[time-nuts] 5070B once more.... (actually 5370A fans)

Lux, James P james.p.lux at jpl.nasa.gov
Wed May 20 16:41:40 UTC 2009




On 5/20/09 9:18 AM, "Roy Phillips" <phill.r1 at btinternet.com> wrote:

> Mark
> Thanks for your comments. I suspect that there was a period when the "Papst"
> fan was the de facto standard in many equipments, it has considerable depth
> and obviously moves a lot of air.

There is no real correlation between noise level and airflow or efficiency.
(a very tiny part of the energy goes into making noise).  A 20-30 dB
difference in SPL isn't unusual, for identical airflow.

You might check into other brands/models that have the same flow at the same
static pressure.

Another big noise source is turbulence from components around the fan (e.g.
A strut that intercepts a shed vortex from each blade can make a lot of
noise. If Nstruts = Nblades you're in bad shape.




 I can certainly see the need in the case
> of Power Supplies, I have an HP6632A which can provide 100 watts of power.
> But a good example of overkill was the HP 3456A Digital Voltmeter, the
> earlier models were fitted with a fan, which was subsequently removed in
> later issues. I have an older model and I have disconnected the fan (it was
> a small type), it was obviously not needed.
>  I have an HP 5334A, and a HP5335A, the latter being more obtrusive. Perhaps
> the design considerations were based on the US, with its higher summer
> temperatures,not such a problem for us Europeans.
> Roy
> 
> 
> 
> ----- Original Message -----
> From: "Mark Sims" <holrum at hotmail.com>
> To: <time-nuts at febo.com>
> Sent: Wednesday, May 20, 2009 4:53 PM
> Subject: [time-nuts] 5070B once more.... (actually 5370A fans)
> 
> 
> 
> 
> Yes,  I have replaced the fans in four 5370A and 5370B counters with modern
> 12V brushless DC motor units connected to the 10V supply.  VERY nice and
> quiet.  I did before and after thermocouple tests in the chassis.  The
> temperatures were basically unchanged (+/- 3C).  Variances could easily have
> been due to the probes shifting.
> 
> I have also done several dozen HP16500 logic analyzers and Tektronix TM5003
> and TM5006 mainfarmes.  On the TM5003 and TM5006, I run the fan on 8V.  They
> are almost dead silent.
> 
> 
> Use the lowest current fan that you can find...  they tend to be the
> quietest.
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