Dome auxiliary systems

Cabling and Conduit

Cabling to the telescope is done through conduit that runs from below the computer rack into the pier. There is a hole in the bottom of the azimuth cone and cables may be run up through that hole.

The easiest way to run cable to the telescope is to tie off one end of the cable on the telescope structure, then drop the cable through the hole in the top of the azimuth plate and work it until it goes below the azimuth cone. Next, get an extension ladder and place it alongside the pier on the north side. Just below the floor of the dome is a small access door that opens with a flat-bladed screwdriver. Open the door. You'll see where the cables turn the corner into the conduit. Take the loose cable and direct it into the conduit. The conduit itself has access doors. Unfortunately, the design of the dome is such that the doors do not open very far. Do your best to reach in through the access doors in the conduit and guide the cable to a place where you can grab it from the exit hole under the rack.

Cables must be checked periodically to make sure there are no wraps down in the azimuth cone. There is sufficient slack in the cables (and new cable runs should be done with sufficient slack) that the azimuth would need to wrap several times before cable wraps become an issue. To check on the cables, look down in the azimuth cone and check that the cables are hanging freely and not twisting around themselves.

Rotator cables should be checked for wraps at each init as directed in the telescope operations guide.

When working on conduit, be aware that mice and rats often get into the conduit. You should take hanta virus precautions. Wear a dust/nuisance mask rated for protection against organic vapors. There are masks in the 1-meter control room. Also, Mark Klaene at Apache Point Observatory has masks that can be used. Wear rubber gloves. If rodent droppings are found, make a mixture of 50mixture on the droppings to neutralize any potential hanta virus. Once work is completed, discard the rubber gloves and mask.

Instrument Rack

The instrument rack sits against the eastern wall of the observatory enclosure. Ideally the rack should keep the computers and other sensitive electronics at a comfortable operating temperature, while not allowing heat from that equipment to affect dome seeing.

Ron Yarger, on the APO staff, is a qualified air-conditioning service technician. He can be consulted regarding the heat exchanger unit on the roof of the enclosure over the left-hand side. (This unit has been removed!).

The left side of the rack houses, from bottom to top, the motor controllers, weather station (in front of motor controllers), telescope control (TCS) box, observatory control (OCS) box, guider/filter wheel control, and main power box. All of the motors and controller boxes are plugged into a power strip at the very top of the rack. This power strip is plugged into the main power box, which gets its power from the Masterswitch unit in the right side of the rack. The only utility of running the power through the main power box is that it enables the power switches on this box, and in particular, the emergency stop button which has an access point just inside the front door. Beware that the main power box takes several seconds after power is supplied before power goes out to the motors, etc.

There is also a temperature control senson on the main power box that will kill power if the temperature goes out of range. This is an Omega series CN9000A/Model CN9111A controller which we have set to have a wide allowable range of temperature. There is a manual in one of the notebooks for this and also a PDF file (M1191.pdf) in the docs directory. This unit started to fail in 2009 (with calibration errors EE8) so it was temporarily removed and the temperature circuit bypassed (10/09).

The right side of the rack houses the telescope control computer, the CCD LN2 autofill control, a monitor, the 16-output APC masterswitch unit, and a UPS unit near the bottom, below the compuer.

The UPS is a APC SU1400RM2U, which is a model that has been discontinued. Replacement batteries (replacement battery cartridge RBC24) were still available in 2008, at which time the batteries were replaced.

Currently the rack is vented into a vent hole in the dome floor that lead via conduit into the pier. There is a fan at the base of the pier, which , when activated, will draw air through the rack. As of 2004, this fan has been put under computer control via the APC power strip. For this to work, rack needs to be fairly well sealed, allowing air to come in only at the top of the rack and passing across the electronics before venting at the bottom of the rack. A filter should be placed over the opening at the top of the rack to prevent moths, etc from being draw into the rack; dimensions of the hole are 16x14 inches. The power strip at the bottom powers the fan in the venting and also the fan in the telescope pier; it is plugged into the Masterswitch unit.

It may be a good idea that a better insulated rack be purchased for the equipment in the 1-meter enclosure. A good source of new racks appears to be ITS Enclosures. It is possible that their enclosures could be placed outside the 1-meter enclosure itself. Their products may be viewed on the web at:

Autofill System

The auto-fill system was purchased from VBS Industries in California. The product manager was David Carnahan. The engineer was Alan Ziegler. They may be reached at (408) 371- 3303. There is a file in the upper drawer of the tan filing cabinet with details regarding the construction of the auto-fill system.

The auto-fill system has a manual control box located in the rack just under the monitor, on the shelf with the screen switcher. The key should always be in the "on" position. Fills are triggered via one of the TCS auxiliary output lines.

The system has an auto-shutoff feature, where The autofill shuts off when Liquid Nitrogen makes contact with a sensor mounted in the fill tube that mounts in the CCD dewar. This sensor has a gold-colored tip and may is located in the right-angle pipe near the top of the fill tube assembly. The wire to the shut-off sensor is in the metal "cable" that is attached to the fill tube. However, we were never able to get this to work reliably. As a result, the sensor connection has been replaced with a plug that closes off the circuit. Dewar fills are shut off using a timed fill duration instead of the sensor.

One should periodically inspect the Autofill lines. Make sure there are no apparent breaks and that nothing has come unscrewed in the plumbing. The most likely place for a disconnect is at the azimuth cone, just below the black solenoid that controls the fill.

Manual Override of the fill

Fills can be triggered in the dome by powering on the autofill system from the APC MasterSwitch and pushing the green button on the front of the VBS manual control box. If needed, a manual fill may be terminated by turning the key to the "off" position. Just be sure to turn it back "on" before returning to the autofill mode.

LN2 Hoisting and Attachment

A 100-liter Liquid Nitrogen dewar is used to supply the E2V detector with coolant. This dewar is connected directly to the VBS Autofill system documented above via a flow regulator. VBS-supplied hose runs from the flow-regulator into the conduit under the enclosure and up through the center of the azimuth cone to the solenoid.

As of 2006, the big LN2 dewars are left below the enclosure, and a long hose goes up through the cone, the valve, and eventually, the dewar. It takes about 7 minutes to get a complete fill of the dewar, without any pressure regulation on the big dewar.

Fans and Louvers

The enclosure's louvers open by simply applying and maintaining power to the enclosure's compressor system.

The way the louvers work is that power is applied to the appropriate socket of the APC master switch. The socket does not supply power directly to the louvers. Instead, it simply energizes a relay that in turn activates a power strip. The louvers come on when power is applied to the power strip. The relay is housed in a small black box that currently sits under the southeastern louvers. The power strip is plugged into an outlet mounted to the relay-enclosure.

There is a large fan in front of the SE louver. This is plugged into one of the controllable APC Masterswitch outlets.

Weather Station

The weather station is well-documented in the Yellow Observatory Binder. One item not documented is that if the weather station loses power for less than ten seconds, it will not come back up fully operational. Someone examining the rack will see lines across all of the places where numbers would normally be displayed. The weather station will not respond to commands from the Tocc. To remedy, simply unplug the weather station for approximately fifteen seconds, then plug it back in.

Tools & Spares

Most required tools are in the red tool boxes on the south side of the 1-meter telescope enclosure. Additional tools may be found in the 3.5-meter and Sloan work areas. As a rule, tool drawers are labeled with the items that are enclosed. When borrowing tools from the 3.5-meter or Sloan, make sure to alert the appropriate personnel (Mark Klaene or Jon Davis, if no one else is available) and return the tools as soon as possible.

The upper-most shelf by the window over control1m in the 1-meter control room contains spare motors and a breakout box for testing the TCS and OCS boxes. There are also spares available in the two large drawers under the white board in the 1-meter control room. There's a small supply of spare relays (including spare dome relays) and motors (including mirror cover motors) in the lower-most drawer of the big tool box on the south side of the 1-meter enclosure.