Topic: The Reliability of the SHT-31 Humidity Sensor & What Psychrometer Should I Buy?

[fkapp]

How are the results going so far with your baked sensors?

Unfortunately I can’t go into detail at the moment due to not having the time and I will follow up with more info as I’m able, but I’ve baked (another) brand new Davis 31 with positive results. Sensor goes to 100% AND this one follows the SHT75 when humidity drops which I’ve never seen before. This one has a clear potting not the black potting which my other “new” sensor had. I don’t know if that is part of the reason for the difference. The clear potting WILL MELT at 220F. It won’t turn completely into a liquid, but you have to be careful. More to follow as I’m able, but I’m cautiously optimistic from what I’ve seen so far and as you know I’ve been pretty critical ...

Curious where did you order the clear potting sensor from? Davis or Ryan at Scaled?

96% humidity day/night. Today is 42% Humidity and sunny day, and has been +/- 2% to the NWS ASOS 2.6 miles away since online, and currently am 2% below the NWS ASOS, so fingers crossed wet bias does not rear its head.

You should actually compare dew points. I've seen as much as a 4% difference between stations when they show the same temp and dew point due to the particular spread at that time. Humidity AFAIC is only worth watching when very high or very low.

Thanks for the tip.
This past Hour comparsion at 3pm ET update (CWOP setup is still under quality check I guess) My dewpoint was 1 degree higher than the 3 Mile away to the South NWS station and 1 Degree Lower than the 10 Miles away to NW NWS station.  I guess overall this is pretty good. will see how trends go long term.

[CW2274]

Good. Always check the time of the stations your comparing to as dew points can vacillate quite a bit compared to the more steady temp.

[CW7491]

Good. Always check the time of the stations your comparing to as dew points can vacillate quite a bit compared to the more steady temp.

This is more than anyone needs to know, so sorry if your eyes glaze over, but it is also important to understand the difference of how ASOS calculates dew point and RH. It isn't apples to apples with how our weather stations do it. ASOS uses a Vaisala sensor that uses its own temperature and humidity sensors to calculate a dew point, just like our Sensirion sensors. This dew point, however, is then used with a different (and official) temperature sensor to calculate a relative humidity. (This allows the NWS to heat their humidity sensor without affecting the official temperature reading and even though the humidity sensor's temperature sensor reads too high, the relative aspect of humidity with respect to temperature results in an accurate dew point calculation.)

This difference is further complicated by the fact that ASOS rounds their raw temperature and dew point temperatures BEFORE calculating the humidity. So be especially careful when comparing to a NWS ASOS using 5 min observations as these observations for temperature and dew point are rounded to the nearest degree C. Hourly (ie typically at :51, :53, or :56) and special observations are rounded to the nearest degree F and make for better comparisons.

This is more than just academic based on how the NWS ASOS uses dew point and temperature to calculate RH. For an extreme example, if the ASOS reads a temp of 9.4°C and a dew point of 8.5°C (an actual RH of 94%), the 5 min observation will be 9°C/9°C (48°F/48°F) and a relative humidity of 100%. If the temp goes up to 9.5°C and the dew point down to 8.4°C (an actual RH of 93%), the 5 min observation will be 10°C/8°C (50°F/46°F) and a RH of 87%. So a 13% humidity change and a 2°C increase in the temperature/dew point spread for only a 1 percentage point change in humidity and a 0.2­°C actual increase in the temp/DP spread!

Hourly observations tend to have less rounding error because they convert the raw °C temp and dew point to a raw °F and round to the nearest °F. So in both these cases the temp would convert and round to 49°F and the dew point to 47°F for a RH of 93%.

This explains why the ASOS humidity and dew point can jump around more and also why you never see a NWS ASOS report 98% or 99% humidity. ASOSs at Air Force bases use a different vendor and methodology, so they will act a little different.

[CW2274]

Good. Always check the time of the stations your comparing to as dew points can vacillate quite a bit compared to the more steady temp.

you never see a NWS ASOS report 98% or 99% humidity.

Not disagreeing with anything you've said (ASOS's averaging algorithm is just part of thing we must deal with when comparing) except, I've seen the ASOS at TUS report 99% more times than I can count. 98%, not sure, but definitely 99.

[CW7491]

Good. Always check the time of the stations your comparing to as dew points can vacillate quite a bit compared to the more steady temp.

you never see a NWS ASOS report 98% or 99% humidity.

Not disagreeing with anything you've said (ASOS's averaging algorithm is just part of thing we must deal with when comparing) except, I've seen the ASOS at TUS report 99% more times than I can count. 98%, not sure, but definitely 99.

Interesting. TUS or DMA? The reason I ask is because DMA being an Air Force base probably uses the FMQ19 or latest variation from Coastal Environmental Systems up here in Seattle and it works like an AWOS and like our stations, not like how I described above. I think it uses a temperature/humidity sensor in an aspirated RM Young. When I lived in DC, Andrews AFB was always at 98 or 99, but I've never seen a NWS ASOS do it.

[CW2274]

Good. Always check the time of the stations your comparing to as dew points can vacillate quite a bit compared to the more steady temp.

you never see a NWS ASOS report 98% or 99% humidity.

Not disagreeing with anything you've said (ASOS's averaging algorithm is just part of thing we must deal with when comparing) except, I've seen the ASOS at TUS report 99% more times than I can count. 98%, not sure, but definitely 99.

Interesting. TUS or DMA?

TUS. They're only 4 miles apart, but DMA will always hit 100% before TUS will. TUS will eventually get there, but in the mean time, it'll sit on 99%. Whether DMA will display 99%, I honestly can't say, but you now have me looking.

[CW7491]

Here is 01JAN19 for both. This is what I'm used to seeing with how the NWS ASOS rounds.

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?product=&past=1&stn=KDMA&unit=0&time=LOCAL&day1=2&month1=01&year1=2019&hour1=0

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?product=&past=1&stn=KTUS&unit=0&time=LOCAL&day1=2&month1=01&year1=2019&hour1=0

[jgentry]

How are the results going so far with your baked sensors?

Unfortunately I can’t go into detail at the moment due to not having the time and I will follow up with more info as I’m able, but I’ve baked (another) brand new Davis 31 with positive results. Sensor goes to 100% AND this one follows the SHT75 when humidity drops which I’ve never seen before. This one has a clear potting not the black potting which my other “new” sensor had. I don’t know if that is part of the reason for the difference. The clear potting WILL MELT at 220F. It won’t turn completely into a liquid, but you have to be careful. More to follow as I’m able, but I’m cautiously optimistic from what I’ve seen so far and as you know I’ve been pretty critical ...

I’m baking an older SHT 31 with the black coating and see how it does. Planning on installing it in my remote unit tomorrow morning as long it’s not raining. You can view data from that 31 here:

https://www.wunderground.com/dashboard/pws/KALTHORS2?cm_ven=localwx_pwsdash

I’ll let everyone know when the 31 goes live. Right now, I have the 75 installed.

Shouldn’t left the filter cap on when I baked it. lol. It melted some.

Hopefully it didn't emit any of the dreaded VOC's....

That’s my thought too.

[CW2274]

Here is 01JAN19 for both. This is what I'm used to seeing with how the NWS ASOS rounds.

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?product=&past=1&stn=KDMA&unit=0&time=LOCAL&day1=2&month1=01&year1=2019&hour1=0

https://mesowest.utah.edu/cgi-bin/droman/meso_base_dyn.cgi?product=&past=1&stn=KTUS&unit=0&time=LOCAL&day1=2&month1=01&year1=2019&hour1=0

I am familiar. I compare here for ease but all the data is rounded compared to Meso. However, this page doesn't update timely until after business hours in the States...as stupid as that is...  but obviously still comparable.

https://www.wrh.noaa.gov/total_forecast/other_obs.php?wfo=twc&zone=AZZ504

[CW7491]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

[CW2274]

Funny thing is, I specifically remember calling Sensirion (I think in San Fran) when I went from an 11 to the 15 and asked the "spoke person" if I needed to "bake" my 15 for proper operation and got a resounding "no". So much for that...
Thanks for the work.

[jgentry]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

[CW2274]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Rain itself does not necessarily equate to full saturation, as a matter of fact, usually doesn't.

[CW7491]

Funny thing is, I specifically remember calling Sensirion (I think in San Fran) when I went from an 11 to the 15 and asked the "spoke person" if I needed to "bake" my 15 for proper operation and got a resounding "no". So much for that...
Thanks for the work.

Yeah, I'm not sure. Maybe it just helps with any potential contaminants in the Davis manufacturing process? Although my SHT75 performs better at the high end from it too. I haven't noticed any real improvement for the SHT75 on the lower end.

[CW7491]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Within a day or two. It did take a little time for it to rehydrate a little, so it was initially slow to come up, but once it did, it hit 100% like never before. But we have lots of saturated conditions here in fog and mist this time of year. It's been raining for hours here right now and it is at 95%, so as CW2274 says, rain doesn't necessarily mean saturated air.

[jgentry]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Rain itself does not necessarily equate to full saturation, as a matter of fact, usually doesn't.

True.

[jgentry]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Within a day or two. It did take a little time for it to rehydrate a little, so it was initially slow to come up, but once it did, it hit 100% like never before. But we have lots of saturated conditions here in fog and mist this time of year. It's been raining for hours here right now and it is at 95%, so as CW2274 says, rain doesn't necessarily mean saturated air.

Gotcha. It’s up to 99% now.

[jgentry]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Within a day or two. It did take a little time for it to rehydrate a little, so it was initially slow to come up, but once it did, it hit 100% like never before. But we have lots of saturated conditions here in fog and mist this time of year. It's been raining for hours here right now and it is at 95%, so as CW2274 says, rain doesn't necessarily mean saturated air.

Gotcha. It’s up to 99% now.

Now it’s flipping back and forth from 99% to 100%. I like it.

[CW7491]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Within a day or two. It did take a little time for it to rehydrate a little, so it was initially slow to come up, but once it did, it hit 100% like never before. But we have lots of saturated conditions here in fog and mist this time of year. It's been raining for hours here right now and it is at 95%, so as CW2274 says, rain doesn't necessarily mean saturated air.

Gotcha. It’s up to 99% now.

Now it’s flipping back and forth from 99% to 100%. I like it.

Great to hear. My baked SHT75 generally gets to 100% quicker. But that they both get there at all with consistency is a win for me.

It also helps with the lower end due to software. Because it will go to 100%, I've put a -2% offset in my Envoy through Weatherlink so that a raw reading of 100% is 98% in Cumulus which I tell to report 98 as 100%. So my humidity will jump from 97% to 100%, but that equates to about a 1°F dew point depression and mimics what I've seen from the NWS ASOS in my earlier post. (Plus Sensirion's datasheet says 99% should be reported as saturated air anyway.) Then the whole rest of the scale I benefit from a -2% offset to help with the high humidity bias. Last really dry spell we had, the SHT75 was reading 3-4% high at about 20% humidity. This will cut that error in half and if I need more, I simply can use the calibration in Cumulus to make further adjustments in lower humidity. I think this will work much more accurately in the mid and low humidity ranges. Before it was a compromise of using a calibration slope that helped enough in the mid range without completely distorting the low range humidity with too much of a correction. Unfortunately, probably not helpful for folks like CW2274 who see extreme low humidity.

[CW2274]

To follow up on more details of my holiday baking, the Davis SHT31 that I originally baked would get to 100% after the bake as I've described. The SHT75 I baked did the same. The SHT31 before would only get to 98%. As humidity dropped into the 80s and 70s, the Davis 31 started to show a wet bias compared to the SHT75 by about 3%. This was consistent with what I have been frustrated with with these Davis sensors. This sensor had black potting and I believe it was manufactured in June 2019.

I got another Davis 31 with clear potting that I believe was manufactured in November 2019. Before the bake, this sensor ran high on humidity at room temperature like all the rest. After the bake, it performed significantly better at room temperature. After the bake it also consistently hit 100%. Most importantly, this sensor will follow the SHT75 almost exactly as the humidity dries out into the 70s. Unfortunately I haven't seen below that. I have never seen a Davis 31 follow the 75. It almost always has a high bias as it dries out, so this is significant to me. I have one more sensor coming and will follow up. I will also follow up if I see lower humidity levels or if I test the current one inside.

With this next sensor I plan to try to shield the potting better during the bake if it is the clear potting as it does melt some. If anyone plans on baking theirs with clear potting, be sure to be careful about the melting. I may simply try to wrap most of the next one in aluminum foil. I should have mentioned that I do remove the filter for baking (sorry jgentry). If this new sensor has black potting I will probably return it.

No problem. Lol. How fast does the baked sensor goes up to 100%? It has been raining all day and my remote station with the baked sensor has peaked at 98% so far.

Within a day or two. It did take a little time for it to rehydrate a little, so it was initially slow to come up, but once it did, it hit 100% like never before. But we have lots of saturated conditions here in fog and mist this time of year. It's been raining for hours here right now and it is at 95%, so as CW2274 says, rain doesn't necessarily mean saturated air.

Gotcha. It’s up to 99% now.

Now it’s flipping back and forth from 99% to 100%. I like it.

Unfortunately, probably not helpful for folks like CW2274 who see extreme low humidity.

Other than not pulling the 100% trigger, I'm still pleased with this sensor's overall performance. I considered the next time I pulled the ISS into the house I'd bake the sensor...but the problem with that is I have zero idea how long it would be before I see a "100%" day. The sensor could be completely back to "normal" by then. Oh well..

[jerryg]

Well i decided to bake my new 31 which was showing about 1 to 2 percent high on the bottom end and on the top end in pretty good fog it was a solid 97 percent and bounced up to 98 percent. Well after baking it now shows to be right on on the lower end and in moderate fog shows a good 98 percent and goes to 99 at times. Now will have to wait to see how it does in dense fog but baking seems to have got it back in calibration.

[jerryg]

I just wanted to add this note about baking the sensor, i had an old sht15 and a sht 11 in a draw of poor sensors, they both maxed at 97%. I figured why not try and see if baking them would work and it worked really well with both of them maxing on my test setup at 99% which is uncommon, most max at 98% but do better when installed outdoors. So i am going to dig around in my sensor draw and see if i can get anymore to come alive. Oh yes the response time is much improved too.

[AWL]

Thanks
So you bake the whole circuit board in the oven?
Or do you unsolder the sensor and bake?

what do you place on, cookie sheet or something?

Valid questions    At what temperature for how long? Hoping one of you "Bakers" might help me out?  Thinking of doing this also. Have a 31 I bought in January 2019 and put it to work in August.  Not very happy at all. Now will only get to 94% in heavy fog lasting for hours. Will sometimes jump up a couple of more percent but only for a few seconds. Have a new one I ordered a week ago on my desk so will change out next week. Have a spare VP2+ in the garage that I might put in service after hopefully baking the 31.

Doug

[jerryg]

I followed the info in a prior post which said a temp. of 220F for 10 hours. I have been doing mine in a toaster over, got the temp set with a thermometer and it worked from about 215 to 225 degrees and has worked out real well.

[AWL]

I followed the info in a prior post which said a temp. of 220F for 10 hours. I have been doing mine in a toaster over, got the temp set with a thermometer and it worked from about 215 to 225 degrees and has worked out real well.

Thank you so much for the information! 10hrs....wow! Looks like I might need a toaster oven also   Long time to run the kitchen oven!

Thanks again, Doug