4 ms·

Side question: with $12M of equipment, wouldn't it make sense to have an independent limiter of some kind to prevent damage? Is there something about this equip

by wissler 13y ago

Side question: with $12M of equipment, wouldn't it make sense to have an independent limiter of some kind to prevent damage? Is there something about this equipment that makes that greater than $12M in difficulty? Because relying on having no bugs just so your hardware isn't destroyed seems like a bad idea...

saym 13y ago
I'm willing to bet the question has a fabricated back-story. If you look at the user's question history: there are some interesting ones, but they all could be justified as a collegiate homework problem.
- quasque 13y ago
  Also, $12 million for an electron microscope seems somewhat on the expensive side, by an order of magnitude.
  - Daniel_Newby 13y ago
    The poor bastards might have had the entire reticle set (photo mask) set for fabricating a microchip loaded in the microscope for inspection.
gnaffle 13y ago
It would absolutely make sense. However, my guess if the story is true would be that one (simpler, cheaper) device caused damage to other, more expensive equipment, in a way that was not foreseen. (Another similar scenario: A software controlled pump not stopping like it should, causing an entire lab bench to be flooded with corrosive liquid). Unfortunately non-software guys often have a lack of appreciation for how subtle some software bugs can be. Re. the mentioned Therac-25 incident in this thread.
rprospero 13y ago
Well, $12m breaks my personal best, but the independent limiter is only delaying the inevitable. You'll have just as many bugs in your hardware as in your software: 1) Include software controls to limit motor position 2) Include hardware kill switch to prevent collisions. 3) Drive unit to the outermost SAFE motor position. 4) Motor limit drops into worm gear 5) Send unit back to original position. 6) Unit doesn't move as worm gear eats limit cable. 7) Since the unit didn't actually move, the software limits are now compared with faulty data. 8) Send the unit out to the far edge again 9) Since the software positions are incorrect, the software limits won't help. 10) Since the limit cable was eaten by the gear, the contact switch won't help. 11) Hear super-mirror array drive into concrete wall. Of course, having a hardware limit switch the trigger on an open circuit would have fixed that problem. Until the time that a faulty solder joint shorts the switch and the mirror drives into the wall. So you can add in a hardware encoder to check the physical position. Which saves you until the unit is manually moved next to the wall between runs without updating the position in software. Since the encoder only gives relative position, the software limits, encoder, and shorted limit switch still gleefully watch as you again drive the super-mirror into a wall.
gizmo686 13y ago
Breaking a $12M piece of equipment could be as simple as blowing a $5 fuse. Most expensive equitment I've worked with (in the $100s/$1000s range) seems to be designed so that the expansive components themselves are pretty well protected, and if you break something it is generally relatively cheep to fix.

by wissler 13y ago

saym 13y ago

I'm willing to bet the question has a fabricated back-story. If you look at the user's question history: there are some interesting ones, but they all could be justified as a collegiate homework problem.

quasque 13y ago
Also, $12 million for an electron microscope seems somewhat on the expensive side, by an order of magnitude.
- Daniel_Newby 13y ago
  The poor bastards might have had the entire reticle set (photo mask) set for fabricating a microchip loaded in the microscope for inspection.

gnaffle 13y ago

It would absolutely make sense. However, my guess if the story is true would be that one (simpler, cheaper) device caused damage to other, more expensive equipment, in a way that was not foreseen. (Another similar scenario: A software controlled pump not stopping like it should, causing an entire lab bench to be flooded with corrosive liquid). Unfortunately non-software guys often have a lack of appreciation for how subtle some software bugs can be. Re. the mentioned Therac-25 incident in this thread.

rprospero 13y ago

Well, $12m breaks my personal best, but the independent limiter is only delaying the inevitable. You'll have just as many bugs in your hardware as in your software: 1) Include software controls to limit motor position 2) Include hardware kill switch to prevent collisions. 3) Drive unit to the outermost SAFE motor position. 4) Motor limit drops into worm gear 5) Send unit back to original position. 6) Unit doesn't move as worm gear eats limit cable. 7) Since the unit didn't actually move, the software limits are now compared with faulty data. 8) Send the unit out to the far edge again 9) Since the software positions are incorrect, the software limits won't help. 10) Since the limit cable was eaten by the gear, the contact switch won't help. 11) Hear super-mirror array drive into concrete wall. Of course, having a hardware limit switch the trigger on an open circuit would have fixed that problem. Until the time that a faulty solder joint shorts the switch and the mirror drives into the wall. So you can add in a hardware encoder to check the physical position. Which saves you until the unit is manually moved next to the wall between runs without updating the position in software. Since the encoder only gives relative position, the software limits, encoder, and shorted limit switch still gleefully watch as you again drive the super-mirror into a wall.

gizmo686 13y ago

Breaking a $12M piece of equipment could be as simple as blowing a $5 fuse. Most expensive equitment I've worked with (in the $100s/$1000s range) seems to be designed so that the expansive components themselves are pretty well protected, and if you break something it is generally relatively cheep to fix.