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p-lead signal conditioning or tach gen usage

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Oct 22, 2009 3:26 pm Post subject: p-lead signal conditioning or tach gen usage

At 03:56 PM 10/22/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Bob:



I think I know where you are going with the tach gen.  We could tap 

the side of the case and put a hall effect on it to "watch" the 

rotor magnets go by.  I suspect the stator windings would need to be 

removed.  Am I on track?


	


   Close. The first time I prototyped a hall-effect

   tach transducer, I salvaged the whole front end bell

   and shaft. Just enough hardware to grab the engine.

   Some time on the lathe produced a new, short rear

   end bell and ECB mount. Another lathe-cut part had

   12 little rod-magnets pressed into it and positioned

   to fly past the hall device on the ECB.

 	  Quote: 	
		  To answer your question, yes, I can get another tach gen for the 

engine with no problems.  About $150 for a new one...a little less 

for a used one.  The Hall Effect can be obtained fro Aircraft Spruce.


	


   The hall device I'm considering is a little surface

   mounted device.

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Oct 22, 2009 6:01 pm Post subject: p-lead signal conditioning or tach gen usage

 	  Quote: 	
		  

Bob, I was thinking of only rectifying one phase not all three.  My 

thought was that the tach gen is rotating at half engine speed, I'd 

get another "peak" in the signal from one phase and essentially 

double the frequency.


	


   Hmmmm . . . yeah, that would work.



        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Nov 02, 2009 6:56 am Post subject: p-lead signal conditioning or tach gen usage

At 04:59 PM 11/1/2009, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Craig Winkelmann" <capav8r(at)gmail.com>



 Bob:



 Put a scope on the tach gen output.  The situation is the signal from the tach gen goes to a 5.1 V zener diode, then to a comparator against a reference voltage to generate a square wave.



 Attached is the picture of the waveform at low rpm (approx 800).  Note the spikes in the wave.  Also, the voltage is near the zener voltage so the zener never gets driven into breakdown so that is why the unit has a flakey rpm reading at low 

 rpm. 	


   Agreed. 



 

  	  Quote: 	
		  So, would the waveform squaring circuit you posted in an earlier post work to square this waveform?  If so, I have 28 VDC available in the aircraft.  I'd need to use a 28-5 V converter chip to get the 5 VDC on the collector as you drew it.  Any suggestions for this? 	


    I don't recall exactly what I sent you earlier

    but this is probably similar.



 [img]cid:.0[/img]

    This squaring circuit has a +0.6v threshold. Since

    your 80mS, 5v trashy square wave goes above and below

    ground, this will square it up nicely. The diode

    keeps the negative excursions at high RPM from going

    exceeding the zener breakdown threshold for the NPN

    device.



 

 

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Mon Nov 02, 2009 2:18 pm Post subject: Re: p-lead signal conditioning or tach gen usage

Bob:



I can eliminate the comparator circuit if I get the output of the squaring circuit to 5 VDC (TTL level).  My thought is to use a Texas Instrument UA7805 Positive Voltage Regulator and connect it to an available 12VDC source in the aircraft.  This should give me a stable 5.0 voltage source.  At 5.0 VDC, the prior squaring circuit diagram used a 4.7K resistor on the collector to limit the current when the transistor is off.  This should square off the signal and provide a TTL level input to the EFIS system in the aircraft.



I can build this on a breadboard and test it in the lab and use a variable speed power drill to rotate the tach gen.



If the above sounds reasonable, I'm off to order the parts from DigiKey.  Thanks for all the help and advice.



Craig



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Nov 03, 2009 8:19 am Post subject: p-lead signal conditioning or tach gen usage

At 04:18 PM 11/2/2009, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Craig Winkelmann" <capav8r(at)gmail.com>



 Bob:



 I can eliminate the comparator circuit if I get the output of the squaring circuit to 5 VDC (TTL level).  My thought is to use a Texas Instrument UA7805 Positive Voltage Regulator and connect it to an available 12VDC source in the aircraft.  This should give me a stable 5.0 voltage source.  At 5.0 VDC, the prior squaring circuit diagram used a 4.7K resistor on the collector to limit the current when the transistor is off.  This should square off the signal and provide a TTL level input to the EFIS system in the aircraft.



 I can build this on a breadboard and test it in the lab and use a variable speed power drill to rotate the tach gen.



 If the above sounds reasonable, I'm off to order the parts from DigiKey.  Thanks for all the help and advice. 	


   Okay, how about this?



 [img]cid:7.1.0.9.0.20091103101407.010d0108(at)aeroelectric.com.0[/img] 



 

 How "square" does the signal need to be?  If you're driving the

 "off the shelf" input to some tachometer originally designed to

 attach to a p-lead or some other transducer, the tach should

 take care of its own "squaring" internally. It may be that all

 you need is to "clean" up the waveform to eliminate bumps and

 warts on transitions that can be interpreted as "extra

 edges".



 

        Bob . . .



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

        ( . . .  a long habit of not thinking   )

        ( a thing wrong, gives it a superficial )

        ( appearance of being right . . .       )

        (                                       )

        (                  -Thomas Paine 1776-  )

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

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ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Tue Nov 03, 2009 6:14 pm Post subject: Re: p-lead signal conditioning or tach gen usage

Bob:



In that case, I'll just run the output into the comparator circuit as the signal input to the comparator goes to this:



        signal in  O-------

                                |

                                >

                                <1K>

                                |

                                O---------O------> to comparator

                                |             |

                                >           ---

                       50K   <5>            |

                                |             |

                                gnd         gnd

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Tue Nov 03, 2009 6:19 pm Post subject: Re: p-lead signal conditioning or tach gen usage

Bob:



Well that got messed up when it posted!  Basically, signal in goes to a voltage divider of 1K resistor and 50K resistor with a 5.1V Zener in parallel with the 50K resistor.  The output goes to the comparator.  Output of the comparator goes to the EFIS as a TTL level signal.



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Nov 04, 2009 6:50 am Post subject: p-lead signal conditioning or tach gen usage

Yeah, but . . .



  If you study the dynamics of the circuit with the transistor,

  it's "active" window is only a few hundred millivolts wide defined

  by the signal level where the transistor first starts to conduct

  until it is saturated. Only "glitches" that exist within that widow

  are transferred through . . . with gain.



  A straight divider/zener network has an active window of

  about 5 volts but no gain. None the less, the "filtering"

  feature we're looking for is degraded. I'm not saying that

  it won't work . . . give it a try. But you may find that

  the little extra gain and tightening of the window to

  be useful and easy to do.  By the way, since your signal

  of interest goes below ground, the bottom resistor in the

  schematic you propose is probably not necessary.

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Nov 04, 2009 6:51 am Post subject: p-lead signal conditioning or tach gen usage

At 08:19 PM 11/3/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Bob:



Well that got messed up when it posted!  Basically, signal in goes 

to a voltage divider of 1K resistor and 50K resistor with a 5.1V 

Zener in parallel with the 50K resistor.  The output goes to the 

comparator.  Output of the comparator goes to the EFIS as a TTL level signal.


	


   OH . . . you mean there are other electro-whizzies

   posed between our pre-conditioning circuit and the

   input to your EFIS?



   I thought we were talking about the whole thing.

   Perhaps you need to sketch the whole system for

   me, I've been seeing it through a gray matter "knothole".

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Thu Nov 05, 2009 1:38 pm Post subject: Re: p-lead signal conditioning or tach gen usage

Bob:



Here is the circuit that is the current interface between the tach gen and the EFIS tach input.  It was originally designed to interface a Hall sensor with a 10 V p-p input.  The 50K resistor in parallel with the zener was to provide a current path (so I am told) should a p-lead be used instead of the Hall sensor.



My thought was to put the circuit you have proposed in the location as shown in the attached document (I could not scan to a .jpg and the .bmp was way too big).



Thanks,



Craig

Tach Interface.doc

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 05, 2009 3:20 pm Post subject: p-lead signal conditioning or tach gen usage

At 03:38 PM 11/5/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Bob:



Here is the circuit that is the current interface between the tach 

gen and the EFIS tach input.  It was originally designed to 

interface a Hall sensor with a 10 V p-p input.  The 50K resistor in 

parallel with the zener was to provide a current path (so I am told) 

should a p-lead be used instead of the Hall sensor.



My thought was to put the circuit you have proposed in the location 

as shown in the attached document (I could not scan to a .jpg and 

the .bmp was way too big).


	


   Okay. I think your 'trash' is coming from artifacts

   on the wave-form that are a result of the combination

   of the two phases of a 3-phase generator. These seem

   to reside some millivolts away from ground  . . . so

   your results are bound to improve if you move your

   comparator's decision-point as close to ground as

   possible.



   Try the simple transistor-zener circuit without

   the comparator. The transistor's "decision point"

   is in the .5 to .7 volt range as a function of

   Vbe characteristics of b-e junction.

        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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

ChangDriver

Joined: 15 Sep 2007
Posts: 266

Posted: Sat Nov 07, 2009 4:57 am Post subject: Re: p-lead signal conditioning or tach gen usage

Bob:



I have assumes that the windings are Y-wound and not delta.  The connector for the unit only has three pins and they are labeled a, b, and c.



I am assuming by your comment that we are using two phases that we have picked up the signal improperly from the tach gen itself.  However, when we tried to get a signal from one pin with the case as ground reference, we had no signal at all.



Craig

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Nov 07, 2009 5:45 am Post subject: p-lead signal conditioning or tach gen usage

At 06:57 AM 11/7/2009, you wrote:

 	  Quote: 	
		  

<capav8r(at)gmail.com>



Bob:



I have assumes that the windings are Y-wound and not delta.  The 

connector for the unit only has three pins and they are labeled a, b, and c.



I am assuming by your comment that we are using two phases that we 

have picked up the signal improperly from the tach gen 

itself.  However, when we tried to get a signal from one pin with 

the case as ground reference, we had no signal at all.


	


   Understand . . . and it's what I would have expected.

   So there's no "improper" connection, only a "less

   than ideal" connection.



   The design goal is to craft a squaring circuit that

   has the narrowest window of uncertainty that is

   centered in the area of the waveform least likely

   to be problematic.



   What are the specs for signal input to your engine

   monitor? Does the square wave need to be of any

   particular "sqareness" i.e. rate of change or

   simply "clean" and free of extraneous changes

   in direction.



   If I were designing such an instrument, I'd

   be interested only in a clean representation

   of period be it a sine wave, pulse, trapezoid,

   etc . . . all I'm doing is counting transitions

   from highest to lowest voltage. I'd do all of

   my "squaring" internally to accommodate the

   needs of the electronics. So I'm betting that

   if you get a clean 5v signal of any shape  . . .

   the electronics will be happy.



        Bob . . .



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

        ( It's MATRONICS FUND RAISER MONTH!    )

        ( Do your part to keep this marvelous  )

        ( tool sharp and available to all our  )

        ( brothers in the OBAM aviation        )

        ( community.                           )

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

Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sun Nov 08, 2009 7:24 am Post subject: Re: p-lead signal conditioning or tach gen usage

I wanted to repost a circuit that I built for an Aeroelectric lister for his problem of interfacing two different tach generators with one tachometer. This is a simple divide by two and signal conditioner that might prove useful in these, or related efforts. 



I have PCBs for this and can build up one for little money.

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

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