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MSL Pressure

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Chapel
Posts: 67
Joined: Mon 30 Jul 2018 10:23 am
Weather Station: Instromet
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MSL Pressure

Post by Chapel » Wed 17 Oct 2018 8:29 am

This should be unrelated directly to CumulusMX and as such is a general question.

I run MX and have an Instromet system including measurement of barometric pressure and I have added an offset to bring it in-line with what I believe to be the correct MSL based on local stations reported on darksky.net, my own barometer and the barometer on my iPhone. The problem is I can set the offset on my local station to give the same reading as the references I have however within 24 hours I am reading 3 or 4 mb lower than the others. I then recalibrate with the offset and all is good for another day or two until things drift out.

Does anyone have thoughts on such an issue? Instromet assure me my pressure module is OK and setting the offset is all that is needed, however should I be doing this weekly? I am starting to wonder if the pressure module is affected by heat as it is indoors, having said that the whole building is usually quite cool regardless of time of year.

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jdc
Posts: 142
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Weather Station: Davis VP2 : Instromet
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Re: MSL Pressure

Post by jdc » Wed 17 Oct 2018 1:24 pm

Not a solution, but I have an Instromet station and Davis VP2 and the values are compared every 15 mins. Also both are checked against a Kew pattern barometer daily and the maximum variation is +/- 2mb. (the Instromet gives whole mb.) The consoles are in different rooms with varying temperatures and this doesn't 'seem' to affect them.
My Samsung phone can be up to 10mb adrift.

freddie
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Re: MSL Pressure

Post by freddie » Wed 17 Oct 2018 6:58 pm

Chapel wrote:I have added an offset to bring it in-line with what I believe to be the correct MSL based on local stations reported on darksky.net
This site could well be using forecast data - particularly for its "now" values, so I would use with caution. Maybe check out Ogimet or similar for up-to-date pressure values.
Chapel wrote:my own barometer and the barometer on my iPhone
Should be okay if the calibration is up-to-date.
Chapel wrote:I am starting to wonder if the pressure module is affected by heat as it is indoors, having said that the whole building is usually quite cool regardless of time of year.
Pressure is affected by changes in temperature, but as the sensor is indoors this variation should be no more than 0.1 hPa/millibar over the course of a day.
Freddie
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