Author Topic: Info on WS-2902 humidity sensor please  (Read 533 times)

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Offline WA4OPQ

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Info on WS-2902 humidity sensor please
« on: August 06, 2018, 11:43:31 PM »
Does anyone know what humidity sensor the WS-2902 uses?
I'm swapping out my WS-1400-IP sensor arrays with the 2902 units.
I hate the HR202L sensors in the WS-1400s and I'd like to read up on the characteristics of the new sensor.

Offline galfert

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Re: Info on WS-2902 humidity sensor please
« Reply #1 on: August 09, 2018, 11:32:30 PM »
I don't know. And I don't really want to take mine apart. Maybe someone else will volunteer to do a tear down and determine sensor replacement viability. I too would like to know what humidity sensor is in there. It really does seem to perform much better than the WS-1400-IP series (WS-1001 and WS-1201).

If anyone does take a WS-2902 apart please post pictures.

Another option is to write to Ed @ Ambient Weather and ask him. Maybe he knows or he can find out.
« Last Edit: August 09, 2018, 11:34:32 PM by galfert »
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Offline WA4OPQ

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Re: Info on WS-2902 humidity sensor please
« Reply #2 on: August 19, 2018, 07:27:17 PM »
I wrote to Ed. He says: "I am sorry but I am not permitted to share this info. "

Offline galfert

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Re: Info on WS-2902 humidity sensor please
« Reply #3 on: August 19, 2018, 07:52:28 PM »
Hmmm....I would reach out to Fine Offset the OEM manufacture of all Ambient Weather stations.

I would also reach out to as many branded resellers of these stations. But you would have to know the model of what they call a WS-2902.

Misol
Froggit
Ecowitt
... etc

I don't have a complete list of branded resellers.
But that is a start. Maybe one of them will answer the question.

In any case your original question was about the WS-2902A and if it had a better sensor than the old model. Well it is different alright. I compare my WS-2902A with those older WS-1400-IP around me and I can see the difference. I don't know if it will last longer, but at least it performs better. Highly recommend it.
« Last Edit: August 19, 2018, 07:54:01 PM by galfert »
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Offline Rychu

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Re: Info on WS-2902 humidity sensor please
« Reply #4 on: September 12, 2018, 04:23:18 PM »
Does anyone know what humidity sensor the WS-2902 uses? (...)

And with what accuracy does it measure temperaturę - according to the instructions?

« Last Edit: September 12, 2018, 04:27:04 PM by Rychu »

Offline galfert

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Re: Info on WS-2902 humidity sensor please
« Reply #5 on: September 12, 2018, 05:37:21 PM »
You can see all the sensor specifications on Ambient's site:

https://www.ambientweather.com/amws2902.html

Well everything except for what exact manufacturer and model the sensor is. I suppose some day someone will open up one of these bad boys.


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Offline Rychu

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Re: Info on WS-2902 humidity sensor please
« Reply #6 on: September 12, 2018, 05:49:40 PM »
I wrote to Ed. He says: "I am sorry but I am not permitted to share this info. "

I checked the accuracy of temperature and humidity in the WS2902 instructions - page 48.
Temp: +/- 2oC
RH: +/- 5%

I enclose the operating characteristics of typical hytherographs already used in weather stations - medium class - SHTx ---> SHT3x.

Conclusions: WS2902 does not have an average sensor SHT30, 31 or even SHT10 but low and it is probably HR202L or e.g HR31.

The producer therefore covers this information with a secret.   ;)

Read SHT30 vs SHT31

« Last Edit: September 12, 2018, 06:17:39 PM by Rychu »

Offline WA4OPQ

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Re: Info on WS-2902 humidity sensor please
« Reply #7 on: September 13, 2018, 09:36:27 AM »
I received a reply from Fine Offset today. It uses a SHT30
And, unlike Ed, I can share this info.
« Last Edit: September 13, 2018, 09:41:44 AM by WA4OPQ »

Offline galfert

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Re: Info on WS-2902 humidity sensor please
« Reply #8 on: September 13, 2018, 12:57:06 PM »
Pretty cool that it has an SHT30. Not as nice as an SHT31 or SHT35 but decent none the less. I'm very impressed with the results on the mid and high end which is what we have here in Florida for humidity. No wet bias and tops out at 99%. That's all I need...as long as it lasts a decent amount of time.

Now I wonder if it is a digital SHT30-DIS-B (I2C) version or an analog SHT30-ARP-B version?

I guess this means we can upgrade it to a 31 or maybe a 35 if it is digital. (The 31 comes in digital and analog, the 35 is only digital)





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Offline Rychu

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Re: Info on WS-2902 humidity sensor please
« Reply #9 on: September 13, 2018, 03:30:30 PM »
Pretty cool that it has an SHT30. (...)

FineOffset installs SHT30 but in Ambient WS2902 there is another sensor from the bottom shelf.

If it was SHT30 then the accuracy should be:
temperature: +/- 0.2 C
(RH) humidity : +/- 3%

and

in the Ambient WS2902 manual - page 48 - there is a record:
temperature: +/- 2 C
(RH) humidity : +/- 5%.

Ask Ed to explain it \:D/
« Last Edit: September 13, 2018, 03:37:42 PM by Rychu »

Offline WA4OPQ

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Re: Info on WS-2902 humidity sensor please
« Reply #10 on: September 13, 2018, 04:27:35 PM »
I snuck a peek inside the 2902 array, the sensor is covered with what looks like a small sack made of perforated paper towel. Some of the glue and weatherproofing is stuck on it so it's can't easily be removed. Until the warranty is up I won't dig further

I still think it's a SHT30; Fine Offset sent me the spec sheet for the digital version so I'll assume it's digital.

I believe Davis is using the SHT31, maybe one of the Davis boys can tell us how long the sensor lasts in an outdoor environment.

And I found a photo of how small the SHT31 is. I don't think I'll be soldering one in without a SMD hot air soldering station.

Offline CW2274

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Re: Info on WS-2902 humidity sensor please
« Reply #11 on: September 13, 2018, 04:39:22 PM »
Pretty cool that it has an SHT30. (...)
If it was SHT30 then the accuracy should be:
(RH) humidity : +/- 3%
Actually, between 10 an 90%, the 30 is rated at 2%.

Offline CW2274

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Re: Info on WS-2902 humidity sensor please
« Reply #12 on: September 13, 2018, 04:47:55 PM »
I believe Davis is using the SHT31, maybe one of the Davis boys can tell us how long the sensor lasts in an outdoor environment.
It's "looking" like the 31 is fairing much better in drier climates (such as mine) than wetter ones. It's also a crap shoot, I just bought 4 more 31's to test and they were all wetter than my 2 year old one which has been in service about 9 months, and use a -2% correction factor as is.

Offline Rychu

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Re: Info on WS-2902 humidity sensor please
« Reply #13 on: September 13, 2018, 05:07:05 PM »
I snuck a peek inside the 2902 array, the sensor is covered with what looks like a small sack made of perforated paper towel. Some of the glue and weatherproofing is stuck on it so it's can't easily be removed. Until the warranty is up I won't dig further (...)

This "paper" is a protection against accidental wetting with water. Sensors are very sensitive to direct water.

Offline galfert

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Re: Info on WS-2902 humidity sensor please
« Reply #14 on: September 13, 2018, 06:10:46 PM »
Pretty cool that it has an SHT30. (...)

FineOffset installs SHT30 but in Ambient WS2902 there is another sensor from the bottom shelf.

If it was SHT30 then the accuracy should be:
temperature: +/- 0.2 C
(RH) humidity : +/- 3%

and

in the Ambient WS2902 manual - page 48 - there is a record:
temperature: +/- 2 C
(RH) humidity : +/- 5%.

Ask Ed to explain it \:D/

The specs can be interpreted in different ways as CW2274 mentioned. It is up to the manufacture what spec they want to quote depending on the range. And there might be differences in how the system firmware as to how it copes with the data for averaging and final reporting. There are are tweaks that the manufacture can do.

Basically what I'm saying is that if Fine Offset said it was an SHT30 then I doubt it is different for Ambient Weather. I don't think they they changed it. It could be also that Ambient is under-reporting the real performance so that when it starts to stray there will be less warranty claims as it would still be withing spec. I'm noticing much better performance than the stated specs.

I snuck a peek inside the 2902 array, the sensor is covered with what looks like a small sack made of perforated paper towel. Some of the glue and weatherproofing is stuck on it so it's can't easily be removed. Until the warranty is up I won't dig further

I still think it's a SHT30; Fine Offset sent me the spec sheet for the digital version so I'll assume it's digital.

I believe Davis is using the SHT31, maybe one of the Davis boys can tell us how long the sensor lasts in an outdoor environment.

And I found a photo of how small the SHT31 is. I don't think I'll be soldering one in without a SMD hot air soldering station.

That perforated sack that looks like a paper towel is a filter for dust. Some Davis folks have ventured to run without a filter, because they are testing performance and trying to get better results. I wouldn't necessarily recommend removing it. I'm just saying other have ventured to test.

The photo you posted of the SHT31 is indeed impressive how small the chip is (the one with the small dimple hole in the middle). You don't have to venture to do SMD soldering. You might be able to replace with a pre-mounted sensor and just solder the leads on the PCB with a regular soldering iron.

If it is indeed digital that would be awesome. Maybe you could reach back out to Fine Offset and verify if it is the digital version or the analog.

The Davis stations use the analog digital version of the 31 (digital but not I2C)*. They have been testing with analog 75 because they can't use the 35. Although there is one person that is developing a digital to analog solution for Davis to use the 35.
*[Thank you CW2274 for the correction above]
« Last Edit: September 13, 2018, 09:35:00 PM by galfert »
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Offline CW2274

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Re: Info on WS-2902 humidity sensor please
« Reply #15 on: September 13, 2018, 06:27:41 PM »
Pretty cool that it has an SHT30. (...)

FineOffset installs SHT30 but in Ambient WS2902 there is another sensor from the bottom shelf.

If it was SHT30 then the accuracy should be:
temperature: +/- 0.2 C
(RH) humidity : +/- 3%

and

in the Ambient WS2902 manual - page 48 - there is a record:
temperature: +/- 2 C
(RH) humidity : +/- 5%.

Ask Ed to explain it \:D/

The specs can be interpreted in different ways as CW2274 mentioned.

The Davis stations use the analog version of the 31.
I took that from Sensirion web site.

No sir, it's digital, just a different protocol than the 35. That's why us mere mortals can't adapt it.

Offline galfert

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Re: Info on WS-2902 humidity sensor please
« Reply #16 on: September 13, 2018, 09:36:41 PM »
CW2274,
Thank you for the correction regarding Davis SHT31 protocol being digital but different than I2C. I noted your correction in my post and credited you. I knew the digital I2C didn't work on Davis and I thought that meant it was analog. I didn't realize there was a different digital protocol. I now see it is referred to as Legacy Digital or Legacy Sensibus single shot (LSS).
« Last Edit: September 13, 2018, 09:46:31 PM by galfert »
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