Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 24405 times)

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Offline WheatonRon

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But just thinking about it, I bet this is the reason why RainWise hasn’t produced a FARS version of the MK III.
Even if that's true, which I highly doubt, I don't care if fans are bad for the humidity portion of the sensor, I'll never quit using one til something comes along that's superior.
The benefits a FARS to me far outweighs the potential negative.

Having a FARS setup results in better temperature accuracy and not so accurate humidity readings—so pick your poison. Which is more important to you?
Davis VP2 with 24 hour FARS, SHT31 (3 complete systems-2 for uploading to the internet the other system for test and play); CWOP--CW5020 and FW3075; WU--KILWHEAT17 and KILWHEAT36; WeatherCloud.net; CoCoRaHS--IL-DP-132; Rainwise 111

Offline ValentineWeather

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But just thinking about it, I bet this is the reason why RainWise hasn’t produced a FARS version of the MK III.
Even if that's true, which I highly doubt, I don't care if fans are bad for the humidity portion of the sensor, I'll never quit using one til something comes along that's superior.
The benefits a FARS to me far outweighs the potential negative.

I was thinking about that also. But then I remembered the RM Young dual sensor temp/hum they run in aspirated shields. Maybe we took the fact because ASOS doesn't aspirate humidity it wasn't done.
Just look at sensor on the RMY temperature tracker and shields they offer both passive and aspirated for the dual sensor probe.
Randy

Offline CW2274

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But just thinking about it, I bet this is the reason why RainWise hasn’t produced a FARS version of the MK III.
Even if that's true, which I highly doubt, I don't care if fans are bad for the humidity portion of the sensor, I'll never quit using one til something comes along that's superior.
The benefits a FARS to me far outweighs the potential negative.

Having a FARS setup results in better temperature accuracy and not so accurate humidity readings—so pick your poison. Which is more important to you?
Look at it this way, what happens when your passive shield is running 4-5F warmer than ambient? What's that do to your humidity.... #-o

Offline WheatonRon

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But just thinking about it, I bet this is the reason why RainWise hasn’t produced a FARS version of the MK III.
Even if that's true, which I highly doubt, I don't care if fans are bad for the humidity portion of the sensor, I'll never quit using one til something comes along that's superior.
The benefits a FARS to me far outweighs the potential negative.

Having a FARS setup results in better temperature accuracy and not so accurate humidity readings—so pick your poison. Which is more important to you?
Look at it this way, what happens when your passive shield is running 4-5F warmer than ambient? What's that do to your humidity.... #-o

As many PWS owners would conclude, “you show me a happy moose, and I will find him an acorn!”

« Last Edit: July 13, 2018, 10:38:19 PM by WheatonRon »
Davis VP2 with 24 hour FARS, SHT31 (3 complete systems-2 for uploading to the internet the other system for test and play); CWOP--CW5020 and FW3075; WU--KILWHEAT17 and KILWHEAT36; WeatherCloud.net; CoCoRaHS--IL-DP-132; Rainwise 111

Offline jgentry

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But just thinking about it, I bet this is the reason why RainWise hasn’t produced a FARS version of the MK III.
Even if that's true, which I highly doubt, I don't care if fans are bad for the humidity portion of the sensor, I'll never quit using one til something comes along that's superior.
The benefits a FARS to me far outweighs the potential negative.

Having a FARS setup results in better temperature accuracy and not so accurate humidity readings—so pick your poison. Which is more important to you?

Personally temperature, but being in a county that’s one of the top fruit crop producers in the state of Alabama (especially peaches) accurate temperature and dew point reports are a must for growers. But I have noticed that a Davis passive shield with a constant breeze performs very well IMO.
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline jgentry

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But just thinking about it, I bet this is the reason why RainWise hasn’t produced a FARS version of the MK III.
Even if that's true, which I highly doubt, I don't care if fans are bad for the humidity portion of the sensor, I'll never quit using one til something comes along that's superior.
The benefits a FARS to me far outweighs the potential negative.

I was thinking about that also. But then I remembered the RM Young dual sensor temp/hum they run in aspirated shields. Maybe we took the fact because ASOS doesn't aspirate humidity it wasn't done.
Just look at sensor on the RMY temperature tracker and shields they offer both passive and aspirated for the dual sensor probe.

If we are able to get a good SHT-31 (purely new one) with the Sensirion filter cap, I think we would be in good shape, even with FARS. The only thing is that we will need to switch them out around 9-12 months due to constant high humidities aging the sensor.
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline ValentineWeather

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RM YOUNG Temperature tracker they suggest the passive shield with the dual sensor.  ](*,)
Welp maybe I was thinking wrong.
Randy

Offline jgentry

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RM YOUNG Temperature tracker they suggest the passive shield with the dual sensor.  ](*,)
Welp maybe I was thinking wrong.

Probably the most idealistic set-up to keep contaminates out of the sensor, and slowing down the aging process of the sensor.

But according to jerryg, he doesn’t have any problems since he has Sensirion’s filter cap protecting the sensor.
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline kcidwx

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So my daughter was on my computer reading this thread and saw the complaints about the SHT-31 not going to 100%. It started raining here a little while ago and she wanted me to share that her weather station goes to 100%. She said maybe you guys should buy one like hers.  :lol:

Hers is a Weather Monitor II.  :lol:  She thinks it's pretty neat she's the only one around here that gets to 100% on WU.  :lol:





My Vaisala HMT337 a few feet away is showing 99.5%. Typically, hers is running about +3% over my HMT337.
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Offline jgentry

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So my daughter was on my computer reading this thread and saw the complaints about the SHT-31 not going to 100%. It started raining here a little while ago and she wanted me to share that her weather station goes to 100%. She said maybe you guys should buy one like hers.  :lol:

Hers is a Weather Monitor II.  :lol:  She thinks it's pretty neat she's the only one around here that gets to 100% on WU.  :lol:





My Vaisala HMT337 a few feet away is showing 99.5%. Typically, hers is running about +3% over my HMT337.


Hahaha.  Tell her that they don’t make em’ like they used too. Shoot, that’s not bad considering how old the WM II is.
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline jgentry

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So my daughter was on my computer reading this thread and saw the complaints about the SHT-31 not going to 100%. It started raining here a little while ago and she wanted me to share that her weather station goes to 100%. She said maybe you guys should buy one like hers.  :lol:

Hers is a Weather Monitor II.  :lol:  She thinks it's pretty neat she's the only one around here that gets to 100% on WU.  :lol:





My Vaisala HMT337 a few feet away is showing 99.5%. Typically, hers is running about +3% over my HMT337.

One of my VP2s (SHT-31 in passive shield) reached 100% for the first time this morning. Will note that it’s a new sensor (only around a month old).
« Last Edit: July 14, 2018, 08:22:44 AM by jgentry »
Davis Vantage Pro2. SHT 31. 24hr FARS. WU: KXALJEMI2 & KALTHORS2 CWOP: C6353 & C6358

  

Offline jerryg

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Update on sf2 and Davis filter at same time. When i put new sensor in use on my main station i used the sf2 filter, the same has been in use on the old sensor for a year, i removed the sf2 from the old and put the Davis in place of it for comparison with the new sensor. Well the sf2 filter specs say the sensor performance is the same with or without the filter so i put the sf2 back on the old sensor with the Davis filter on also. I can not see any difference in performance of the old sensor readings with both filters in use. It looks like it could give added protection in high dust and humidity areas. I figured the manufacturer says the sf2 does not have any effect on the sensor readings that maybe it would be worth a try even though the bigger filter does add some lag time on the readings. It is hard to measure lag time using the Davis set up because of the high sampling rates of the temp and humidity readings. Since i started using the sf2 i have not had any humidity related problems like i did when using the big Davis filter. I will never run a sensor without the sf2 in place. I am going to let the test sensor run for some time with both filters in place to see if anything shows up down the road.

Offline kcidwx

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So my daughter was on my computer reading this thread and saw the complaints about the SHT-31 not going to 100%. It started raining here a little while ago and she wanted me to share that her weather station goes to 100%. She said maybe you guys should buy one like hers.  :lol:

Hers is a Weather Monitor II.  :lol:  She thinks it's pretty neat she's the only one around here that gets to 100% on WU.  :lol:





My Vaisala HMT337 a few feet away is showing 99.5%. Typically, hers is running about +3% over my HMT337.


Hahaha.  Tell her that they don’t make em’ like they used too. Shoot, that’s not bad considering how old the WM II is.

I picked it up on eBay a couple years ago new in the box with three extra temp/humidity sensors still sealed in the package for $125. I thought it would be a good starter weather station for her. I'm very impressed with it. She wants a VP2 6163 for Xmas because she wants (as she calls it) the "sun" sensor. I told her she needs to have a better reason than that. So I told her she needs to justify getting a VP2 in a technical paper presented to me on how the VP2 6163 will enhance her weather watching. She also needs to explain the pros and cons of switching from the WM II to the VP2 including outlining the sensor specs. She also needs to identify any common problems people are having with the VP2 and if there is a solution to those problems. If no solution is available, then how does she plan to live with that problem. I know the SHT-31 not going to 100% will drive her crazy  :lol: So she's been doing a lot of research on here. I gave her until October 1st to finish the paper. Then we'll see if she still wants a VP2. Yes, I expect a lot out of my 4th grader.  :lol:

« Last Edit: July 14, 2018, 11:00:56 AM by kcidwx »
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Offline ValentineWeather

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Update on sf2 and Davis filter at same time. When i put new sensor in use on my main station i used the sf2 filter, the same has been in use on the old sensor for a year, i removed the sf2 from the old and put the Davis in place of it for comparison with the new sensor. Well the sf2 filter specs say the sensor performance is the same with or without the filter so i put the sf2 back on the old sensor with the Davis filter on also. I can not see any difference in performance of the old sensor readings with both filters in use. It looks like it could give added protection in high dust and humidity areas. I figured the manufacturer says the sf2 does not have any effect on the sensor readings that maybe it would be worth a try even though the bigger filter does add some lag time on the readings. It is hard to measure lag time using the Davis set up because of the high sampling rates of the temp and humidity readings. Since i started using the sf2 i have not had any humidity related problems like i did when using the big Davis filter. I will never run a sensor without the sf2 in place. I am going to let the test sensor run for some time with both filters in place to see if anything shows up down the road.

Might be on to something Jerry. Aspiration helps sensor go out fast so the dual filter makes sense.

Maybe doubling up on the Davis fiter material would also be a huge benefit. Instead of 1 have 2 or 3 of the filters inside the filter housing.  :idea: Much easier than gluing Sf2 on I would think and safer not knowing what toxic fumes could be produced with whatever glue or sealer you use. I'm not worried about a little lag time it's still going to be much faster than any passive setup.
Randy

Offline jerryg

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True about glue out gassing but the putty i used is several years old an came in a coil separated by paper to keep it from sticking to itself, so any gassing has long passed. I really like the fact that the sf2 has no effect on the sensor performance. The Davis filter is so large it takes up a lot of room in the sensor chamber an collects a lot of moisture on it so the humidity readings are slow to come down from high readings but once the chamber has dried out along with the filter then the filter becomes less of a problem.

Offline ValentineWeather

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Would doubling the Davis filter increase the filtration? I really believe these sensors are losing calibration because of dust contamination. High humidity plays its role also but seems more likely dust is main issue with the aspiration.

I realize it may slow response time down some but for many here could be better option vs taking a chance with gaseous chemical damaging sensor.
Just thoughts  :idea:
Randy

Offline jerryg

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The only way to know is try it and see how much lag it might add. Here is a putty like mine that should work keeping in mind that it takes a teeny bit to mount the filter. https://www.truevalue.com/plumbers-putty?ctplacement=176385-43411605579&cid=gooshop  Should be enough to mount thousands of filters lol. My main concern was that in long periods of high humidity the sensor was getting wet with the Davis filter and causing the sensor to go bonkers with the readings until it dried out. With the sf2 and getting rid of the high velocity fan and going back to the Davis fan running on ac i have not had that problem anymore.

Offline openvista

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With the sf2 and getting rid of the high velocity fan and going back to the Davis fan running on ac i have not had that problem anymore.

The Davis fan sucks, to be blunt. They break constantly and are way overpriced. You can always cut the velocity of a much more durable fan intended for the elements (the Davis fan is an indoor fan!) using a variable fan controller like Randy linked to upthread.

I wonder if anyone has considered drilling two tiny holes in the board and mounting the SF2 with the provided clips rather than cutting them off. Is there a way to avoid traces in the PCB?
Davis Vantage Pro2 FARS | https://marquetteweather.com | EW7933

Online JudinNorman

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After this latest fiasco with VP2 are any of you thinking about going to another maker? Or do you all have to much invested in Davis products to just abandon?

Seems like a lot of us got lured to Davis for its price. We humans don't like the cheapest option nor the expensive so we went in so called middle with Davis who promotes a professional station

I'm considering a Rain wise.

Offline ValentineWeather

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I think RW humidity has same issue and the temperature has no aspiration. As much as we bitch Davis is still best product out there and they know it.
Randy

Offline kcidwx

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Before I put eval board #3 outside and ruined it, I did another 100% humidity test in the chamber. Your best bet for hitting 100% is right out of the box on day one because it just goes downhill from there.

Temperatures are very consistent across all three but did go up some over time.

Chamber Conditions
Humidity: 100.0%
Temperature: 83.0°F





« Last Edit: July 14, 2018, 01:47:11 PM by kcidwx »
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Offline ValentineWeather

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Yesterday I hit 99% on my new sensor today max 98%...Tomorrow?
I did just pull it out and double filtered with the Davis filters.
Randy

Offline openvista

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Before I put eval board #3 outside and ruined it, I did another 100% humidity test in the chamber. Your best bet for hitting 100% is right out of the box on day one because it just goes downhill from there.

Temperatures are very consistent across all three but did go up some over time.

Chamber Conditions
Humidity: 100.0%
Temperature: 83.0°F




Wait a minute. Are these drifting UP in temperature over time? Looks like they started with a cold bias and now have a warm bias. Sensirion says they should be within 0.36F so these sensors would be out of spec. That's assuming the chamber temperature is exactly accurate and not drifting itself.
Davis Vantage Pro2 FARS | https://marquetteweather.com | EW7933

Offline ValentineWeather

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I saw that humidity and temperature are out of specs. 
Randy

Offline jerryg

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Really the readings are in spec, temp is +- .5f and humidity is typically +-2% but can run up higher to 3% or so.

 

anything