Topic: Pressure discrepancy between GW1000 and GW1100

[broadstairs]

Looking at pressure today I notice my two gateways were showing different pressure values.

GW1000 abs 1019.2 rel 1023.7 with abs correction 3.4 and rel correction 4.5
GW1100 abs 1015.8 rel 1020.3 with abs correction 3.4 and rel correction 4.5

the temperature locally is identical and they are about 10 feet in height difference the GW1100 being upstairs but 10 feet should be negligible.

So if you look at the difference the GW1100 appears not to have the correction values applied, or at least the GW1100 is 3.4 below the GW1000 for abs and 4.5 below for rel.

I could accept a small difference but I feel 3 or 4 hpa is probably a bit far out.

So my question is which correct or is my GW1000 starting to fail? The GW1100 seems to be the nearest to reality comparing to nearby reliable sources.

Stuart

[olicat]

Hi!

I could accept a small difference but I feel 3 or 4 hpa is probably a bit far out.

But that is still within the specified range. Have a look to the specs:

Barometric pressure range: 300 – 1,100 hPa (8.85 – 32.5 inHg); accuracy: ± 5 hPa; 0.1 hPa (0.01 inHg)

The basic problem is that the absolute air pressure is already output incorrectly or differently. This should first be adjusted (offset!) and then the offset for the relative air pressure added.

At least that's the way I use it here with my various weather stations.

Oliver

[broadstairs]

Yes but when I got the GW1000 I did the required calculations to set the offsets and now they are wrong, I used the same for the GW1100 and they still work OK. So the GW1000 has drifted in about 18 months.

Stuart.

[davidefa]

The manual for the hp2003n sensor on page 2 has a (typical, not guaranteed ) long term drift of +/-2mbar after 1 year.
If we consider this drift linear in time ( it is not specified, so it is only a supposition ) we have a drift of +/-3mbar after 18 months and a 0.3mbar variation for the height difference.
So the variation you measured seems to be within specs/to be expected.
This may mean that these 'things' do not stay calibrated for long.

P.S.
For comparison the ( high resolution/stability ) bmp390 ( gszlag is referring to in this post ) has a drift of only +/-0.16hPa after 12 months )

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[gszlag]

Both ABS pressure values should be reading fairly close with the one upstairs being slightly lower ... about 0.3 mb less.

We need your elevation for the lowest sensor but a REL offset of of the same 4.5 mb suggest both sensors are at the same approx elevation of 37 or 38 meters?

If possible - might be easier to move both sensors side by side temporarily for easier calibration. You want both sensors to have the same ABS value if they are side by side.To do this, you adjust the ABS offset of each sensor until both ABS values are reading the same. Then move the GW1100 back upstairs and adjust REL offset using the higher elevation.

You can either calculate the REL offset for each GWxxxxby using the digital dutch standard atmosphere calculator or match the REL value with your source .
You may want to check this post for the procedure:
https://www.wxforum.net/index.php?topic=43477.msg442840#msg442840

If after recalibrating, you find one sensor "drifting" then yes, there could be a problem.

[broadstairs]

Thanks guys... yes the height ASL is about 38 metres for downstairs. I'll re-calibrate the GW1000.

Stuart

[gszlag]

The manual for the hp2003n sensor on page 2 has a (typical, not guaranteed ) long term drift of +/-2mbar after 1 year.
If we consider this drift linear in time ( it is not specified, so it is only a supposition ) we have a drift of +/-3mbar after 18 months and a 0.3mbar variation for the height difference.
So the variation you measured seems to be within specs/to be expected.
This may mean that these 'things' do not stay calibrated for long.

P.S.
For comparison the ( high resolution/stability ) bmp390 ( gszlag is referring to in this post ) has a drift of only +/-0.16hPa after 12 months )

 [ You are not allowed to view attachments ]

Thanks for the specs!. I always wondering how our sensors performed and I have to say, I winced more than a few times in reading the numbers.

I think it is time that Ecowitt upgrades their barometric sensors.
I still have the BMP390 ( bought early 2021) and it went quickly went out-of-stock for a long time. It is back in stock at Adafruit.

The BMP390 has just been superseded by the BMP581 and the specs look pretty good. As far as I can see, it is not available as a consumer board just yet.
https://www.bosch-sensortec.com/products/environmental-sensors/pressure-sensors/bmp581/
Note the low 12 month drift of 0.1 hPa and the low solder drift.

You can buy an evaluation board but I think I will wait.