Tuesday, December 25, 2012

First Pressure Check on Lacrosse C86234

We have a new Lacrosse weather station model C86234 from Costco. On sale for about $60, list is some $280. Seems to work well so far. (Did a rain gauge check today at about 0.1"/h for 3 or 4 hours, and will write that up shortly. Rain study is the main reason we got the device.  It has a tipping bucket gauge that is wireless for about 200 ft, to a temp and humidity gauge that is then wireless for an additional 80 ft to an electronic panel, which can then be accessed up to 30 ft by BT to a PC.

We obviously have barometers coming out out ears here, but the pressure was easy to check quickly with online resources, which we explain here home units can be checked as well.  We are  in sight of the WPOW1 NWS station here, so that is an easy comparison. You can download their data for past 24h and paste into a spread sheet.  The 24h data is UTC; the onscreen data is local or UTC. WPOW1 great plot of the pressure and trend and even pressure plus wind.  The Lacrosse barograph display on the device is not very useful, but you can download the data to PC, but the process is a bit clunky, and the connection is lost if you close the program.  But it will make a plot or you can export to txt and import to excel.

Here is the plot from today at WPOW1. We did the fit backwards in time, so for comparison, I add another flipped over and stretched to match the excel output.

Next we imported both sets of data to excel and then subtracted them. This is a crude test as I am not 100% certain on the times as I had just set up the lacrosse and had to guess a correction since it had stored data with the wrong times in it.... but this does not really matter, it just means it will be easier if done properly.
This is both sets of data overlaid, so we see at a distance that they comparison is pretty good at least on a cursory level.  Small, short-lived  trends are well reproduced. Next we show the difference, with the scatter marked off which is about ± 0.3 mb, centered at -0.3 mb.  I would guess we are slightly higher than that, maybe -0.4 or a bit more.  We can check that later. In any event, first pass their barrometer looks pretty good over the range 1000 to 1020...especially for $60! 

On the other hand, most electronic units will work well over that range.  It is outside of this that is the bigger challenge, ie P > 1025mb and P < 990 mb.  We will know this soon and post a follow up or amend this one.

We can later take this in to our calibration bench and test it there, but the main point of this exercise is to demonstrate how you can do this quickly by comparison to a nearby station.  If you do not have a nearby station, you can interpolate with our online free function at www.starpath.com/barometers.

Next we  will add part 2 to our ongoing notes on rain now that we have a tipping bucket rain guage at hand.

1 comment:

David Burch said...

One year Later... the device has totally quit working! The pressure and temperature seem to be random numbers at this point. I think this failed earlier, but i just did not notice it. So not quite such a bargain after all.