Friday, January 29, 2016

Weather Station problems Oregon Scientific WMR100

This is a technical write up describing the problems I've been having with my primary weather station in Northeast Shoreline, the one I use for my historic data. The station is an old Oregon Scientific WMR100 that has been in service now at it's current location since September 29th, 2008.

Couple of weeks ago I started to notice a temperature issue with the station.  It was reading on average about 8-10°F higher than surrounding personal and professional weather stations. After doing some reading I learned that sometimes the internal components get corrosion or wet (housing is not water proof, only water resistant) and this typically causes a 10 degree rise in accuracy.

Wednesday night I brought down the station mast and removed the station for service, at first I attempted fresh batteries and a full hard reset to see if that would bring it back to normal, no such luck. So, I brought it inside and begin taking it apart.

The WMR100 sensor array partially disassembled and opened up.

Nothing was terribly exciting inside the unit other than a couple dozen spiders and a lot of spider webs, insect remains and other related debris. I cleaned everything up but didn't find any apparent cause of the temperature inaccuracy that I was able to see upon visual inspection. The sensor it's self has some kind of bronze glass thermistor or thermocouple bead, the PCB displayed "TH" for the abbreviation of the temperature sensor component. It is also using a resistive type humidity sensor element. Since the sensors in the little white box were full of spider webs, I brushed them all off with an old toothbrush and some isopropyl alcohol.  This was wrong, as it destroyed the relative humidity accuracy for several days, it appears to have recovered now.  I briefly got the temperature accuracy to match the indoor temperature where I was working on it, but when I got it all re-assembled it was settling for about 5 degrees hot again.  Disassembled and re-assembled again attempting to figure out why but it wouldn't leave the 5 degrees hot range.

So at this point in time it's close, appears to be anywhere from 3-5°F warmer than surrounding stations. At this time I am not in the position to replace this with the same or better model but eventually I plan to upgrade to a Davis Vantage Pro 2 cabled, wireless doesn't provide a good smooth constant stream of data so wind gusts can easily be missed, as they often are with wireless units.

If I get some more time this weekend or next week I'm going to take the station back down again and see if there was something I missed that might be causing the accuracy issue with temperature, the humidity sensor seems to have recovered on it's own.  I read that resistive humidity sensors sometimes take a day or two to outgas after contamination.

At this time, for temperature data I am relying on my secondary station I have set up in Lake Forest Park, on my webpage the data can be accessed under the "LFP Data" link in the navigation bar.


  1. Hi, I ve got the same issue. The Temperature goes up with humidity and show 20°C higher than expected temp.

  2. Well with mine I wasn't able to fix the problem. I had gotten it a little better by cleaning the temperature sensor but it wasn't great. Old age gets these units, a wind storm last march actually damaged it so it no longer had the wind sensor. For now I've replaced it with an Acurite 5 in one system.