correction for non-zeroed PT torque

Discussion in 'Power Training' started by 9606, May 26, 2006.

  1. 9606

    9606 New Member

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    Well, I did it again. I did an important group road workout without zeroing the tordue. I would like to go into the raw .csv file and correct for this.
    I think I am picking up rpm from the hub; my crank pickup or wiring may be dysfunctional.
    The .csv file shows varying torque values when the cadence is zero. There are surprisingly few records with zero cadence, especially considering this was a group road ride vs a Computrainer session.
    Any suggestions?

    (Yes, I could probably contact Saris PT but this forum may be more responsive!)

    Thank you
     
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  2. F1_Fan

    F1_Fan New Member

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    Maybe I'm wrong but I've never had to zero my PT SL since buying it last year. Perhaps it's time to send the unit off for service?

    Make sure you have the Torque Auto-zero set to "yes".
     
  3. 9606

    9606 New Member

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    Thank you.
    But what do I do with my ride file of yesterday.
    What sort of math wizardry can I do.
    I was hoping that the torque value for each zero cadence would be constant. Then I would just subtract that value from every torque value. As I noted, the torque values at zero cadence are not constant.
     
  4. F1_Fan

    F1_Fan New Member

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    What is the variation in the "zero" readings? If they're wildly variable then you may be stuck but if they're in a tighter range then I'd just import the file into Excel and apply a rough correction to all the values in the file in order to get the torque roughly zeroed. The relationship between power and torque should be linear within the range of your power.
     
  5. Alex Simmons

    Alex Simmons Member

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    If the variance of torque reading is minimal during periods of zero cadence, then what you plan to do will be close enough, just pick the torque value that represents the majority of zero cadence values but use the protocol described below as the PT torque is not directly proportional to power (depends on gearing).

    If the variance in zero cadence torque reading is more substantial then maybe cadence sensor only working intermittently? Or you have a bigger problem.

    I get some torque readings while not pedalling for a sec or two after stopping, mainly due to track standing at traffic lights/intersections.

    Anyway, here is the protocol for correcting PT non-zero torque as described by John Verheul:

    RE: PT Non-zero Torque

    Spreadsheet worked like a charm the one time I used it, but then I forgot
    where it was. So now I just do it myself in Excel.

    1) Open the PT file in Excel.
    2) Sort it by torque (ascending) so you find the lowest torque value (or, as
    chris says, just look for periods of coasting and observe the torque there).
    3) Click Edit -> Undo to put the file back in it's original order (or
    re-sort by time).
    4) Create a column that is a formula, you want to subtract the lowest
    observed torque value from the torque column. Column should be as long as
    the file itself.
    5) Calculate power using the new torque using the instructions Rick Sladkey
    gives in the FAQ. That is, power = 1746*recalculated torque*(speed/2093).
    Adjust the 2093 number (which is wheel circumference) if using other than a
    700x23 wheel/tire.
    6) Copy the new power cells and paste -> special (values) over the original
    power column. Do the same with the new torque values.
    7) Delete the now extraneous recalculated columns, save the file as a .csv
    again, and now import into CPSoft.
    8) Lobby Hunter & company to add the torque-zero-fix to CPSoft (along with
    an SRM slope fix). :)

    John Verheul
     
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