AeroPod, PowerPod and Newton

Hello,

I would like to adjust the temperature setting in Isaac as I believe the software is not retrieving the temperature adjustment that I've manually set on the Newton unit. I've read the Help pages which tell me I can set this under "Preferences" >> "Ride Data". However, when I navigate to this screen I am not presented with such functionality. Am I being docile?

Running Isaac 3.0.2 with September 2014 help manual.

Best...

Hello, anybody out there?

I thought the temperature adjustment only works on the Newton display but it still downloads the raw temperature to Isaac

Thanks for your input Ken. I too observe that I can alter the temperature on the Newton, but as you state yourself, the raw (or original temperature) is loaded unto Isaac. Would anyone from Velocomp like to comment on this?

At present we don't have a way in Isaac to alter the temperature.

Ok, if you cannot alter the temperature, then how can the Newton calculate accurate power data? Isn't that the whole point of the Newton?

I am very surprised for all the sophisticated components, algorithms and software, a function this simple which use to be available in previous version of the software has been removed.

Is that it? Or will this function become available in future releases of Isaac (to be at least consistent with the manual)?

actually the temperature factor is not all that significant in the overall calculation of power. The temperature is used to interpret the density of air which is also affected by humidity and elevation so in the big picture the change of temperature all other things held constant is not going to affect the calculation of power by that much. So it may not be 100% accurate, but accuracy is a strange thing because you need something as a standard and as we know every type or brand of power meter has it's own issues with accuracy. What is really more important is precision and as long as your Newton measures the temperature with a constant bias who cares, the precision is the important thing so you can compare today's results with yesterday's results and tomorrow's results and feel the reason for difference is you not the meter. So I do believe the Newton is precise and it is probably accurate enough.

What is important for sensor accuracy is relative temperature (temperature deviations from the start point). The absolute temperature setting has no effect on relative temperature changes. There is no compromise in the accuracy of the Newton.

What is a simple adjustment for some can be a troublesome complication for others. We have elected to make things as simple as possible.

I'm all for simplicity - and I'll take your word for it, but it's a shame the user doesn't have the ability to adjust the temperature in Isaac.

I don't buy the "constant bias who cares" point. I have a number of power meters (for testing purposes) and I don't think I'm being unreasonable when I demand that they should all be within an acceptable range of each other (less than 5% at worst). I like the Newton (I agree it's precise), but I question the derivation of CdA (particularly when a rider moves their hands around the bike, like most do) which as we all know is one of the the biggest factors when calculating power. For me this compromises accuracy big time.

The point I'm trying to make is 200W should be 200W, not 180W on this device and 220W on that device. You wouldn't buy a metre ruler to be be told it could be 1.10m or maybe 0.90m, would you?

I promise you, we know how the Newton works . The Newton sensors work off of temperature changes (which are very accurate), not absolute temperatures.

Temperature has nothing to do with CdA, so I'm not sure how to respond otherwise.

I believe you, I know the Newton works!

And I also know CdA has nothing to do with temperature. I've tried to kill two birds with one stone and clouded what I'm trying to say. I'll leave CdA for another day...

So, second attempt to provide some clarity. Stay with me...

Temperature

I did a road ride last night. The temperature in my garage, outside and reported by local weather stations was around 0 C. As a former meteorologist and from experience, I'm not going to argue with that.

During the ride temperature hovered around zero according to Newton.

When I uploaded my ride into Isaac the temperature in the data summary panel displayed -6 C. Believe me I know what -6 C feels like in a Scottish winter. It was not -6 C. Neither was it -6 C when I got home (still zero).

So we have a difference of 6 degrees Celsius, i.e. what the Newton is reading and what Isaac is displaying for the ride.

Let's assume (with good reason) the temperature didn't change during the ride. We still have a 6 degree Celsius difference.

Keeping it as simple of possible and playing around with Boyle's law, we have the situation where...(P is pressure, V is volume, T is temperature, den is density, * represents Newton and " represents Isaac)

P* V* T" den*
----------- = ----
P" V" T* den"

Let's say the pressure (and hence the volume) didn't change during the ride, so...

T" den*
--- = ----
T* den"

The contribution of density to the calculation of power is...

0.5 den CdA v^3 (where v is velocity)

But den* is not den" due to the difference in temperature so the power calculated and displayed on the Newton will be different from the power calculated and displayed in Isaac. Correct?

I know the temperature has to be in Kelvin, so the density difference doesn't affect the difference in power (a couple of watts), but I feel it's an avoidable difference.

Am I barking up the right tree or barking mad?

Two points:

1) Temperature data is recorded in the ride file, so Isaac numbers are the same as recorded in the Newton. The "-6C" number shown in the stats window means that, at the start of the ride, the Newton was reading -6C.

2) Your calculations are fine, but they use wind speed as the basis of power measurement.

We don't use wind speed in our power calculations; we use air pressure. That is, the front sensor measures air pressure, not wind speed.

As your equations show, air density does with temperature (and it varies with altitude too); however, since the Newton is making a direct measurement of air pressure, it doesn't need to know the correct temperature or altitude; the air pressure measurement already accounts for both!

We do, of course, use temperature when converting air pressure into wind speed. You're correct that absolute temperature is required for the most accurate wind speed calculation; if your Newton is "off" by 6C, then wind speed measurements would be off by about 2% (not much), well below the recording resolution of wind speed.

Thanks for clarifying. And some interesting points too. In essence you are using a sensitive pitot tube to measure air pressure - that's what the wind sensor really is? I get it.

One problem still remains though. My Newton read zero degrees at the start of my ride, not -6C.

In fact the difference in temperature between the Newton at the start of the ride and its corresponding Isaac file is 6 degrees. The two simply don't match up. For all of my rides the Newton displays the correct temperature whereas the corresponding Isaac file (after uploading the data) is consistently 6 degrees lower.

Hence, my post in the first place. All I wanted to do was to apply a temperature offset to get more accurate power data.

I will ask Travis.

it would be really nice if the temperature was accurate. Though I fully understand that it is not that important for the power calculations, it would be nice if when I download my data the temperature it says is what my weather station states.

We will see what we can do.

Splendid! I look forward to the update. Thanks.

Velocomp wrote:We will see what we can do.

Hi John any update on the ability to correct temperature? We have agreed it makes no difference to the power calculation but it would be nice that when it downloads to my training file it was the correct environmental temperature not some random number. My unit always seems to read higher than the real outside temperature. Is the only way to get it to read correctly is to change the temperature in the Newton to be biased lower?
thanks