Author Topic: La Crosse V40-Pro Pressure Values Consistently Low  (Read 2079 times)

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Offline Cloudscout

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La Crosse V40-Pro Pressure Values Consistently Low
« on: July 09, 2018, 02:18:17 PM »
I picked up a La Crosse V40-Pro "Professional Remote Monitoring Weather Station" last week.  I got it connected to WU but the pressure readings that it's reporting to WU are consistently 0.2 in/hg lower than the results reported by the nearest airport (about 6 miles away) and another PWS operated by a local TV station about 2 miles away.  I have a BME280-based device that I built and when I correct its readings to sea level pressure, it is always within about 0.01 in/hg of the airport and the TV station's numbers as well.  The relative changes in pressure seem to be okay but the actual numbers are consistently low and it's driving me crazy.  Any thoughts?

Offline Jstx

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Re: La Crosse V40-Pro Pressure Values Consistently Low
« Reply #1 on: July 10, 2018, 09:45:23 AM »
Does this unit, or it's software handling interface, have an accessible options menu?
Most PWS's do, which should allow you to input an "offset" factor value to make corrections to a slightly 'off' sensor.
My La Crosse Tech WS-2813 can apply 'corrections' at the console itself, or in the WUHU logger software app, which has extensive options.

Offline Cloudscout

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Re: La Crosse V40-Pro Pressure Values Consistently Low
« Reply #2 on: July 12, 2018, 04:25:58 PM »
No, there's no option for an offset or anything.

The deviation was much worse but it improved when I restarted the station.  I restarted it again but it didn't make a difference.  The next day, I tried restarting it again.  This time, the accuracy improved a little more.  I waited another day and restarted the unit one more time.  Now its accuracy seems good.  It's generally within 0.02 in/hg of what my other sensor, the local news station's PWS and the nearest airport's METAR numbers are showing.

Offline galfert

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Re: La Crosse V40-Pro Pressure Values Consistently Low
« Reply #3 on: September 10, 2018, 11:18:51 PM »
The barometer in the V40-pro is hands off to the user. No setting is required nor is it provided. The words: barometer, pressure, elevation, altitude are not even in the user manual. But the separate FAQ does mention barometer and pressure.

From the FAQ document:

Your station calibrates barometric pressure based on its location over time to generate an accurate, personal forecast. Please allow 7-10 days for barometer calibration. 

• The forecast station samples the barometric pressure every twelve minutes. These samples are averaged hourly and daily then stored in nonvolatile memory. The three hour pressure indicator change is based off of the last four average hourly readings.   

• IMPORTANT: As the Weather station builds memory, it will compare the current average pressure to the past forty day average pressure for increased accuracy. The longer the Weather station operates in one location the more accurate the forecast indicators will be.

Also some of the difference you may be seeing is that Sea Level Pressure is not the same as airport METAR pressure. Because that is Altimeter pressure, a bit different than Sea Level Pressure. Your station may be reporting SLP instead of ALT.  Some people choose to calibrate their station to ALT instead of SLP to be in line with airport METAR. But for your station manual calibration is not an option.
« Last Edit: September 13, 2018, 11:58:57 PM by galfert »
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