Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 107791 times)

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Offline jerryg

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Well it looks to me like none of the sensors like it cold  :lol:. You need to move down here where freezing temps are a rarity. The meter has been steady on -3.9 and the 31 has been holding at -2.9 no better than the 75. It looks like in cold weather areas you need to cull out the sensors to find one like the first 31. Heck you get down to that temp what difference does a degree or to make anyway, cold is cold  :lol:.

Offline ValentineWeather

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Nice obs Randy. I'll probably get a new 31 and swap it out from the 75 before we start getting well below freezing. I still like the idea of the low thermal mass pin model, but I'll have to wait for the 35. rdsman is doing good work over in that other thread with reading the data from the 35.

Really, I need to visit but so busy over here. LOL

Yeah this was good info for those running the 75 and have an occasional below zero day. I average over 20 a year so it's a little much so will also swapp the 75 for the 31 come cold weather unless we get other options like the 35.
Randy

Offline ValentineWeather

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Well it looks to me like none of the sensors like it cold  :lol:. You need to move down here where freezing temps are a rarity. The meter has been steady on -3.9 and the 31 has been holding at -2.9 no better than the 75. It looks like in cold weather areas you need to cull out the sensors to find one like the first 31. Heck you get down to that temp what difference does a degree or to make anyway, cold is cold  :lol:.

Most of my family is down in Houston area. But I live in weather paradise right here.. :lol:
Randy

Offline ValentineWeather

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Final graph on low temperature test.
 [ You are not allowed to view attachments ]
Randy

Offline CW2274

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Frankly, at -11F, I was quite impressed with the 31. Even the dew seemed to play along with the 75.

Offline jerryg

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Man Randy if you consider -30 weather heaven then i think you brain froze at some point  :lol:

Offline CW2274

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Man Randy if you consider -30 weather heaven then i think you brain froze at some point  :lol:
Took the words right outta my mouth, then I thought about the three or four days in a row last year I was over 116F and decided to  :-$.

Offline jerryg

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Update subzero  meter -5.2  three 31's read -5.4   -5.5    and the worst one -6.0

Offline ValentineWeather

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I've ran multiple 31's since they came out (usually 3 different stations together) and the one thing I like besides accuracy on temperature new or old given exact same conditions they will run .1f or less of each other for hours usually at night where conditions are the same. Nothing like the old 11 and 15's where you could have new sensors running 1/2 degree apart.

Testing these passive shields has changed the consistency a little. All were fars units prior and now I have 3 different passives and only 1 fars running. 
« Last Edit: August 29, 2018, 06:28:33 AM by ValentineWeather »
Randy

Offline jerryg

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I always thought that about the 31 but i have been watching my 3 75's for the last hour and they too have been sitting on 77.0 and 94% humidity with a .1 temp difference now and then. It looks like the 75 has that same ability before the sun comes up and changes things. So 75 in warmer times and 31 in colder times for temp. Like you said it should double the useful life of your sensors using them 6 months out of the year.  :grin:

Offline ValentineWeather

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Yes IMO the 76  75 is solid performer where humidity plays a big role which happens to be where most people live because of man's attraction to water which was once needed for commerce and travel.
« Last Edit: August 29, 2018, 11:21:27 AM by ValentineWeather »
Randy

Offline jgentry

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Yes IMO the 76  75 is solid performer where humidity plays a big role which happens to be where most people live because of man's attraction to water which was once needed for commerce and travel.

It would be interesting to see how the 75 performs in the 0°-30°F range. Based from another thread, it seems like the 75 performs well when temps are in the upper 20s in comparison with the 35
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Offline dendrite

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I don't think that was a temp comparison or that it had anything to do with temp accuracy. It's his attempt to convert the I2C to sensibus. He's trying to understand how the 75 is read and adapt the 35 to that. Basically he has it down to 0.0-0.1F and 0.0-0.1% RH. IOW, what the 75 would report as say 85.4F, the 35 would read it as 85.3F or 85.4F. So there is probably some 0.05F error in there which he is trying to fine tune. Personally, a 0.0-0.1F conversion error on top of the 0.1-0.2F sensor accuracy is good enough for me.

Offline jgentry

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I don't think that was a temp comparison or that it had anything to do with temp accuracy. It's his attempt to convert the I2C to sensibus. He's trying to understand how the 75 is read and adapt the 35 to that. Basically he has it down to 0.0-0.1F and 0.0-0.1% RH. IOW, what the 75 would report as say 85.4F, the 35 would read it as 85.3F or 85.4F. So there is probably some 0.05F error in there which he is trying to fine tune. Personally, a 0.0-0.1F conversion error on top of the 0.1-0.2F sensor accuracy is good enough for me.

Aight. Gotcha.
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Offline rdsman

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I don't think that was a temp comparison or that it had anything to do with temp accuracy. It's his attempt to convert the I2C to sensibus. He's trying to understand how the 75 is read and adapt the 35 to that. Basically he has it down to 0.0-0.1F and 0.0-0.1% RH. IOW, what the 75 would report as say 85.4F, the 35 would read it as 85.3F or 85.4F.

You are correct sir..........
 I probably need to amend that post!
Ray

Offline ValentineWeather

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For those interested in the sht75 and may not have soldering skills or any luck with the crimping version, I've found this option. Haven't done this myself however so nothing confirmed.
The plug/cord was made for the sht75.... called 3M-CABLES FOR EK-H4 made for evaluation kit.
 
The plug is 3 meters and rather expensive at $80. You only need 1 however as the sensors go bad just replace the SHT75.
Looks like the connector on the stock plugs is the RJ12 which has 6 gold connectors. Only 4 will be used however. You will need to figure out which 4 go where for the sensor to work and crimp plug accordingly with tool.

I referenced this video about plugs on youtube to determine what was being used. The stock sht31 plug has 6 contacts the red and black are not connected to the SHT31 sensor.

Youtube video on plugs: https://www.youtube.com/watch?v=fjNCUDrdULw

Link to sht75 plug/cord sold by digikey: https://www.digikey.com/product-detail/en/sensirion-ag/3M-CABLES-FOR-EK-H4/1649-1055-ND/5982944

Anyone with more knowledge please chime in on this.
Randy

Offline ValentineWeather

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Yesterday the SHT75 and 31 temperature were the same all day within .3F because wind speeds were up so humidity should have also followed and been the same. They weren't. 
This is graph shows humidity difference throughout day. As you can see morning and evening are the same but during critical time of day when temperatures go up the 75 runs in normal range vs the 31 averaging about 5% higher sometimes more sometimes less.  DP averages about 2°F higher on 31 also. 
Randy

Offline openvista

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For those interested in the sht75 and may not have soldering skills or any luck with the crimping version, I've found this option. Haven't done this myself however so nothing confirmed.
The plug/cord was made for the sht75.... called 3M-CABLES FOR EK-H4 made for evaluation kit.
 
The plug is 3 meters and rather expensive at $80. You only need 1 however as the sensors go bad just replace the SHT75.
Looks like the connector on the stock plugs is the RJ12 which has 6 gold connectors. Only 4 will be used however. You will need to figure out which 4 go where for the sensor to work and crimp plug accordingly with tool.

I referenced this video about plugs on youtube to determine what was being used. The stock sht31 plug has 6 contacts the red and black are not connected to the SHT31 sensor.

Youtube video on plugs: https://www.youtube.com/watch?v=fjNCUDrdULw

Link to sht75 plug/cord sold by digikey: https://www.digikey.com/product-detail/en/sensirion-ag/3M-CABLES-FOR-EK-H4/1649-1055-ND/5982944

Anyone with more knowledge please chime in on this.

According to the datasheet (https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/0_Datasheets/Humidity/Sensirion_Humidity_Sensors_EK-H4_Datasheet.pdf), the cable terminates in an RJ45 jack. So you would need to chop that off and splice it into the end of a 31/15/11 sensor cable or the like.

Also might want to put some conformal coating over the sensor end of the cable too to prevent water ingress.
Davis Vantage Pro2 AC FARS | https://marquetteweather.com | EW7933

Offline ValentineWeather

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For those interested in the sht75 and may not have soldering skills or any luck with the crimping version, I've found this option. Haven't done this myself however so nothing confirmed.
The plug/cord was made for the sht75.... called 3M-CABLES FOR EK-H4 made for evaluation kit.
 
The plug is 3 meters and rather expensive at $80. You only need 1 however as the sensors go bad just replace the SHT75.
Looks like the connector on the stock plugs is the RJ12 which has 6 gold connectors. Only 4 will be used however. You will need to figure out which 4 go where for the sensor to work and crimp plug accordingly with tool.

I referenced this video about plugs on youtube to determine what was being used. The stock sht31 plug has 6 contacts the red and black are not connected to the SHT31 sensor.

Youtube video on plugs: https://www.youtube.com/watch?v=fjNCUDrdULw

Link to sht75 plug/cord sold by digikey: https://www.digikey.com/product-detail/en/sensirion-ag/3M-CABLES-FOR-EK-H4/1649-1055-ND/5982944

Anyone with more knowledge please chime in on this.

According to the datasheet (https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/0_Datasheets/Humidity/Sensirion_Humidity_Sensors_EK-H4_Datasheet.pdf), the cable terminates in an RJ45 jack. So you would need to chop that off and splice it into the end of a 31/15/11 sensor cable or the like.

Also might want to put some conformal coating over the sensor end of the cable too to prevent water ingress.

So should work no problem with a crimping tool $13 and RJ12 jack?
Randy

Offline openvista

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For those interested in the sht75 and may not have soldering skills or any luck with the crimping version, I've found this option. Haven't done this myself however so nothing confirmed.
The plug/cord was made for the sht75.... called 3M-CABLES FOR EK-H4 made for evaluation kit.
 
The plug is 3 meters and rather expensive at $80. You only need 1 however as the sensors go bad just replace the SHT75.
Looks like the connector on the stock plugs is the RJ12 which has 6 gold connectors. Only 4 will be used however. You will need to figure out which 4 go where for the sensor to work and crimp plug accordingly with tool.

I referenced this video about plugs on youtube to determine what was being used. The stock sht31 plug has 6 contacts the red and black are not connected to the SHT31 sensor.

Youtube video on plugs: https://www.youtube.com/watch?v=fjNCUDrdULw

Link to sht75 plug/cord sold by digikey: https://www.digikey.com/product-detail/en/sensirion-ag/3M-CABLES-FOR-EK-H4/1649-1055-ND/5982944

Anyone with more knowledge please chime in on this.

According to the datasheet (https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/0_Datasheets/Humidity/Sensirion_Humidity_Sensors_EK-H4_Datasheet.pdf), the cable terminates in an RJ45 jack. So you would need to chop that off and splice it into the end of a 31/15/11 sensor cable or the like.

Also might want to put some conformal coating over the sensor end of the cable too to prevent water ingress.

So should work no problem with a crimping tool $13 and RJ12 jack?

You wouldn't need to crimp if you can re-purpose an existing Davis sensor cable. But if you want to go with a fresh RJ12 plug, then, yes, you'd need to wire in the jack appropriately.

Here's the guide for the Davis cable:
White (clock)
Yellow (vdd)
Green (gnd)
Blue (data)

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Offline ValentineWeather

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Good deal Jerry just PM'd me, I was asking him for direction on this also.  He said another option is just splice old plug directly no crimping tool necessary. 
Randy

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1146 on: September 01, 2018, 06:59:29 PM »
Waiting on the glue to dry. The connector is definitely flimsy and you would need the board for support. This is going to be installed in my station at my friend’s farm with the Davis stock passive shield.

I’m now curious if the Campbell Scientific version of the 75 would work with the Davis transmitter? If I could use the CS version (which is a probe) for the MeteoShield Pro shield, that would be awesome.
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Offline dendrite

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1147 on: September 01, 2018, 10:13:37 PM »
So what are the observations of the 75 so far? I like mine (sitting at 59.1F and 97% RH @ 10pm right now) and will probably stick with it until November. Unfortunately I feel we'll be waiting awhile for a pin SHT35 although if we could get the i2c to sensibus converter we could use that breakout from Closed Cube.

https://www.tindie.com/products/closedcube/sht35-d-digital-humidity-and-temperature-sensor/

Anyway, hope all of you are seeing RH readings more in spec with the 75.

Offline dendrite

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1148 on: September 01, 2018, 10:29:26 PM »
Yesterday the SHT75 and 31 temperature were the same all day within .3F because wind speeds were up so humidity should have also followed and been the same. They weren't. 
This is graph shows humidity difference throughout day. As you can see morning and evening are the same but during critical time of day when temperatures go up the 75 runs in normal range vs the 31 averaging about 5% higher sometimes more sometimes less.  DP averages about 2°F higher on 31 also.
Just saw this. I noticed your dewpoint charts on Gladstone are right in line and you've been running neck and neck generally with VTN.

Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1149 on: September 02, 2018, 09:00:11 AM »
Better vs 31 on humidity. I'll swap 75 for 31 in November for temperature. I may keep 75 in one of the shields so differences can be logged at low temperatures . At -11 we know its reading +2 high and seemed to bottom out at +2 but without a colder deep freeze won't know for sure.
Randy