This is correct. There is also a lid w/flange that is bolted down. The material comes OUT of the auger feeder you've drawn. It goes IN the top of the hopper. The lid is bolted down because the whole thing is under pressure.
(a really neat idea snipped...)
Everything you mention would have to fit under the lid. I'm not
*even* going to try and work on a rod that has to slide back and forth freely and seal it and keep it free to move under pressure. It IS a neat idea though.
I haven't tried it except sitting on my desk. No powder, no clumping (except for my brames right now). The LED and PT are about 1 1/2 inches from each other. I can try (later) and see if anything *will* stick, but I need to get something working, then stick it in a mockup of the hopper. Thanks for your interest, though.
Bang the top edge, and detect the spectrum of vibrations. The soft material will dampen anything from below a certain point, so maybe the spectrum will shift down as the level goes down.
On Fri, 11 Dec 2009 08:10:51 -0800 (PST), snipped-for-privacy@gmail.com wrote: (reformatted slightly for readability)
---snip---
I really hate converting units... I have enough trouble typing consistently.
18"Dia x 24"H... that's a surface area of
3.14159*(2.54*(18/2))^2, or 1642cm^2,
with a height of 2.54*24, or 61cm.
When the powder level is 1cm ("almost gone"), the downward force should be 0.2gm or less. When the canister is full, it should be around 0.2*61, or 12.2gm. Wikipedia gives the weight of a U.S. penny ($0.01) as 2.5gm, so we're talking about eight pennies. Not much.
Divide this into four levels and you get 2.5gm for the lowest. Even less.
But... suppose we made the "weight" number bigger?
You indicate an auger-style feedout. Let's say it occupies the center of the bottom of the canister (worst case), leaving only half of the canister's surface area free for alteration: . . . . . . | | | | | | +------\ / -----+ \ / \ / || || (to auger) Now let's add an annular bellows (plastic bag, balloon, etc.) with a take-off tube "O" to the bottom of the canister in such a way that it doesn't interfere with the outflow:
As the powder level increases, it compresses the bellows, Since the bellows covers half the canister surface area, the pressure on it when the powder is 1cm deep is now (1642/2)*0.2, or 164gm. Half full, the bellows will have (1642/2)*0.2*(61/2)gm... about 5kg, and a full canister should be around 10kg.
Does that sound about right for a full canister? (10/0.454) or 22 pounds?
Assuming my math hasn't dropped an order of magnitude or two, I'd think that this would be enough to drive a pressure sensor, even down at the 1/4 full mark (I recall you mentioning four sensors), even if we assume there would be some "loss" converting the powder weight to air pressure.
And if the auger feedout takes up less room that I assumed, the pressures involved would be even greater.
Another idea would be using the same ring-shape and putting one or more loadcells under it, all carefully isolated from the powder, "of course" (translation: "I'm glad _I_ don't have to do it" )
Hope this helps...
Frank McKenney
--
...[I]t was assumed by American statesmen that whatever was uttered
or urged in the name of moral or legal principle bore with it no
specific responsibility on the part of him who urged it, even
though the principle might be of questionable applicability to the
situation at hand and the practical effects of adherence to it
drastic and far-reaching. We were at liberty to exhort, to plead,
to hamper, to embarrass. If others failed to hear us, we would cause
them to appear in ungraceful postures before the eyes of world
opinion. If, on the other hand, they gave heed to our urgings, they
would do so at their own risk; we would not feel bound to help them
with the resulting problems -- they were on their own.
-- George F. Kennan / American Diplomacy 1900-1950
That should get it. If not, --confirm voltage at the '+' input of comparator =3D Vcc/2 --bypass cap on the LM339 --check comparator by shorting the phototransistor. That should extinguish the indicator LED. --This is an open collector output LM339--you haven't substituted an op amp with a totem-pole output, right?
What color is the indicator LED? Some will light with very low leakage currents. A 10k pullup across the LED would fix that.
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