[Amps] Bag-o-meter calcs in US units

[Ian White GM3SEK]

Jeff Blaine wrote:
>
>A "rough idea" can get a guy a long way.  Especially when the average 
>Joe has "no idea."
>

That's exactly the right perspective, and you got the detailed method 
right too.

Way back, I worked in a lab that was making very similar kinds of flow 
measurements to professional standards - and believe me, measurements 
involving small blowers, low back pressures and discharge into open air 
are *much* harder than you think. Techniques that work in ducted HVAC 
systems or large BC transmitters will not work accurately in small 
amplifiers. Respiratory peak flow meters, eBay anemometers and water 
manometers are heading into a maze of errors and corrections that people 
haven't even begun to think about!

I wish I'd known about the plastic bag method back then, for with a few 
refinements we would have used it in the lab. It really can be that 
good.

Even without refinements you can obtain surprisingly accurate results. 
The hardest part is to get beyond the "garbage" image and see the 
science.


>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...
>
Narrowing down the neck of the bag has a small effect, but if you're 
really concerned you can measure the volume by suspending the empty bag 
in a barrel of water and measuring how much water it takes to fill it... 
but we're back to that image problem again.


-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek