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.
73 John G3UUT
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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