Topic: Sensirion SHT-75 is now unavailable

[ValentineWeather]

Here is the doc. about it when mixing older sensors with post 2016 transmitters or vice versa. 

Using a new transmitter with an old temperature humidity sensor will result in
·         Temperature reading 0.5C (0.9F) low.

Using an old transmitter with an new temperature humidity sensor will result in
·         Temperature reading 0.5C (0.9F) high.

[ValentineWeather]

The 75 is anywhere from 2-5% lower on humidity. Occasionally they will read the same but rare. Both are in same shield being aspirated by fan. The 75 is much more responsive to changes sometimes as much as 1° difference in temperature for just a few seconds. I prefer the 75 when its not going below 0F.
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[ValentineWeather]

For anyone still wanting to try the 75 like Drew did I'll refer you to this post with link to premade SHT75 plugs. All you need to do is change the jack to RJ12.
Don't forget the (.9F) offset when using new transmitter.

When you order through Digikey you will get (4) -6' long sensor plugs per order.
For filter I use 100 mesh silk, anything from 100-300 will work with plenty of airflow. I'm not in a real wet environment but have had no issues with moisture using the 100 mesh.

https://www.wxforum.net/index.php?topic=34658.msg360823#msg360823

100 Mesh I purchased wrapped with sewing thread to cover sensor completely. Enough here to cover many sensors.

https://www.amazon.com/gp/product/B00JOYKV9I/ref=oh_aui_search_asin_title?ie=UTF8&psc=1

[drew1021]

Yeah definitely more responsive than the 31

[ValentineWeather]

Something I've noticed since putting the SHT75 inside the FARS with the 31 it averages around 1F more on peak temperatures because of response time being so much better. I'm actually closer to airport ASOS using the 75 vs the SHT31. 

Now I'm understanding why this sensor is considered a meteorological grade and used by Campbell Scientific.

Quote: The unique design of the SHT75 allows for the best possible thermal coupling to the environment and decoupling from potential heat sources on the main board. In combination with the individual precision calibration, the on-chip calibration memory, and the digital two-wire interface, this guarantees the best possible sensor performance in demanding applications with easy and fast system integration.

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[jgentry]

Something I've noticed since putting the SHT75 inside the FARS with the 31 it averages around 1F more on peak temperatures because of response time being so much better. I'm actually closer to airport ASOS using the 75 vs the SHT31. 

Now I'm understanding why this sensor is considered a meteorological grade and used by Campbell Scientific.

Quote: The unique design of the SHT75 allows for the best possible thermal coupling to the environment and decoupling from potential heat sources on the main board. In combination with the individual precision calibration, the on-chip calibration memory, and the digital two-wire interface, this guarantees the best possible sensor performance in demanding applications with easy and fast system integration.

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I’m definitely not regretting my switch to the 75. Still disappointed with its wet bias in the mid ranges but it’s nowhere near as bad as the 31. But then again, my humidity is up and down all the time. I’m sure more stable and drier environments, the sensors performs even better. Even though my high end humidities will be off, I’ll take only calibrating -4% over -8%-10%.

Has anyone on this forum used Bosch temp/hum/pressure sensors? If so, how does it compares to Sensirion?

[PSJohn]

Do you guys mind me asking for a little background on the VP2 pertaining to the different sensors(31,75)?

What sensor does Davis use for the VP2? (I purchased mine in 4/2014). Is it the 21?

I have seen where one can purchase the 31 and it is a "simple" swap, you plug it in to the ISS, adjust +.9° and your good. Can you purchase the 75 with is being "VP2 ready" or do you need additional steps to make it work(plug, mount to board, etc)?

thanks all

[ValentineWeather]

Do you guys mind me asking for a little background on the VP2 pertaining to the different sensors(31,75)?

What sensor does Davis use for the VP2? (I purchased mine in 4/2014). Is it the 21?

I have seen where one can purchase the 31 and it is a "simple" swap, you plug it in to the ISS, adjust +.9° and your good. Can you purchase the 75 with is being "VP2 ready" or do you need additional steps to make it work(plug, mount to board, etc)?

thanks all

In 2014 you should have the SHT15.
Yes to upgrade from the 15 to 31 is simple plug and play and make adjustment -.9 being you are using the older transmitter with new SHT31.
 
The SHT75 is an older sensor so no adjustment would be needed. However going to the SHT75 gets more complicated you need the 6' plug available from digikey to use the SHT75 or be very skilled at soldering.  If you go with the plug purchased through digikey order just 1, it includes 4 plugs per order. $80

The link I posted above shows how to wire the required RJ12 jack needed to plug into the Davis ISS. 

[CW2274]

Do you guys mind me asking for a little background on the VP2 pertaining to the different sensors(31,75)?

What sensor does Davis use for the VP2? (I purchased mine in 4/2014). Is it the 21?

I have seen where one can purchase the 31 and it is a "simple" swap, you plug it in to the ISS, adjust +.9° and your good. Can you purchase the 75 with is being "VP2 ready" or do you need additional steps to make it work(plug, mount to board, etc)?

thanks all

In 2014 you should have the SHT15.

I'm not positive Randy, but I don't think the 15 was ever OE, the 11 switched directly to the 31. In my case, the 15 I used I had installed to replace the 11. Only way to know for sure is to look.

[ValentineWeather]

Could be the 15 was available in 2014 for sure, maybe it was always just an upgrade. If so his 2014 has the SHT11.

[CW2274]

2014 is about the time I had my 15 installed, maybe a year earlier.

[johnd]

SHT15 was standard in Europe for a limited period but never in US AFAIK.

[drew1021]

Well we finally have a day with rain, temperatures in the 50's, humidity in the high 90's, with a 10 mph breeze? I have to be honest I'm not too thrilled with the 75's high end performance. Local ASOS at 0900 this morning was at 96%, my 75 was at 90% and all other local PW stations were between 95-99%. This is with a -3% offset on my vp2. If I corrected the offset to zero then my low end performance would suffer. Maybe I'll just go back to my 31 with its dry low end bias. I know during the summer months when dp's hit the 70-75 degree range then the 75 may shine so I will leave it disconnected and in place for now.

[ValentineWeather]

I've never seen the 75 run below the ASOS unless it was near top 100% range. I use negative bias for lower scale but upper end doesn't suffer using Cumulus (non mx) software.   

[drew1021]

I've never seen the 75 run below the ASOS unless it was near top 100% range. I use negative bias for lower scale but upper end doesn't suffer using Cumulus (non mx) software.

Do you think that I could have a bad sensor? One possible issue could be that I used the mesh from an old Davis sensor cover. I'm expecting the mesh you recommended any day now. I really hate to scrap the idea, especially considering the amount I've invested in it.

[CW2274]

This is with a -3% offset on my vp2. If I corrected the offset to zero then my low end performance would suffer. Maybe I'll just go back to my 31 with its dry low end bias.

Yes, it can be a pain. I run a -2% with my 31, and stays there exclusively until I get above ~93% or below ~5%, then I'm back to no correction at all. I have no correcting software, but make due with what I have. Overall, I can't complain too much, as in between those values it's quite good.

[CW2274]

I've never seen the 75 run below the ASOS unless it was near top 100% range. I use negative bias for lower scale but upper end doesn't suffer using Cumulus (non mx) software.

One possible issue could be that I used the mesh from an old Davis sensor cover.

I personally use the SF2 cap on my 31 and it has been on there for a year now. Don't know if there's an equivalent for the 75 or not.

[drew1021]

This is with a -3% offset on my vp2. If I corrected the offset to zero then my low end performance would suffer. Maybe I'll just go back to my 31 with its dry low end bias.

Yes, it can be a pain. I run a -2% with my 31, and stays there exclusively until I get above ~93% or below ~5%, then I'm back to no correction at all. I have no correcting software, but make due with what I have. Overall, I can't complain too much, as in between those values it's quite good.

Yeah I'm also using a -2% correction factor for my 31. With that I'm experiencing a +4% error between about 30% to 80%. The lowest humidity I've seen around here was 7% and it was right on when compared to local ASOS.

[drew1021]

I don't have the sf2 cap however I'm thinking about replacing the mesh screen in my original cap with the mesh I have coming.

[ValentineWeather]

I've never seen the 75 run below the ASOS unless it was near top 100% range. I use negative bias for lower scale but upper end doesn't suffer using Cumulus (non mx) software.

Do you think that I could have a bad sensor? One possible issue could be that I used the mesh from an old Davis sensor cover. I'm expecting the mesh you recommended any day now. I really hate to scrap the idea, especially considering the amount I've invested in it.

See what happens with the new mesh. Or test without a filter for a few days. You can always get a few backups of the 75's before they are all gone. I've got a stick of 10 I purchased last year for $22 each from a place thats now out. 

I really like the response time and fact they take some (not all) of the humidity bias out.

[drew1021]

I have one extra 75 that I was planning to put in place after the pollen season ends, spring cleaning you know. I'm not too crazy about pulling the ISS down to mess with the sensor again, but I probably will because I just can't resist. I'll keep you informed.And yes, I agree on the response time.

[drew1021]

Does anyone know what part of the 75 sensor does the sensing take place. I'm assuming it's the side with the writing, possibly the rounded section. Also, are there any handling precautions? I.e static protection needed? Gloves?
Thanks,

[CW2274]

The sensor is the black thingy and the slit is where the air is sensed. See "warnings".
https://www.newark.com/sensirion/sht75/humidity-temperature-sensor/dp/18M2988

[drew1021]

OK folks, without going into great detail I will after just two days use, sum up my opinion of the 75 so far. It's GREAT!  Excellent high end and mid range performance. I can't give my opinion on low end performance due to the current airmass over us. Maybe later in the week.
Looks like a keeper to me.

[ValentineWeather]

Great  .