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Weather Station Hardware => Davis Instruments Weather Stations => Topic started by: JudinNorman on May 23, 2017, 12:32:51 PM
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Any weather station geeks care to share some thoughts on the SHT31 sensor Davis uses no in the VP2? I'm wondering if it's worth the cost to upgrade if my current older sensor is working just fine.
Jud
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If you have fan aspiration (FARS), expect to see the temperature change quite a bit more than you're accustomed to now. I was shocked at how responsive it is. Not saying that's a bad thing, but it makes comparisons with neighboring stations harder because almost inevitably their readings will lag your station even if comparisons are made in real time.
Beware that despite the tight stated accuracy specifications (+/- 0.38F from freezing upward), these are not NIST certified or pre-calibrated sensors. So their baseline may be off. In my case, I had to adjust mine -0.4F after averaging many comparison readings with a very accurate, certified check gauge. Every one of those check readings, whether taken on a breezy, cloudy, thermally-stable night or inside in my garage, showed the SHT31 to be biased warm up to 0.5F (the median was actually 0.45 but I'm conservative and put in a -0.4 offset). Even after adjusting, continued checks have shown that a consistent warm bias appears to remain (somewhere on the order of 0.2F), although not enough to warrant further adjustment so far.
I'm not suggesting all SHT31s run warm, just advising you not to take the manufacturer's word for it. If you aren't overly concerned with fine accuracy, this may be a moot issue.
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Thanks ya all for the comments.
In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
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In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Good question! I inquired as to the specs of my local COOP station and the NWS blew me off even though I addressed an employee who doubles as the CoCoRaHS coordinator for this region (and who had set me up a couple years back). We've had a couple positive email exchanges in the past. Maybe your local office will be more responsive.
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be). Or perhaps it's better to take it on a case-by-case basis depending on the resources and conscientiousness of the local WFO. It could also come down to the difference between what the NWS is supposed to be doing versus what they are actually doing (or not doing). So even if the specs for their sensors are similar or better, who knows how accurate they are at any given moment.
The COOP records here are, to put it politely, a bit of a mess. Record keeping is inconsistent. One month last year, half the entries were missing! The sensor suite is sited within 20ft of a 25ft brick building wall. This is also where official precip, including snow, is measured. The nearby building shadows precip coming from several directions. Do I believe they calibrate this station? Not really. Could that be why they failed to respond to a simple question (asked very politely)? Perhaps.
Like I said, your mileage may vary.
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The original VP2 came with the SHT11. Some of the later VP2's were being shipped with SHT15's but within a year they changed over to the 31's. The SHT11's aren't very accurate especially below freezing at 0C-32F they are already +/- 1.1C (2°F) off and it gets much worse as temps drop. It also suffers on high end but not as bad.
The SHT15's are better but if you live in cold country the 31 is only way to go.
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openvista if you upgraded to the SHT31 sensor using the older transmitter build before Jan 2016 it needs the -.9 offset.
I've never found the SHT31 to run warm is why I'm saying this. I've crosschecked with NIST certified at 32F and found them very accurate needing no adjustment other than the -(.9) if using older transmitter.
Correction Jan 2016 is the cut off date.
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Correction Jan 2016 is the cut off date.
Strictly speaking, you need to look for AS revision. There were some (a few) ISS units built post 1/1/2016 that don't have SHT31, but these would be recognisable as eg AR revision. So yes any SIM board pre-AS revision needs the offset.
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openvista if you upgraded to the SHT31 sensor using the older transmitter build before Jan 2017 it needs the -.9 offset.
I've never found the SHT31 to run warm is why I'm saying this. I've crosschecked with NIST certified at 32F and found them very accurate needing no adjustment other than the -(.9) if using older transmitter.
Yes, I should have clarified that. I started with a -0.9F offset as instructed by Davis and currently have it set to -1.3F (subtracting another 0.4F) based on my calibration checks. It could be that I drew a sensor that was anomalous, but if I did, then perhaps someone else could too. I will continue checking it in different conditions to be sure that the offset is correct (controlling for the necessary variables like radiation, hysteresis, FARS, siting, margin of error, etc).
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Where is the best (least expensive) place to get this sensor?
Dennis
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Yes! I have a problem Houston. I have triple redundancy setup with 3-sht31's aspirated shields and they are all very close. Even humidity is matching but does vary slightly more between sensors.
I trust the accuracy and like I said have cross checked with expired but once certified NIST certificate thermometers.
This was our frost the other morning so took a snapshot. One last frost tonight I see just issued.
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Where is the best (least expensive) place to get this sensor?
Dennis
I use Scaled Instruments out of Florida most of the time for Davis Inst.
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Any weather station geeks care to share some thoughts on the SHT31 sensor Davis uses no in the VP2? I'm wondering if it's worth the cost to upgrade if my current older sensor is working just fine.
Jud
I would say if you're a die-hard temperature-accuracy fanatic like I am, then the cost of the upgrade is worth it. The sensor is much improved from the 11. Faster response time and tighter specs. Can't go wrong, IMO. I'm just happy that my VP2 purchased in February last year already came with the 31. Also, if you take the filter off, the response time is INSANE! Many times I would get .2-.4 ups and downs with each update, it was crazy. However, that can dirty up the sensor so I put the filter back on.
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In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be).
In the U.S., ASOS/AWOS are used for official measurements for a given particular area. Since practically all are located on an airport, regular maintenance/calibration is performed for safety of the flying public, ASOS's by the FAA, AWOS's by the NWS. (I'm sure there's exceptions). Whether RAWS for example are used in lieu if the others aren't physically near by, I do not know, but the ones in my area have been down before and fixed within a day or so.
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In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be).
In the U.S., ASOS/AWOS are used for official measurements for a given particular area. Since practically all are located on an airport, regular maintenance/calibration is performed for safety of the flying public, ASOS's by the FAA, AWOS's by the NWS. (I'm sure there's exceptions). Whether RAWS for example are used in lieu if the others aren't physically near by, I do not know, but the ones in my area have been down before and fixed within a day or so.
Yes, there are exceptions. Of the 6 towns with records available on the website of my local Weather Forecast Office (WFO), only 1 of the stations is at an airport. 4 of them are at water treatment plants and 1 of them is a RAWS (remote automated weather station).
My town's COOP is run entirely by volunteers who are solely responsible for maintaining the continuity of 140+ years of records. I've previously described just how well that's going :roll:. This should give you an idea of where it falls in the list of priorities overall. Like I said, your mileage may vary.
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In terms of specs how does the SHT31 specs compare to the sensors the NWS COOP stations use ?
Also, I wouldn't assume that the COOP stations are regularly calibrated (although they may be).
In the U.S., ASOS/AWOS are used for official measurements for a given particular area. Since practically all are located on an airport, regular maintenance/calibration is performed for safety of the flying public, ASOS's by the FAA, AWOS's by the NWS. (I'm sure there's exceptions). Whether RAWS for example are used in lieu if the others aren't physically near by, I do not know, but the ones in my area have been down before and fixed within a day or so.
My town's COOP is run entirely by volunteers who are solely responsible for maintaining the continuity of 140+ years of records. I've previously described just how well that's going :roll:. This should give you an idea of where it falls in the list of priorities overall. Like I said, your mileage may vary.
Sad to see that "official" record keeping can be mitigated to the back burner. But, like you said, priorities. :-|
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Thanks to all those who replied. I'm going to be getting a new SHT31.
Jud
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Correction Jan 2016 is the cut off date.
Strictly speaking, you need to look for AS revision. There were some (a few) ISS units built post 1/1/2016 that don't have SHT31, but these would be recognisable as eg AR revision. So yes any SIM board pre-AS revision needs the offset.
Hi John, I got my setup from you in Feb '17, what temp will mine have in it please?
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For transmitter firmware anything built Jan 2016 or later I've found through orders with Scaled Instruments had the latest SHT31 firmware. The code doesn't have to be AS or later despite what Davis says as long as it was manufactured in Jan 2016. You can open transmitter and look at first 4 numbers after the 2 letters.
Example code of AP160101201 (Jan 2016)
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Not that easy for me, mine is up on the mass :/
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There's that Damn hind sight.....
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A few days of the SHT31 being in service it's 0.2 to 0.4 F higher than my Davis Temperature station sensor for high and low temperatures while my old temp/hum sensor was 0.2 to 0.4 F colder than the Temperature station sensor. It's a little disappointing my VP2 mean temperatures now will be around 0.4 to 0.8 F higher than the past 10 years just as a result of a simple sensor switch.
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it's 0.2 to 0.4 F higher than my Davis Temperature station sensor for high and low temperatures while my old temp/hum sensor was 0.2 to 0.4 F colder than the Temperature station sensor.
Two things: Firstly, what's your "Davis Temperature station sensor" :?: :???:
Secondly, how do you know it's not "wrong" and your 31 isn't "right"?
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And just for further clarification, you stated in another thread that you did put in the minus 0.9F offset, right?
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If the Davis had an older SHT11 remember they aren't as accurate and very likely was off, especially if several years old they can drift.
If comparing to a nearby professional station remember they most likely have ideal setup so wouldn't surprise me if you weren't reading higher in your back yard.
I would bet the SHT31 is accurate, and the older sensor has the problem.
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Davis Temperature station sensor is the sensor that is part of the Davis Temperature Station, just measures temperature, no humidity.
Not sure which is right, just disappointing after 10 years of data the new data will not be close. It screws up the freeze data, old sensor read 32.0 which would go down as a freeze but the new sensor would read 32.8 for example and would be considered a freeze. My first and last freeze days will be off.
Jud
it's 0.2 to 0.4 F higher than my Davis Temperature station sensor for high and low temperatures while my old temp/hum sensor was 0.2 to 0.4 F colder than the Temperature station sensor.
Two things: Firstly, what's your "Davis Temperature station sensor" :?: :???:
Secondly, how do you know it's not "wrong" and your 31 isn't "right"?
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Yes the -0.9 F offset is in the console.
And just for further clarification, you stated in another thread that you did put in the minus 0.9F offset, right?
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That could be the case but I have no idea or way to check, all that I have is the data which has been consistant over the years compared to nearby stations, I have not noticed my average temperatures getting colder or warmer compared to nearby.
Jud
If the Davis had an older SHT11 remember they aren't as accurate and very likely was off, especially if several years old they can drift.
If comparing to a nearby professional station remember they most likely have ideal setup so wouldn't surprise me if you weren't reading higher in your back yard.
I would bet the SHT31 is accurate, and the older sensor has the problem.
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Davis Temperature station sensor is the sensor that is part of the Davis Temperature Station, just measures temperature, no humidity.
Not sure which is right, just disappointing after 10 years of data the new data will not be close. It screws up the freeze data, old sensor read 32.0 which would go down as a freeze but the new sensor would read 32.8 for example and would be considered a freeze. My first and last freeze days will be off.
Jud
Sooo, you're saying that you're unhappy that your 31 is almost for surely more accurate than either of your other sensors? When I put my 31 in I was elated at it's performance, and still am, and so is everyone else I know of. I think I'd give it shot.
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I'm unhappy there is such a difference between old and new sensor. Not sure if I can maintain my same database or should start a new one.
Davis Temperature station sensor is the sensor that is part of the Davis Temperature Station, just measures temperature, no humidity.
Not sure which is right, just disappointing after 10 years of data the new data will not be close. It screws up the freeze data, old sensor read 32.0 which would go down as a freeze but the new sensor would read 32.8 for example and would be considered a freeze. My first and last freeze days will be off.
Jud
Sooo, you're saying that you're unhappy that your 31 is almost for surely more accurate than either of your other sensors? When I put my 31 in I was elated at it's performance, and still am, and so is everyone else I know of. I think I'd give it shot.
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The NWS and other official climatological databases do not start new databases just because they upgrade their observing equipment. They would never have any past data to compare current data to! Don't be upset that the older sensor wasn't quite up to par with the newer one. You're dealing with a matter of a few tenths of a degree, not several whole degrees off so it's not that big of a difference in the grand scheme of things, especially over a ten year period.
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As far as worrying about freezing temperatures the stainless with the temperature station is just as accurate as the SHT31 so they should come together nicely.
Where it starts losing accuracy, as temperatures rise at 82° its already +/- (1°) and at 110°F its bad at +/- (2°).
Just be glad you upgraded to the SHT31 and enjoy. 8-)
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I'm unhappy there is such a difference between old and new sensor. Not sure if I can maintain my same database or should start a new one.
Davis Temperature station sensor is the sensor that is part of the Davis Temperature Station, just measures temperature, no humidity.
Not sure which is right, just disappointing after 10 years of data the new data will not be close. It screws up the freeze data, old sensor read 32.0 which would go down as a freeze but the new sensor would read 32.8 for example and would be considered a freeze. My first and last freeze days will be off.
Jud
Sooo, you're saying that you're unhappy that your 31 is almost for surely more accurate than either of your other sensors? When I put my 31 in I was elated at it's performance, and still am, and so is everyone else I know of. I think I'd give it shot.
Sure it sucks that there's such a drastic difference between old and new and that your old has drifted over the years, but take solace in the fact that you upgraded to the very newest in temp/humidity technology. More accurate, tighter specs, what more can you ask for? ;)
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Over a week with the SHT31 installed. The average temperature is 0.2 F higher than the Temperature Station, the old Temp/Hum sensor averaged 0.3 F colder than the Temperature Station for years. I would assume all these sensors are within their specs for accuracy.
I may set up a wooden shelter with NWS thermometers. I visited a volunteer observer 48 miles from here who has been been using the same glass thermometers for 32 years which are still working like day one.
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I visited a volunteer observer 48 miles from here who has been been using the same glass thermometers for 32 years which are still working like day one.
And will til it breaks.
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For transmitter firmware anything built Jan 2016 or later I've found through orders with Scaled Instruments had the latest SHT31 firmware. The code doesn't have to be AS or later despite what Davis says as long as it was manufactured in Jan 2016. You can open transmitter and look at first 4 numbers after the 2 letters.
Example code of AP160101201 (Jan 2016)
Now I'm really confused.
My ISS is AR160914029.
The ISS board has Assy# 07315.115 Rev E3.
The Current Temp Sensor as a white sticker with Part# 7346.176J.
Don't seem to get many reference when I search for any of those codes.
It's an Aussie unit from our official distributor, & was on backorder waiting, for fresh stock when I ordered it back in August 2016.
Should have popped the screen off the above temp sensor when I had the Shield apart converting it to DFARS, as I find no official information as to exactly what the 7346.176C sensor is.
Real question though, is do I need to apply the offset when my SHT31 arrives.
Thanks
Phil.
Edit:
How do you determine the firmware revision of the ISS (as opposed to the console).
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
Phil.
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Easiest way when new SHT31 comes pop dust shield and compare to old sensor. The new sht31's are very small don't sit as high as the SHT11 and 15's.
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Easiest way when new SHT31 comes pop dust shield and compare to old sensor. The new sht31's are very small don't set as high as the SHT11 and 15's.
Basically you'll know if you have a 31 if you can't read the 31 AT ALL. Even under a microscope the damn thing is still hard to read.
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Here is 15 and new 31. No mistaken once filter cap is removed.
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
Almost certainly not I would have thought, since any heating element must consume power but which is in very short supply in a wireless VP2 ISS.
But since you've mentioned it, I do find myself curious as to how heating a temperature sensor can enhance its accuracy?
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
But since you've mentioned it, I do find myself curious as to how heating a temperature sensor can enhance its accuracy?
Yeah, there's probably a few of us trying to figure out this one.... :???:
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
But since you've mentioned it, I do find myself curious as to how heating a temperature sensor can enhance its accuracy?
Yeah, there's probably a few of us trying to figure out this one.... :???:
Although the whole device is tiny, (2.5 x 2.5mm), maybe the heater is very localised to the humidity sensing element & isolated from the temp sensor part or the device.
Also the data sheet states the heaters power at 4.5 to 33mW, and being that it's a completely digital device, any heating input influencing the temp element could be calculated & adjusted for within the device. The data sheet says it's for "plausibility testing only".
But I've read other stuff discussing it's relevance to improved humidity readings in high humidity circumstances when condensation is present.
Dunno, but in loose terms you could say turn the heater on for a bit, ignore the temp for a bit & focus on the humidity; turn it off; go back to reading the temp again.
Also plausible is a device (as in board) with two STH31's present. One with the heater on the other heater off.
Bit Academic, but interesting anyway.
Phil
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
But since you've mentioned it, I do find myself curious as to how heating a temperature sensor can enhance its accuracy?
Yeah, there's probably a few of us trying to figure out this one.... :???:
Also the data sheet states the heaters power at 4.5 to 33mW, and being that it's a completely digital device, any heating input influencing the temp element could be calculated & adjusted for within the device. The data sheet says it's for "plausibility testing only".
Could you please post this "data sheet?" Don't know about anyone else, but I have no idea what you're refering to.
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As I recall from the SHT11 and/or SHT15 datasheets, the on-sensor heater is used to recondition the sensor after exposure to solvents during assembly/soldering. But I could be wrong...
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Okay, found this, but I have no idea what "plausibility checking" is.
4.10
Heater
The SHT3xis equipped with an internal heater, which is meant for plausibility checking only. The temperature increase achieved by the heater depends on various parameters and lies in the range of a few degrees centigrade. It can be switched on and off by command, see table below. The status is listed in the status register. After a reset the heater is disabled (default condition)
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
But since you've mentioned it, I do find myself curious as to how heating a temperature sensor can enhance its accuracy?
Yeah, there's probably a few of us trying to figure out this one.... :???:
Also the data sheet states the heaters power at 4.5 to 33mW, and being that it's a completely digital device, any heating input influencing the temp element could be calculated & adjusted for within the device. The data sheet says it's for "plausibility testing only".
Could you please post this "data sheet?" Don't know about anyone else, but I have no idea what you're refering to.
This is the official data sheet for the device.
https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_SHT3x_Datasheet_digital.pdf
Few searches make mention the heater in relation to humidity & condensation.
Phil.
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Would also be curious to know if Davis is using the Heater in the SHT31 in later firmware revisions to improve temperature accuracy.
But since you've mentioned it, I do find myself curious as to how heating a temperature sensor can enhance its accuracy?
Yeah, there's probably a few of us trying to figure out this one.... :???:
Also the data sheet states the heaters power at 4.5 to 33mW, and being that it's a completely digital device, any heating input influencing the temp element could be calculated & adjusted for within the device. The data sheet says it's for "plausibility testing only".
Could you please post this "data sheet?" Don't know about anyone else, but I have no idea what you're refering to.
This is the official data sheet for the device.
https://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/2_Humidity_Sensors/Sensirion_Humidity_Sensors_SHT3x_Datasheet_digital.pdf
Few searches make mention the heater in relation to humidity & condensation.
Phil.
Yes, that's where I got my quote from two post ago.
I guess the point is you're reading into this as a potential benefit, as far as I can tell this is nothing more than a diagnostic tool.
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Might Try & actually install this today.
Just in regards to the off-set, do I need to Increase or Decrease the reading at the console by the 0.5°C off-set.
Thanks
Phil.
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Might Try & actually install this today.
Just in regards to the off-set, do I need to Increase or Decrease the reading at the console by the 0.5°C off-set.
Thanks
Phil.
If I'm not mistaken, you need to decrease the reading.
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Revisiting this issue 4 years later upon purchasing a WeatherLink Live.
Was advised by Davis Aus that no offset is required, which I disagree with as the WLL is receiving data from my original ISS.
That is confirmed by the fact that with no offset the WLL is reading 0.5°C above my original console which has the offset applied.
Weird think though is that if I enter an offset of -0.5°C in the WLL settings, on saving it reverts to -0.9°C.
Also tried applying -0.4°C, and that reverted to -0.7°C, as below.
Still find the whole AR/AS revision comments to be confusing as Manufacture dates are also mentioned, and mine is 1609 which according to other comments is after the date firmware was changed to accept SHT31's.
Edit:- the whole 0.9 becoming 0.5 looks horribly like a °C to °F ratio.
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Revisiting this issue 4 years later upon purchasing a WeatherLink Live.
Was advised by Davis Aus that no offset is required, which I disagree with as the WLL is receiving data from my original ISS.
That is confirmed by the fact that with no offset the WLL is reading 0.5°C above my original console which has the offset applied.
Weird think though is that if I enter an offset of -0.5°C in the WLL settings, on saving it reverts to -0.9°C.
Also tried applying -0.4°C, and that reverted to -0.7°C, as below.
Still find the whole AR/AS revision comments to be confusing as Manufacture dates are also mentioned, and mine is 1609 which according to other comments is after the date firmware was changed to accept SHT31's.
Edit:- the whole 0.9 becoming 0.5 looks horribly like a °C to °F ratio.
As a new WLL user I had a similar issue when adding the year rain amount. I needed to add 557mm but every time i did add it, it kept coming out at 740mm for the yearly rain. I had to input 438.4mm so that the rain would show 557mm for the year, i spoke to support about it but i felt that with all the other issues i reported that in the end they fobbed me off on to the API support. I was quite peed off by that point and told him that with all the issues i was seriously debating on whether or not to drop back to basic one the trial ended, guess what, support got back to me the day after the money came out for the year. None of the issues are fixed so far and this was since around the end of Sept/beginning of October. A major one is on the web browser (not the app) the rain amount under the Mobilize tab - Irrigation is just crazily incorrect, i.e. way, way under, eg Yesterdays rain was 19.2mm Mobilize irrigation section shows it as 0.8mm and on the 19th of Sept we had 66.6mm (yeah i know, right lol) yet Mobilize irrigation shows it as 2.6mm, gonna go out on a limb here and assume that its showing it in Inches? for this issue, not sue about the Yearly rain amount par though... Had support got back to me prior to that money coming out, i would have cancelled the subscription! I really like the WLL app & website to be honest but it is lacking though and sadly, as it stands, its not enough for a renewal next year, i don't need the data side of it and that's another issue, looking at the Data on the webpage, its very laggy, i have an I7, 16gb ram with SSD HDD and 2 graphics cards in this laptop, it shouldn't be laggy...
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I'll add my $.02 to this old-ish thread.
I recently replaced my SHT15 sensor with an SHT31. I had previously replaced the SHT11 with a SHT15 (soldered a new component onto the board) because the SHT11 stopped working properly. Well this time the humidity/dewpoint had been malfunctioning but the temp seemed fine. So I ordered the new SHT31 assy from Scaled Instruments. I knew about the +0.5°C [0.9°F] offset but decided to get some empirical data anyway. I put the new sensor outside next to the ISS for like 15 minutes. Then I checked the console reading, plugged in the new sensor, and checked the console again. It read 0.8°F higher. I let it sit for a while and it went down several tenths (approx. temp was 45°F, late afternoon so the temp was dropping). I switched back to the SHT15 and it was 0.9°F lower. Good enough for me! I swapped everything out and applied the -0.9°F offset to the console.
Cheers!
Nick