I looked at the Quantar/Quantro diagram for their
100/125w PAs. They have one or two fans in them. The
current is sensed as a voltage drop across a pair of
9.1 ohm resistors in the ground lead. This feeds two
op-amps/comparators. If the current is too low or too
high, either comparator output goes high and turns on
a transistor through a diode OR gate. This feeds a mux
chip along with a thermistor that senses PA
temperature. The control module queries the mux chip
and decides if the PA fans are working or not and/or
if the PA is getting too hot. More details on request.
Of course this doesn't necessarily tell you if the
fans have failed yet are still drawing the same amount
of current.
If you have any kind of plenum setup, you can buy a
small pressure sensor from Jameco and try to monitor
the positive air pressure. It's better than nothing at
all. You still may have to manipulate the output
signal, and if the fans aren't on 100% of the time,
you may want to gate the pressure signal with a "fan
on" signal so you don't get a false failure when the
fans aren't running.
Bob M.
======
--- "Adam C. Feuer" <[EMAIL PROTECTED]> wrote:
> Thanks guys for the interesting thoughts. All 6 of
> the PA's are
> solid state. They are the Quintron / Glenayre 90
> watters.
>
>
> At 12:46 PM 7/23/2007, you wrote:
> >
> > > If the blower is used to cool a tube pa the
> thermostat detection
> > > hardware is probably way to slow.
> >
> >I was assuming a SS PA, but maybe that was a
> mis-assumption.
> >
> > > Many vane indicators are of the long arm micro
> switch type. Easy
> > > enough to make your own but you can probably
> find them through
> > > companies like McMaster, C&H Sales Company,
> Grainger (all in
> > > Southern California) and many Heating & Air
> Conditioning Supply
> > > Stores.
> >
> >I hate vane switches, having seen way too many
> failures over the years.
> >Vanes breaking off, microswitches getting stuck due
> to all of the gunk that
> >accumulates, etc. Good transmitters use
> differential pressure sensors to
> >measure the difference between the two halves of
> the tube compartment. Too
> >much differential and you've got a blockage in the
> tube fins or socket. Not
> >enough differential and either the blower isn't
> running, the intake filter
> >is clogged, or the chimney is blocked. I always
> monitor stack temperature
> >too as a backup.
> >
> >For a SS PA, I still think a thermostat is the most
> reliable.
> >
> >I had a 5kW watt FM transmitter that somebody
> bypassed the air interlocks
> >on. The squirrel cage blower lost a blade and
> jammed up. Looked like a
> >miniature version of Cheryobyl in there after all
> was said and done...and
> >off to the scrap yard it went (it was 30 years old
> and due for retirement
> >anyway).
> >
> > --- Jeff
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