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The most common mode for VAMPIRES operation is the differential polarisation mode. Most steps are common between NRM and full-pupil mode; simply set the NRM mask wheel to EmptySlot for full-pupil mode. Other options are the same.
To acquire data, vControl sends the chosen timing settings via ethernet to a separate Raspberry Pi computer, operating in near-realtime, which in turn sends near-realtime control signals to an Arduino-based microcontroller. The microcontroller runs in true realtime, sending precise timing signals (~5 microsecond precision) to the camera triggers and FLC modulator.
However when viewing live video in realtime in vControl, all triggering is taking place internally within the cameras and the FLC is not used. This means that integration time settings set for live video preview are not necessarily the same as being used for acquisition - so be careful!.
This section will go through the observing procedure step-by-step.
Once you've read this all and are a pro, here is a quick reminder:
targetname_setnumber, e.g. alfOri_01, to correspond to entries in the log. Timestamps and metadata are appended automatically.Loop in the Acquisition panel, and hit Execute Series!Once you're in vControl, check the cameras are working by hitting the Start Video button and make sure something (noise / light) appears in the two camera windows. If so, press Stop Video and you're good to go. First, go through and adjust the various settings:
Note you can only change camera settings when the camera is stopped.
Readout Mode - choose between Non-Frame Transfer and Frame Transfer modes - see Andor documentation for gory details. In frame transfer mode the shortest exposure time is 1/(frame rate), this is not an issue in NFT. Data acquisition is always in NFT so this does not affect that. But NFT can be useful for very short integration times in live preview mode.
Exp Time - this sets the exposure time (in seconds) for live video mode only. It does not change the exposure time used for data acquisition series. This allows you to set a much shorter integration time using NFT (non frame-transfer) mode than is possible with external triggering. Typically you would adjust the exposure time here to get the desired counts, and then use that to set the integration time in Acquisition settings (see below).
EM Gain - sets the EM Gain; a number between 0 (EM Gain off) and 300. Actually, it can be set higher than 300 but you must only do this if you are truly in the single photon per pixel regime, otherwise it will damage the camera. For all common uses you should never need to go above 300. Adjust so that the peak counts are a few thousand (but no greater than ~20 000). This affects both live-video and data-acquisition.
Everything else - leave at defaults for now.
TODO: explain advanced camera settings, cyc time and effect of nframes (acquire nCubes).
This controls settings related to actual data-acquisition series (i.e. it programs the Arduino timing controller). You can hit Test Timing Controller to make sure it's all working - if so, you should see a few lines ending with OK - acquisition complete at the console.
Num Frms - Sets the number of frame in a given image cube. Since the HWP is rotated between cubes, this should be a number that gives you less than a minute of acquisition time. 800 frames is traditional for 512x512 (56 fps), or 1600 for 256x256. The FLC switches between each frame, so 800 frames would give 400 frames of polarisation state A, and 400 frames of state B.
int Time - the actual integration time in microseconds for each frame. The fastest possible for 512x512 frames is 18000 us, and the fastest in 256x256 is 10000 us. The longest possible integration time is 1000000 us (1 s), limited by the FLC itself.
FLC Offset - offset (in us) between start of camera trigger and FLC switch. Leave at 0 for now.
Start delay - delay (in us) between pulling the FLC gate high and the first frame. Leave at 100000 us for now.
To evaluate the exposure times and EM Gain settings described above, it is useful to use the line profile tool. To set the line profile, follow the following steps:
Set Line Profile buttonProf. max box. To hide or show the overplotted line, use the Show line checkbox.The line profile uses a built-in Matlab graphics function which means it is rather picky about the order you do things. Just refer to the above steps...
TODO - fix the line profile behaviour at other subwindow sizes, or at least document the problem here!
Control binning and subwindowing. Normally binning is not used, so H bin and V bin should be 1. H width and V width set the subwindow size. 512 is maximum, though usually 256 is good. Very high speeds can be achieved by setting the window smaller - see Andor documentation for details. H cent and V cent give the centre of the subwindow - these are almost always left at 256.
Crop mode should be set to Norm for normal operation. Iso mode is used with an external focal-plane mask to achieve very fast speeds. But this mode is in development and not yet documented.
(TODO: describe subwindow and crop speeds and settings)
Use in combination with the Steer Im/Pup window to adjust the aperture mask settings. Positions are stored in the Preset File (as specified in the Preset File field). This can be be edited if desired, e.g. to update new mask positions - it's in ~/code/vControl/WheelPresets.
Choose a mask from the Mask drop-down menu and press Move Wheel to move to the new position. This will adjust the wheel rotation position and the X and Y position. The wheel angle can be manually set (using the Set Degrees) and Nudged if desired. Various masks are listed, but for science only the following should be used:
When moving the mask wheel (especially for the first time for a given mask on an observing run) you must look at Bramcam to make sure the mask is aligned properly. You may need to adjust Bramcam's exposure time / gain / stretch as per it's keyboard shortcuts (press F1 for help in Bramcam). If needed you can adjust the X and Y position using the Steer Im/Pup window as described subsequently. Make sure you keep the same positions for the whole run or it won't calibrate properly!
Hit the purple Steer Im/Pup button to launch the separate steering window. The Up/Down and Left/Right rows allow the NRM masks to be adjusted (whilst viewing Bramcam). Click the respective button to nudge it in that direction, or directly type a position (in Zaber steps) into the text boxes.
After an automatic mask move (e.g. when a new mask selected) press
Refreshto update positions
The top Focus panel allows focusing of the two main cameras. Vampires has a global, absolute focus adjustment (the Abs+ / Abs- row) which moves the camera-lens assembly, and a differential focus (the Diff+ / Diff- row) which moves one camera with respect to the other for co-focusing. These focuses may be nudged with the buttons or an absolute value entered into the text box. The Abs focus is in units of mm, while the Diff focus is in Zaber steps.
Co-focusing is performed via a separate automated procedure and should already be correct - you shouldn't change this. Only change the Abs focus if a focus adjustment is required (e.g. when going between ver different wavelengths).
If something goes wrong and you restart vControl, make sure you press the
Steer Im/Pupbutton again to launch the window. A stale copy of the window may still be open!
Filter Wheel panel and press Move Filter Wheel.Waveplates panel should be set to AO188_HWP.Remember - the exposure time setting for live video preview is not automatically the same as being used for data acquisition - double-check this!
Once everything is set up to your satisfaction, you can go ahead and acquire data. Enter a filename in the filename box, usually the name of the target and a set number, e.g. alfOri_02. Date/time stamps and settings metadata are appended to the filename automatically. Data is saved to /data/YYYYMMDD/. Then enter the desired number of 'loops' in the Loop box. A loop consists of the 4 HWP positions. E.g. if you enter 10 in the `Loop' box, you will get 40 files (each a cube of the number of frames defined in Acquisition settings.
Then press Execute Series and data acquisition will begin!
Note that you want to press
Execute Seriesto take data. TheExecute Acquisitionbutton only takes a single cube.
Once data acquisition has begun you must keep an eye on it, especially at the start. If not already there, you should see the quarter-wave plates rotate to their calibrated position for the chosen filter. In the console you will see the responses from AO188 confirming that the HWP has rotated - you should see it say things like OKAY hwp move 22.50. Keep an eye out for errors. You should see ongoing reports of acquisitions completing and writing to files. In the status bar of the vControl GUI you will see it counting up the frames for each cube.
Keep an eye on the console ('Command Window') and vControl status bar, looking out for errors! Make sure happy messages confirming completed acquisitions and successful HWP moves keep showing up. If they stop, either something has gone terribly wrong or your acquisition has finished.
The vControl background turns blue while acquisition is ongoing, and will return grey when it's done. But things can go wrong...
Usually things go ok, but occasionally acquisition freezes mid-cube, believed to be due to an Andor buffer-overflow problem. This is currently being investigated, but for now there is a kludge (or two)...
An internal watchdog timer checks that new frames arrive in a reasonable time. If not, an error is thrown and the vControl background should turn a warning blood-red, and then an auto-restart sequence begins. This is very much a kludge, and it appends __RESTARTED__ to the filenames of the resumed series, so you know it happened.
However other things can possibly go wrong, including network problems or other failures which mean you won't see the error messages. A separate watchdog script can be run locally, described here.
In more serious errors, the cameras may stop working or not even initialise - see here for the solution.
Due to the fact that the acquisition is largely at the mercy of the Arduino’s timing signals, aborting can be tricky. But it usually works. Press the red Abort! button, and wait. The abort flag stays set, and as each loop ends it will pass this flag up. Thus once it completes the current waveplate angle, etc, it should cleanly abort, and the grey background and 'Idle' status will reappear.
Once you’ve aborted, things may be unstable (the Andor camera gets quite upset at these things). If you're worried, restart vControl to be safe, before continuing observations. Restart using the Exit button on the lower-right corner.
When you've finished, there's not much to do, except take a dark frame. The easiest way is to put the Mirror into position in the mask wheel to block all light, and then take a single series with the same integration times and EM Gains as used throughout the night.
When done, exit vControl by pressing the Exit button at the bottom of the vControl window. This will also close the camera's shutters, protecting them from bright daytime engineering.
Always exit vControl by pressing the `Exit' button at the bottom of the GUI window. Otherwise it will not shut down the cameras properly and could lead to damage.