Jim,
A "rough idea" can get a guy a long way. Especially when the average Joe has
"no idea."
I think narrowing down the neck of the bag may or may not impact the stated
volume. But even if you are 25% off from "accurate" -
that's still "good enough" for a lot of cases...
73, Jeff ACØC
www.ac0c.com
-----Original Message-----
From: Jim Barber
Sent: Wednesday, April 13, 2011 5:55 PM
To: Jeff Blaine
Cc: AMPS
Subject: Re: [Amps] Bag-o-meter calcs in US units
Not my idea, just trying it on for size.
Ian mentioned who thought it up originally, but I've forgotten already.
What were we talking about? ;-)
73,
Jim N7CXI
On 4/13/2011 3:16 PM, Jeff Blaine wrote:
> Now THAT is out of the bag thinking! Brilliant.
>
> 73, Jeff ACØC
> www.ac0c.com
>
> -----Original Message-----
> From: Jim Barber
> Sent: Wednesday, April 13, 2011 3:14 PM
> To: AMPS
> Subject: [Amps] Bag-o-meter calcs in US units
>
> Not to run it into the ground, but does this look right?
> (in US units)
>
> . Construct a duct of heavy paper to match/mate the air output duct on
> the amplifier, tape it to a US-standard 33-gallon trash bag
>
> . Flatten the bag to eliminate as much trapped air as possible
>
> . Fire up the amp and allow the blower to come up to speed
>
> . Stuff the paper duct onto the amplifier output duct (get as good a
> seal as possible) and simultaneously start the watch
>
> . Stop the watch at the point where the bag is fully inflated
>
> So assuming it took roughly 2.5 seconds to inflate the 33-gallon bag:
>
> (1) 33 gallons * 0.13368 = 4.414 cubic feet
>
> (2) 2.5 seconds / 60 = .0417 minutes
>
> (3) 4.414 / .0417 = (is roughly equal to) 106 cubic feet per minute (CFM)
>
> Seems like the very short inflation time would reduce the practical
> accuracy of the measurement for larger amplifiers, but you could
> certainly get a rough number. Very useful.
>
> 73,
> Jim N7CXI
>
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