Caltech Submillimeter Observatory

Caltech Submillimeter Observatory Office,  111 Nowelo St., Hilo, Hawai'i 96720  Voice: (808) 935-1909 Fax: (808) 961-6273

Beginning of Night

Check Instrument

1. Check if Lakeshore (on platform) reads >5000kOhms. If so, SHARC is at operating temperature. Disconnect the Lakeshore cable and the FET thermometer cable from the dewar. Else, check laminated sheet (in control room) for instructions on finishing the cycle. Switch off current supply and Lakeshore (both on the right-side platform floor).
2. Check SHARC panel (box with switches and LEDs, at chest height just as you walk to the platform). Box should be on. Heater switch should be in 'FET Heater' position. Pre-amp and A/D switches should be 'ON'. Corresponding LEDs should be lit.
3. Check if filter wheel is at correct position. The counter on top of SHARC dewar should read 7500 for 350um filter. Adjust if necessary.
4. Check Pre-amp and Gain setting. On the little aluminum box attached to the dewar, check if switch is on the 'ON' position, and gain is set to the higher level (8000).
5. Check A/D box (at the base of the dewar). Ckeck if power switch is 'ON'. It will not hurt to press the 'RESET' button once to ensure it's not stuck in some funny state.
6. Check Tertiary mirror position. If you can see the secondary through the beam path, you should be fine. If not, then the tertiary is flipped to divert the beam to the sidecab. Unscrew, and flip out of the beam, then tape it to the side.
7. Remove mirror covers (Plexi-glass cover on the flat mirror, foam cover on the ellipsoid under SHARC). You may also wipe the SHARC window (bottom of dewar) if there is apparent condensation.

Computer Issues

1. Switch on or Reset the Mac (SHARC computer) in the control room. It's a good idea to restart it at the begininng of the night, just to make sure. It will boot up and start the SHARC server automatically. If the speakers are on (a good idea), it will let you know when it's ready (it'll say 'Make it so' -- thanks to Dominic's wonderful set of sounds), and a yellow dialog-box will pop up for a short while. You can start issuing the setup commands from the UIP. (Before you do that, it may be a good idea to clean up unnecessary processes on the Alpha [see next point]).

Soon after the 'SHARC' command is issued in the UIP (see later), the Mac should make all sorts of noises. Sometimes, it does not (network problems). In such a case press the 'STOP' button on the SHARC server, exit from UIP (Ctrl-Y and then type 'exit'), get back into UIP, press the arrow (start) button on the SHARC server and reissue that SHARC command again. If the failure persists, try rebooting the Mac. (Sometimes it takes several attempts before success...)
 
2. To clean up on the Alpha: Log in to alpha1 as 'system' (call me if you need password). Issue a 'sho sys' command. It will give you a list of processes running. Kill all processes that are AOS related, and probably the 'Downconverter Client' as well. To kill a process type 'stop /id=XXXXXXX', where XXXXXX is the process id as listed by 'sho sys'.

If SHARC just crashed (froze), also kill all SHARC processes. Then type 'run uip_exe:locks' to display some UIP related processes. Here again kill the SHAR related ones.
This is a radical way of doing things (not quite as they are intended), but makes sure you start from a nice clean state. I.e., unless you are an expert at the software end of things, this is probably the best way to go about it. It works...

Initialization Command Set

You will need to issue these commands every time you restart the SHARC server, or if you exited from the UIP. Only the 'SHARC' and 'SEC' commands are absolutely necessary, but it is a good idea to issue the others as well to make sure everything is set up correctly (do not trust defaults).
 

Chopper Adjustment Tips

The chopper control box is the silver panel at waist height on the rack in the sidecab. It has 6 turn-knobs, a couple of switches, some LEDs, and a bunch of BNC cables attached.

For a start, look up the settings appropriate to your desired chopper. Once you have set the oscilloscope cursors to the correct levels (to know where you want to have your chopper signal to lie -- change scale if necessary) and set the control knobs on the chopper control box to the suggested positions, you can start the chopper and play with the gain and offset knobs to make the chopper signal fit between the cursor lines.

Check that the switch on the chopper control box is on 'TTL'. If the red LED is lit, press the black button on the right to start the chopper (the left one stops it). Else, the chopper was going already.

Make sure one of the BNCs going to the scope is connected to 'TTL monitor' (via a T-splitter), and not to the 'Analog monitor' port. Reconnect if necessary.

On the scope CH1, and CH2 will have the chopper position, and the TTL control signals. You may need to adjust the trigger level to get updates. If you see the signals you can turn the TTL channel off (you won't need it) so that only the chopper signal is displayed.
 

A good starting set of positions for all chops

Chop Throw Specific Settings

Fine-Tuning the Chopper

1. You will only need to play with P (primary) and G (gain) knobs. First, try to find G (in that ballpark) which will give you the flattest looking signal (it may be ripply a bit). From this point P and G will have to be manipulated in complement to each other to keep the signal flat (if you do something with P, you'll have to compensate with G, to get the signal back to flat).

 
2. Making small adjustments at a time, depending on waveform, do the following:

- if signal is round, or want to increase flat portion: Increase P (compensate with decreasing G) in small steps, until ripple starts to form on signal. Back-off a little to make the ripple small enough not to worry about (<5").
- if signal has a ripple after the transition, decrease P (compensate with increasing G) in small steps, until ripple disappears, or becomes negligibly small (<5").
Note. Ripples that vary from cycle to cycle are caused by winds, and there is nothing that can be done about it.
 
3. For perfectioninsts - If a small hump appears around the middle of the flat section of the signal, it can be removed by changing I (integral) somewhat, and readjusting P and G as suggested above. Try different settings of I and see where the hump can be made dissappear.

 
4. You should check on the chopper regularly (at least once every hour, and preferably between all sets of longer integrations), especially at the begining of the night, as warm-up will affect the mechanical response characteristics of the secondary, therefore altering the chopper wave-form as you go. Readjust (step 2) whenever necessary.