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Today's Trip Meters Conundrum

Discussion in 'Model S: User Interface' started by brianman, Jul 24, 2013.

  1. brianman

    brianman Burrito Founder

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    #1 brianman, Jul 24, 2013
    Last edited: Jul 24, 2013
    This image was not doctored (other than the red ellipse) and is not fake.

    Any ideas what's going on here?

    TheTaleOfTwoTripMeters2.png
     
  2. Doug_G

    Doug_G Lead Moderator

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    You reset Trip B, drove 200 feet, and then reset Trip A?
     
  3. brianman

    brianman Burrito Founder

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    Both meters were at 0 when I took delivery. I've never reset either of them.

    Had 65 miles at delivery, for those not wanting to do the math themselves. I've had that number memorized for a long time. :)
     
  4. cfOH

    cfOH Member

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    No idea about the trip meters, but I did notice that 451 Wh/mi average. Well done, sir! ;-D
     
  5. brianman

    brianman Burrito Founder

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    Heh.
     
  6. superraz375

    superraz375 Member

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    Perhaps the Tesla Motors factory was testing your car.

    They reset one of the trips (while the AC was still on) and then reset the second trip.

    This would explain the slight difference in energy between the two.
     
  7. brianman

    brianman Burrito Founder

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    #7 brianman, Jul 24, 2013
    Last edited: Jul 24, 2013
    Shouldn't I have been seeing this discrepancy for months now? I just noticed it today. I'm not saying it started today but it wasn't originally mismatched.


    Update:

    Skimming back through my pictures, the numbers were matched at 934.8 owner miles (1,000 vehicle miles) and at 10045 owner miles (10,110 vehicle miles).

    The discrepancy began sometime in this range (2013/07/11:07:27 PT, 2013/07/11:19:47 PT).



    Now that I have an interesting timeframe to research, I've fired off a mail to ownership because I'm very curious. Not concerned, just curious.
     
  8. SCW-Greg

    SCW-Greg Active Member

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    Because you car *is* truly like a spaceship. It's the difference in time the neutrinos took to arrive... versus all other electrons. You might notice that you car looks bluish from the front and reddish from behind... with those numbers your puttin up on the board! ;)
     
  9. Klaus

    Klaus Member

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    Even more impressive - >900 Whr/mi between miles -5 and -4 on the history graph.

    brianman, you'll probably need Leilani to dethrone you from the apex position of energy users @ TMC ☺
     
  10. brianman

    brianman Burrito Founder

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    She somewhat acquiesced at my request for a ride in her racecar, but it wasn't at Teslive. At least, that's what I recall she said in one of the threads... but I might have just wanted her to have said that.

    - - - Updated - - -

    It's easy to burn juice going uphill.
     
  11. NigelM

    NigelM Recovering Member

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    'A' measures the front wheels and 'B' measures the back wheels, when you get a little slippage from a wet surface, or in your case more likely from worn tires, you use more fractionally more power without achieving additional forward motion.
     
  12. brianman

    brianman Burrito Founder

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    Now I'm confused. How is power applied to the front wheels?
     
  13. NigelM

    NigelM Recovering Member

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    You don't have the AWD version?
     
  14. Doug_G

    Doug_G Lead Moderator

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    A is the left side, B the right, and you've been driving in circles lately...
     
  15. brianman

    brianman Burrito Founder

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    So Spark keeps telling me.

    - - - Updated - - -

    Where are those puppy dog eyes again...

    Update: Found 'em!
     
  16. Discoducky

    Discoducky Active Member

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    More data points are needed. I doubt they are diverging but rather have a different algorithm applied. When you drive do they update at the same time?
     
  17. brianman

    brianman Burrito Founder

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    I noticed it on the way home, so I don't have a lot of observational data yet. Looking back through my pictures the biggest gap I see is 0.2 and the smallest gap I've seen since the evening of July 11th is 0.1 kWh. On the way home, I noticed that the 0.2 separate displays only briefly and then it snaps to 0.1 so I'm guessing they are like 0.11 or 0.12 kWh apart.

    Prior to this report, I had no reason to think the two trip meters were any different. They're just "A" and "B" with -- I thought -- the same behavior just a different set of storage locations for the data.
     
  18. deonb

    deonb Active Member

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    I would think what happens is that the Total Energy is constantly being archived while you're driving. So e.g. every microsecond or so it's taking the current kW usage and archiving the value as kWh over time. (Assuming it's a digital and not analog measure. However, even with an analog measure there has to still be a process of archiving rotations into digital measurements).

    Anyway, it has to do this in several places, adding the number to Trip Meter A, Trip Meter B, and Since Last Charge.

    However, I bet it's not doing the update while under a lock. With the result is that if the archiving is done, and there is a reading change at the exact few nanoseconds between updating Trip Meter A and Trip Meter B you can have a slightly different value added to each of the 2 numbers.

    It probably also doesn't help that there is rounding involved.
     
  19. Todd Burch

    Todd Burch Electron Pilot

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    My guess is that the numbers are being truncated to one decimal place instead of being rounded, plus they're using floats to store the data and enough mathematical operations have been performed (integration using the Trapezoid rule, perhaps) that some error has started to creep into a decimal place?

    If they're truncating, the difference between the two at delivery could have been 0.9999999 kWh, and the difference now 1.000000001 kWh.
     

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