Topic: SHT11 sensor failures in Davis VP2 ISS and 6382 Temp/Hum Stations

[SLOweather]

We've talked about this subject in a couple of other threads, but I wanted to start a thread just for failures of these sensors in these stations to amass a little knowledge base, and pass on some info I just learned.

If you have had one of these fail, please post how it acted when it failed (no temp/out of range temp/no humidity/out of range humidity/etc.)

Background: Depending on weather you measure to the south or west, we live 6-10 miles from the Pacific Ocean. I either maintain or know the owners of a dozen or so VP2 stations. In the past few years, I have replaced at least 2 temp/hum sensor boards, and know of 3 or 4 more. Emperically, it seems that the closer to the ocean the station is, the shorter the life of the sensor.

Lately I have been replacing the SHT11 sensor itself on the board at considerable savings.

I know from other forum posts that Davis has continued to refine the design of the sensor board, and that it may be that earlier problems we observed were caused by corrosion rather than the sensor.

Today, I went right to the source and spoke with a support engineer at Sensirion, the SHT11 manufacturer.

He was unaware of any current issues with the chip that would cause it to fail except for corrosion of the connections to the sensor. My experience with successfully replacing the sensors would seem to indicate that Davis's current potting is working and the chip itself is the point of failure, However in the interest of completeness, I have access to one more bad sensor that I will try reflowing the solder on before I replace the chip.

In any case, he did me offer a couple of suggestions:

1) Examine the sensor opening under a microscope for corrosion, salt crystals, or debris. I don't have ready access to a 'scope, but I'm going to see what I can see with a 10x loupe.

2) Flush the sensor with distilled water and, after air-drying, see if it works. I'll try that on the other dead sensor.

And, if you have a dead sensor you don't want, I'd love to take a look at it.

[moehoward4]

My T/H sensor on my VP2 ISS died after about 4 years. We had been getting a lot of rain and the first time it acted up, I got dashes in those spots. After a day or two of dry weather, it came back to life. 3-4 weeks later, a lot more rain, and it took much more time to come back...4 or 5 days. I ordered a new T/H sensor from Archer and replaced it. I have a 637/82 and a regular 6382 both with newer revision #'s, time will tell.....Jack

[Yfory]

I will place my last comment here, in discussion new discussion, since it is becoming more general.

+++

This is a good discussion.

I have been working with a high quality Honeywell humidity senor for a few weeks now and I can verify your comments about taking care to weather proof the humidity sensor itself - as odd as that sounds.

I am experimenting with the Honeywell HIH humidity sensor series and Honeywell is very specific about the conditions the sensor will experience.

If a sensor is to be exposed directly to water droplets or wet environments, they suggest a very special "covered" version which resists water droplets but still measures air or other gas humidity. Obviously the sensors can not be sealed but the problem of wet (industrial) environments are very difficult to monitor for humidity without permanently damaging or at least changing the output of the sensor by getting the actual sensor surface wet!!!

It is the technology of the "cover" that is tricky.

The HIH series has an analog output which happens to interest me. The HIH series must be digitized to work with most weather stations.

+++

[DanS]

Quote: "If you have had one of these fail, please post how it acted when it failed (no temp/out of range temp/no humidity/out of range humidity/etc.)"

Not installed in a Davis but the sensor chip itself applies here. My failure wasn't immediate. The humidity slowly increased over a day or 2 until it reached the upper 90% range and stayed there. After this, the temperature bottomed out to the chip's lower range limit, around -39.8 if I recall. With a magnifying glass I could see cob web looking debris inside on the glass chip portion with the plastic cover removed.

[AVman]

The Davis VP2 I take care of has read -90 and no humidity the whole time I have monitored it, which is about a month.  The station is on top of the Gloucester, MA middle school which is next to a salt marsh, and all of Gloucester is on the Atlantic Ocean.

I will do some investigating once I manage to get the station down, but it is a tricky to get everyone coordinated to take it down, and I have 5 VP1's at the other schools.  You can see the bad state of affairs here danchase.net

Point of note, the Vantage Pro 1 seems to have a much more robust temperature sensor, I posted a pic here http://www.wxforum.net/index.php?topic=14175.msg141465#msg141465
I wonder if you could use this old style on the VP2 for salty environments in stead of the complex and relatively expensive SHT11?

[johnd]

I wonder if you could use this old style on the VP2 for salty environments in stead of the complex and relatively expensive SHT11?

Yes, you could in principle - the post 2006 VP2 SIM boards were always supposed to be auto-sensing as to which type of sensor element was fitted.

The catch is of course that the old type of sensor element are virtually unobtainable now.

[jerryg]

Mined failed while reading the correct humidity which was around 98% it suddenly dropped to around 50% and stayed there. I replaced it with a spare sensor and later checked the sensor with my spare vp2 and it was reading right, so i thought it must have dried out being in the house and the high humidity had something to do with it. I set it aside for awhile and one day decided to check it again and it read 0% then after awhile i looked again and it was up to 45% so i wrapped a wet cloth around it and it went to a max of 95% and when i took the cloth it settled down to 10% so i replaced it with the sht15 sensor and it is working fine.

[AVman]

Here is the dead sht11 from a VP2.  You can see the legs and whatnot are corroded from the salt air. Davis sent me a rev 2009 board to replace it and suggested I invert it, which seems like a good idea:

instead of screw it to the bottom of the station like it was

Hopefully it will work for a long time when I put it back.
And thank you johnd for the help, if this sensor dies I will try and replace it with a board from an old VP1 we have as parts. 

[jerryg]

I just had another sensor fail. Had been working fine for over a year then zap, dead as a doornail. I noticed the temp and humidity was not changing on wu and looked at the console and had the dashed lines,  replaced the sensor with a spare and everything back up and running ok. I replaced the sensor with a sht15 and all is good now. My first station sensor died after only one month in use also. Both of these sensors failed when there was alot of lightning around but no near by strikes. I wonder if they are sensitive to the air being electrically charged?

[avatar42]

For those that find this down the road. I was seeing the -90 temp and 255% humidity. The problem was coons had chewed through a couple wires. If you see this check your connections and wires.

[DanS]

I just had another sensor fail. Had been working fine for over a year then zap, dead as a doornail. I noticed the temp and humidity was not changing on wu and looked at the console and had the dashed lines,  replaced the sensor with a spare and everything back up and running ok. I replaced the sensor with a sht15 and all is good now. My first station sensor died after only one month in use also. Both of these sensors failed when there was alot of lightning around but no near by strikes. I wonder if they are sensitive to the air being electrically charged?

Along the "air being electrically charged" thought, I'm wondering if it would do any good to run a ground rod below the ISS up to the sensors circuit minus/ground side to bleed off possible charges? You seem to have this happen quite a bit.

[therock64]

Hi;
I have a problem here on the Atlantic side... It seems like I can only get about 2-3 years out of my T/H sensors... For the past 12 years I have replaced 3... The last one was 2010, all is still good for now. When it does go I get a temp of -68 deg C and the hum is a dash. Last time I got 2 so I have a back up... I think the problem I have is the sudden Temp ups and downs and the salt water content in the air. My main problem, I think is our famous North-Easters,  where the snow and rain are horz and blows up and around. One time when I replaced the sensor I had snow packed inside the wedges, so it may be a problem with water on the sensors for expended periods on time. ALL my sensors died during the winter months, you know when it is more work to replace...  So it may be the low temps and high Hum with me...

[_Niklas_]

My sensor went bad a few weeks ago, Im going to try and replace it with an SHT-11.

Do you guys know how the wiring goes, which pins go where from the SHT-11 to the Davis ISS ?

/Niklas

[DanS]

My sensor went bad a few weeks ago, Im going to try and replace it with an SHT-11.

Do you guys know how the wiring goes, which pins go where from the SHT-11 to the Davis ISS ?

/Niklas

Hi Niklas. Couldn't you just pull the old one and replace it with the new one? The pin-out should be identical.

[_Niklas_]

My sensor went bad a few weeks ago, Im going to try and replace it with an SHT-11.

Do you guys know how the wiring goes, which pins go where from the SHT-11 to the Davis ISS ?

/Niklas

Hi Niklas. Couldn't you just pull the old one and replace it with the new one? The pin-out should be identical.

Yeah, that would work best I guess, but Im not that good with the soldering gun yet. Those sensors are small, and my hands are too big..

I found sensor already mounted to a small electronics card.. with pins that you attach jumper cables too.. sord of.. 

Got it up and running yesterday, so now I can sleep good at night again..   

Lets see how long it lasts, I live in a not too hostile environment so its not exposed to severe weather elements..

Niklas

[njc68]

Greetings,

Had this sensor fail after about 4.5-5 years.  Dewpoint/RH readings are very low.  Interestingly, in the daytime (70-80F nom) I get a reasonable reading.  Nighttime (50-60F or lower) the dewpoint goes down near or below 0F, but it's foggy so the dewpoint must be pretty close to the temp).  I disassembled the unit last night and the solder looked good as did the sensor itself.  I hit it pretty good with a heat gun, knowing full well it would likely permanently damage it but I wanted to experiment.  It actually seems to have improved or possibly even fixed it.  Regardless, I have a SHT15 on order from Mouser for ~$30.  Beats the Davis price.

Regards,
Nick

[Weather Spares]

We offer a repair service for these units swapping the faulty SHT11 for SHT15 units, including the newer ones that are sealed to reduce moisture getting to the solder points.

Pretty much every sensor that has come in is showing the same symptoms of showing poor readings particularly in warm moist conditions. A couple of deep slow breaths directly over the sensor cause the temperature to rise to around 28C (82F) and the humidity plummets to <10% followed shortly by --%. Obviously breath is quite moist and it shouldn't be dropping like a stone.

We very rarely see problems on the temperature side of the sensors.