Blocked wind port doing the opposite!?!

[andrewlees]

Hi,
I've brought this up before with 0 feedback, so I'm revisiting it. My understanding of a blocked wind port, is it essentially mimics (and accentuates) the effect of riding in bunch: the measured wind decreases thus recorded power drops. My Newton has been known to the do the complete opposite: power numbers go sky high.
I am including a ride from today that was 100% in the rain (like, torrential) and little to no wind. From the 10km to 24km mark I was riding with 4 people, then the rest by myself. You can see from 40km to 58km the wind goes haywire and records an excessive headwind.
I'm looking from some input as what is happening because I'm stumped as it just doesn't make sense.
Thanks.
Andrew

[Velocomp]

The front sensor of the Newton reads air pressure, not wind speed (it's the number of air molecules hitting you each second that count). Air density decreases as elevation changes, so the air pressure sensor actually reads the difference between the ambient air pressure, and the pressure in the port. It is, in fact, a dynamic air pressure sensor, and it has to holes inside it--one to read the wind port sensor, and one to read the ambient air pressure (the pressure inside the Newton housing). The dynamic difference between the readings between the inside/outside holes determines the sensor's reading.

When the wind port becomes blocked (generally due to rain), the pressure on the air pressure sensor "latches" at a constant value. In your case, as you climbed the hill the wind readings were really negative.

As you descend from the top of the hill, the wind readings suddenly become crazy positive. What's happening? In fact, the blocked wind port is still latched. However, as you descend the environmental air pressure begins to increase, causing the sensor output sign to change and go positive.

You can use the Tools/Repair/Repair Blocked Wind Sensor function to get things reasonably normal. Repaired ride file and graph are attached.

[andrewlees]

Thanks John! And thanks for the description. That makes a lot more sense to me now.
Have you or anyone you know tried a sort of rain deflector over the front of the ibike? Something far enough away to allow air in but still keeps the rain out? I know the air tube extension helps out with this.