Interferometry in manual mode with software version 5.0.3

Author: Complete rewrite. 2008 April 4. RAL.

  • added DTX clock incantation 20080408 RI
  • added note to kill log 20080411 RI
  • removed DTX clock incantation (no longer needed), and updated the hot load and Walsh switching sections. 20080430 RR
  • Twiki tweak AH

Changes for version 5.0.3:
  • Recommended method is to use execfile to run a complete CCL script, modified from template example files.
  • CorrGUI run on oper01 (if you run it at all)
  • Pointing model run automatically
  • Frequency for refraction correction set in scripts.

In what follows:

  • > denotes the unix shell prompt,
  • >>> the python prompt,
  • CCL>>> the CCL prompt and
  • psi> the prompt for psi scripts.

To get the PSI prompt type:

>cd /groups/psi/Public_PSI

>./psi

All sessions should be run on oper01.

0.Prerequisites

The following assumes that the system has been set up according to:

  1. Antenna Startup and Shutdown Procedures
  2. System Software Setup
  3. Radiometer Software Setup

This will ensure that the antennas are movable and in focus, with pointing models loaded, the receivers are set up, the line-length correction is turned on and being logged.

1.Run the logpower script

This utility will log total power data, az,el position and the hotload status and temperature from the specified antenna into an ASCII file in /groups/sci/interferometry/YYYYMMDD. Needed if you are planning to use the hot load for calibration.

>/groups/sci/scripts/5.0.2/logpower.py -a both -s 4

will log data from both antennas, creating the YYYYMMDD directory if it does not already exist.

2. Set up a data directory

IF you have NOT run the logpower script and the data directory does not yet exist, create it:

>mkdir /groups/sci/interferometry/YYYYMMDD

where YYYYMMDD is the current UT date.

3. Create an array

On the OMC

View -> create array

This brings up a panel showing all potential antennas

Click Manual -> indicators for antennas 1 and 2 turn green

Left click on 1

Shift left click on 2

Both indicators should turn blue

Click on Create

Wait until the antennas are assigned to the array (click on Alma -> antennas; both antennas should be assigned to the new array CONTROL/Arraynnn).

4. Create an observing script

Load /groups/sci/scripts/5.0.3/irc10216_SO2.py as a template into an editor. It uses the high resolution FDM correlator mode. If you want the standard low-resolution TDM mode, (useful for nearly live looks at the phase) see one of:

/groups/sci/scripts/5.0.3/3C273_long.py 1 scan, 30 subscans each of 2 minutes on 3C273 /groups/sci/scripts/5.0.3/3C84_0359.py 20 scans, each on 1 2min subscan, alternating between 3C273 and 3C279

Keep in mind that they are older and probably need updating.

Rename your file to avoid inadvertantly saving over the template.

Things you might want to edit in the file:

a) Number of cycles

cycles=n

n is the number of cycles of the main repeat loop

b) Integration time

corrConf.integrationDuration.setValue(n)

n is the number of 48ms correlator dumps in an integration. Standard value is 210 (10.08s). Values between 21 and 210 are typical.

c) subscan duration

corrConf.subScanDuration.setValue(n)

n is the number of integrations per subscan. These should correspond to 2 minutes or less (a subscan is the amount of data transferred from correlator to archive). Standard values 12 integrations of 10.08s. At the ATF each subscan has some overhead (~10s?) during which no data is taken.

d) Observing frequency

sfi_obs_mode.setFrequency(freq)

freq is the observing frequency, in Hz. Standard value is 103.83375e9; for CS observations, use 98E9.

e) Walsh switching

Once the observing frequency has been set, turn on Walsh switching: PSI>rs walsh 3,4 Tells Vx to use Walsh function 3, and AEC to use 4. 0 and 1 should also work. The order does not matter as long as each antenna is using a different function.

To actually turn on (enable) Walsh switching: PSI>rs walsh ef

NOTE! The performance will be degraded if you retune the receiver frequency while Walsh switching is on. Disable it with PSI>rs walsh d before changing frequencies (and then enable it again). This is a problem for nearly all of the scripts, since they run setFrequency().

f) Sources (including calibrators) to be observed

execfile('/groups/sci/scripts/sources.py') name_src = 'OMC-1' ra_src, dec_ = sources.radec_from_name(name1) src1 = create_source_RADec(ra1, dec1)

Here, sourcename1 must be one of the sources in the catalog /groups/sci/scripts/sources.text. If you want to observe something else, add it to the catalog for future use. Make as many blocks as you need for the sources you want to observe, e.g.

name_cal='0530+135' ra_cal, dec_cal = sources.radec_from_name(name_cal) src_cal = create_source_RADec(ra_cal, dec_cal)

f) Optimizing signal levels

You should first go to the target position in order to optimize on the right airmass:

sfi_obs_mode.setDirection(ra_src, dec_src, fieldName=name_src)

The command used for 5.0.3 is

sfi_obs_mode.optimizeSignalLevels(2.0)

Unlike in 5.0.2, you should use a value of 2.0 to get voltages around 1V.

g) Using the hot load

Insert this block immediately before observing the sources.

import CCL.FEB

name_hl = 'hotload' src_hl = create_source_RADec(ra_src, dec_src) # use source 1 position sfi_obs_mode.setDirection(ra_src, dec_src, fieldName=name_hl)

# Put in the hot loads. febs ={} for ant in array.antennas(): febs[ant] = CCL.FEB.FEB(ant) febs[ant].SET_CHOPPER_TO_LOAD()

# 30s should be plenty of time for a hot load obs. nints_per_subscan = int(30.0 / (0.048 * n48ms_per_intdur)) if nints_per_subscan < 1: nints_per_subscan = 1 corrConf.subScanDuration.setValue(nints_per_subscan) nints_per_subscan = corrConf.subScanDuration.getValue()

print "Starting the hot load observation." sfi_obs_mode.beginScan([ScanIntentMod.TARGET], src_hl) sfi_obs_mode.beginSubscan(spectSpec,corrConf,[SubscanIntentMod.ON_SOURCE]) sfi_obs_mode.endSubscan() sfi_obs_mode.endScan()

# Take out the hot loads. for ant in febs: febs[ant].SET_CHOPPER_TO_SKY()

h) Cable delay

# Specify the cable_delay in seconds. cable_delay = 119.275e-9 # Empirical 2008 Apr 27 sds.setAntennaCableDelay('DA41',cable_delay)

Be prepared for this number to change if electronics modules are replaced. See Appendix B, below for details of how to change it.

i) Order of observations

Best explained by some examples. A simple block with one source, scan and subscan

sfi_obs_mode.setDirection(ra1, dec1, fieldName=name1) sfi_obs_mode.beginScan([ScanIntentMod.TARGET], src1) sfi_obs_mode.beginSubscan(spectSpec,corrConf,[SubscanIntentMod.ON_SOURCE]) sfi_obs_mode.endSubscan()

The same, but repeated cycles times:

sfi_obs_mode.setDirection(ra1, dec1, fieldName=name1)

sfi_obs_mode.beginScan([ScanIntentMod.TARGET], src1)

for i in range(cycles):

sfi_obs_mode.beginSubscan(spectSpec,corrConf,[SubscanIntentMod.ON_SOURCE])

sfi_obs_mode.endSubscan()

sfi_obs_mode.endScan()

Note: indentation is important, and very tricky (don't even try!) on the CCL command line. Use an editor and execfile for even short snippets requiring indentation.

Alternating between two sources:

for i in range(cycles):

sfi_obs_mode.setDirection(ra1, dec1, fieldName=name1)

sfi_obs_mode.beginScan([ScanIntentMod.TARGET], src1)

sfi_obs_mode.beginSubscan(spectSpec,corrConf,[SubscanIntentMod.ON_SOURCE])

sfi_obs_mode.endSubscan()

sfi_obs_mode.endScan()

sfi_obs_mode.setDirection(ra2, dec2, fieldName=name2)

sfi_obs_mode.beginScan([ScanIntentMod.TARGET], src2)

sfi_obs_mode.beginSubscan(spectSpec,corrConf,[SubscanIntentMod.ON_SOURCE])

sfi_obs_mode.endSubscan()

sfi_obs_mode.endScan()

5. Check that the correlator is synchronised with the rest of the system

>ssh ccc

>arrayTimeCompare CORR/ARRAY_TIME/CDP_NODE/N01

>exit

You should see a line:

delta = remote-local: 0[acs]

If the number is NOT 0, then the correlator subsystem will have to be restarted and the correlator computers power cycled (see Appendix C).

6. Start a CCL session and execute the observing script

* It is recommended that you have your observing script available in * * an emacs window so that you can follow execution and cut/paste * * non-CCL commands from it. But beware of indentation when doing so. *

* If you want to enable Walsh functions (phase switching) see * * Appendix A *

>mmc --arrayname=CONTROL/Arraynnn

where nnn is the number of the array you created in (3) - 001, 002, etc. This brings up the CCL prompt CCL>>>

CCL>>>execfile('/groups/sci/scripts/observations.py')

Keep an eye on the Labview IF total power displays and the mount panels. You should see glitches in the total power, followed by a steady trace around 1V as the setFrequency and optimizeSignalLevels commands are executed. At this point, it is safe to turn on the CorrGUI [see (6), below]. You will be able to see the setDirection command execute by watching the mount panel (or antennas) unless you are already on source.

Also look at the OMC dataflow window. Note the exec block id (which will be something like uid://X1eb/X2482/X1), as this is needed for data reduction. You will need to resize the field to see this. You will be able to see the progress of the observation in the scan and subscan fields. These read n - m, where n is the number of (sub)scans initiated and m the number completed. After the end of execution, the indicator on the left of the dataflow entry will be green, the numbers of completed scans and subscans should be as you set them in the script and control will be returned to the CCL prompt.

7. Executing CCL commands by hand

For debugging purposes, you may want to execute commands from the script by cutting and pasting from an emacs window. Be careful to preserve the indentation: - Avoid extra spaces at the beginnings of lines - Preserve indentation in for loops - Paste lines inside for loops one at a time - Terminate a for loop with a blank line

When executing a subscan in this way, paste in the sfi_obs_mode.endSubscan() command as soon as the sfi_obs_mode.beginSubscan(spectSpec,corrConf,[SubscanIntentMod.ON_SOURCE] command returns control - otherwise the subscan will not finish. Also take care to make sure that there are no unmatched begin/end execution. scan or subscan commands.

This method is prone to finger trouble.

8. Start the CorrGUI

Don't do it! Seriously. The main problem is that it should not be running before the array = getArray() command in the observing script. Even if you wait until after getArray() the first time, you'll probably forget to kill CorrGUI before starting your next Execution Block (i.e. array). The secondary problem is that it isn't very useful unless the correlator is in a low resolution mode.

You were warned:

CorrGUI can be used to monitor the autocorrelations, cross-correlation phase and amplitude. To start it type:

>CorrGUI&

at a shell prompt. In this mode, subscan data will be displayed automatically.

* Do not use any of the CorrGUI buttons in this mode. *

You will see displays of:

Vertex antenna autocorrelation amplitude (top L) Alcatel antenna autocorrelation amplitude (top R) Cross-correlation amplitude (bottom L) Cross-correlation phase (bottom R)

all plotted against channel number. If things are working well, the phase should be fairly flat across the band and you should be able to see the target clearly in the cross-correlation amplitude (need to link and example here).

9. Tidying up after an observation

  1. Close down the CorrGUI if you had it running (press the Quit button)
  2. Exit from CCL by typing CTRL D on the CCL>> shell
  3. Destroy the array: On OMC Scheduler -> Destroy array

wait until the antennas panel shows both DV01 and DA41 unassigned to be sure that the array has actually been destroyed.

In OMC, you can get rid of the defunct array's tab by going to View->Manage Display.

You can now start another observation.

10. Exporting the data and making a measurement set

'>cd /groups/sci/interferometry/YYYYMMDD
'>asdmExport -b uid://X1eb/Xnnnn/X1

where nnnn is the number of the exec block noted earlier. This creates a directory uid___X1eb_Xnnnn_X1

'>asdm2MS --ocm ca uid___X1eb_Xnnnn_X1

creates a measurement set called uid___X1eb_Xnnnn_X1.ms.

Now change permissions so that everyone can read/write it:

'>chmod -R ugo+wrx uid___X1eb_Xnnnn_X1.ms

11. Plotting the data using CASA

Appendix A: Additional information

###########################

A1. Correcting a delay error

###########################

After a change of electronics modules (e.g. digitizer clock), fibre length etc., the cable delay may change. The symptom is a linear phase change across the band. For a variation with a positive slope and about 2 wraps across the bandwidth, the delay should be increased by about 1 ns. To correct:

CCL>>>sds.getAntennaCableDelay('DA41')

reports the current cable delay (which should be as set by the observing script). To set a new value:

CCL>>>sds.setAntennaCableDelay('DA41',delay)

where delay is in s (e.g. 511.8375e-9).

Make sure that the delay server is set up and that the antennas are tracking by executing the standard observing script commands as far as

CCL>>>sfi_obs_mode.setDirection(ra1, dec1, fieldName=name1)

Do not start a scan from CCL. Then start CorrGUI and initiate continuous subscans: - Select TDM mode - Integration set to a multiple of 1.008s -

###################

A2. Walsh functions

###################

Walsh Funtions only after tunning ! (after set_frequency(xxe9) function call)

In order to remove spurious signals such as DC offsets, ALMA will use 180 phase modulation at the rirst LO, decoded after the digitizer. In order to test this, without desynchronization problems, we can apply Walsh functions 0 (constant) and 1 (Emerson, ALMA Memo 565), essentially as in traditional phase switching. To do this:

Set up the receivers as usual

# Install Walsh functions 0 and 1 in Vertex and Alcatel respectively. 0 and 1 can also be replaced with 3 and 4. PSI>rs walsh 0,1

# Enable Walsh function switching PSI>rs walsh ef

If you are watching in CorrGUI, and in TDM mode, you should still see the internal beacon signal in channel 180, but the spurious 250MHz harmonics should vanish.

# Disable Walsh switching PSI>rs walsh d

Walsh switching works wonders if you do not tune to another frequency while it is on. If you do, performance will be degraded.

Appendix B: Trouble-shooting

#######################

B1. Correlator problems

#######################

If you get a timeout error when trying to start CorrGUI, the times are probably not synchronised between the correlator and the rest of the world.

exit CorrGUI

Check whether the correlator containers are up (green) on OMC. If they are all OK:

correlator subsystem -> shutdown -> operational

If any of the containers are down:

correlator subsystem -> shutdown

You need to power-cycle ccc (if CCC containers are down) and/or cdp00 (for CDP containers).

'>pstrip -u almaproc cob-pdu list

which gives a listing

1 - cdp ON 2 - ccc ON ..........

so to power-cycle ccc and cdp00:

'>pstrip -u almaproc cob-pdu cycle 1
'>pstrip -u almaproc cob-pdu cycle 2

To check:

'>ssh ccc
'>ssh cdp00

You should be able to log in to both machines once they are up. Then exit.

Then restart the containers and bring the correlator subsystem to operational.

#################################################

B2.On-line monitoring of the LLC for phase jumps

#################################################

To monitor LLC phase jumps visually, look at the LLC Labview displays on snickers. To get these, click on LLC1 -> details on the central lo rack display; similarly for LLC2. The frequency of phase jumps depends on the rate of ambient temperature change, and are more often on AEC due to the extra fibre length. These data will be stored in: /groups/psi/Public_PSI/Data/Daily/2007/yyyy-mm-dd-LLC_02/ provided that the psi monitor script has been started (see system software startup checklist). A new file is created at UT midnight automatically.

This topic: ALMA > WebHome > AlmaSci > AlmImcal > ControlNotes
Topic revision: 2008-05-04, AntonioHales
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