Top End Optical Assembly Safety Function
- Tim Williams
The concentrated focused beam of sunlight produced by a 4.0m mirror is around 16.9 kW. Enough energy to boil a liter of water in about 3 seconds. The concentrated focused beam can and has cause damage to telescope components at or near the prime focus and at other points along the optical path.
Top End Optical Assembly Safety Function
Safety Function | Top End Optical Assembly |
Hazard | Focused sunlight on components of the TEOA |
Triggering Event | Any of the following:
|
Priority | The Light Path shall take priority over all other control functions. |
Modes | When light path is not blocked
|
Reaction | Block light path using sequence: Heat Stop Assembly Safety Shutter Close M1 Cover then Close Aperture Cover |
Safe State | Heat Stop Assembly Safety Shutter closed Aperture Cover closed M1 Mirror Cover closed |
Required Integrity | SIL2 |
The operation of the TEOA Safety Function has been integrated into the GIC_GLX code in the Light_Path routine, in the SafetyProgram, in the SafetyTask of the GIC_GLX controller.
If the event of a heat absorber overtemp, heat stop overtemp, or heat stop low coolant flow. The safety shutter will be triggered first which will then trigger the remaining Light Path reactions.
Time |
| Reaction | Comment |
|---|---|---|---|
0:00 | 2.5s | Safety Shutter starts closing |
|
0:02.5 | 15s | M1 Cover starts closing | Safety Shutter must be closed. |
0:17.5 | 135s | Aperture Cover starts closing | M1 Cover must be closed. |
2:32.5 |
|
| Aperture Cover must be closed. |
The reaction begins by closing the Safety Shutter. When the safety shutter moves from the fully open position the M1 Cover closing is triggered. If the safety shutter fails to move after being commanded, 2.5 seconds later the M1 Cover is commanded to close anyway. If the safety shutter fails to close within 2.5 seconds a Safety Shutter Timeout Fault is generated and latched.
After the M1 Cover is fully closed or 15 seconds later, which ever comes first, the Aperture cover is commanded to close. If the M1 cover fails to fully close within 15 seconds an M1 Cover Timeout Fault is generated and latched.
If the Aperture Cover fully closes within 2:15 after being commanded the safe state has been reached and the sequence is terminated. If the Aperture Cover fails to fully close within 2:15 of being commanded to close an Aperture Cover Timeout Fault will be generated and latched.