# Standoff distance

My Tempest is currently mounted about 3" away from a pole that’s a little under 3/4" in diameter. I know this isn’t ideal as there will be eddy currents and such coming off the pole which may affect the wind sensor if the wind is coming from that direction.

My question is how far away would I need to mount it to reduce the effect to a relatively negligible amount? Of course the easiest would be to leave it as-is, if the effect isn’t too great. Next easiest would be an 8" standoff. After that, I’d be looking at something more like a 24" standoff. If that’s not enough, things get a bit more difficult.

To keep things simple, let’s start by ignoring the impact of vibrations on the rain sensor. I’m less concerned about accurate rain than I am about wind.

I guess I can answer my own question, assuming the Tempest’s anemometer’s characteristics are similar to a “normal” anemometer. Looking more closely at the siting guide ( https://www.weather.gov/media/epz/mesonet/CWOP-Siting.pdf ) I see:

When placed on the side of a mast (rather than at the top), the sensor should be placed on a horizontal boom extending outwards from the mast, at a distance of 3 times the mast diameter. [So, if mounted on a 2-inch diameter pole, the boom should extend out 6 inches away from the pole].

So technically the 3" I currently have is basically OK since 3*0.75"=2.25". But I might still move it out to 8" since it wouldn’t be that hard to do.

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My gut feeling would be that for a normal anemometer that would work, as they gain the most momentum from the wind that is a bit sideways from the center of the device. The tempest reads the speed of the air between the transducers and would be more sensitive to the turbulence caused by the mast. So go for the 8"

I would mount the unit on the south side of the pole so there isn’t a shadow of the pole crossing over the brightness/uv sensor.

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@sunny Thanks. Yeah, I mounted it on the south side for that reason. Although since my UV sensor seems to be permanently failing, for now it doesn’t really matter much.

And I just ordered the bits I’ll need to move it out to 8".