Telescope Mount Functional Safety

Mount Base LIC

The Mount Base LIC is responsible for interlocks, limits, and emergency stop functions for the Telescope Mount Azimuth and Altitude Axes; Cable Wraps; M1 Mirror Cover; and M5/M6 Access Platforms.

For details of implementation see LIC design requirements document.

Telescope Mount Azimuth Axis

Telescope Final Travel Limit

When a Final Limit is detected by using safety encoder, the reaction of the GIS to bring the axis to a stop as quickly as possible, remove power from all Azimuth Drive Controllers (category 1 stop) and apply the brakes.

Telescope Azimuth Drive Over-Speed

Abnormally high velocities indicate a failure of Azimuth Axis Bogie Drive. The reaction of the GIS is to bring the axis to a stop as quickly as possible, remove power from all Azimuth Drive Controllers and apply the brakes (category 1 stop).

Trapped Key Interlock

This is actually a group of trapped keys which when one or more are removed will inhibit Telescope motion by removing power. This key is required to enter the Azimuth Cable Wrap or Azimuth Mechanical areas.

Telescope Azimuth Axis Interlock

This safety function is the result of combinational logic in the GIS that determines another subsystem poses a hazard to Telescope Azimuth Axis motion.

This interlock is asserted unless all the following are true:

• Enclosure Bridge Crane stowed

• Enclosure Jib Crane stowed

The reaction of the GIS is to remove power from the Telescope Azimuth Axis drives.

Telescope Altitude Axis

Telescope Altitude Drive Over-Speed

Velocities above a predetermined level indicate a failure of an Altitude Axis Drive. The reaction of the GIS is to remove power from the Altitude Drive Controllers and apply the brakes (category 0 stop).

Telescope Positive Altitude Final Travel Limit

When a Positive Altitude Final Limit is detected, the reaction of the GIS is to remove Telescope drive power (category 0 stop) and apply the brakes.

Telescope Negative Altitude Final Travel Limit

When a Negative Altitude Final Limit is detected, the reaction of the GIS is to remove Telescope drive power (category 0 stop) and apply the brakes.

Telescope Altitude Cable Wrap Over-Tension

The GIS shall inhibit motion and remove power to the Telescope Drives (category 0 stop) if the tension of the Altitude Cable Wrap exceeds predetermined limits.

Manual Lockout Pin

The manual lockout pin is a physical means by which the motion of the Telescope can be prevented. If this pin is not fully removed the GIS shall remove Telescope drive power.

Trapped Key Interlock

This is actually a group of trapped keys which when one or more are removed inhibits Enclosure and/or Telescope motion by removing power.

Telescope Altitude Axis Interlock

This safety function is the result of combinational logic in the GIS that determines another subsystem poses a hazard to Telescope Altitude Axis motion.

This interlock is asserted unless all the following are true:

• Enclosure Bridge Crane stowed

• Enclosure Jib Crane stowed

• TEOA Platform stowed or fully deployed (see section 4.9.5)

• Boom Lift Stowed

The reaction of the GIS is to disable power to the Telescope Altitude Axis Drives.

M1 Cover Interlock

The M1 cover is allowed to open under specific circumstances.

Similar to the Entrance Aperture below, the M1 cover may open when no sunlight can strike the mirror (see 4.4.2 Off Sun Pointing). Additionally if the telescope is pointed directly at the sun and the safety shutter is open and the heat stop is not in an over-temperature condition the M1 Cover may open.

Telescope Floor Access Panels Not Closed

Telescope Drive Power is disabled unless are Telescope Floor Access Panels are closed.

M5/M6 Access Platform Not Stowed

Telescope Altitude Drive Power is disabled unless the M5/M6 is fully stowed.

OSS Access Platform Not Stowed

Telescope Altitude Drive Power is disabled unless the M5/M6 is fully stowed.

Access Doors Not Closed

Telescope Elevation Drive Power is disabled unless the Access Door is closed.

Telescope Azimuth Cable Wrap Access

This area requires a trapped key to access. Inserting the trapped key allows removal of one or more secondary personnel safety keys. All personnel who enter are required to carry a personnel safety key.

Telescope Azimuth Mechanical Level

Access to the Mechanical Level requires a trapped key. Inserting the trapped key allows removal of one or more secondary personnel safety keys. All personnel who enter are required to carry a personnel safety key.