WXforum.net
Weather Station Hardware => Davis Instruments Weather Stations => Topic started by: jgentry on February 25, 2019, 08:39:51 PM
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Looks like the Sensirion SHT-75 is finally unavailable. Will say that sensor did performed better at times than the 31 but overall, performed about the same in terms of humidity IMO. But I’ll rather have the 75 over the 31 anyday.
But if anyone can figure how to get the Davis transmitter or console to work with the HYT-221 sensor from Innovative Sensor Technology, I’ll be eternally grateful.
For those that have used the HYT-221, does it have a wet or dry bias?
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Saw Digikey has a little over 400 left. Just bought a few more just in case.
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Last year Newark had a stick of 10 for $22 each now $29. Just purchase 10 or so and never worry about it, over 1000 in stock. By the time you need new sensors something new will be out. least I'm hoping.
https://www.newark.com/sensirion/sht75/humidity-temperature-sensor/dp/18M2988?MER=bn_level5_5NP_EngagementRecSingleItem_1
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Just for info, i found a site that has a lot of them in stock but it is in China which means they are probably reject sensors lol. They say they are Sensirion sensors so i ordered one just to see if they are any good, free one month shipping lol. The price is good at $21.85 if they work, so will have one here in several weeks and will compare it to good sensor and let everyone know the results.
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Got email this am that sensor has shipped, now we will see how long it takes to get here. :shock:
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[tup] Good.
Hope there not rejects as you mentioned. Or worse Chinese knockoffs like they do with everything else.
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Yea that's the deal, but looking at the pictures the sensor has the Sensirion markings and is in the factory package, so hope everything on the up and up. I wonder if Sensirion culls the sensors by performance and prices them different? They say the sensors are from Sensirion so we shall see. The Chinese or the best knock off artist in the world so who knows.
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
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Well now i am confused, how did you get a analog sensor to work in a digital sensors place? I thought that would not work. Ok did some checking and it looks like the sensor switch happened around the 2006-2007 iss change over and those would do either sensor but not sure if that holds true for later iss boards.
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
100% in agreement with you.
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Well now i am confused, how did you get a analog sensor to work in a digital sensors place? I thought that would not work. Ok did some checking and it looks like the sensor switch happened around the 2006-2007 iss change over and those would do either sensor but not sure if that holds true for later iss boards.
I'm wondering too. Unless he has an old VP unit.
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Hell, I'm so confused on what goes with what anymore, I quit asking...
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When they switched to the digital sensor around 2006, they made the ISS capable of working with the new digital sensor as well as the old analog sensor I presume because they still had analog sensors in the supply chain. The incompatibility comes in with trying to use a digital sensor with a pre-2006 ISS. I had an old analog sensor from a pre-2006 cabled VP2. My current wireless ISS is a 2006 model that came with the SHT11 and is compatible with the old analog sensor.
I believe more recent ISSs up to the current are still compatible with the analog sensor, but I’m not certain, especially after the recent modification for the SHT31. It’s almost irrelevant though as the real trouble is finding an analog sensor as they have been out of production for years now.
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Ok now that makes sense, an older iss. I guess at sometime that backward capability was dropped, doesn't really matter anyway just didn't know you had a iss that old and still working. Have you been using that iss all these years or did you take it out of storage?
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Yeah I wish I would have never gotten rid of my analog sensors now. Another advantage I think they had was that you could perform field calibration using adjustment screws. I wonder if the old temp/hum modules are compatible with newer analog sensors today?
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Ok now that makes sense, an older iss. I guess at sometime that backward capability was dropped, doesn't really matter anyway just didn't know you had a iss that old and still working. Have you been using that iss all these years or did you take it out of storage?
It’s actually been working almost all these years. There were a few years I was living in places I could not have it set up.
Yeah I wish I would have never gotten rid of my analog sensors now. Another advantage I think they had was that you could perform field calibration using adjustment screws. I wonder if the old temp/hum modules are compatible with newer analog sensors today?
The VP2 analog sensor doesn’t have those calibration screws. Those maybe were for the WMII? The humidity element is a 2 pin thin film capacitor. If you could find a manufacturer of the actual element, it could be plug and play. I’ve searched in vain to find a potential replacement if I were to need it, but it seems obsolete. I guess that’s why everyone from Davis to Rainwise have gone to Sensirion. The specs on paper are superior for the digital sensors, but the real world application seems to tell another story.
I’ve reposted pictures from elsewhere on this forum. The blue dot is the thermistor and the thin film humidity element is removable.
Looks like a cheap version of Vaisala
https://store.vaisala.com/eu/vaisala-intercap-humidity-sensor/15778HM/dp
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[quote author=CW7491
The VP2 analog sensor doesn’t have those calibration screws. Those maybe were for the WMII? The humidity element is a 2 pin thin film capacitor. If you could find a manufacturer of the actual element, it could be plug and play. I’ve searched in vain to find a potential replacement if I were to need it, but it seems obsolete. I guess that’s why everyone from Davis to Rainwise have gone to Sensirion. The specs on paper are superior for the digital sensors, but the real world application seems to tell another story.
I’ve reposted pictures from elsewhere on this forum. The blue dot is the thermistor and the thin film humidity element is removable.
Looks like a cheap version of Vaisala
https://store.vaisala.com/eu/vaisala-intercap-humidity-sensor/15778HM/dp
[attachment id=1 msg=372306][attachment id=2 msg=372306]
[/quote]
That "thin film humidity element" is sort of cute, reminds one of a washed sheet flapping on a clothesline (y'all remember your mom doing the laundry?). That's all I got...
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
You’re definitely right about the old sensor! Just looking through your data, it matches up with the airport really well. Sensirion sucks when it comes to humidity.
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Yeah, I’m in Europe for the next week or so for work and I’m unable to spot check with my psychro dyne. It’s too bad too because the low humidity levels the last several days are really anomalous in the Seattle area this time of year. Lots of extreme local effects from proximity to water and downsloping and upsloping winds. By the time I get back, the pattern is likely to pass.
I’ve actually been concerned that it might even be reading too low at low humidity levels, but until I can compare side by side to the psychro dyne, it’s hard to say. I’m located between KTIW and KSEA. I’ve been running right between them for dewpoint. Seems reasonable for the downsloping winds and the proximity to the sound. For anyone interested, I can post the spot check results from the psychro dyne when I am back.
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Yeah, I’m in Europe for the next week or so for work and I’m unable to spot check with my psychro dyne. It’s too bad too because the low humidity levels the last several days are really anomalous in the Seattle area this time of year. Lots of extreme local effects from proximity to water and downsloping and upsloping winds. By the time I get back, the pattern is likely to pass.
I’ve actually been concerned that it might even be reading too low at low humidity levels, but until I can compare side by side to the psychro dyne, it’s hard to say. I’m located between KTIW and KSEA. I’ve been running right between them for dewpoint. Seems reasonable for the downsloping winds and the proximity to the sound. For anyone interested, I can post the spot check results from the psychro dyne when I am back.
I’ll definitely be interested.
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Contacted Davis about switching their temp/hum sensor from Sensirion to theHYT-221 sensor. Will let you know what they say
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Ok got my new 75 sensor in from China today, so it took about 2 weeks to get here, and i have it running in test setup. It is a real Sensirion sensor in the factory packaging and shipped in a static free bag. Now i will let it run for a few days to let it adjust itself and get moistened up. First readings temp looks right on and the humidity is close but needs some time to settle in. The main thing it is a real sensor and it is alive for now lol.
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Here is link to order sensor https://www.aliexpress.com/item/Free-shipping-New-and-original-SENSIRION-Digital-Humidity-Sensor-SHT75-SIP-4-Best-quality/32891484373.html?spm=a2g0s.12269583.0.0.4e21426dUeqTaF
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Using my Kestrel DROP to guide me in this process, I decided to do an offset on my console for humidity by subtracting 3% and my DP is now accurate. Yes, my high humidity readings will be off but overall, my DP will be accurate.
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Using my Kestrel DROP to guide me in this process, I decided to do an offset on my console for humidity by subtracting 3% and my DP is now accurate. Yes, my high humidity readings will be off but overall, my DP will be accurate.
With my 31 I use -2% and it works very well between ~3 to 90%. If I expect significant time outside those extremes, I'll take the correction out then reapply it when necessary.
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Using my Kestrel DROP to guide me in this process, I decided to do an offset on my console for humidity by subtracting 3% and my DP is now accurate. Yes, my high humidity readings will be off but overall, my DP will be accurate.
With my 31 I use -2% and it works very well between ~3 to 90%. If I expect significant time outside those extremes, I'll take the correction out then reapply it when necessary.
With the 31, I had to do 8%. So you must have a good 31
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Using my Kestrel DROP to guide me in this process, I decided to do an offset on my console for humidity by subtracting 3% and my DP is now accurate. Yes, my high humidity readings will be off but overall, my DP will be accurate.
With my 31 I use -2% and it works very well between ~3 to 90%. If I expect significant time outside those extremes, I'll take the correction out then reapply it when necessary.
With the 31, I had to do 8%. So you must have a good 31
After all the chat on here about the 31, I think it's pretty much a foregone conclusion that it's a much better overall performer (humidity wise) in drier climates, and it doesn't get much drier than it does here. It's also been in service over 2.5 years.
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Using my Kestrel DROP to guide me in this process, I decided to do an offset on my console for humidity by subtracting 3% and my DP is now accurate. Yes, my high humidity readings will be off but overall, my DP will be accurate.
With my 31 I use -2% and it works very well between ~3 to 90%. If I expect significant time outside those extremes, I'll take the correction out then reapply it when necessary.
With the 31, I had to do 8%. So you must have a good 31
After all the chat on here about the 31, I think it's pretty much a foregone conclusion that it's a much better overall performer (humidity wise) in drier climates, and it doesn't get much drier than it does here. It's also been in service over 2.5 years.
We have recently had a few very dry days here. Most of the time my 75 runs about 4-7 percent lower than my 31. Once you get to the lower 20% though the 31 rapidly catches up. By the mid to upper teens RH% they read very close to each other. Of course this doesn't occur too much here in the southeast so the 75 is overall supperior sensor her IMHO.
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Using my Kestrel DROP to guide me in this process, I decided to do an offset on my console for humidity by subtracting 3% and my DP is now accurate. Yes, my high humidity readings will be off but overall, my DP will be accurate.
With my 31 I use -2% and it works very well between ~3 to 90%. If I expect significant time outside those extremes, I'll take the correction out then reapply it when necessary.
With the 31, I had to do 8%. So you must have a good 31
After all the chat on here about the 31, I think it's pretty much a foregone conclusion that it's a much better overall performer (humidity wise) in drier climates, and it doesn't get much drier than it does here. It's also been in service over 2.5 years.
We have recently had a few very dry days here. Most of the time my 75 runs about 4-7 percent lower than my 31. Once you get to the lower 20% though the 31 rapidly catches up. By the mid to upper teens RH% they read very close to each other. Of course this doesn't occur too much here in the southeast so the 75 is overall supperior sensor her IMHO.
No doubt the 75 (humidity wise) is better for you, and most likely about everyone else. As far as "catching up", I can't really say on the spot as I don't have a side by side comparison, but have a pretty good idea.
As I look at my last year's records, at this time, I was already in the teens to single digits daily for humidity, and it would remain there for the next four months until the monsoon arrived.
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The 75 was made for metrological use and was the standard sensor for Campbell Scientific https://www.campbellsci.com/cs215-l
The 75 is superior IMO to the 31 except possibly extreme cold but even there it was within 1.3° at around -15°. The 75 was phased out because it doesn't use the I2c protocol but other than that great accurate fast responding sensor meant to be used outdoors unlike the 31. It's not perfect with prolonged high humidity like all sensirion sensors but does perform better overall with high humidity vs the 31 with faster recovery time and doesn't display the high bias in upper dewpoint range above 58° like the 31 does.
There is no doubt in my mind which sensor I'll be using once sub-zero temperature are no longer a threat.
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Just as a footnote and it's probably not very relevant to anyone here because it involves using EM, but:
A sensor with an SDI-12 output is in principle compatible with a Davis Enviromonitor node. It would still have to implemented as a recognised sensor by the EM team at Davis and that night well take some time to prioritise and then to achieve, but in principle it could work.
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Just as a footnote and it's probably not very relevant to anyone here because it involves using EM, but:
A sensor with an SDI-12 output is in principle compatible with a Davis Enviromonitor node. It would still have to implemented as a recognised sensor by the EM team at Davis and that night well take some time to prioritise and then to achieve, but in principle it could work.
Hey John, I emailed Davis a few days ago about an idea of switching the use of Sensirion sensors to the HYT 221 sensor but they never gave a response? Typically they respond to me within a day or two so I’m curious why they didn’t respond?
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Just as a footnote and it's probably not very relevant to anyone here because it involves using EM, but:
A sensor with an SDI-12 output is in principle compatible with a Davis Enviromonitor node. It would still have to implemented as a recognised sensor by the EM team at Davis and that night well take some time to prioritise and then to achieve, but in principle it could work.
I’m curious why they didn’t respond?
Not John here, but my 2cents is that it would appear incriminating on pointing to the fact that the 31 has issues. They haven't addressed anything prior to this, why start now.
I truly doubt you'll get a response.
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Hey John, I emailed Davis a few days ago about an idea of switching the use of Sensirion sensors to the HYT 221 sensor but they never gave a response? Typically they respond to me within a day or two so I’m curious why they didn’t respond?
I really wouldn't read too much into that. My guess is that it's a typical company situation in that the support people are in a completely different group to the developers/engineers for new products. Support is trained and set up to deal with all the common support questions (which this isn't and so support would struggle to answer this one directly) while product development is not customer-facing. Suggestions for new products are - again I can only guess at the likely scenario - probably forwarded into a different mailbox and read by someone at intervals, but hardly ever answered individually. And priorities for new products might only be reviewed maybe once or twice a year?
One other point that perhaps bears repeating: For better or worse I'm afraid that this is not a high profile or commonly raised issue. To the best of my recollection I've _never_ had a user complain much about RH accuracy (other than maybe a failure to reach exactly 100%). Users I deal with are much more exercised about other priorities for product development like a more consistently accurate rain gauge or a better console or better local software (though that bus has sailed). I'm not doubting the issue for a second but it just doesn't seem to rank as a major unprompted concern for many users and it's the majority concerns that Davis will inevitably respond to.
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Hey John, I emailed Davis a few days ago about an idea of switching the use of Sensirion sensors to the HYT 221 sensor but they never gave a response? Typically they respond to me within a day or two so I’m curious why they didn’t respond?
I really wouldn't read too much into that. My guess is that it's a typical company situation in that the support people are in a completely different group to the developers/engineers for new products. Support is trained and set up to deal with all the common support questions (which this isn't and so support would struggle to answer this one directly) while product development is not customer-facing. Suggestions for new products are - again I can only guess at the likely scenario - probably forwarded into a different mailbox and read by someone at intervals, but hardly ever answered individually. And priorities for new products might only be reviewed maybe once or twice a year?
One other point that perhaps bears repeating: For better or worse I'm afraid that this is not a high profile or commonly raised issue. To the best of my recollection I've _never_ had a user complain much about RH accuracy (other than maybe a failure to reach exactly 100%). Users I deal with are much more exercised about other priorities for product development like a more consistently accurate rain gauge or a better console or better local software (though that bus has sailed). I'm not doubting the issue for a second but it just doesn't seem rank as a major unprompted concern for many users and it's the majority concerns that Davis will inevitably respond to.
Thanks! Just wished they would’ve emailed me back saying that they passed it along to the right folks. Had one tech question in there that could’ve been answered but oh well.
But I do think if they switch to the HYT 221 sensor, it would be a huge step (along with fixing rain gauge issues) in making Davis VP2 a really viable option for research, etc. That’s just IMO.
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Update, well finally got some dense fog and the sensor has been doing real well in following my main sensor. Humidity topped out at 99% on both stations and temp has been right on so it looks like these sensors are a good batch and not seconds or knock offs.
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
Man I wish I had that same analog sensor. Looking at your data and comparing it to the ASOS tells me it’s a great sensor. Even though the 75 is better than the 31, I’m still having to do an offset of -3-4%. Even though the sensor has “dried” out for a few days. I wish there was a way to obtain those old temp/hum sensors. If anyone knows the makers of those sensors, please let me know.
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
Man I wish I had that same analog sensor. Looking at your data and comparing it to the ASOS tells me it’s a great sensor. Even though the 75 is better than the 31, I’m still having to do an offset of -3-4%. Even though the sensor has “dried” out for a few days. I wish there was a way to obtain those old temp/hum sensors. If anyone knows the makers of those sensors, please let me know.
I realize information on these old analog sensors is largely irrelevant, but I thought I’d provide an update. After being gone for several weeks, I’ve been back for a few days and combined with what I was seeing remotely and after numerous spot checks with my psycho-dyne, I found that the analog sensor was about 3-4% too dry. The temperature has been very accurate, but in a temperate range from about 43-75F.
The good news about the dry humidity sensor is that it read 3-4% low across the entire scale and topped out at 97% (although I have been able to force it with a warm damp cloth to 100%). I’ve applied a +4% humidity offset, which allows the sensor to easily hit 100% and it has been +/-2% of my psychro-dyne with humidity all the way down into the upper teens (which we just experienced here recently). It recovers from high humidity much quicker than the Sensirion. Sometimes the sensor reads a little wet, other times a little dry. It’s nice to see this random error versus the constant systemic high humidity bias I was used to.
With that said, I did make a side by side comparison with the SHT75 with humidity down in the 20s. They read almost identical (with the +4% offset on the analog) and right on with the psycho-dyne, but with the caveat that the SHT75 had been indoors in a very dry environment and not exposed to the prolonged high humidity that seems to be that sensor’s weakness.
Compared to the nearest ASOS (KTIW), the analog compares favorably. Local effects here can be extreme in warm, dry conditions with proximity to water, wind direction and down and upsloping winds. My psycho-dyne always matches ASOS nearly exactly when I’ve done side by side comparisons, so as a sort of transfer standard, I trust it more than comparing to an ASOS with unique differences over 4 miles away
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I made my sensor swap over to the SHT75 yesterday. I'll go back on the SHT31 when below zero F is a threat again come November.
I'm running both in same AC aspirated shield, the 75 dp averages 2° lower vs the 31 even with mid 30's dewpoint unless it's raining like today the 75 is running higher by 1 degree responding to the added moisture in the air. It's just the better sensor humidity wise IMO.
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
Man I wish I had that same analog sensor. Looking at your data and comparing it to the ASOS tells me it’s a great sensor. Even though the 75 is better than the 31, I’m still having to do an offset of -3-4%. Even though the sensor has “dried” out for a few days. I wish there was a way to obtain those old temp/hum sensors. If anyone knows the makers of those sensors, please let me know.
I realize information on these old analog sensors is largely irrelevant, but I thought I’d provide an update. After being gone for several weeks, I’ve been back for a few days and combined with what I was seeing remotely and after numerous spot checks with my psycho-dyne, I found that the analog sensor was about 3-4% too dry. The temperature has been very accurate, but in a temperate range from about 43-75F.
The good news about the dry humidity sensor is that it read 3-4% low across the entire scale and topped out at 97% (although I have been able to force it with a warm damp cloth to 100%). I’ve applied a +4% humidity offset, which allows the sensor to easily hit 100% and it has been +/-2% of my psychro-dyne with humidity all the way down into the upper teens (which we just experienced here recently). It recovers from high humidity much quicker than the Sensirion. Sometimes the sensor reads a little wet, other times a little dry. It’s nice to see this random error versus the constant systemic high humidity bias I was used to.
With that said, I did make a side by side comparison with the SHT75 with humidity down in the 20s. They read almost identical (with the +4% offset on the analog) and right on with the psycho-dyne, but with the caveat that the SHT75 had been indoors in a very dry environment and not exposed to the prolonged high humidity that seems to be that sensor’s weakness.
Compared to the nearest ASOS (KTIW), the analog compares favorably. Local effects here can be extreme in warm, dry conditions with proximity to water, wind direction and down and upsloping winds. My psycho-dyne always matches ASOS nearly exactly when I’ve done side by side comparisons, so as a sort of transfer standard, I trust it more than comparing to an ASOS with unique differences over 4 miles away
Thanks for the input! Really, if Davis would let their pride go and switch their temp/humidity sensor to the HYT 221 or one that is good, then I’ll have nothing much to complain about the Davis station. Lol
But I’m curious to know if the transmitter needed changing in order to take the I2C or does the console need reprogramming?
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I’ve finally given up on Sensirion in general. I have the good fortune of having held on to my old analog temperature/humidity sensor from the pre2006 VP2 days (the 7346.029). At 14 years old, I wasn’t sure what kind of performance I’d get from it, although for most of that time it hasn’t been exposed to the extremes of outdoor conditions. I plugged it in and it worked and the temperature matched my other sensors. I placed a wet cloth over it and it read 100% humidity within 5 mins. I installed it as my primary sensor on 23Feb. We’ve had unusually dry weather in western Washington for this time of year (humidity down near 30%) the last 2 days. It has performed well.
Previously I was using the SHT75, which for humidity was performing better than the Davis 31, but with the continuous wet conditions, it still suffered from a pretty bad wet bias when things would dry out. I used an offset and calibration on the SHT75 of (1.061x)-5 in Cumulus. With the analog, I am using no calibration or offset. It’s really a shame Davis could not source these humidity elements any longer. I’ll see how it does over the long term, but if you’re interested to see how it compares, the nearest NWS ASOS is KTIW. KSEA and KBFI aren’t too far (see link). Everything prior to 23Feb was the SHT75 with calibration setting. Everything after is the old analog.
https://weather.gladstonefamily.net/qchart/C7491?date=20190227&addnl=KTIW&addnl=KSEA&addnl=KBFI
05Feb really gives a good demonstration of the wet bias after a long wet period with the Sensirion:
https://weather.gladstonefamily.net/qchart/C7491?date=20190206&addnl=KTIW&addnl=KSEA&addnl=KBFI
Man I wish I had that same analog sensor. Looking at your data and comparing it to the ASOS tells me it’s a great sensor. Even though the 75 is better than the 31, I’m still having to do an offset of -3-4%. Even though the sensor has “dried” out for a few days. I wish there was a way to obtain those old temp/hum sensors. If anyone knows the makers of those sensors, please let me know.
I realize information on these old analog sensors is largely irrelevant, but I thought I’d provide an update. After being gone for several weeks, I’ve been back for a few days and combined with what I was seeing remotely and after numerous spot checks with my psycho-dyne, I found that the analog sensor was about 3-4% too dry. The temperature has been very accurate, but in a temperate range from about 43-75F.
The good news about the dry humidity sensor is that it read 3-4% low across the entire scale and topped out at 97% (although I have been able to force it with a warm damp cloth to 100%). I’ve applied a +4% humidity offset, which allows the sensor to easily hit 100% and it has been +/-2% of my psychro-dyne with humidity all the way down into the upper teens (which we just experienced here recently). It recovers from high humidity much quicker than the Sensirion. Sometimes the sensor reads a little wet, other times a little dry. It’s nice to see this random error versus the constant systemic high humidity bias I was used to.
With that said, I did make a side by side comparison with the SHT75 with humidity down in the 20s. They read almost identical (with the +4% offset on the analog) and right on with the psycho-dyne, but with the caveat that the SHT75 had been indoors in a very dry environment and not exposed to the prolonged high humidity that seems to be that sensor’s weakness.
Compared to the nearest ASOS (KTIW), the analog compares favorably. Local effects here can be extreme in warm, dry conditions with proximity to water, wind direction and down and upsloping winds. My psycho-dyne always matches ASOS nearly exactly when I’ve done side by side comparisons, so as a sort of transfer standard, I trust it more than comparing to an ASOS with unique differences over 4 miles away
Really, if Davis would let their pride go
I highly doubt it has anything to do with pride.
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Finally got a response back from Davis. They are forwarding my email to their design team. So hopefully they will look into the HYT-221 sensor and give it a shot.
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Finally got a response back from Davis. They are forwarding my email to their design team. So hopefully they will look into the HYT-221 sensor and give it a shot.
Looks like Newark has them on sale.
https://www.newark.com/ist-innovative-sensor-technology/hyt-221/sensor-humidity-digital-w-filter/dp/44W8408
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Finally got a response back from Davis. They are forwarding my email to their design team. So hopefully they will look into the HYT-221 sensor and give it a shot.
But how can Davis do that without a significant redesign of the SIM board (which perhaps isn't very likely at this stage of the VP2's life-cycle)?
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Finally got a response back from Davis. They are forwarding my email to their design team. So hopefully they will look into the HYT-221 sensor and give it a shot.
But how can Davis do that without a significant redesign of the SIM board (which perhaps isn't very likely at this stage of the VP2's life-cycle)?
Will Davis come out with a new station or just continue in improving the VP2?
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Will Davis come out with a new station or just continue in improving the VP2?
I genuinely don't know - either outcome is possible, at least in the shorter term, there being no real rumours of an imminent VP3 at this stage AFAIAA.
AFAICT Davis's focus is currently on enhancements to data handling from the existing sensors and stations with Weatherlink Live and further progress with the weatherlink.com features roadmap, which still has some way to run, plus some tweaks eg to the VP2 rain gauge, which we know about.
But I can't see into 2021 and beyond, and surely at some point there will be a new station model. It wouldn't surprise me if this was based around an EM node (though that's wild speculation based on zero inside knowledge). Of course if you had a temp/hum sensor that you liked with an SDI-12 interface then that is compatible electronically with an EM node already, though you'd still have to persuade Davis to build in software support, but that's potentially easier than a hardware redesign.
Edit: Speculating further, one thing that wouldn't surprise me would be to see a version of WLL that had receiver circuits for the Zigbee wireless that EM uses, in place of the VP2-type protocol. This would provide a mechanism for local data handling for EM nodes rather than requiring the EM gateway for remote 3G uploads. Or another way of doing something similar would be a modified EM gateway where the 3G modem board was replaced by a VP2 multi-transmitter board capable of beaming back all the data to an existing WLL unit.
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Will Davis come out with a new station or just continue in improving the VP2?
I genuinely don't know - either outcome is possible, at least in the shorter term, there being no real rumours of an imminent VP3 at this stage AFAIAA.
AFAICT Davis's focus is currently on enhancements to data handling from the existing sensors and stations with Weatherlink Live and further progress with the weatherlink.com features roadmap, which still has some way to run, plus some tweaks eg to the VP2 rain gauge, which we know about.
But I can't see into 2021 and beyond, and surely at some point there will be a new station model. It wouldn't surprise me if this was based around an EM node (though that's wild speculation based on zero inside knowledge). Of course if you had a temp/hum sensor that you liked with an SDI-12 interface then that is compatible electronically with an EM node already, though you'd still have to persuade Davis to build in software support, but that's potentially easier than a hardware redesign.
Edit: Speculating further, one thing that wouldn't surprise me would be to see a version of WLL that had receiver circuits for the Zigbee wireless that EM uses, in place of the VP2-type protocol. This would provide a mechanism for local data handling for EM nodes rather than requiring the EM gateway for remote 3G uploads. Or another way of doing something similar would be a modified EM gateway where the 3G modem board was replaced by a VP2 multi-transmitter board capable of beaming back all the data to an existing WLL unit.
Gotcha. I’m definitely no electronics expert but could they design an adapter and sell it to those who want to use I2C sensors? I’m glad they are improving the rain gauge, but I do think they need to resolve their humidity issues ASAP. Which their main problem is that they use Sensirion sensors.
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I want to share my experiences so far with switching over to the 75. I brought my ISS inside and after letting the sensor acclimate to the inside environment and comparing with my Belford 566 I had to input a +1 degree offset for temp. Humidity runs about +5% so no change from my 31, at least at room temperature. My 31 runs dry, however never exceeded 97%. I installed both the 31 and 75 into my ISS leaving the 75 hooked up. The only reason I can think why I had to input a +1 offset for temp may be because I'm using the very latest version transmitter. The ISS is back outside now so we'll see how it tracks.
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That's right if you are using a new iss and install an older sensor then you have to put in a +.9 offset, just the opposite when putting a 31 into and older iss.
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Thanks Jerry! Good to know what I figured out on my own turned out to be right. Now if I can figure out the humidity issue.
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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.
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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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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
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Yeah definitely more responsive than the 31 [tup]
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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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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?
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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
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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.
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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.
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Could be the 15 was available in 2014 for sure, maybe it was always just an upgrade. If so his 2014 has the SHT11.
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2014 is about the time I had my 15 installed, maybe a year earlier.
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SHT15 was standard in Europe for a limited period but never in US AFAIK.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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. [tup]
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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,
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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
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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.
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Great [tup].
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Great [tup].
And thank you Randy for your help!
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It finally dawn on me, but when you put a .9°F offset for the 75 (due to up to date transmitter & old sensor) it makes the DP go up 1°. To get an actual DP report from the 75, I did a -2% offset. But it’s strange that the console doesn’t adjust RH when you do a temperature calibration.
I guess it’s better to be slow than never. Lol
On a off topic note, the new Davis one spoon tipper is worth the investment to get and replace your old tipping spoons!
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But it’s strange that the console doesn’t adjust RH when you do a temperature calibration.
That's because the humidity is a straight out measurement, just like the temp. If you change the temp., the dew point is recalculated to reflect the humidity measured. That's also why there's an offset offered for both temp and humidity, but not the dew point.
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But it’s strange that the console doesn’t adjust RH when you do a temperature calibration.
That's because the humidity is a straight out measurement, just like the temp. If you change the temp., the dew point is recalculated to reflect the humidity measured. That's also why there's an offset offered for both temp and humidity, but not the dew point.
Gotcha