RPM spikes on tachometer

[N930RV]

During first flight I got an alarm for over speed (lycoming O320 +Sensenich prop max RPM 2600).  When looking at display it was reading in the 2300 RPM range.  Did data dump after landing and plotted RPM.  There are many very short duration spikes in rpm which I know are not real.  Has anyone else seen this? If so what did you do to correct it?  Should I try increasing the P lead series resistor ?

  Thanks Bill

 

[dynonsupport]

Bill,
If you are getting RPM spikes at higher RPM's, increasing the P-lead resistor is the first thing we suggest. You can go right to 100K-ish, which seems to work well for many people. The exact value or tolerance of the resistor doesn't matter.

 

[N930RV]

Thanks, I'll try that this weekend.

Any chance of having data storage/download capability from the D100 like you have from the D120?

Bill

 

[dynonsupport]

Hey, if all we need to do is say there's a "chance" of something happening, then heck yea, there's a chance!

Seriously, we do hope to add EFIS datalogging to the software someday, but as usual, we have to say that we don't have a solid timeframe on that for now.

 

[N930RV]

Hello Dynon support,

   Well, I tried the 100K resistors (as you suggested) and still have the spike problem, so I'll be trying 150K this weekend.  I know the manual says that 150k is max. but I assume that I can keep increasing until I loose the signal.
  I would guess that you are using some sort of voltage divider technique on the input so is it possible that your resistor to ground is either incorrect or has a poor solder connection?

Just looking for ways to solve the problem without having to add additional hardware such as tach transducer.

Thank in advance
  Bill

 

[dynonsupport]

Correct - eventually the high resistance will mask the real pulses.

Some mags are just really noisy for reasons that aren't perfectly clear. In these cases, sometimes the transducer is the path of least resistance.