Skwerl

Very interesting example. I don't think I've seen a DME with such a recent range 6 (it was literally like 20 minutes ago on the engine) and also such a bad report on a Tip. I'd be pretty curious to hear the seller's response if you show it to him.

talkenrain

That conversation will happen later today. It's a dealer so I suspect he will not won't to talk about it.

stronbl

When someone pointed out a single range 6 over rev and suggested a glitch, I thought how could that be, pretty sure it's not a glitchy software problem ... but perhaps it's a sampling and aliasing problem.

Should be simple enough to test the idea.

From Fourier analysis, we know we need to sample the highest frequency to be able to faithfully re-create all lower frequencies. Let's pick 9000 rpm just to be safe (if we get a 9000 rpm money shift in a 997, we're not gonna be happy).

So 9000 rpm / 60 sec / min = 150 rotations per second .
By Nyquist we need to sample at least 2x that frequency or 300 rotations per second. So to get a sample rate in milliseconds, 1000 /300 = 3.33 millisecond sample rate.

Ok, the sensors on the engine that read the analog rotation and convert it to a digital signal to be transmitted to the DME and logged need to sample about every 3 milliseconds to faithfully re-create an analog 9000 rpm event in the digital world.

But what if the system only samples at let's say 4 milliseconds, we could faithfully only recreate an analog 7500 rpm event. So if a higher rpm is reported we cannot be certain it is real versus simply an aliased signal; perhaps a "glitch" in this regard (for example, an 8800 rpm event may be very real and recorded, we just don't know with certainty this is the case - unless the engine blows - then we know with certainty ). And that's the problem with aliased signals, they cannot be distinguish from real signals.

To be fair this is rather simplified example and I do not know the sampling rate into the DME. I would hope it is sufficient to not have aliasing effects at the top of range 6.

Apologies for the "left turn", returning to the subject at hand ...

Johnny DB

A tiptronic will let you money shift when in manual mode???

talkenrain

That's what I keep reading... reports of so many inexperienced drivers shifting down way to aggressively by accident. Apparently while in manual mode, the TIP will allow it. I don't know this for a fact, maybe a TIP owner with experience can chime in?

Skwerl

I have heard of Range 1s and 2s on Tiptronics, theoretically induced by the sheer inertia of the pistons when accelerating fast and hitting redline, but Range 5s and 6s is a new one for me.