Tach Time Issue

[davemgill]

I have been using Hobbs time to record flights up until today when I decided to start using Tach Time. I set the tach time to the same as the hobbs and the cruise rpm setting to 2500. I then flew 2 flights.
The first started at 44.9 Tach and ended at 45.6 and the hobbs at 45.8, about right for the flight cruising at around 2300.
The next flight back to base was the same length and cruise setting but the tach time ended at 46.7 same as the tach. i.e. tach was running faster than real time despite the engine rpm being less that the cruise setting. :-?

Once I stopped the engine I noticed the tach time alternating between 46.7 & 48.? However I suspect this may be because I altered the time and it was showing the original and new times.

 

[dynonsupport]

That's an odd one for sure. A few questions:

Has the dithering between the two values persisted across power cycles? In other words, when you go back and check on the tach time now, is it the reprogrammed value, the old one, or is it still flickering?

What version of firmware are you running on the unit?

Have you been on a flight since, and has the behavior repeated itself?

Also, just to sanity check things, please reconfirm that 2500 rpm is the cruise rpm you have programmed under the tach setup.

 

[davemgill]

I haven't flown since so I don't know about the dithering. I might be flying over the weekend so I will check then.

I'm using 4.0.4 updated a couple of flights ago.

Yes, 2500 is the value set in the Tachometer setting page.

 

[davemgill]

Ok, I have some more information. The flickering didn't happen when the unit was switched on agian. I then did a bit of flying and downloaded the data log from the unit.

The first couple of flights recorded as expected, I did the second at a low rpm to prove the tach time was running less then real time. The last 2 flights have a strange thing happening as the engine is shut down.
Between labels 1581 & 1583 - 1582 is missing for some reason and the tach time jumps 1.0625
Between labels 1797 & 1998 - The tach time jumps 0.375

I've attached the data log and my settings.

Regards
David

 

[dynonsupport]

There's something going on here, but it will take some more investigation to uncover what. Can you confirm that you haven't changed your cruise setting?

 

[davemgill]

No I haven't changed it, it's been 2500 since I installed the unit.

The only thing I can think of that might not be 'standard' is the one mag input is from the mag and set at 1 pulse/rev and the other is fed from the lightspeed ignition and set at 2 pulse/rev.

 

[dynonsupport]

There might be something there. See your email inbox for further troubleshooting on this one.

 

[davemgill]

Hi Mike,

I replied to the email with the backup on the 8th June and also to the general support address on the 13th June but haven't received a reply yet. I don't know if your spam filter has filtered me or you are just busy

Regards
David

 

[dynonsupport]

Sorry about that. It's now in our list of things to look into fixing, but we don't have an update yet.

 

[PhantomPholly]

Please post your resolution if it regards a Mag / Lightspeed setup as I am in the process of completing my installation.

Thanks!

 

[N930RV]

Dynon,
Has your team of expert troubleshooters been able to determine the cause of the Tach time dither? If so what if anything can be done now or will we have to wait for a software fix?

 

[dynonsupport]

We're still working on it, but it looks like we've had a good breakthrough just minutes ago actually. We're hoping that it will be fixed in the next firmware update, due out soon with the autopilot.

 

[dynonsupport]

A little more on this. The issue is related to the fact that you have different pulse per revolution settings on the left and right channels. When the engine is shut down, the EMS goes looking for RPM on the left channel, then the right, left, right, etc. and incorrectly updates the tach time in real time based on the pulses/revolution for each side as it hunts.

So, an interim solution for now would be to disconnect either one of your left or right channels to the EMS. Then, set BOTH the left and right pulse per revolution settings to the one you leave connected.

 

[PhantomPholly]

lol - isn't software wonderful?

I think I'll leave mine both connected and live with the discrepancy until you get a fix...