h a l f b a k e r y[marked-for-tagline]
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
Please log in.
Before you can vote, you need to register.
Please log in or create an account.
|
This is a nichey idea, probably for an audience of 1.
In some centrifuges, the tubes are supported around their
neck, leaving the body of the tube visible. This is especially
true for vacuum centrifuges, which are used for evaporating
liquids under vacuum (the centrifuging stops liquid from
bubbling up out of the tube). In many cases, the lid of the
centrifuge is transparent (or could be made so), which means
you can see your tubes whizzing around.
In general, there is no advantage to being able to see the
tubes whilst they whizz - they're just a circular blur. However,
a xenon strobe built into the centrifuge and synced with the
rotor would give you a freeze-frame view of your samples
while they spin. This would be useful in determining whether,
for example, your gunk has pelleted or (in the case of a
vacuum centrifuge) whether you've removed enough liquid.
This would save having to stop and then restart the centrifuge
(which is a bad idea if you're trying to pellet something
anyway).
[link]
|
| |
I thought this already existed? |
|
| |
We consider that there may be a risk of inducing epileptic seizures in unwary users and onlookers, so [+]. |
|
| |
The rotation speed of the centrifuge will generally be high
enough to put the strobe rate above the frequency that can
trigger seizures. |
|
| |
Yes, but that can be put right, shirley ? A hit-and-miss trigger sequence delivering a 3 to 5 Hz flash ? |
|
| |
[8th], perhaps you could just buy your own xenon tacho strobe
and take it into a crowded place. In any event, please get out
of my lab. And put that back. |
|
| |
We only wanted one as a souvenir ..
it's not really stealing or anything ... |
|
| |
Besides, after we took your family for a guided tour of our Cube, all sorts of things seemed to be missing. So you're hardly in a position to criticize ... |
|
| |
Ebola is not, by any stretch of the imagination, a "souvenir". |
|
| |
Perhaps we have misunderstood "souvenir ". Everyone who's had it and survived says they'll never forget it ... |
|
| |
//rotation speed of the centrifuge will generally be high
enough//
You don't need the strobe to flash once-per-rev, but you
DO need the duration of the flash to be short enough to
"freeze" the motion.
Eg: a 300mm diameter centrifuge doing 6,000rpm has a
tip speed of 2.39m/s. To "stop" it, you would want it
moving less than, say, 0.25mm; a duration of 1/10,000 of
a second.
(Quick Google...)
Hmm, that's not actually too bad... |
|
| |
Quite so. A xenon strobe will handle that (just). But you
probably do want one flash per rev, simply to get enough light
to see the sample by. |
|
| |
<Obligatory Chief Brodie paraphrase> |
|
| |
" You're going to need a bigger strobe." |
|
| |
[MaxwellBuchanan]; that's 100Hz (continuing with my
example values), so again not too bad. With the power of
LEDs these days, I don't think "get enough light" will be a
problem. I would think every 4th rev (ie: 25Hz; video frame-
rate) would be plenty.
How accurately can the rpm be measured/matched? |
|
| |
LEDs might be enough, that's true. Speed sensing is not an
issue. Centrifuges normally have a little magnet on the base
of their drive shaft, that is sensed by a Hall-effect device and
is used to regulate (and measure) speed. Just use that pulse
to trigger the strobe. |
|
| |
There is a much simpler solution. |
|
| |
Onto the top of the centrufuge shaft, place an opaque dusc with a slot in it above the position of interest. |
|
| |
Above the disc, place a bright light source in a fixed position to shine down through a fixed aperture when the two slots line up. |
|
| |
At the same point in its rotation, the moving slot will uncover the light source, illuminating the target. |
|
| |
Simple; cheap; foolproof; self synchronizing. |
|
| |
Yes, but not as cheap, simple and self-synchronising as using
the already-present once-per-revolution pulse from the rotor
shaft. |
|
| |
Wouldn't a better solution be to mount a camera on the centrifuge rotor,
powered by batteries and connected for video by a radio link (e.g.
Bluetooth), or bothed by a rotary transformer? |
|
| |
Wouldn't the actual better solution be to use a proper analytical centrifuge
that has hardware built in for quantitative measurement of the progress of
your centrifugation? |
|
| |
//mount a camera on the centrifuge rotor// Cumbersome. |
|
| |
For analytical centrifuges, yes there are other better options.
But a cheap, simple centrifuge (such as the centrifuge part of
a vacuum centrifuge) could be so easily adapted, requiring
only the use of the existing rotation sensor to trigger the
strobe. We're not talking precise analytical tool here - I just
want to be able to see if my gunk has pelleted, or if my
sample has dried down. |
|
| |
// I just want to be able to see if my gunk has pelleted, or if my sample has dried down. // |
|
| |
<Contemplates possible double-entendres/> |
|
| |
<Wonders how carefully [MB] considered his choice of words, if at all/> |
|
| |
<Compares text with similar stream-of-consciousness annotations/> |
|
| |
<Mulls possibility that [MB] is unknowingly channelling the spirit of James Joyce/> |
|
| |
<Decides in favour of theory that [MB] has been over-indulging in the vintage* Albanian turnip brandy again/> |
|
| |
<Sits back to await further annotations/> |
|
| |
*"None sold 'till a week old !" |
|
| |
Had you considered mounting the observer's head in the centre of the centrifuge? |
|
| |
Following [8th]'s annotation, yes. |
|
| |
Does this open up experiments of pulsed light on reagents whilst under Gs? Because science is really good at one variable/measurable dimension. |
|
| |
"place an opaque dusc with a slot in it above the
position of interest..." |
|
| |
Came here to day this, only with the word 'disc'. :) |
|
| |
It's a neat low tech solution. There's no sync required
as the shield with the slot could just be bolted to the
same assembly. |
|
| |
The strobe has some advantages though. It has the
potential to be brighter. You can see multiple tubes
at once. And by decoupling the strobe and the
centrifuge you can rotate the image of the tubes to
examine different ones; something that would be
mechanincally complex with the slot assembly. |
|
| |
// You can see multiple tubes at once. ... examine different ones // |
|
| |
No good for [MB], then; he has trouble concentrating on even one thing at a time ... |
|
| |
As a QA guy who served five years doing inspection in the centrifuge mines, I endorse this idea. (+) |
|
| |