not beep or ring alarms. This should be used with caution!
+  - Now monitor the Delay difference and see if it has stabilised. You can do this in several ways:
+    - Watch the Delay difference values in the log monitor window. You can get more frequent updates by issuing regular ''clkoff'' and ''maserdelay'' commands from e-RemoteCtrl
+    - Get Log Monitor to extract a history of the delay and delay difference values by pressing the "Export Data" button. When you do this, several ascii files will be written to /vlbobs/ivs/logs. The file that will be of most interest is (e.g. for Yarragadee) /vlbobs/ivs/logs/yg_ddif.txt. You can open this file and read it's contents, or you can use a plotting program like gnuplot to plot the values. This is especially useful if you want to see if the new offset is stable or not:
+      - from a terminal window:<code>cd /vlbobs/ivs/logs
+gnuplot
+plot 'yg_ddif.txt' u linesp
+</code> This will plot the delay difference against day number. You can use the right mouse button in the plot window to zoom in. Every time you press "Export data" the output files are refreshed and you can replot the values in gnuplot either by typing 'replot' or by pressing the "Replot" button in the plot window. Other possible useful files to plot are ''yg_maser2gps.txt'', the difference between the maser and GPS 1PPS, and ''yg_fmout.txt'', the difference between GPS and Mark5 output 1PPS.
+      - Seperate windows [0|1|2] can be opened for each station by replacing the final command above with:<code>
+set terminal 'wxt' 2; plot 'yg_ddif.txt'
+</code>
+=== So when do I need to reconfigure the DBBC, run fmset etc? ===
+If the delay difference is stable you don't need to do anything.
+If the delay difference is more than 20 us, or gets so large that the ''clkoff'' or ''maserdelay'' values lose precision, run ''fmset'' to get the delays back to something manageable. //Make sure you are not recording while running fmset! Issuing a ''halt'' command from e-RemoteCtrl followed by ''disk_record=off'' is usually a safe method.//
+The first thing to do is try the command
+<code>counter</code>
+in e-RemoteCtrl. Check to see if this worked by typing ''clkoff'' and ''maserdelay''. If this doesn't fix it, proceed with the steps below.
+If the delay difference is drifting (usually linearly), the DBBC probably needs reconfiguring. This can be done from e-RemoteCtrl as follows (again, best to halt the schedule and make sure you're not recording):
+<code>dbbc=reconf</code>
+Monitor how things are going in the DBBC VNC session. A reconfig takes about 2 minutes. When it's completed, synchronise the dbbc:
+<code>dbbc=pps_sync</code>
+Then in a terminal window on pcfs[hb|ke|yg], run fmset to get the clocks lined up.
+Now resume observations with a ''cont'' or ''schedule='' command.
 ==== PCFS log window reports problem with ReadPower.sh ====

AuScope VLBI Operations Wiki

User Tools

Site Tools

This wiki is not maintained! Do not use this when setting up AuScope experiments!

Differences

Page Tools