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Tachometer problems

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winter.geoff(at)gmail.com
Guest

Posted: Tue Jan 05, 2010 4:47 pm Post subject: Tachometer problems

Hi All



I fly a Corby Starlet using an 1835 VW with a Bendix D4 RN-2021 dual magneto.

 Both magnetos are grounded through separate magneto switches on my panel. I use

one of these leads to also run my tachometer. This has all been working just fine, but I've

now replaced the original Westach tacho with a new VDO tachourmeter, item # 333-035-11.

 I have the VDO tacho set for 4 stroke, 4 cylinder, single coil operation.

The rpm reading appears accurate, but it is continually fluctuating. Every second or so the

rpm drops anything from 200 to 1000 rpm momentarily, then returns to normal.

 Could anyone advise what I need to do to smooth out the reading. I've tried putting a diode inline with no joy.

Could anyone suggest some specific combination of capacitor/resistor/diode inline or parallel to the tacho I could try to smooth things out?   Failed to get any help from VDO so any advice would be very much appreciated.

 



Cheers

Geoff

   [quote][b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jan 06, 2010 9:35 am Post subject: Tachometer problems

 	  Quote: 	
		  Could anyone suggest some specific combination of 

capacitor/resistor/diode inline or parallel to the tacho I could try 

to smooth things out?   Failed to get any help from VDO so any 

advice would be very much appreciated.


	


   It's a WAG. Without knowing how the input circuits

   of the tachometer are crafted, then it's VERY difficult

   to figure out what it doesn't like about the signal

   provided by your magneto p-leads. The fact that

   the reading "drops" suggests a low signal level

   . . . hard to imagine on a p-lead!



   However, the VDO input signal conditioning may have

   over-attenuated the incoming signal as a by-product

   of their own design goals for signal conditioning.



   In this case, there's not much you can do outside

   the tach short of building some sort of signal-

   conditioning device to satisfy the tachometer's

   demands.



   Bob . . .

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winter.geoff(at)gmail.com
Guest

Posted: Thu Jan 07, 2010 9:24 pm Post subject: Tachometer problems

Bob



Thanks very much for that, I appreciate your time.  I feared I wasn't looking at an easy fix.  I think I'll revert to the old instrument and have a ponder.

Best regards

 Geoff



On Thu, Jan 7, 2010 at 4:33 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

 [quote]--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> 

 

 

  	  Quote: 	
		   Could anyone suggest some specific combination of capacitor/resistor/diode inline or parallel to the tacho I could try to smooth things out?   Failed to get any help from VDO so any advice would be very much appreciated.

  	
 



   It's a WAG. Without knowing how the input circuits

   of the tachometer are crafted, then it's VERY difficult

   to figure out what it doesn't like about the signal

   provided by your magneto p-leads. The fact that

   the reading "drops" suggests a low signal level

   . . . hard to imagine on a p-lead!

 

   However, the VDO input signal conditioning may have

   over-attenuated the incoming signal as a by-product

   of their own design goals for signal conditioning.

 

   In this case, there's not much you can do outside

   the tach short of building some sort of signal-

   conditioning device to satisfy the tachometer's

   demands.

 

   Bob . . . 



 

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[b]

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