How to take encoder logs and analyse the
results with PLOT
1)
Logging encoders
If a problem is suspected
while the TCS is running (e.g. telescope oscillating on an axis), you can start
an encoder log file (say for 5 minutes) by typing log
enc on 5.
By default the duration of the
log is 15 minutes (the time argument can be omitted).
The logging ends automatically
after the time asked, but you can end manually before the expiration by typing log enc off.
The n previous
minutes can be logged with log eng keep n. That’s useful if
for example the telescope has to be stopped (violent oscillations with
amplifier currents going wild, which is bad both mechanically and electrically)
and you want to keep a record of what happened.
2)
Analysis with PLOT
·
Where are the log files?
At the WHT, connect to LPAS4
as genuser or as tcsmgr. (Connect to LPAS2
at the INT).
Log files are kept in the
directory DISK$LOGS:[WHT.DATA.ENCODER] so if you don’t want to type
the whole thing over and over again to check several files, change directory: set def DISK$LOGS:[WHT.DATA.ENCODER]. You could in principle change
directory with CD after starting PLOT, and list
the whole directory with DIR.
To check for example what are
the log files for november 24, 2004, type
dir /date enc041124* ; which results in:
Directory DISK$LOGS:[WHT.DATA.ENCODER]
ENC041124.DAT;5 24-NOV-2004
22:43:24.38
ENC041124.DAT;4 24-NOV-2004
16:09:51.79
ENC041124.DAT;3 24-NOV-2004
15:37:06.87
ENC041124.DAT;2 24-NOV-2004
10:09:35.77
ENC041124.DAT;1 24-NOV-2004
02:33:47.78
Total of 5 files.
If several logs are kept on
the same day, the oldest is tagged ;1 and the most
recent has the highest number.
Remark: the snapshot files
taken by the Telescope Operator are kept in the directory A1:[WHT.DATA.SNAPSHOT]. They are ascii files but named *.SNAP and are a
photo of the TCS info page at the moment of the record. Just print them (PRINT
command on the Alpha).
·
Work with PLOT
Start the program by invoking it.
Typing HELP lists the available commands, and give information on
each subject, but you can live with the following:
Load a log file: DATA ENC041124.DAT;1 to load that particular log file; DATA ENC041124 will load the latest version (the file ;5 in this
case).
Choose the output device: DEV XWIN to get an XWindow for the plots, or DEV
PS to
send all the plots in a Postscript file (in that case each PLO command adds a plot to the file PGPLOT.PS which will be saved
in the current directory only when PLOT is EXIted)
Read the axes: READ 1 UTC will load the time on the X axis; READ
2 AZIMUTH GEAR will send the azimuth incremental encoder reading on the Y axis.
Plot at full range: type LIMits then PLO
Zoom on an interesting zone: use the command BOX to zoom in X and Y. In our example, we can do BOX
220 250 98 100 then PLOT which gives the following graph
This shows an oscillation
started after an offset, while the telescope was tracking.
Export data in an ASCII file
for a further analysis (for ex. with Matlab)
Up to three variables can be
stored in the same file.
PLOT> OUTFILE name.txt
PLOT> READ 1 UTC
PLOT> READ 2 AZIMUTH GEAR
PLOT> READ 3 AZIMUTH VEL_DEM
PLOT> WRITE
PLOT> EXIT the file will be closed only
when PLOT is exited. Then for further analysis, use FTP to transfer to your
favorite laptop or other.
·
Other example: how to get the focus
LVDT graphs after the secondary mirror is put back:
Put the telescope in Computer
mode, start a log : log enc on 10. If it’s already at zenith,
send the telescope to low altitude (alt 10) then back to
zenith (alt 90). Close the log with log
enc off.
Use PLOT to draw each
Secondary Position encoder as a function of altitude: READ
1 Altitude abs; READ 2 Secpos1; LIM; PLO. The result should look like this: