Echelle - Observing Specialist Information

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This page last updated: February 25, 2007 - JMD
This page last checked: September 28, 2004 - JMD

Contents

Care and Feeding of the Echelle Spectrograph

Checking the Echelle Fill times from the Saddlebag (SHOWFILLTIMES command)

Echelle Slit Changes and Maintenace

Focusing the Echelle relative to the Slit

Low Level Echelle MCC Commands

The Schmidt camera tank is a highish-vacuum (10-7 to 10^-8 Torr) dewar for the SITe 2048^2 CCD detector which images the spectrum. It has two LN2 reservoirs. The large one has a hold time of about 22 hours and is used to cool the charcoal getter and a gold-plated copper cold shield. The cold shield sits inside the camera just outside the beam path to collect stray gas molecules and keep them from sticking to the (warmer) CCD. The smaller reservoir has a hold time of about 8 hours, and is used to cool the detector, which is regulated with a heater resistor to keep its temperature at -120 C. The reservoirs are sized so that if the LN2 supply is cut off the CCD reservoir goes empty first and the shield reservoir will stay full long enough that the detector is almost at room temperature before the getter warms up and releases gas into the tank. It works a little better to help the CCD along by turning up the heater normally used to regulate it; more on that below. 

The reservoirs are on an autofill system controlled by the saddlebag which is on the fork side of the tank and a chassis in the pit rack. The reservoirs fill together once every four hours, and they can trigger a fill if one of them goes empty. The LEDs in the pit rack chassis that indicate a fill in progress are taped up, but there are "empty" LEDs and a "fillfault" LED which are visible if they are lit. A fillfault is not necessarily cause for panic; it indicates that the last fill took longer to complete than the system thought it should (and actually didn't complete, but timed out) but could be caused by low pressure in the transfer dewar, a pinched hose, etc. Watch to see how the system behaves during the next fill to make sure there isn't a trend toward very high LN2 consumption. The various responses to an "empty" condition are detailed below under "Crisis Management." 

The saddlebag contains an analog circuit board which provides the CCD voltages, does the temperature regulation, processing and digitization of the pixel data and a Forth micro-controller which communicates with the instrument Mac, provides the CCD clocking signals and runs the autofill system. Attached to the saddlebag is another box which contains the fiber converters for the CCD data and the shutter controller. To run the saddlebag, the power supply box in the bottom of the pit rack and the small power supply box sitting on top of it (it runs the fiber driver box) must be turned on and the RS232 cables and fiber drivers plugged in and powered on both ends. Since the autofill chassis is also connected to the saddlebag, to do a proper power cycle of the saddlebag it is necessary to cycle the autofill chassis along with the power supply box. It is better to turn power back on to the autofill chassis before the saddlebag power supply box so that the autofill chassis catches the fill request generated by the saddlebag micro-controller at boot. 

The transfer dewar is connected to the reservoirs via vacuum-jacketed lines that have KF-40 fittings on the reservoir end. There are two mating KF-40 fill tubes at the reservoirs (the two fill tubes are actually interchangable, but the valve hardware, which is the "out," is set up to mount on one particular side). We make the KF-40 joint with regular rubber O-rings (no grease of any kind--it seems to form some kind of solid precipitate at cryogenic temperatures) and plastic (for thermal insulation and because they are easier to work with for this purpose) KF-40 clamps. They have to be quite tight, and it is not an easy connection to get right. If you have to re-do it, be sure to watch a fill to see that LN2 doesn't leak out at the KF-40 joint. The transfer dewar needs to be filled every 2 days or so, and is run at 7 psi, regulated by a pop-off (there are also pop-offs on each reservoir, set to 7 psi). The popoffs have teflon O-rings in them, and seem to deal with the cryogenic gas just fine; they hum and sing every once in a while but always reseal, preventing a crippling loss of pressure in the autofill system. 

There are yellow valve handles on both reservoirs, and these are plumbed in parallel with the solenoid valves and allow a manual fill. There is a gas port which can be used to vent the pressure, and a "Pressure Building" valve which is useful if the dewar gets so overfilled that there isn't room for enough gas to pressurize it. There are faucet-style handles for gate valves on the transfer dewar to valve off the three liquid ports independently. 

DO NOT FORGET TO KEEP BOTH VALVES TO THE INSTRUMENT OPEN. 

The only really serious thing that can go wrong is to have the shield reservoir go empty and warm up the getter while the detector is still cold. The pressure will go high enough to cause the ion pump current to go too high so that it should be shut off, resulting in a soft vacuum with a cold detector for everything to stick to and a long turnaround before the instrument can be used again, since it will have to go back on the vacuum pump. There is an ion pump which runs all the time, operated by a Varian Minivac controller mounted in the rack in the pit. The reading on the gauge should be about zero for normal operation; the "polarity" and "high-voltage on" lights are taped up. If green lights start to show on the front panel, the vacuum in the tank is not as good as it should be. The instrument control computer is a mac located in the control room. 

To start the echelle ICC software, double-click on the echelle.com41 icon and under the Yerk menu, choose "Start Word." Housekeeping: Health and happiness monitoring of the camera is, unfortunately, a bit akward right now. That will improve, I hope by the end of January. To talk to the camera, there is a "Housekeeping" menu on the instrument mac which will execute some of the commands discussed below and display the reply in a pop-up window, or open up a Zterm window. The discussion below assumes you are typing at the saddlebag in Zterm. 

To check that everything is OK, type CAMCHECK. You should get just an "ok" back, though it will take a few seconds while it checks everything out. If the saddlebag has been power cycled or rebooted, you will get the message EXEC_BOOT UNACKNOWLEDGED. Type IACK to acknowledge the boot and clear the error message. If there has been an empty trigger or a fillfault in the autofill system, you will get error messages for that, too. CLEAREMPTY and CLEARFFAULT will remove them until they reoccur. 

An error will also be reported if one of the CCD voltages is not at its proper value, if the CCD temperature is too far above or below its set point, if the heater voltage goes too close to zero or if communication between the circuitboards in the saddlebag is somehow not going smoothly. To see the CCD temperature, type 0 TCHECK (always all caps when talking to the saddlebag). You will also get the value of heatervolts, which ranges from about -0.65V (0V minus a diode drop) to about +10V. This is a measure of how much effort is required to keep the CCD at its set point; lower voltage means that the CCD naturally wants to sit warmer. When it goes below zero, the reservoir is probably empty or almost so and the CCD will begin to warm up soon. The CCD temperature reading will bounce around, usually by about +/- 3 degrees from what it should read, so don't panic if you expect to see -120C and get -118. This is all noise in the readback of the temperature, not oscillations in the temperature control loop. If the saddlebag has just been power cycled, the CCD temperature will be too low and CAMCHECK will report an error which should go away as the temperature comes back to the set point. 

To find out what the autofill system is doing, type LN2STAT. FILLTIME will tell you what the fill interval is (240 minutes by default) and NEXT_FILL how many minutes before the next fill is scheduled to occur. LN2_FILL is either ON if the autofill system is enabled or OFF it is not. The last entry is a two-column table for each dewar (0 and 1 right now, proper names are coming). The entries are 0 if the item is false for that dewar, 1 if it is true. SETUP means that the saddlebag is monitoring the fill of that dewar (looking for fillfaults, empty conditions, etc) and EMPTY means that the autofill system detected that the dewar went empty. There is also some other less-useful information about how the autofill system is configured. To stop the autofill system, type STOPFILLSEQ, to start it type STARTFILLSEQ. It starts automatically when the micro boots (which means that if it is power cycled a lot, LN2 consumption from the transfer dewar will go up a bit). To change the fill interval, type n SETFILLTIME, where n is integer minutes. To measure the temperature of the reservoirs, right now it is necessary to use a test cable and a voltmeter. The cable is in the echelle cabinet in the 3.5m workroom, and it plugs into the military connector on top of the reservoir. The banana plugs are labeled. Operating temperature for the reservoir is about 300 ohms, for the shield about 450 ohms. 

To look at the CCD voltages, type 0 VCHECK, and to find out how the camera is set up for data taking, etc, type CAMSTAT. COLD will do a cold restart of the microprocessor which is as good as power cycling. For now, the housekeeping proceedure should be to do the following each day: -- a CAMCHECK -- check that the pressure in the transfer dewar is at least 5 psi -- look at the front panel of the ion pump controller to see that the pump current is not significantly (>1 mA) above zero -- check for the "Empty" or "Fillfault" lights on the autofill chassis in the pit rack -- fill the transfer dewar if it is at or below 1/2 full -- log the upper tank vacuum and the transfer dewar level Crisis management: Call anytime, day or night, if there is a problem or question or something doesn't seem right. You can call Shu-i also, and you might do that first since she is (obviously) closer for now. If the UPS starts misbehaving and the instrument isn't getting power properly, it is possible to keep the instrument running happily (though not to observe) with just the ion pump, saddlebag power supply and autofill chassis powered on.

 It is not too bad to manually fill the dewars for a day or two, in which case it is only necessary to have the ion pump powered. Tests in the lab showed that it is possible to run for well over 12 hours with the ion pump off (and the shield resevoir cold) and still have the pressure low enough to turn the ion pump back on. In the unlikely event that the CCD reservoir goes empty and the detector warms up, there should be little or no effect on the vacuum since the getter and cold shield are on the longer hold-time reservoir and the ion pump should still be working. Check to see that the pressure is still OK, i.e. the ion pump current is still nearly 0. The pressure can also be checked with the camera tank internal ion gauge (near the back, on the fork side), which can be plugged into the SenTorr gauge controller on the vacuum cart in place of the regular ion gauge that is attached to the spool. If all looks well, go ahead and cool it again. If this isn't already standard procedure here, the CCD should be read out while it is cooling. A sequence of several hundred 30 second darks (30 seconds so you can pause it to talk to the camera if you need to) until it gets close to operating temperature is fine for this. Make sure the ion gauge is off so the chip isn't flooded while it is cooling; you can turn it on to read it, just turn it back off again. If the ion pump current starts going up, check it again in at most an hour to see if it continues to increase. If it continues to rise take the fill hose and the valve plumbing off the CCD reservoir and put a KF40 fitting that has some kind of pipe or swagelock plumbing attachment (there are several around here) on one of the fill tubes. Please do not put pipe or other hard objects down into the fill tubes, as they are very delicate; some kind of soft hose like urethane is probably fine though please use care. Blow pressurized N2 into the reservoir to speed evaporation of the LN2 so that the detector gets warm before the vacuum gets too bad. Use your judgement on the pressure; I have used the gas port on a 180L dewar which was certainly greater than 10 psi, but if you think the pressure you are using is too high, it probably is. To further encourage the detector to warm up, set the CCD to regulate at as high a temperature as it can (about 12C) by typing in a Zterm window to the saddlebag 0 TSET 0 VSET. You have to remember to turn power to the saddlebag off once the detector gets warm, as it dissipates enough power in its quiescent state that it can get quite hot. If the shield reservoir goes empty and the CCD is still cold, follow the above proceedure to empty the reservoir and warm it up as soon as possible. Please, please try not to let this happen. We ran this camera for close to a year in the lab in Chicago and some minimal precautions were enough to prevent it.

 NEVER, NEVER, DO NOT EVER recool the camera after the shield reservoir has warmed up without first putting it back on the vacuum pump.

 If any of these vacuum problems occur, be sure to watch the pressure in the tank. The ion pump will someday shut itself off if the pump current gets too high, but for now it needs to be manually shut off if the pressure is too high for it to work, preferably before things get that bad so as to be kind to the pump (extended operation above about 10^-5 Torr will decrease its lifespan enormously and perhaps kill it). There is a portable thermocouple controller which is normally used to read the vacuum gauge on the main part of the spectrograph; use it to read the thermocouple on the camera tank and put the tank on the vacuum pump (the scroll/turbo system only, most especially if any part of it is cold) if the pressure seems to be going up too high too fast. If the pump isn't on the observing level and the pressure is climbing above an atmosphere, open the camera tank vacuum valve. Right now there are two vacuum valves in series, a KF50 butterfly valve right at the camera tank and a KF40 bellows valve after that, so both have to be opened to vent the tank. There isn't a rupture disk or popoff on the tank because we haven't found anything we trust yet. 

Cooling the camera tank: If the camera tank has checked out leak-free, then after the ion gauge in the tank gets somewhat below 10^-5 torr the shield reservoir (and ONLY the shield reservoir) can be cooled. This is best done manually with the valve handles on the reservoirs, as the shield reservoir has enough thermal mass that it takes upwars of a half hour to fill from room temperature. Keep reading out the pressure at the ion gauge, and in the mid- to upper- 10^-6 Torr range the ion pump can be turned on. It will probably spend a few seconds with the red "high current" light on then slowly drop down to a few mA and more slowly, over several hours, drop to near zero mA. Once the pump current is that low, it is safe to cool the CCD reservoir. Again I recommend doing it manually the first time, though it takes considerably less time to cool than the shield reservoir did. As discussed above, the CCD should be read out as it is cooled to keep thermally generated electrons from freezing into traps. Once the reservoir is full, enable the autofill system (STARTFILLSEQ to the saddlebag, or just type COLD which will reboot the controller and automatically start the autofill system) and the instrument should be ready to roll.

Checking the Echelle Fill times from the Saddlebag (SHOWFILLTIMES command)

The SHOWFILLTIMES command is a Forth command that runs on the saddlebag. In order to invoke it, you must (at the Echelle ICC in the computer room):

- stop the ICC (so obviously, you cannot do this while observing....)

- Start ZTerm from the Apple Menu's Apps&Utils listing

- type SHOWFILLTIMES. DEWAR1 is the shield, DEWAR2 is the CCD dewar. Note times that do not match

"normal" fill times: oh, 340-390s and 140-180s.

- Quit ZTerm DON'T LEAVE OUT THIS STEP!!!

- Relaunch the ICC (middle of the desktop, version "yadda yadda FOR CRAIG".

Echelle Slit Changes and Maintenace

There are three steps to changing slits:

1. Loading the Slit in a Slit Holder
2. Installing the Slit Holder in the Echelle
3. Updating the Slit Maskfile for TUI

The first step is not always necessary. The third step is sometimes needed even if the slits haven't changed.

First note: For purposes of physical handling, "the slit" refers to a round piece of steel polished on one side, with a small hole in the middle; we have many of these, but only three are commonly used. "The slit holder" is a "well" and a "collar" of black anodyzed metal that are screwed together to hold the slit; we have two of these assemblies. When I'm referring to its appearance on a slitviewer image, "the slit" refers to the hole through which light reaches the echelle.

Second note: the slits themselves are not terribly sensitive to dust, fingerprints, etc. -- or at least, there's very little effect on science as a result of these contaminants. Use reasonable care when handling them to avoid scratches, but there's no need to go to extremes. Use more care when loading the slit holder into the instrument, since there are expensive optical elements nearby -- but again, none of those elements are directly used for the science instrument itself, only for the slitviewer and the calibration lamps.

1. Find the slit you want and load it into a holder if necessary.

The echelle slits are kept in a smallish white box labeled "echelle apertures" in the cabinet immediately outside Craig's office. Open the box and sort through the bags. The default slit is 1.6"x3" -- that bag will probably be empty since the slit is already in the instrument. The next most popular slit is the square 1.6"x1.6". Also sometimes used is our smallest slit, which is labeled "old 100u pinhole" -- I think this one works out to approximately 0.9" on the sky.

Since there are three common slits and two slit holders, the one you want may or may not be in the slit holder already. Take it out of the bag, unwrap it and look at it. If it's in a little black well with screws in it, everything's ready and you can skip to step 2. If it's just a small round piece of steel, you need to find the other slit which is already in the holder.

Before removing the unwanted slit from the slit holder, take a look at the position of the screws holding the collar in place. You will try to approximate this position when you put the holder back together, although it doesn't have to be perfect. Take out the screws and remove the collar, then tip the unwanted slit out of the well onto a tissue, wrap it up and put it in the bag. Put the desired slit into the well with the polished side up, supporting it with your fingers from below.

BEFORE YOU PUT THE COLLAR BACK ON, CHECK THE ORIENTATION OF THE SLIT. This is very important because the slit orientation affects the science -- it's especially vital for rectangular slits, but also important for square ones. The slit should have two radial marks on its edges; those marks must be lined up with the screw holes for the collar. Adjust the slit with your fingers from below to get those marks lined up as accurately as possible with the holes. Once it's lined up, carefully replace the collar and screw it in place.

2. Install the Slit Holder Into the Echelle

First, get the echelle into the proper state using TUI. The cal mirror should be at the Sky position. This ensures that there will be one less optical element in the way of your hands. To make the change, you will need a flashlight or headlight and a 3/32 allen wrench. Also take your selected slit in the holder, wrapped in tissue in its bag, and the empty bag for the slit which is about to come out of the instrument.

Go up to the dome and move a kickstep to the side of the echelle facing the front of the dome. Unlatch and open the echelle "top box," immediately adjacent to the telescope fork. As you look down at the top box, the slitviewer and its assembly of lenses are at the near side, the calibration lamps and their integrating box are at the far side, and the slit is attached to the echelle window just to the left of the middle.

The slit holder is held at the instrument window with a hex screw at the top and one at the bottom. Like the screws for the collar, these have an adjustable range. The hook-shaped flange on the slit holder must register snugly against the steel bar on the near side of the echelle window in order for the slit to be correctly oriented.

Use the allen wrench to take out the top and bottom screws from the old slit holder, trying to avoid fingerprints on the slitviewer folding mirror or the slitviewer lens while you work. Friction will keep the slit holder in place without the screws. Save the screws and pull the slit holder away from the echelle window, rotating a little if necessary to get it free. It should come out easily.

Wrap the old slit together with its holder and put it in the empty bag, then take out the new slit and unwrap it. Set it in place, making sure that the flange is on the near side. Once it's in the slot, rotate it so that the flange connects solidly with the steel bar. Insert the screws and get them started. Check the flange positioning again before tightening the screws down fully.

Close the echelle top box and take the old slit in its bag and the empty bag for the slit now in the instrument back to the "Echelle apertures" box.

3. Update the Slit Maskfile File for TUI

See the Wiki page here for the latest updates on making slit maskfiles.

Guiding off the slitviewer requires that the images be flattened. This is done using a config image called a mask file.

It is essential that each time that a slit in the instrument is changed that a new mask is created. (Note: the masknames file, apotop@tycho:MC/runtime/echslit is no longer used!) Guiding off the Echelle Slitviewer could be seriously affected should the maskfile not match the slit position. The maskfile must be created BEFORE the observer uses the instrument for their cals.

Here are the essential steps to create a new mask file for the Echelle Slitviewer.

TUI/Echelle Config> Make certain that Cal. Mirror position is selected to Sky.

Rotate the tertiary to na1 position, open the NA1 eyelid, have the mirror covers closed, Bright Quartz lamps on.

Use the clear filter. We recommended an exposure time of 3-5 sec. Check that you have between 20K and 30K counts in the image and not saturated anywhere in the image.

TUI/Echelle Slitviewer> Take 3 slit images, making a note of the sequence numbers for each image taken.

Log into tron@hub35m

jeppe> ssh tron@hub35m, see passwd list for details.

From tron cd to the dcam directory.

tron> cd /export/images/ecam/UTdate

Make the mask file from the 3 images you took (make sure to use the eXXXX.fits files and not the procXXXXX.fits files!). You might need to experiment with the threshold value (0 < threshold < 1). Threshold value is the value below which all features will be masked out in the processed image.

tron> mkecammask filename1 filename2 filename3 /tmp/maskfile.fits threshold

• example: mkecammask e0004.fits e0005.fits e0006.fits /tmp/emask.fits 0.6

ALWAYS inspect a mask file before implementing it. Make sure it doesnt look crazy.

tron> ds9 /tmp/emask.fits

Copy the file to the proper keep location. It is OK to overwrite an old maskfile if you are confident the new one is ok. It is very important to make the name of your maskfile to ecam.fits.

tron> cp /tmp/emask.fits /export/images/keep/masks/ecam.fits

Now that a new maskfile has been created we need to ensure that it gets used by restarting the ecam process in TUI

TUI/log> hub startNubs ecam

Take another slitview image and make sure the mask works and covers the slit properly.

Remember to turn off the Bright Quartz lamps, and then you're all done!

Focusing the Echelle relative to the Slit

This procedure is normally only done about once a year for maintenance, and should not be required at other times unless something has gone badly wrong. Consult with Russet, Craig, or Mark before adjusting the echelle's internal focus.

To figure out if you have reason to move the motors take a ThAr image. If the ThAr lines are MUCH larger than usual (~2 pixels) and either double-peaked or donuts with a visible spider in the middle, then the one or more of the motors are not in the correct position. You will have to access certain 'secret' controls within Remark to initiate movements of various motors.

To access the echelle "expert mode" motor controls from Remark:

1. Bring up the config window for the echelle.
2. Hold down the Shift and Control keys and click on the blue Info at the top of the window. You will get a warning window from Remark, then the bottom half of the config window will display the Slit Focus, CCD Tip, CCD Tilt, and CCD Focus positions for the echelle.
3. Sync to make sure the positions shown are correct.

The nominal positions (as of September 2002):

Slit Focus: +3200
Tip: +7000
Tilt: +5000
CCD Focus: -1000

Accessing the Secret Home Buttons:

NOTE: As of August 2001, these buttons DO NOT WORK from Remark, although you can make them appear and press them. In order to home a motor, you must bring up the Expert Mode controls and the Home buttons on the Echelle ICC Mac -- the window functions in the same way as the Remark config window.

1. Hold down the Shift key and click on the blue caption for the motor you are interested in (e.g., CCD Focus).
2. Two buttons will appear: Zero and Home. When pressed at the ICC, the Home button moves the motor to home and zeroes the counter. The Zero button simply zeroes the counter at the CURRENT motor position -- do not press this button unless you are certain the motor is at zero. You are not certain the motor is at zero unless you just homed it (which also zeroed the counter), so don't bother with the Zero button at all!

To Restore the Motors to Their Nominal Positions
( in the extremely unlikely event that they get lost)

If the ThAr spectrum looks horrible AND the motor positions displayed after a Sync are not the nominal positions the you must Home each affected motor one at a time from the ICC. The Home procedure takes several minutes. You can verify that it's homing correctly by watching the output on the motor controller PC on the intermediate level. If you don't want to go up to the intermediate level, wait at least three minutes and then Sync. If the Sync completes, that means the motor is done homing. Then set the motor positions to the nominal settings shown above and press the Move button. Sync after each move. When the motors appear to be in the correct position, take another ThAr spectrum and it should look much better.

If the motors do not appear to home successfully, if they are not at zero after homing, if they do not move correctly to the requested positions in one or two tries, or if the ThAr spectrum looks awful even when the motors appear to be in the correct place, call for help.

Hide the secret Home buttons and exit expert mode with the same key+click sequences you used to get in. The expert mode window will remain open in your Remark until deliberately closed, even if you restart Remark. Close them to avoid accidentally pressing a button or changing a motor position.

Low Level Echelle MCC Commands

Here you can find some documentation for low-level commands which can be typed into the echelle motor controller PC on the intermediate level. USE WITH EXTREME CAUTION. The documentation may not be entirely correct. In some places it shows the motors numbered 1-8, which appears to be correct for those circumstances. In other places it shows the same motor list numbered 0-7, and we haven't verified whether or not that difference is appropriate in other circumstances.

How to Manually Fill the Echelle with Nitrogen!