Incorrect/Fluctuating Tach Time

[banzai37]

After a recent avionics install, my tach time is incorrect and fluctuates while operating.

For example, on today's flight, I started with 564.4 Dynon Hobbs Time, and 487.8 Dynon Tach Time.
Midflight, the Dynon Hobbs was 566.4 (2 hrs) and the tach time fluctuated between 489.1 and 490.3 (1.3 hrs and 2.5 hrs)
The tach time does not fluctuate at startup. The fluctuation is every second or so and starts at a delta of 0.1, and grows.
In this flight, right before shutdown, I ended with 567.6 Dynon Tach Time (3.2 hrs) and the tach time fluctuated between 490.0 and 492.1, representing 2.2 hours and 4.3 hours) - neither of which is correct. This was a X/C flight at a constant 2400 RPM (with the EMS set to a cruise RPM of 2400), so the Tach time should closely match the Hobbs.

The tachometer is steady and seems fine.

What could be causing this?

Thanks,
- Ben

 

[RV8JD]

Are you running v16.2.4 and have one standard mag and another ignition system? If so, you may be suffering from a Tach Time bug in v16.2.4. It is caused by the difference in pulse per revolution settings between one standard mag and another ignition system that is using a different pulse per revolution. See the thread below. Post #8 from Dynon explains it and gives a workaround.

Hobbs Time and Tach Time Flight Durations with v16.2.4

I updated my SkyView Touch from v16.0.4 to v16.2.4 and have flown four flights with v16.2.4. Since updating to v16.2.4 the Tach Time flight duration has been longer than the Hobbs Time flight duration. This is a change from my norm, where the Hobbs Time flight duration is almost always longer...

forum.flydynon.com

 

[banzai37]

Yes - those are exactly my symptoms. Thanks for pointing me to the other thread.

 

[djones]

16.3.2 is now released and available on the website. It does have a fix for the tach time issue.

 

[banzai37]

Great - thank you!

 

[banzai37]

I installed 16.3.2 and the issue appears to be resolved. Thank you.