Author Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?  (Read 31513 times)

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Online jerryg

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1150 on: September 02, 2018, 10:18:42 AM »
Well i can not be sure but i think i just had a 75 fall victim to the fars, i had a new 75 running in the fars for comparison and it hit 99 a couple times but alas it now won't go over 95 percent sometimes bumps 96. We had several nights of light fog and the humidity was high for quite a while each night and now low humidity readings. I am going to try drying and hydrating it to see what happens.

Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1151 on: September 02, 2018, 10:34:47 AM »
Well i can not be sure but i think i just had a 75 fall victim to the fars, i had a new 75 running in the fars for comparison and it hit 99 a couple times but alas it now won't go over 95 percent sometimes bumps 96. We had several nights of light fog and the humidity was high for quite a while each night and now low humidity readings. I am going to try drying and hydrating it to see what happens.

Are 75's no better with prolonged high humidity? Seems like they should reset after awhile.
I would swap it out and put in DIY test chamber or wet rag test and see what it will do. 
Randy

Online jerryg

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1152 on: September 02, 2018, 11:06:04 AM »
Maybe i am just unlucky lol, i did put it in my tester and it maxed out at 95 so i am letting it dry in oven for most of the day and will try it again. Hope it comes alive again. It may just have been a bad sensor.

Offline hwcorder

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1153 on: September 02, 2018, 11:07:46 AM »
Maybe i am just unlucky lol, i did put it in my tester and it maxed out at 95 so i am letting it dry in oven for most of the day and will try it again. Hope it comes alive again. It may just have been a bad sensor.

Were you using the stock filter or something else?

Online jerryg

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1154 on: September 02, 2018, 11:15:23 AM »
Using the factory filter sf1.

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1155 on: September 02, 2018, 11:24:36 AM »
Well i can not be sure but i think i just had a 75 fall victim to the fars, i had a new 75 running in the fars for comparison and it hit 99 a couple times but alas it now won't go over 95 percent sometimes bumps 96. We had several nights of light fog and the humidity was high for quite a while each night and now low humidity readings. I am going to try drying and hydrating it to see what happens.

Was it installed in your RM Young FARS?
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1156 on: September 02, 2018, 11:28:13 AM »
Maybe i am just unlucky lol, i did put it in my tester and it maxed out at 95 so i am letting it dry in oven for most of the day and will try it again. Hope it comes alive again. It may just have been a bad sensor.

Were you using the stock filter or something else?

hwcorder, whenever you get a chance, check your PM. Got a question about Campbell Scientific. Thanks!
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline hwcorder

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1157 on: September 02, 2018, 11:28:39 AM »
Using the factory filter sf1.

Hmmm, hopefully just a fluke then.  Mine recently has been topping out slightly lower about 96-97% as opposed to the 98% it used to.  Its about two years old however.  Probably time to switch it out but it does so well in the lower to mid range I've been putting it off.

Online jerryg

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1158 on: September 02, 2018, 11:33:41 AM »
It was in the standard Davis fars with stock fan.

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1159 on: September 02, 2018, 12:27:03 PM »
It was in the standard Davis fars with stock fan.

Oh wow. Let’s just hope it was a bad sensor.
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Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1160 on: September 02, 2018, 07:07:08 PM »
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.

Wonder if you can get this thing cheaper? So far, I’ve not been able to find it. With the help of my step father, we must’ve screwed something up. My 75 tells me it’s -40° to -70°. Lol
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Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1161 on: September 02, 2018, 07:24:51 PM »
Was it tested and working prior to sealing?

Sounds like the numbers I was getting so after I destroyed all connectors (5) gave up.
Randy

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1162 on: September 02, 2018, 07:28:25 PM »
Was it tested and working prior to sealing?

Sounds like the numbers I was getting so after I destroyed all connectors (5) gave up.

Foolishly had it sealed up before testing but was able to take the sensor itself off the mounting board. It does have some glue on the back of the sensor though.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Online jerryg

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1163 on: September 02, 2018, 08:28:18 PM »
Plug the sensor back in and press down on the connector i had one that went flaky on the reading and it would come and go when i pressed on the plug. Those teeth that bite into the wires are sort of flimsy.

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1164 on: September 03, 2018, 07:00:39 AM »
Valentine, I see where your 75 finally went up to 100%
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Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1165 on: September 03, 2018, 07:44:45 AM »
Valentine, I see where your 75 finally went up to 100%

Actually it didn't, what you see is my SHT31 on FARS. Little disappointed in the 75's ability to go beyond 97% in passive shield.
I think it would make 98% in FARS however because there is zero wind not even whisper at ground level.
Dense fog this morning so should of been there. Truthfully these SHT75 are no better than the 31's it's a crap shoot whether sensor can reach even 98%. Where they are superior is the no high humidity bias but for cold climates inferior on temperature. Too bad we don't have a sensor that can do it all.

If sensor makes 98% Cumulus will display 100%. I have another 31 that goes to 100% every time at remote station inside a PRO shield also.
Randy

Offline jgentry

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1166 on: September 03, 2018, 08:17:19 AM »
Valentine, I see where your 75 finally went up to 100%

Actually it didn't, what you see is my SHT31 on FARS. Little disappointed in the 75's ability to go beyond 97% in passive shield.
I think it would make 98% in FARS however because there is zero wind not even whisper at ground level.
Dense fog this morning so should of been there. Truthfully these SHT75 are no better than the 31's it's a crap shoot whether sensor can reach even 98%. Where they are superior is the no high humidity bias but for cold climates inferior on temperature. Too bad we don't have a sensor that can do it all.

If sensor makes 98% Cumulus will display 100%. I have another 31 that goes to 100% every time at remote station inside a PRO shield also.

Oh wow.  That’s a bummer!
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1167 on: September 03, 2018, 08:24:19 AM »
Like I said had 75 been inside the fars it would make another 1% 98% no problem from all my observations fars does better on mornings with no wind.
I've only had 1 sensor out of maybe a dozen ever reach 100% on its own and that's the sensor at remote site now. Thinking of bringing it back home as main unit.
How long it last is  :?:.
Randy

Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1168 on: September 03, 2018, 09:01:25 AM »
3 of 4 shields hit 98% finally. Takes longer on passive shields vs the fars. All have 31's, I will go back to the 75's next spring.  :-(
Randy

Offline dendrite

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1169 on: September 03, 2018, 09:46:42 AM »
4 mornings in a row with 99/100% at my place. I guess YMMV. Anyone test a psychrometer or the acurites in those 97/98% conditions?

Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1170 on: September 03, 2018, 10:03:36 AM »
4 mornings in a row with 99/100% at my place. I guess YMMV. Anyone test a psychrometer or the acurites in those 97/98% conditions?

Under porch the acurite hit 98%
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Randy

Offline hwcorder

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1171 on: September 03, 2018, 11:46:04 AM »
From my experience with any of these sensors whether it be the sht 15, 75, or 31 if it doesn't have a wet bias in the low to mid RH it will usually not read above 98%.  If it does reach the 99% to 100% it tends to read too wet a lower values. Very rare does it seem like I find a sensor that does both.  My preference is to have better accuracy in the mid ranges than to have a sensor that reads 100%, but that"s just me. 

Online jerryg

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1172 on: September 03, 2018, 01:05:00 PM »
I agree, i don't believe in our price range we will ever get the perfect sensor. I got over the must have 100% reading a while ago and temp. is pretty straight forward in the normal range, so have leaned toward best dp reading. What is most important anyway 100% reading on humidity accurate temp. or best dp?

Offline ValentineWeather

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1173 on: September 03, 2018, 04:59:26 PM »
Something different, have the SHT75 back in service but this time inside FARS. FARS sensor chamber is big enough for the skinny 75 and big 31 at same time. So should I feel a need to swap over to 31 it will be quick and easy.

Added extension on the 75 also so can reach TX1 easily without moving transmitters around.
Randy

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Re: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?
« Reply #1174 on: September 03, 2018, 06:34:32 PM »
Something different, have the SHT75 back in service but this time inside FARS. FARS sensor chamber is big enough for the skinny 75 and big 31 at same time. So should I feel a need to swap over to 31 it will be quick and easy.

Added extension on the 75 also so can reach TX1 easily without moving transmitters around.

Has anybody tried using a short 1-2 foot RJ45 male/female extension cable between the ISS and sensor to eliminate having to open the ISS each time while changing between sensors?

If yes, where did you get it from?
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