Today's Message Index:
----------------------
1. 05:02 AM - Re: Hall Effect rpm sensor (jhausch)
2. 06:29 AM - Tacho pulses (Eric M. Jones)
3. 03:39 PM - Re: Re: Viking Schematic (Robert L. Nuckolls, III)
4. 03:55 PM - Re: Re: RPM Sensor (Robert L. Nuckolls, III)
5. 04:00 PM - Re: Re: Hall Effect rpm sensor (Robert L. Nuckolls, III)
6. 04:54 PM - Re: Re: RPM Sensor (Michael Welch)
7. 05:02 PM - Re: Re: RPM Sensor (Michael Welch)
8. 06:28 PM - Re: Viking Schematic (user9253)
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Subject: | Re: Hall Effect rpm sensor |
Bob,
I have been receiving Mike's responses to my email. I only receive a daily digest
from the list. I will leave it up to him to post the collection/recap of
our conversation on the web.
I was a bit surprised to see my work email signature pop up on the list, but I
guess that's the nature of the internet.
I've contacted encoder and prox vendors looking for 100' submersible solutions.
I think that is the most challenging part of this application as viewed from
my world. We have items rated for high pressure washdown, but 3 atm of constant
pressure is likely another story.... You'd think a fully potted solid state
solution would be fine, but my gut tells me the saltwater will creep in at
the cable entry point and perhaps along the mating surfaces between the housing
and potting material - searching for any void it can find to get at the electronics....
I agree with you that multiple PPR (pulses per rev) are needed to provide some
accuracy/display stability.
We'll see where this goes... certainly an interesting application.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=376197#376197
Message 2
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Based on recent discussions:
Just a note to remind builders that I have a free tacho-pulse divide-by-two circuit
if anyone wants one. I usually have PCBs too (cheap but not free) or can
furnish the ExpressPCB design free. Contact me off list.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=376201#376201
Attachments:
http://forums.matronics.com//files/tacho_divider_133.jpg
http://forums.matronics.com//files/tach_adapter_1_785.pdf
Message 3
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Subject: | Re: Viking Schematic |
At 12:22 PM 6/19/2012, you wrote:
>
>Bob,
>My friend is building an RV-12 with an automotive engine, the
>Viking, which is fuel injected and electrically dependent. The
>power requirements for the ECU are not known but Viking uses 15 amp fuses.
I've looked over the published instructions
from Viking and the drawing you attached.
The 'instructions' from Viking bear no demonstrable
understanding of failure tolerant architecture
for aircraft applications. There's a similar
'disconnect' from legacy and modern processes
and techniques for aircraft wiring.
If your friend is willing to bring his project
to "The List" and submit performance numbers
to mission goals, I (and probably others) would
be willing to help him sort the bits and pieces
to arrive at the elegant solution.
But the drawing taken together with abysmal
instructions do not describe a 'sandbox'
in which I would want to play. I would further
advise you to distance yourself from this
project. I've been made aware of several problem
projects wherein the builders conversed with me
but for reasons of their own, chose to do other
things . . . yet they claim to have consulted
me in the crafting of their system.
The engine is VERY experimental . . . which
is not a singular cause for concern. But the
entire electrical system is even more "experimental".
Burt Rutan used to advise, "do your engine experiments
on a TC aircraft and your airframe experiments with
a TC engine." The overarching point is to drive
risks to a minimum which must INCLUDE educating the
owner/pilot on how the system works and what to do
when things don't work.
I suggest your worries over the bus isolation diode
is but the tip of an iceberg in terms of having
identified and crafted work-arounds for all perceived
risks. Driving those risks up with decidedly untried
or demonstrably unsuited techniques and materials.
Bob . . .
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At 12:43 PM 6/20/2012, you wrote:
Jim, Bob, list members,
Thank you for your responses. My initial request was brief, in an
attempt to pay respect to the Matronics rules, since obviously my
needs are not aviation related. They are, however, electronic in
nature, and I, for one, always enjoy every electronic post, aviation
or not, because I always enjoy learning from the best!! Since Bob
suggests bringing the subject onto the this list, I hope those that
read this topic are able to glean some electronic knowledge and, or
share their skills.
So, with an understanding this topic is not aero-electric, but yet
it certainly is electronic, so it may help educate some of us
electronic novices, here goes;
<snip>
Okay, 100' water pressure (50 PSI is no sweat). Digital display with
say 1 RPM resolution and 0.5 RPM accuracy at 300 RPM maximum. Jim was
asking about how the shaft speed to be measured was made available for
electronic inspection . . . it could be as simple as counting passages
of a woodruff key. In your case, the relatively slow speed combined
with 1 part in 300 resolution probably precludes looking at one-count-per-rev
signal sources . . . jitter in spacing of the counting edges can
make an otherwise smoothly rotating shaft appear to be unstable.
What length and diameter of the shaft is available to mount say
a disk of magnets to be counted? Jim may have other ideas to offer
but my first thought was based on a hall switch watching an array
of 10 magnets. This could easily be made water proof to those
pressures. Jim may be aware of an off the shelf, programmable
instrument that would convert 300 counts per minute into a 300.0
RPM display. Such a device could be built too . . . the electronics
is easy, PACKAGING is the hard part . . . especially for salt
water service.
Is this machine to be processor or computer guided? Would you
want a tachometer to computer interface capability to know
the current RPM?
Except for the salt-water under pressure requirement and
decidedly non-aircraft style motor shaft, this tachometer
display task is not unlike that for aircraft applications.
After selecting and interfacing a suitable sensor, one needs
to know the 'scale factor' (pulses-per-revolution) from
the sensor so that the readout can be appropriately
configured.
Bob . . .
Message 5
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Subject: | Re: Hall Effect rpm sensor |
At 06:59 AM 6/21/2012, you wrote:
Bob,
I have been receiving Mike's responses to my email. I only receive a
daily digest from the list. I will leave it up to him to post the
collection/recap of our conversation on the web.
I was a bit surprised to see my work email signature pop up on the
list, but I guess that's the nature of the internet.
You were in a cc list and the reply-all response got you
dumped into the List data flow but not in the bucket of List
subscribed addresses.
I've contacted encoder and prox vendors looking for 100' submersible
solutions. I think that is the most challenging part of this
application as viewed from my world. We have items rated for high
pressure washdown, but 3 atm of constant pressure is likely another
story.... You'd think a fully potted solid state solution would be
fine, but my gut tells me the saltwater will creep in at the cable
entry point and perhaps along the mating surfaces between the housing
and potting material - searching for any void it can find to get at
the electronics....
If you can find a square-wave (hall effect) driven instrument
with the approrpiate features for scaling say 3000 ppm to a 300
rpm display, we can hammer a high pressure sensor together.
I agree with you that multiple PPR (pulses per rev) are needed to
provide some accuracy/display stability.
We'll see where this goes... certainly an interesting application.
Agreed. Let's see what kind of shaft is exposed
to the inquisitive world of instrumentation.
Bob . . .
Message 6
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Bob,
See below for the answers to your questions.
>
> Okay, 100' water pressure (50 PSI is no sweat). Digital display with
> say 1 RPM resolution and 0.5 RPM accuracy at 300 RPM maximum. Jim was
> asking about how the shaft speed to be measured was made available for
> electronic inspection . . . it could be as simple as counting passages
> of a woodruff key. In your case, the relatively slow speed combined
> with 1 part in 300 resolution probably precludes looking at
one-count-per-rev
> signal sources . . . jitter in spacing of the counting edges can
> make an otherwise smoothly rotating shaft appear to be unstable.
Regarding the pressure needed to work well, good (50 psi).
The digital display with 1 rpm and .5rpm accuracy sounds perfect.
I anticipate a splined shaft of approx. 1.75" diameter (for
sprockets). If I need to add an extra couple of inches to allow for a
rotating
wheel, that would be no problem at all!! Are we talking
about roughly 10 strong magnets, say...on a 6" diameter wheel? If so,
that
would be VERY easy to fabricate a fiberglass disc,
encapsulating said magnets near the rim.
>
> What length and diameter of the shaft is available to mount say
> a disk of magnets to be counted? Jim may have other ideas to offer
> but my first thought was based on a hall switch watching an array
> of 10 magnets. (Mine, too, and this would be an easy task to build)
> This could easily be made water proof to those
> pressures. Jim may be aware of an off the shelf, programmable
> instrument that would convert 300 counts per minute into a 300.0
> RPM display. Such a device could be built too . . . the electronics
> is easy, PACKAGING is the hard part . . . especially for salt
> water service.
Other than the sensor to read those rotating magnets,
what else would
need to be underwater? The sensor? That should be a
sealed unit, no?
Other than the 10-magnet disc and sensor, all other
item are topside.
The gauge/display unit would be in a water-tite
console.
> Is this machine to be processor or computer guided? Would you
> want a tachometer to computer interface capability to know
> the current RPM?
> Except for the salt-water under pressure requirement and
> decidedly non-aircraft style motor shaft, this tachometer
> display task is not unlike that for aircraft applications.
> After selecting and interfacing a suitable sensor, one needs
> to know the 'scale factor' (pulses-per-revolution) from
> the sensor so that the readout can be appropriately
> configured.
>
No, not computer guided or driven. Hands on operation,
but requiring only occasional
adjustment, from information from the various rpm
gauges.
I think 10 pulses per rev is plenty good resolution. If
we can read these magnets by way
of a familiar sensor you have in mind, I'll make a parts
order tomorrow, and get going making the disc.
Bob, back a year ago when we were talking neodymium
magnets & Hall Effect sensors
for an airspeed indicator, I bought a handful of 1/8" x
1/8" x 1/2". They be small, but they be
purdy strong! Will they work? Any ideas for the sensor?
>
> Bob . . .
>
>
>
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Bob,
Is there any way we can make these display units work with our design?
I REALLY like their products,
I have two of them in my plane. One for turbo boost (from a MAP
sensor), and one of their EGT gauges
and senders. Nice stuff!
http://www.auberins.com/index.php?main_page=product_info&cPath=16&prod
ucts_id=212
The displays units are easy to mount, and are bright in sunlight.
Mike Welch
Message 8
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Subject: | Re: Viking Schematic |
Bob,
Thanks for your words of wisdom so eloquently stated.
I think that the Viking powered aircraft can be wired, for the most part, using
one of your drawings. There is one item unique to the Viking that is not addressed:
ECU SELECT. The Viking website recommends using one DPDT switch wired
in parallel to act as a SPDT switch. This switch will select either a high or
low voltage and send it to the dual ECUs to enable either ECU1 or ECU2. My
concern is that if this switch fails, the pilot will not be able to switch to
the backup ECU if needed. Or if the switch fails open, who knows which ECU will
be enabled, if any. It is unknown what bad things might happen if both ECUs
are enabled at the same time, even for a second.
Is it safe to use one switch to choose between ECUs? If not, is there a better
way than to use 2 mechanically interlocked switches? Perhaps a solid state
circuit powered by the aircraft supply so that it would not load down the ECU.
Joe
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=376273#376273
Attachments:
http://forums.matronics.com//files/select_207.jpg
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