Sam
Joined: 18 May 2008
Posts: 135
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 Posted: Sat Jul 11, 2009 5:09 pm Post subject: Inaccurate RPM readings usingf Lightspeed Plasma II+ digit |
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Yes, I have been down that road. Long story short - the Dynon can only handle one input. I think it reads one input or the other, switching back and forth resulting in a confused signal.
Sam
On Sat, Jul 11, 2009 at 7:30 PM, Vincent Himsl <vshimsl(at)live.com (vshimsl(at)live.com)> wrote:
[quote] I have the digital pulse information from my Lightspeed plasma II+ electronic ignition feeding one input to my Dynon D-180 and a magneto P-lead tap through 30 k resistor (per Dynon manual) to the other RPM input of my Dynon D-180.
Problem is that with the P-lead Pulse per revolution set to 1, and the Plasm II+ Pulse / rev set to 2, my Dynon reads 2 to 3 hundred rpm low at 900 rpm (verified by Tru-Tach) and 4 to 6 hundred low at the high end (2100 to 2700 rpm).
I removed the Dynon and using a square wave generator providing 12 volt pk-pk referenced to ground tested both inputs of the Dynon. It is right on. I also dropped the voltage down to as little as 8 Volts Pk-Pk and the Dynon remained accurate.
Suspecting that the Dynon averages both inputs, I tested each input by removing the other. Both the Plasma II+ and the P-lead were reading low rpm's compared to a tru-tac (which can be calibrated by aiming it at flourescent lighting...pretty slick).
By Resetting the pulse rate of the Dynon to 1.5 for the Plasma II+, I get readings that are consistently 60 rpm low. The P-lead with the recommended Dynon resistance of 30K reads 2 to 300 low.
My temporary fix at the moment is to remove the P-lead input to the Dynon from the Magneto (Slick brand via aerosport) and keep the Plasma II+ input set to 1.5 pulses / rev even though the Lightspeed manual says it should be 2 pulses.
Has anyone else been down this road? If so would appreciate hearing the solution before I haul a scope to the airport.
Regards,
Vince_Himsl
RV8 N8432 Flying! (10 hours)
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Sam Hoskins
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