John G3UUT wrote:
>Well that's a relief! I was planning on spending the weekend messing
>around with bin liners and water butts. It looks like these things are
>available real cheap on Ebay.
>
I'm not sure if a peak flow meter will work, because of the
back-pressure through the device itself. The bag method may look crude,
but it has the advantage of a very low back pressure.
To save you from getting cold and wet, a British swing bin bag is about
50 litres. (This is probably a Euro standard size, and also a good shape
for attaching to the outlet vent.)
With care, cardboard and packing tape, you can make volume flow
measurements within about 10%, which is plenty good enough.
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
>On 13/04/2011 12 :25, Angel Vilaseca wrote:
>> An accurate way to measure airflow is to use a peak airflow meter. See
>> picture here:
>>
>> http://en.wikipedia.org/wiki/File:Peak_flow_meter_vert.jpg
>>
>> This is a low-cost device used by persons with asthma to self-monitor
>> their disease. Widely available worldwide.
>>
>> 73 de
>>
>> Angel Vilaseca HB9SLV
>>
>> Ian White GM3SEK a écrit :
>>> Roger (sub1) wrote:
>>>
>>>
>>>> One other point, I've seen the question raised about how much pressure
>>>> was a fan generating. For a given tube and existing system you can
>>>> treat air flow and pressure the same as voltage and current. IF you are
>>>> getting the required air flow you MUST have the required air pressure.
>>>> Insufficient pressure and you will have insufficient flow. Get the
>>>> proper flow and you will have the proper pressure.
>>>>
>>>> IF the radiator is plugged or partially clogged you will have high
>>>> pressure and low flow. But again, it the flow if proper then so is the
>>>> pressure.
>>>>
>>>>
>>> Air flow rate is what really matters in cooling, and all data sheets for
>>> air-cooled tubes will state the minimum volume flow rate required.
>>> Pressure drop is only an indirect way of measuring the volume flow
>>> rate... and actually a very poor way.
>>>
>>> Pressure drop measurements in real amplifiers are very prone to errors,
>>> because the reading will depend critically on the orientation of the
>>> manometer pickup tubes relative to the air flow. We have no idea what
>>> the tube manufacturers did to minimize those errors... or even if they
>>> were aware of them. Because of all these problems, pressure drop is
>>> probably the wrong thing for us amateurs to measure.
>>>
>>> It's actually MUCH easier to measure the volume flow rate directly. No
>>> elaborate equipment is needed - simply time how long it takes for the
>>> outlet air to fully inflate a large, lightweight plastic bag. With a
>>> little care you can measure the volume flow rate within about 10%, which
>>> is far more accurate than a pressure measurement.
>>>
>>> The original idea came from George Daughters K6GT, and details are right
>>> here in the AMPS archives:
>>> <http://lists.contesting.com/archives//html/Amps/1998-03/msg00172.html>
>>>
--
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