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Home > Forum > Triathlon Forum > SRM caliberation value manual override in WKO

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SRM caliberation value manual override in WKO
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spgtwice
Jul 19, 14 15:15
Post #1 of 14 (2345 views)
question for the gurus. i have an SRM powermeter on the bike. I use the Garmin 810 head unit, not the PC6, etc.
i load into TrainingAgent/device agent and load to cycling peaks.

i realized after a race today i hadnt calibrated, when i went to check the daily calibration, the frequency was store at 489 and then when i hit calibrate it was like 459, which is around the norm lately for that powermeter /bike/weather.

in the SRM win software, you used ot be able to go in an edit the slope and calibration values for situations like this before loading to training peaks.

not sure if garmin has it, or if its stored someplace.

anyone know if there is a way to modify that calibration value in the .fit file before loading to training peaks....or as importantlly, whats the correlation to power if one was riding with a saved 489 when it was really 459. its is 30/459s more power? less power? 1 for 1 difference? just curious.

thanks in advance.
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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kjanracing
Jul 20, 14 18:53
Post #2 of 14 (2285 views)
I've never seen a slope correction in WKO like in SRMWin. Read the SRM owners manual, you might get your answer. The slope is linear. So I think your error would be the percentage of the slope error times your power. So if your saved slope was lower than the actual slope, wouldn't your actual power be higher than what you are reading or downloading?
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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echappist
Jul 20, 14 20:18
Post #3 of 14 (2272 views)
that's not the calibration, that's the offset

489 and 459 are in units of Hz, and you need your actual calibration # (i.e. slope) in order to determine the relevance.

so essentially, difference of 30 Hz. you need to convert this to torque by using the slope, which are in units of Hz/Nm. For example, my Duracci reads 23.2 Hz/Nm, so 30 Hz *1 Nm/23.2 Hz = 1.29 Nm. to convert to power, you need your cadence (angular velocity) in radian/s. So say you pedal at 95 rpm, this is 1.58 rps or 4.96 radian/s. So your PM is reading 6.4 watts off when you are at 95 rpm, and this will vary depending on your cadence.

If your unit was reading 489 during your race when it should have been reading 459, your unit is applying too much of an offset, thus under reporting
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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inv
Jul 21, 14 2:04
Post #4 of 14 (2246 views)
You can use Golden Cheetah for it. Also, You can calculate ~change of the average watts with the formula:
Instanteous watts = [(Sensor output in Hz)-(Zero Offset in Hz)] / (SRM Slope in Hz/N.m) * Crank angular velocity in rad/sec)
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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kileyay
Jul 21, 14 2:32
Post #5 of 14 (2240 views)
spgtwice wrote:
question for the gurus. i have an SRM powermeter on the bike. I use the Garmin 810 head unit, not the PC6, etc.

Buy the PC8 when it comes out. You're wasting your time
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Re: SRM caliberation value manual override in WKO [kileyay] [ In reply to ]
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spgtwice
Jul 21, 14 6:04
Post #6 of 14 (2215 views)
ive been a user for SRMs for probably 10 years, dating way way back. they have an amazing power meter, best around. their service group is some of the best around. they are super responsive.
the head unit, is not the best around. not. the garmin is backlit which is key for training in the early mornings. the screens are customizable in terms of font/display size, the GPS is invalueable at times for training. the battery last forever...etc. there are probably another 10 things it does superior. the 8 could be THE one, but right now, i like that 810 a ton.
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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kileyay
Jul 21, 14 7:16
Post #7 of 14 (2206 views)
spgtwice wrote:
ive been a user for SRMs for probably 10 years, dating way way back. they have an amazing power meter, best around. their service group is some of the best around. they are super responsive.
the head unit, is not the best around. not. the garmin is backlit which is key for training in the early mornings. the screens are customizable in terms of font/display size, the GPS is invalueable at times for training. the battery last forever...etc. there are probably another 10 things it does superior. the 8 could be THE one, but right now, i like that 810 a ton.

Wait until you try the 1000.
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Re: SRM caliberation value manual override in WKO [kileyay] [ In reply to ]
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spgtwice
Jul 21, 14 7:18
Post #8 of 14 (2205 views)
 i did. im tied intothe local shop.i used it for a week. i gave it bak to them. i think it needs a few firmware revisions. and i didnt like the buttons. the software on the1000 operates a bit slowly compared to the 810, just too much going on for the cpu compared to the 810.
atleast that was my take. the 810 does all i need for now.
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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Watt Matters
Jul 21, 14 20:52
Post #9 of 14 (2183 views)
spgtwice wrote:
ive been a user for SRMs for probably 10 years, dating way way back. they have an amazing power meter, best around. their service group is some of the best around. they are super responsive.
the head unit, is not the best around. not. the garmin is backlit which is key for training in the early mornings. the screens are customizable in terms of font/display size, the GPS is invalueable at times for training. the battery last forever...etc. there are probably another 10 things it does superior. the 8 could be THE one, but right now, i like that 810 a ton.
Of those 12 things important to you, is the integrity and accuracy of the data one of them?
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Re: SRM caliberation value manual override in WKO [Watt Matters] [ In reply to ]
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spgtwice
Jul 22, 14 2:30
Post #10 of 14 (2165 views)
No it's not. I like to run around like a chicken w my head cut off. I guess I'm weird like that


The garmin and srm if u remember to calibrate the daily offset should show identical values it's just displaying an equation based on the hz values it is transmitted via the crank

What makes u think the garmin head unit does display accurate values or better stated the same values as a PCx head unit?
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Re: SRM caliberation value manual override in WKO [spgtwice] [ In reply to ]
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Watt Matters
Jul 22, 14 14:19
Post #11 of 14 (2134 views)
spgtwice wrote:
No it's not. I like to run around like a chicken w my head cut off. I guess I'm weird like that


The garmin and srm if u remember to calibrate the daily offset should show identical values it's just displaying an equation based on the hz values it is transmitted via the crank

What makes u think the garmin head unit does display accurate values or better stated the same values as a PCx head unit?
Experience with examining the power trace from both. I have seen Garmin units significantly deviate from reality, in particular when rides involve much starting/stopping pedalling. They have a tendency to make up power data that doesn't exist in reality.
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Re: SRM caliberation value manual override in WKO [Watt Matters] [ In reply to ]
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king-tony
Jul 22, 14 20:12
Post #12 of 14 (2103 views)
Watt Matters wrote:
Experience with examining the power trace from both. I have seen Garmin units significantly deviate from reality, in particular when rides involve much starting/stopping pedalling. They have a tendency to make up power data that doesn't exist in reality.

How do you examine the power trace?
My insomnia destroying blog can be found here http://tfalin.blogspot.com/

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Re: SRM caliberation value manual override in WKO [king-tony] [ In reply to ]
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Watt Matters
Jul 22, 14 20:19
Post #13 of 14 (2099 views)
king-tony wrote:
Watt Matters wrote:

Experience with examining the power trace from both. I have seen Garmin units significantly deviate from reality, in particular when rides involve much starting/stopping pedalling. They have a tendency to make up power data that doesn't exist in reality.


How do you examine the power trace?
You look at it, and/or the numbers that create it.
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Re: SRM caliberation value manual override in WKO [Watt Matters] [ In reply to ]
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king-tony
Jul 22, 14 20:24
Post #14 of 14 (2097 views)
Watt Matters wrote:
You look at it, and/or the numbers that create it.

So you are pairing two head units (Garmin & PCX) with an SRM at the same time and trying to watch stochastic data real time on both displays? Or are you saving both files and converting them to WKO format and then comparing them using the multifile option?
My insomnia destroying blog can be found here http://tfalin.blogspot.com/

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