Cadence reads '---' on PT standard CPU while spinning quickly

Discussion in 'Power Training' started by retrograde, Apr 24, 2006.

  1. retrograde

    retrograde New Member

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    Yesterday I was doing a high-spin recovery ride and my PowerTap Standard CPU cadence display would frequently read '---.' Power and speed readings never dropped, just cadence.

    Does the CPU do this when cadence exceeds 140rpm (or whatever the upper limit for hub-sensed cadence)?

    I don't think I was actually spinning at >140rpm, more like 120. However the cadence readings were very erratic, I imagine in large part because I was riding over a bumpy concrete-slap bike path.

    Is all this to be expected? Is losing cadence an indication that the hub batteries are nearly gone (in the same way that losing HR means it's time to replace the CPU battery)?

    In general, how many mile or months do hub batteries last?. Any rule of thumb regarding when to replace them?
     
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  2. Flatscan

    Flatscan New Member

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    Sorry, I don't have direct experience with your problem, but I've read some about it. It sounds like your power/torque spikes that the PT uses to calculate cadence were particularly antagonistic to the heuristic used, hence the --- and erratic readings.

    Since power and speed were fine, I'd say that your hub batteries don't need replacement.
     
  3. retrograde

    retrograde New Member

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    '...antagonistic to the heuristic'

    I like that phrase. Will file that one away for future use.

    Thanks.
     
  4. frenchyge

    frenchyge New Member

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    High-cadence/low power is particularly problematic because of the low overall torque and lack of significant torque peaks. My cadence graph gets very erratic above ~105 rpm, even when power is high, although I don't typically lose the indication altogether.
     
  5. Krazyderek

    Krazyderek New Member

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    I find the same thing anything over 100, or 105 and it starts to jump around quite a bit, once you start getting up above 115(sprinting, or spin up's), it starts to blank out simply because of the limitation of the eratic torque being measured. If you really want more accuracy, you'll have to bit the bullet and order a new receiver with the dedicated cadence sensor, and a pro cpu.

    I have both and i actualy find the black bodied standard power tap to be way more reliable, and a hell of alot less buggy.
     
  6. retrograde

    retrograde New Member

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    Right ... during this evening's outing I did manage to get it to read up to 120 before it started to glitch, but that was over a very smooth stretch of road as I concentrated on being still and settled in the saddle.

    I usually ride with HR displayed, so I guess I was a bit startled to see the display flashing dashes.
     
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