Reliability (was: Underwater Sensing, switches and democracy)
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Posts: 46,084
Jose Luis Juarez wrote:
<snip>
* A switch can (and it must assumed that it will) fail eventually.
Let me expand and reinforce Jose's statement:
Any given electromechanical device *will* eventually fail!
It's only a matter of time, and the number of cycles of operations that the
device is subjected to. Yes, there are things that can be done to improve
the reliability of devices (like higher levels of integration, better
quality components, etc.) - but... it's still going to break someday.
This goes for your dishwasher, your washing machine, and that hard disk
drive you haven't backed up in the last six months or more that has all your
"important stuff" on it. It's all too easy to get complacent about things
like that. I also can't tell you how many times I've seen clients jumping
up and down, tearing their hair out and screaming at the top of their lungs
because their hard drive "gave up the ghost" and took all of their
bookkeeping data for the last 5 years with it. During the course of visit
to a client, I'd inquire as to when was the last time their data was backed
up. Most of the time, I'd either receive a blank stare, or that "deer in
the headlights" look.
<snip>
> Of course you do it by wiring in series your N switches, if they are
> "Normally Closed" contacts (the strongly recommended type), or in parallel
> if the are "Normally Open" contacts (to avoid). This was called
> "interlocking" in the past. The switch (es) in control should open the
> conveyor motor contactor directly, as this is your last chance to stop it!
I heartily agree with Jose's statements here. Years back, I was a radar
systems technician on F-4J Phantom II jets, in which there were numerous
interlocks with the "normally closed" contacts; one in particular was the
"weight on wheels" switch. If the aircraft was on the ground, the "weight
on wheels" interlock would open, preventing the radar system from radiating
RF on the ground, which otherwise would be hazardous to ground personnel.
Regards,
Steve
<snip>
* A switch can (and it must assumed that it will) fail eventually.
Let me expand and reinforce Jose's statement:
Any given electromechanical device *will* eventually fail!
It's only a matter of time, and the number of cycles of operations that the
device is subjected to. Yes, there are things that can be done to improve
the reliability of devices (like higher levels of integration, better
quality components, etc.) - but... it's still going to break someday.
This goes for your dishwasher, your washing machine, and that hard disk
drive you haven't backed up in the last six months or more that has all your
"important stuff" on it. It's all too easy to get complacent about things
like that. I also can't tell you how many times I've seen clients jumping
up and down, tearing their hair out and screaming at the top of their lungs
because their hard drive "gave up the ghost" and took all of their
bookkeeping data for the last 5 years with it. During the course of visit
to a client, I'd inquire as to when was the last time their data was backed
up. Most of the time, I'd either receive a blank stare, or that "deer in
the headlights" look.
<snip>
> Of course you do it by wiring in series your N switches, if they are
> "Normally Closed" contacts (the strongly recommended type), or in parallel
> if the are "Normally Open" contacts (to avoid). This was called
> "interlocking" in the past. The switch (es) in control should open the
> conveyor motor contactor directly, as this is your last chance to stop it!
I heartily agree with Jose's statements here. Years back, I was a radar
systems technician on F-4J Phantom II jets, in which there were numerous
interlocks with the "normally closed" contacts; one in particular was the
"weight on wheels" switch. If the aircraft was on the ground, the "weight
on wheels" interlock would open, preventing the radar system from radiating
RF on the ground, which otherwise would be hazardous to ground personnel.
Regards,
Steve