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Tachometer Generator Wiring
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ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Sat Sep 12, 2009 5:09 pm Post subject: Tachometer Generator Wiring

I have a tachometer generator on my aircraft.  I am changing the tach from an analog to digital tach.  The wiring from the tach gen is two leads and neither are shielded.  Given this is an AC signal in the aircraft, I was wondering if these leads need to be shielded.  Any advice or insight into tach gens would be welcome.



Thank you,



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Sep 13, 2009 5:21 am Post subject: Tachometer Generator Wiring

At 08:09 PM 9/12/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



I have a tachometer generator on my aircraft.  I am changing the 

tach from an analog to digital tach.  The wiring from the tach gen 

is two leads and neither are shielded.  Given this is an AC signal 

in the aircraft, I was wondering if these leads need to be 

shielded.  Any advice or insight into tach gens would be welcome.


	


   No. It's a sine-wave, low voltage, low frequency

   signal that does not propagate electrostatically

   between bundles.



        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Sun Sep 13, 2009 12:30 pm Post subject: Re: Tachometer Generator Wiring

Thanks Bob.  I have been told by some other folks that the tach gen can be a significant source of noise.  It is my understanding that in the original wiring in this aircraft (Yak) the tach gen leads were shielded.



Craig

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Sun Sep 13, 2009 3:46 pm Post subject: Re: Tachometer Generator Wiring

Bob:



The problem I have is that at RPM below 1000, I get noise in the signal and the tach jumps all over the place.  Over 1000 RPM and all is fine.  The radial engine idles at 500 rpm so this is a problem.  



The tach gen wires go to a circuit that is a basically a voltage divider and a comparator to provide a clean pulse for the engine monitor system.



It has been suggested to 1) shield the tach gen wires to reduce noise, 2) add a 0.1 microfarad ceramic capacitor as a filter, and/or 3) change the voltage at which the comparator triggers (raise the limit for it to trigger).



Any thoughts would be appreciated.



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 14, 2009 10:13 am Post subject: Tachometer Generator Wiring

At 03:30 PM 9/13/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Thanks Bob.  I have been told by some other folks that the tach gen 

can be a significant source of noise.  It is my understanding that 

in the original wiring in this aircraft (Yak) the tach gen leads were shielded.



Craig




	


   I dont' see how . . . These are 3-phase, pm

   alternators delivering data on a twisted trio

   of wires . . .



        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Tue Sep 15, 2009 3:52 am Post subject: Re: Tachometer Generator Wiring

I am deducing from this discussion that the tach gen is the likely source of the noise.  



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Sep 15, 2009 5:14 am Post subject: Tachometer Generator Wiring

At 06:52 AM 9/15/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



I am deducing from this discussion that the tach gen is the likely 

source of the noise.



Craig


	


  When you say "tach gen" . . . exactly what kind of

  device are you describing?  The ORIGINAL tachometer

  generators were permanent magnet, 3-phase alternators

  that produced about 20 VRMS of sine wave energy that

  was applied to a drag-cup "speedometer" on the panel

  calibrated in RPM. This was about the most noise-free

  system on board the airplane. Low frequency, sine wave,

  (i.e. SLOW rise times), 3-wire twisted pair signal

  cable.



  But just as every copy machine has been referred to

  as a Xerox machine, lots of tachometer TRANSDUCERS have

  been called TACH GENERATORS. But even then, once we

  depart the realm of 3-phase energy on a twisted trio,

  the kinds of signals produced by most transducers are

  very low energy (magnets flying past hall sensors).

  The crank position sensors on a Light Speed ignition

  are tach transducers and crank position sensors. They

  are not potential sources of noise to the rest of the

  airplane's systems.

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Tue Sep 15, 2009 11:18 am Post subject: Re: Tachometer Generator Wiring

Bob:



Thanks for the info.  Very helpful.  I have misled you a bit though.  The tach gen on the M-14P is a three phase generator.  The waveform shaping circuit I have (between the tach gen and the engine monitoring system) was designed for a rotax engine (which is a different signal generator that the russian tach gen).



The signal shaping circuit is wired between two phases of the output of the tach gen.



The circuit accepts one lead to the grounded anode of a zener diode (breakdown voltage of 5.1) in parallel with a 50K resistor.  The second lead connects to a 1K resistor that is in parallel with the above.  The output of the above goes to a comparator with a reference voltage of 4.25 volts.



I think my problem is having two ac signals going to a circuit that was designed for the output of the Rotax 912 tach signal generator.



I need a max of a 5 volt signal for the engine monitor.  My current thought is to see if you have a schematic for the circuit you described for using the p-lead and send this signal to the board above or, if the output can be kept to a 5 volt peak, then use your circuit as the feed for the tach signal.  This would then eliminate the tach gen.



Craig

nuckollsr

Joined: 24 Mar 2009
Posts: 95
Location: Medicine Lodge, KS

Posted: Tue Sep 15, 2009 8:39 pm Post subject: Re: Tachometer Generator Wiring

Thanks for the info.  Very helpful.  I have misled you a bit though.  The tach gen on the M-14P is a three phase generator.  The waveform shaping circuit I have (between the tach gen and the engine monitoring system) was designed for a rotax engine (which is a different signal generator that the russian tach gen).



The signal shaping circuit is wired between two phases of the output of the tach gen.



   yes . . . and probably a different frequency vs. rpm

   scale factor. 



The circuit accepts one lead to the grounded anode of a zener diode (breakdown voltage of 5.1) in parallel with a 50K resistor.  The second lead connects to a 1K resistor that is in parallel with the above.  The output of the above goes to a comparator with a reference voltage of 4.25 volts.



   You may be making this too complicated. 

  Consider this simple squaring circuit



http://tinyurl.com/pe5rnh



   . . .  that should be active

   down to the slower speeds.



I think my problem is having two ac signals going to a circuit that was designed for the output of the Rotax 912 tach signal generator.



I need a max of a 5 volt signal for the engine monitor.  My current thought is to see if you have a schematic for the circuit you described for using the p-lead and send this signal to the board above or, if the output can be kept to a 5 volt peak, then use your circuit as the feed for the tach signal.  This would then eliminate the tach gen.



   I think the tach generator is your very best bet.

   The signal is clean, low voltage and doesn't

   generate risk of whacking the ignition system.



   I think you'll find that the above circuit will

   produce a very clean 5v signal who's period is

   proportional to rpm.



       Bob . . .

Tach_Gen_Signal_Conditioner.pdf

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ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Wed Sep 16, 2009 12:37 pm Post subject: Re: Tachometer Generator Wiring

Bob:



Thank you.  As always, you keep it simple and do stuff that works.  I have also determined that the two phases connected to the circuit I have was wired improperly.  With two phases there was no ground reference until the tach gen (M-14P) saw a higher RPM.  It was supposed to be wired to one phase and the other lead grounded (after review of the design),



I have not looked at the waveform out of the M-14P tach gen, but from what you describe it is a simple and nice way to generate a signal.  I had one guy swear that the tach gen was a "serious source of noise" in his airplane.  At such a low frequency and at 20 V p-p, I don't see how.



I'm going to the airplane Friday to do a bit of rewiring.



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Sep 16, 2009 1:51 pm Post subject: Tachometer Generator Wiring

At 03:37 PM 9/16/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Bob:



Thank you.  As always, you keep it simple and do stuff that 

works.  I have also determined that the two phases connected to the 

circuit I have was wired improperly.  With two phases there was no 

ground reference until the tach gen (M-14P) saw a higher RPM.  It 

was supposed to be wired to one phase and the other lead grounded 

(after review of the design),



I have not looked at the waveform out of the M-14P tach gen, but 

from what you describe it is a simple and nice way to generate a 

signal.  I had one guy swear that the tach gen was a "serious source 

of noise" in his airplane.  At such a low frequency and at 20 V p-p, 

I don't see how.



I'm going to the airplane Friday to do a bit of rewiring.


	


   Good show sir. Let us know what you find.

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Wed Oct 21, 2009 8:32 pm Post subject: Re: Tachometer Generator Wiring

Bob:



One other item, the tach gen turns at half of the engine rpm.  So, the signal from the tach gen would need to be fully rectified to make this work (for me to get enough pulses per revolution as 1 ppr is the lowest recognized by the EFIS system).



If the tach gen signal is 20 VRMS as you mentioned, is there a simple rectifier circuit you'd recommend?



This should finish the work on this tach issue.



Thanks Bob,



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Oct 22, 2009 6:10 am Post subject: Tachometer Generator Wiring

At 11:32 PM 10/21/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Bob:



One other item, the tach gen turns at half of the engine rpm.  So, 

the signal from the tach gen would need to be fully rectified to 

make this work (for me to get enough pulses per revolution as 1 ppr 

is the lowest recognized by the EFIS system).



If the tach gen signal is 20 VRMS as you mentioned, is there a 

simple rectifier circuit you'd recommend?



This should finish the work on this tach issue.


	


    I have no idea what your particular tach generator's

    operating specs are. My offering was based on the

    3-phase, permanent magnet tach-generators that I

    was manufacturing/replacing 30 years ago.



    Folks often refer to their tach transducer as a

    "tach generator" when in fact, it may be any

    technology that converts shaft rotations to some

    periodic signal. The exact nature of that signal

    is driven by requirement for the companion instrument.



    The last tach transducer project I worked was

    for the Bonanza 2" instrument upgrade program

    where the instrument expected 8 pulses per rev

    at 12v. We mounted 8 magnets on a disk and spun

    them next to a hall sensor. But the device you're

    working with can be an probably is something

    entirely different.



    Do you have part numbers and a wiring diagram

    for the orignal system associated with your

    "tach generator"?\



    Assuming that it IS an sine-wave, AC device,

    then you don't want to rectify it, you'll probably

    want to 'square' the signal with a simple over-driven

    amplifier. Didn't I suggest a circuit for this?

        Bob . . .



         ---------------------------------------

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

         ---------------------------------------

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Thu Dec 03, 2009 11:36 am Post subject: Re: Tachometer Generator Wiring

Bob:



Just want to provide feedback on your help....I found a squaring circuit that was pre-made and installed it and it works perfect.  Thanks for all your help.



Craig

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Thu Sep 29, 2011 8:01 am Post subject: Re: Tachometer Generator Wiring

To Bob and All,

At my age, I know it is only a matter of time before I forget to latch the canopy before takeoff on a hot sunny day.  I have learned from the mistakes of others and will fly the plane and latch the canopy after landing.  But I would rather not forget to latch the canopy.  I want to install an audio and visual alarm that will only go off when the canopy is unlatched AND the engine is at takeoff RPM.  The easy part of the project will be installing a limit switch on the canopy latch.  My plan is to use a PIC12F509 microprocessor that will monitor the limit switch and also count the engine RPM.  There is a tachometer coil on the engine that sends an AC signal to the Dynon D-180 through a 30K resistor.  I want to tap into that signal for my project but am worried about loading down the circuit and affecting the Dynon tach readout.  My first question is, can the tach signal be fed directly into a microprocessor input or should I use some type of buffer?  If a buffer circuit is needed, can I use Bob's transistor squaring circuit above or will it load down the circuit to the Dynon?

  I found this circuit on the internet:  http://www.redcircuits.com//Page17.htm

If I used that circuit, I would eliminate the voltage doubler components (C1, C2, D1, D2)  and power the Hex Inverter from a separate supply.  Using an op-amp or FET are possibilities if I could find a schematic.  I am open to any comments or suggestions.

Joe

_________________
Joe Gores

andrew.d.zachar(at)gmail.
Guest

Posted: Thu Sep 29, 2011 8:26 am Post subject: Tachometer Generator Wiring

What about using a second limit switch hooked up to your throttle lever/knob?



That might be simpler...



On Thu, Sep 29, 2011 at 12:01 PM, user9253 <fran4sew(at)banyanol.com (fran4sew(at)banyanol.com)> wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "user9253" <fran4sew(at)banyanol.com (fran4sew(at)banyanol.com)>

  

 To Bob and All,

 At my age, I know it is only a matter of time before I forget to latch the canopy before takeoff on a hot sunny day.  I have learned from the mistakes of others and will fly the plane and latch the canopy after landing.  But I would rather not forget to latch the canopy.  I want to install an audio and visual alarm that will only go off when the canopy is unlatched AND the engine is at takeoff RPM.  The easy part of the project will be installing a limit switch on the canopy latch.  My plan is to use a PIC12F509 microprocessor that will monitor the limit switch and also count the engine RPM.  There is a tachometer coil on the engine that sends an AC signal to the Dynon D-180 through a 30K resistor.  I want to tap into that signal for my project but am worried about loading down the circuit and affecting the Dynon tach readout.  My first question is, can the tach signal be fed directly into a microprocessor input or should I use some type of buffer?  If a buffer circuit is ne!

   eded, can I use Bob's transistor squaring circuit above or will it load down the circuit to the Dynon?

   I found this circuit on the internet:  http://www.redcircuits.com//Page17.htm

 If I used that circuit, I would eliminate the voltage doubler components (C1, C2, D1, D2)  and power the Hex Inverter from a separate supply.  Using an op-amp or FET are possibilities if I could find a schematic.  I am open to any comments or suggestions.

  Joe

 

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Andrew Zachar

andrew.d.zachar(at)gmail.com (andrew.d.zachar(at)gmail.com)

 

  [quote][b]

Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Thu Sep 29, 2011 8:47 am Post subject: Tachometer Generator Wiring

Joe;



Another simple solution would be a second limit switch in series with the one on the latch attached to the throttle in such a way that at takeoff power setting it closes and if the one on the latch is also closed (latch open) then the alarms sound.



Bob McC



 	  Quote: 	
		   Subject: Re: Tachometer Generator Wiring

 From: fran4sew(at)banyanol.com

 Date: Thu, 29 Sep 2011 09:01:29 -0700

 To: aeroelectric-list(at)matronics.com

 

 --> AeroElectric-List message posted by: "user9253" <fran4sew(at)banyanol.com>

 

 To Bob and All,

 At my age, I know it is only a matter of time before I forget to latch the canopy before takeoff on a hot sunny day.  I have learned from the mistakes of others and will fly the plane and latch the canopy after landing.  But I would rather not forget to latch the canopy.  I want to install an audio and visual alarm that will only go off when the canopy is unlatched AND the engine is at takeoff RPM.  The easy part of the project will be installing a limit switch on the canopy latch.  My plan is to use a PIC12F509 microprocessor that will monitor the limit switch and also count the engine RPM.  There is a tachometer coil on the engine that sends an AC signal to the Dynon D-180 through a 30K resistor.  I want to tap into that signal for my project but am worried about loading down the circuit and affecting the Dynon tach readout.  My first question is, can the tach signal be fed directly into a microprocessor input or should I use some type of buffer?  If a buffer circuit is ne!

  eded, can I use Bob's transistor squaring circuit above or will it load down the circuit to the Dynon?

   I found this circuit on the internet:  http://www.redcircuits.com//Page17.htm

 If I used that circuit, I would eliminate the voltage doubler components (C1, C2, D1, D2)  and power the Hex Inverter from a separate supply.  Using an op-amp or FET are possibilities if I could find a schematic.  I am open to any comments or suggestions.

 Joe

 

 --------

 Joe Gores

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=353522#353522

 

 

 

 Archive Search & Download, 7-Day Browse, Chat, FAQ,

&gt   --> http://www.matronics.com/Navigator?AeroElectric-List
	


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_________________
Bob McC
Falco #908
(just starting)

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Thu Sep 29, 2011 9:35 am Post subject: Re: Tachometer Generator Wiring

Thanks Bob McC & Andrew for the throttle switch ideas.  Trouble is, I can not think of any way to install a switch on the throttle knob.  There is a knurled locking disk in the way.  I could install a limit switch on the other end of the throttle linkage at the carburetor.  But that will require fabricating some type of bracket to hold the switch and figuring out how to mount it to the engine without interfering with the throttle operation.  And the wiring and switch will be subject to heat and vibration.  I would rather monitor the RPM electronically because making electronic circuits is fun for me.

Joe

_________________
Joe Gores

gerry.vandyk(at)shaw.ca
Guest

Posted: Thu Sep 29, 2011 10:40 am Post subject: Tachometer Generator Wiring

Joe, just a thought...

How about having the canopy warning come on at run-up RPM rather than

take-off RPM.  I'd think it'd be best to pick this up before taking the

runway.



Gerry



--

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Thu Sep 29, 2011 2:01 pm Post subject: Re: Tachometer Generator Wiring

 	  Quote: 	
		  How about having the canopy warning come on at run-up RPM rather than

take-off RPM. 	


Gerry,

That is a good idea.  I could get into the habit of latching the canopy before run-up.  In the event that the takeoff is delayed and I unlatch the canopy, the alarm will still go off on the takeoff roll, but at a lower RPM.

Joe

_________________
Joe Gores

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