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Prop Tach Sender

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rampil

Joined: 04 May 2007
Posts: 870

Posted: Thu Dec 06, 2007 9:29 am Post subject: Prop Tach Sender

Greetings All,



A tech tidbit for the group.



I have been investigating why my prop tach sensor doesn't work and

finally discovered the solution, which I put forth for other who may

wind up in this boat.



I have an AirMaster prop and a Blue Mountain EFIS. So far there is no

way for the BMA to read the engine RPM signal (although that may

change soon).  The AirMaster hub has a magnet embedded in it's contact

plate for its own internal RPM sensing.  Since I could not expose the 

electric RPM signal, I put my own Hall effect sensor on a bracket mounted

to the Rotax gear box of my 912uls.  The sensor I used is a Westach

720-12R.



This sensor never produced a pulse train signal for the Blue Mountain

to analyze.



I finally put a scope on the probe and discovered that indeed not pulses

were generated by a spinning prop. (I really did not want my scope

that close to the spinning prop  )



It turns out that the Hall Effect sensor uses a neat integrated sensor

chip which it turns out is sensitive only to a SINGLE magnetic polarity.

By random chance, AirMaster uses the wrong one. (North vs South, etc).

The Westach pulses just fine when I swish a different magnet past it.



It turns out that Westach can build the probe with sensitivity to the 

opposite magnet face.  The part number is you need this new probe

is  720-12RAM.  Same price as the original 720-12R probe.



Hope this solves someone else's mystery too!



Ira  N224XS

_________________
Ira N224XS

Mark Burton

Joined: 10 Jan 2006
Posts: 74

Posted: Thu Dec 06, 2007 10:41 am Post subject: Re: Prop Tach Sender

Hi Ira,



Don't you still need a tacho of some kind showing engine RPM (rather than prop RPM)?



Cheers,



Mark

terrys(at)cisco.com
Guest

Posted: Thu Dec 06, 2007 11:12 am Post subject: Prop Tach Sender

Hi Mark,



The Katana airplanes and motor gliders which use the 912 or 914 have a

tach which shows prop speed, not engine speed.  It provides numbers more

familiar to pilots of other planes powered by direct drive engines.

When I checked out in the 912 powered DA-20 I found the prop-speed tach

readings were easily understood because they were similar to the tach

numbers of the Lycoming and Continental powered planes I had flown

before.  When we started flying our Europa with an engine-speed tach it

took longer to get accustomed to the numbers seen, and what they meant.



Regards,

Terry Seaver

A135 / N135TD

 



--

Mark Burton

Joined: 10 Jan 2006
Posts: 74

Posted: Thu Dec 06, 2007 11:23 am Post subject: Re: Prop Tach Sender

Hi Terry,



I suspect that in the UK we must have a tacho showing engine RPM. Can anyone confirm whether the PFA require that or not?



Cheers,



Mark

rampil

Joined: 04 May 2007
Posts: 870

Posted: Thu Dec 06, 2007 11:51 am Post subject: Re: Prop Tach Sender

Hi All,



As it turns out I have the new UMA Rotax-specific tach which

shows engine revs.  I just wanted to RPM recorded on the EFIS for

flight testing since I am a quant.

Honestly though, I can imagine why the PFA would insist on engine speed.



The ratio is fixed at 2.43!

Redline 5750(engine) = 2366(prop)

Max Cont 5500 = 2264 prop

Cruise 5000  = 2060 prop



The redlines don't move, who care what the underlying number is.



Actually, if PFA insists, I'd like to hear their reasoning

_________________
Ira N224XS

europa(at)pstewart.f2s.co
Guest

Posted: Thu Dec 06, 2007 11:55 am Post subject: Prop Tach Sender

Ira



It certainly solves a problem for us as we approach running the  

engine for the first time with our BMA E1.  We have a 720-12R but  

haven't fitted it yet. Very interested in how you have it configured  

- channel etc. Where exactly across the radius of the contact plate  

is the embedded magnet - if you had a photo of your set up?  Did you  

get your probe from Westach direct or via ACS?



Regards



Paul

G-GIDY

(running out of jobs to do!!!!!)

On 6 Dec 2007, at 17:29, rampil wrote:



 	  Quote: 	
		   



 Greetings All,



 A tech tidbit for the group.



 I have been investigating why my prop tach sensor doesn't work and

 finally discovered the solution, which I put forth for other who may

 wind up in this boat.



 I have an AirMaster prop and a Blue Mountain EFIS. So far there is no

 way for the BMA to read the engine RPM signal (although that may

 change soon).  The AirMaster hub has a magnet embedded in it's contact

 plate for its own internal RPM sensing.  Since I could not expose the

 electric RPM signal, I put my own Hall effect sensor on a bracket  

 mounted

 to the Rotax gear box of my 912uls.  The sensor I used is a Westach

 720-12R.



 This sensor never produced a pulse train signal for the Blue Mountain

 to analyze.



 I finally put a scope on the probe and discovered that indeed not  

 pulses

 were generated by a spinning prop. (I really did not want my scope

 that close to the spinning prop  )



 It turns out that the Hall Effect sensor uses a neat integrated sensor

 chip which it turns out is sensitive only to a SINGLE magnetic  

 polarity.

 By random chance, AirMaster uses the wrong one. (North vs South, etc).

 The Westach pulses just fine when I swish a different magnet past it.



 It turns out that Westach can build the probe with sensitivity to the

 opposite magnet face.  The part number is you need this new probe

 is  720-12RAM.  Same price as the original 720-12R probe.



 Hope this solves someone else's mystery too!



 Ira  N224XS



 --------

 Ira N224XS





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=150815#150815

rampil

Joined: 04 May 2007
Posts: 870

Posted: Thu Dec 06, 2007 1:18 pm Post subject: Re: Prop Tach Sender

Hi Paul,



Here are pix of my original bracket holding a 720-4 sensor which did

not work either (longer story). 

The new bracket has an L on top to position the 720-12 in apposition

to the magnetic slug which you will find just outside the outermost

conductor ring. On my prop the magnet is buried in light-colored epoxy.

If needed, I can photo the new set-up when next at the hangar.



I purchased the new sender directly from Westach, the original from

ACS

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_________________
Ira N224XS

jodel(at)nildram.co.uk
Guest

Posted: Thu Dec 06, 2007 2:49 pm Post subject: Prop Tach Sender

There is a C of A Tecnam that live at Perth (EGPT) that has a Gauge that

shows Prop RPM not engine.



Simon



--

h&jeuropa

Joined: 07 Nov 2006
Posts: 645

Posted: Fri Dec 07, 2007 4:41 am Post subject: Re: Prop Tach Sender

Hi All,



We ran into this and talked to Martin at Airmaster.  It turns out that the Honeywell sensor Airmaster uses works with either magnetic polarity, so the magnet you receive from them could be oriented north or south.  Paul - check first because the one you have may work in your application.



Even with the correctly oriented Westach sensor, sometimes the BMA tach worked fine up to red line readings, other times it stopped working around 4000 RPM.  We tried various mounting configurations, but were never able to make it work in our plane.  However, we never put a scope on it to see what the signal looked like.  We also tried the same Honeywell sensor Airmaster uses and couldn't get that to work with the BMA EFIS.



Jim & Heather Butcher

rampil

Joined: 04 May 2007
Posts: 870

Posted: Fri Dec 07, 2007 9:17 am Post subject: Re: Prop Tach Sender

Putting on my old EE cap, it is worth noting that the subject of Hall

effect sensors is at once very simple, yet very complex.

These little guys are sold by the millions every year, there are 

at least a dozen in any recent car.



The sensor itself is absolute simplicity - just a small strip of semiconductor

with electrical contacts on four sides.



The problem for OBAM builders is that there are possibly 1000 different

commercial sensors available widely varying in size, cost, sensitivity, and

complexity - bare sensors all the way to microcomputers.



The random orientation of the magnet in the Airmaster just makes life

a bit more complex if you want to detect its passage with your own

sensor. It would have been easiest for us to have an exposed, buffered

TTL pulse line out of the Airmaster controller.  Failing that, you can buy

the Westach Aviation grade, potted, rugged sensor, or buy a raw sensor

and pot and mount it yourself.



So many choices, so little time to explore!

As for Jim's problem, I sympathize, but I don't know the details. Possibly

a bad connection or a waveshape issue.  Strangely or perhaps not, I find

I am using my little digital scope quite a bit with my Europa  

Ira

_________________
Ira N224XS

budyerly(at)msn.com
Guest

Posted: Mon Dec 10, 2007 7:14 am Post subject: Prop Tach Sender

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Ira,

 Great investigative work as usual...  

 It must be the coriolis effect.

  

 Westach has always been great about for their flexibility.  A real  credit goes to them also.

 I would have had them change the part number to 720-12IRA

 Bud

 [quote]   ---

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