[time-nuts] HP5370 power supply measurements

[Bob Camp]

Hi

Back when these pieces of gear were being made “new”, HP Spokane had a 
“fan silencer machine”. They used a strobe and a microphone to identify imbalanced
blades and then took chunks out of them. They *claimed* it made the fans significantly 
less noisy….Watching it in action on a noisy factory floor … not so clear. 

Bob

> On Jul 15, 2016, at 4:25 PM, Tommy Phone <tholmes at woh.rr.com> wrote:
> 
> Some thirty years ago fans for automotive radiator cooling were designed with 7 unevenly spaced blades to reduce the siren effect yet yield comparable air flow. Careful layout and blade sweep back along with an annular ring made it entirely feasible to have a statically and dynamically balanced fan as it came out of the mold. I always wondered why the folks who make these little fans can't figure out how to do that. Maybe getting comparable CFM from a much smaller fan violates some Reynolds number requirement for turbulence control. 
> 
> From Tom Holmes, N8ZM
> 
>> On Jul 15, 2016, at 3:52 PM, William H. Fite <omniryx at gmail.com> wrote:
>> 
>> That is, in fact, precisely how you do it.
>> 
>> 
>>> On Friday, July 15, 2016, Orin Eman <orin.eman at gmail.com> wrote:
>>> 
>>> On Fri, Jul 15, 2016 at 10:55 AM, Poul-Henning Kamp <phk at phk.freebsd.dk
>>> <javascript:;>>
>>> wrote:
>>> 
>>>> --------
>>>> In message <
>>>> CANy2iXq6ONvriDoFgNFkEBQjDKntP7t8KuE7BOUpxJWLCuxLsw at mail.gmail.com
>>> <javascript:;>>
>>>> , "William H. Fite" writes:
>>>>> David Kirkby scripsit:
>>>>>> 
>>>>>> I often here of people replacing fans with quiter ones, but I suspect
>>>> that
>>>>>> all they really do is reduce the airflow.
>>>>> 
>>>>> Not necessarily, Dave. The Austrian company, Noctua, for one, makes
>>>>> extremely quiet fans with excellent airflow.
>>>> 
>>>> ... at zero pressure differential, which is easy to do (Think: ceiling
>>>> fan).
>>>> 
>>>> 
>>> 
>>> Right.
>>> 
>>> You have to look at the curves on the data sheet that shows air flow vs.
>>> static pressure (and be careful about the static pressure scale).  I found
>>> that a 'quiet' fan would often be flowing one tenth as much air as the
>>> original fan at the static pressure at which the original fan was rated.
>>> 
>>> In a given instrument, you may get away with the quieter fan, but how would
>>> you tell other than putting a thermometer inside and making a before/after
>>> comparison?
>>> 
>>> Orin.
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>> 
>> 
>> -- 
>> Yes, Black lives do matter.
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