humidity and aspiration

[hills]

Can anyone tell me if aspirating my sensors screen would affect humidity greatly?

By way of explanation, I used to have a solar powered fan aspirating my screen, so therefore it only worked during the day. At night time I would have the highest humidity out of all of the weather underground stations around here, but I used to attribute that to the fact that I am at the highest elevation.

Yesterday I converted to a continually powered fan and last night my humidity was only around average compared to all the other WU stations at about 46% instead of the usual 90% previously.

Would my humidity readings be more accurate now or would the fan be making them too low? The closest station to me is currently reading 72% and prior to my upgrade I was consistenly higher than theirs overnight.

[Gina]

I think aspirating will improve the accuracy and your figures bear this out. Before I aspirated my unit, I was getting almost constant 90%+ readings. Now the readings seem to make much more sense. Professional Stevenson screens are aspirated I gather. My fan is on a continuous supply, though running quite slowly.

[beteljuice]

That sounds like your screen is 'storing' heat. As the ambient temperature drops (night) the air within the screen is trying to condense (increase in local RH) and there obviously is not enough 'free' ventilation to equalize in / out temperatures quickly.

Do you still have your original 'shroud' on your sensor unit - if so remove it (as long as you are confident that your screen is reasonably rain proof !), it is now hampering ventilation. ie. you have two jackets instead of one

[hills]

Yeah I do still have the original shroud. I think my new one should be at least as weatherproof as the original, so i'll give that a shot.

Thanks for the replies!