• Detector Illumination: Keep the filter wheel on the Block position (Filter 1, Odometer Reading 10.00), when the detector is not is use. This prevents possibly high levels of light from reaching the detector. Although saturation is not known to cause harmful effects, it is best to play it safe, especially when observing during the day or near the moon, when the spotlights in the Cass. cage are on, etc.

• Power: Turn the detector power off when:
  • the liquid helium runs out. The bias voltages could damage a warm detector.
  • the instrument is left unattended for any significant length of time.

• Static Electricity: The detector in SpectroCam-10 is sensitive to Electrostatic Discharge (ESD). With the dewar closed the detector is reasonably well protected, except for the electrical connectors on the top plate. Keep these connectors capped when not in use.

There are a few specific rules to follow in order to operate the GSM safely:

• Coarse Sensor and Commutation: The GSM's coarse sensor loop controls the commutation of the motor. Therefore, it must be properly calibrated so the commutation information is correct. If the commutation control is faulty, the GSM will not function at all, and the motor will turn the carousel into the hard stops when power is applied. Be sure to properly adjust the coarse loop, and check it regularly (at least once a day), because it is sensitive to temperature changes both inside and outside the dewar.

  The fine loop is not so critical because drifts are over a smaller angle and can be easily corrected in software.

• Motor Power Switch: Never turn on this switch (on the GSM power supply) until the Main GSM power has been turned on, and either the Auto/Manual switch on the GSM electronics is in Manual, or the GSM electronics have been initialized from the PC with a command like gm c.

  When turning on the Motor Power, listen for a loud ``clunk'' from inside the dewar. If you hear one, turn the Motor Power off immediately. Also, check the LEDs on the GSM electronics box; the green one should be lit signifying the GSM is in Fine Lock mode. There are software mode indicators also; be sure you know how to interpret them.

  If you hear a ``clunk'' or see the lights misbehave, this usually means the coarse sensor loop has not been properly adjusted, or the GSM electronics have not been initialized from the PC. Follow the directions carefully!

1. Do not let O-Rings freeze. When filling the liquid helium or liquid nitrogen cans, be sure that the necks do not ice up all the way down to their base. When filling the outer can from a pressurized LN2 storage dewar, use the long fill tube that extends well down into the LN2 can. Put a rubber extension tube on the end of each neck to move the coldest part of the tube (the end) farther from the O-Ring.

2. Ice Plugs. The secondary helium fill tube (used for filling the dewar on the telescope) has a small inside diameter and is very likely to develop an ice plug if precautions are not taken. Although this does not endanger the dewar (as long as the main helium neck stays clear), it will be impossible to refill the helium with the dewar on the telescope. The liquid helium in the can may also begin to oscillate, reducing the hold time. Blow dry nitrogen gas through the tube before the first helium fill to be sure it does not have any liquid water or nitrogen trapped in it. Attach a long rubber hose to the end of the bayonet extension to minimize the backflow of air and moisture into the neck.

3. LN2 Pumping. We pump on the outer LN2 can to lower its temperature and reduce the thermal radiation from internal optical surfaces. Pumped nitrogen, at a temperature of about 60 K, cryopumps quite strongly, so never leave the outer can open to air unless the temperature has risen to 77 K and the nitrogen has melted. Otherwise the air and water vapor sucked into the can because of cryopumping may cause an ice plug. When the LN2 is being pumped, be aware that if there is a power failure or pump problem, the pinch valve on the LN2 pump hose should be closed to preserve the vacuum in the can. With the pinch valve closed, the dewar is safe for an indefinite period. However, the liquid helium blowoff rate will increase by a factor of two if the nitrogen warms up to 77 K, so the helium will have to refilled more frequently to keep the detector cold.

1. Use great care when rolling the cart or rotating the dewar that the dewar does not hit a wall, table, etc. It wouldn't take much of a hit to dent or puncture the thin (1/8 inch) dewar wall.

2. Insert the four allen bolts into the four mounting posts on the side of the dewar when the dewar is in the cart. Always check that these four bolts are in place before rotating the dewar, to be sure that the dewar will not fall out its mounts.

3. Have a firm grip on the dewar before releasing the lock handles to rotate the dewar. The center of gravity depends the quantity of cryogens in the dewar and the number of electronics boxes mounted on its side.

4. Dewar Window The dewar window is made of Zinc Selenide (ZnSe). The selenium is toxic, so don't handle the window with bare hands. Keep the window cover plate on as much as possible to prevent the window from getting dirty or broken. A broken window with the dewar under vacuum and cold could easily result in the total destruction of the instrument.