Weather or not to believe ....

FullCircle

FullCircle

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Idling my life away today, so a post to see who has what on the barometer front...

Yesterday, I brought my Science Museum Weather station home from the boat where it has resided for a couple of years. Clean up the contacts, new batteries in, wipe all the salt from the case, reset all the variables, and off it goes.
So I parked it next to my Aldi purchased unit, and compared them. They were miles apart, in terms of baro pressure, temperature and humidity.
So last night we had
Science Museum (SM
Temp 22.1c
Humidity 68%
Baro 1015mb

Aldi Temp 19.8c
Humidity 82%
Baro 1035mb

I looked again this morning, as the units have had time to soak to the same level
and they are still way different on the baro reading, but the others, including the weather 'forecast' are acceptable tolerance differences.

Science Museum (SM)
Temp 17.7c
Humidity 62%
Baro 1024mb

Aldi Temp 18.1c
Humidity 60%
Baro 1047mb

It appears that the Aldi baro is way out. I went and got the trusty baro off the wall in the hall, and that is measuring 30.12 ins Hg or 1017mb approx.

Recognising that all baros will be different, what is the standard tolerance allowable, and where can I find a reference unit. After all, it does not matter if it is reading wrong, as, just like a compass, I can develop a deviation card.

Anybody got a clue?







weatherstations.jpg
Barometer.jpg
 
It is usual for barometers to have a correction adjustment to allow for altitude differences. I expect even the electronic ones have this. You can obtain the local barometric pressure utilising a friendly radio ham who can receive information from a local airport and adjust the barometers accordingly.

John
 
both should allow you to re-set the index error. wait until we have high pressure and check local pressure from weather people (e.g. bramblemet in solent) make sure you are also at sea level and adjust.
 
I've got a Science Museum jobbie too, and it seems to be very reliable. The question is whether absolute accuracy more important than accurate trending - I was taught that looking at changes in pressure give an indication of likely weather changes, so whether the pressure is 1017 mBar or 1024 mBar is less important than it is now 1017mBar and it was 1027mBar by the same instrument 12 hours ago.

I also have a Plastimo aneroid barometer on the boat which just doesn't work, but matches the chronometer on the other side of the forward bulkhead, so my el cheapo Science Museum doo dah is better than nought (or Plastimo).
 
Seriously though. Is this a bit like the effect you get on bathroom scales where such a small compression can't be accurate. Does a professional barometer have a bigger 'chamber' (for want of the correct word)?

Even if the shown figures are not the same you would hope that the trend might be right and that's what counts isn't it?
 
I have the other Ascot weather station sold by Aldi, (there were two types when I bought mine, one in landscape format similar to yours, and one portrait type, which I bought). The instructions explain how to set the barometer to the correct pressure reading. Paragraph 5.6.1.a in my set of instructions explains all.
If your instructions are missing try pressing the EINST/BARO key on the back until the pressure display flashes, then press the down arrow key which will reduce the displayed pressure by 1 mb per press. Finally press the EINST/BARO key again to confirm the setting.
P.S. Colmce beat me to it!
 
Ahaaaaaaa!!!!!!!!! /forums/images/graemlins/smile.gif

OK, So I have reset them now, and will leave them to trend neck and neck until I get back next Friday.

The old baro is still below them though. But as I have been in a 977mb storm out in the North North Sea, I am going to leave the electronic ones where they are, so it doesn't frighten me. /forums/images/graemlins/crazy.gif
 
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