In the past I have had a feeling my Fine Offset weather station has not been recording all of our rainfall. Then when we had a storm today, my weather station recorded about 5mm less than my manual weather gauge so I knew I’d better look into it. I knew that the weewx software had limits set for various readings to eliminate spurious readings so I thought I’d start there. I couldn’t find anything that made sense though.
Time for Google! I eventually found an obscure reference to max_rain_rate in the file fousb.py having a maximum rate to stop strange readings which the Fine Offset stations are apparently prone to. The default is 24cm/hr so any rainfall over this is ignored.
All of my data for the day was still in the console so I disconnected it from the Raspberry Pi and plugged it into a Cumulus setup on my laptop and downloaded the data. I found one entry at a rate of 288mm/hr or 28.8cm/hour. This started to make sense. Obviously the location the weewx software is written doesn’t experience the downpours SE Qld is prone to in our summer storms. A bit more googling and checking out the comments in fousb.py and I had the answer. I had to enter some code in the setup file weewx.conf to override the default.
151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 | ##############################################################################[FineOffsetUSB] # This section is for the Fine Offset series of weather stations. # The station model, e.g., WH1080, WS1090, WS2080, WH3081 model = WH1080 # The polling mode can be PERIODIC or ADAPTIVE polling_mode = PERIODIC # How often to poll the station for data, in seconds polling_interval = 60 # The pressure calibration offset, in hPa (millibars) pressure_offset = 0 max_rain_rate = 36 # cm/hr, default is 24, changed because heavy rain not being measured. # The driver to use: driver = weewx.drivers.fousb############################################################################## |
Hi Steve,
You may want to revise that figure. We received 11mm in 12 minutes this afternoon
My Cumulus software and Fine Offset WH1080 recorded 90mm/hr at one point.
Cheers
Ian
Hi Ian,
Weewx uses cm/hr as their unit instead of mm/hr. I now have it set for 36cm/hr so that should cover most cases but I will keep an eye on it and adjust if necessary. We do get torrential rain in this neck of the woods don’t we.
Steve
Hi folks
As I understand it, you feel you have a software problem at high rain rates. I wonder if it is not just a physical problem. Those little buckets have to fill up, dump their load and get ready for the next filling. It seems to me there is a limit to how fast this can take place.
Regards, Irving
I think it should be ok Irving. Even at the top rate of 36cm or 360mm/hr, that's only one tip every three seconds so it should handle that ok. (360mm/0.3mm per tip = 1200 tips in an hour)
You might lose a bit of water when the buckets are horizontal as it tips but it would be minimal.