Temp/Humidity sensor Davis VP2

[TonyC]

It seems that 3 years is the time that weather stations start packing up. My previous LaCrosse was that age when things started to fail on it. My VP2 has just passed its third birthday and the temp/hum sensor has gone faulty. Doing a google search shows that this problem is common with stations that age. The cost of replacement parts is very high. The temp/hum sensor is priced at $133 on Davisnet. Having problems contacting them, so I've been looking around for any alternative.

The sensor consists of a SHT11 (or SHT15) chip with a 0.1uf capacitor across voltage input. The chip itself you can buy for around $25, so it's hard to fathom why the replacement board is so expensive. The drawback is that a lot of dexterity is required to remove and re-solder the chip on the old board.

Has anyone else looked into this?. I've located a Sparkfun breakout board with a SHT15 chip mounted so in theory, hooking the cable up to it should be all that's required apart from weather protecting the sensor chip. All I need is the courage to give it a go!

If anyone has played around in this area, some feedback would be good.

cheers
Tony C.

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[TonyC]

I've decided to give it a try and have ordered the Sparkfun board to satisfy my curiosity.
Will keep you posted as to whether this is a viable replacement and if it is, details on how to go about it.
I've obtained the pin-out connection details of the ISS RJ12 and will fit a cable to the board so that I can test it without having to dismantle everything first.

cheers
TC

[TonyC]

UPdate on the Temp/Humidity sensor problems.

After a long consultation with Dr Google it appears there have been on-going problems with this sensor which Davis have been experimenting with different methodology to solve. Moving the sensor from the top of the plate to the bottom. Coating the board with a rubberised covering and I believe the latest sensor boards now have the rubber compound removed. As the problems only manifest over time and due to the different environs each station operates under, I can understand the difficulties Davis have.

One theory is the rubber compound has a carbon element and under extended moisture conditions (fog, wind driven mist etc) condensation will build up under the compound which reacts with chip circuitry. It seems to hit the humidity more so than the temperature.

I removed my sensor this morning and sure enough it had the rubber compound. Instead of removing it all, I just removed the piece which surrounds the SHT11 chip leaving the rest which covers the wiring connections and tracks on the board intact.
I used a hairdrier for 5 minutes on a very low heat setting to dry off any moisture. Assembling it all and firing up the station the humidity is reading within a more sensible range. I have a portable temp/humidity meter and the Davis is reading about about 5% lower than than it. Temperature matches reasonably close with the Davis a touch higher.

A southerly front is about to hit so it will be interesting to see what happens.
[edit 15mins later]
Temp has gone down and humidity has plummeted with it, so... so much for that experiment. Back to the drawing board.

cheers
TC

[Phil]

I have just had the same happen to my VP2 and have ordered a new one from Davis in Hamilton, total price inclkuding freight $106,

[TonyC]

After a lot of frigging around I ended up buy the genuine article from Davis for the same price. How old was yours? 3 years seems to be the time they pack up.

cheers
TC

[David]

My one stopped working in April 2013, which was 3 years 5 months since set-up. But it is worth noting it had been quite wet around the time of failure, so I wondered if moisture had got into the sensor somehow.

I actually just replaced the fan for my radiation shield yesterday. Looks like I really need new rechargeable NiCad batteries for the fan as well. I have had to take the old ones out due to them affecting the fan speed (making it really slow). As a result, I now have a good fan speed in direct sunlight but no fan speed at all once the solar panel loses sunlight. Might be waiting 3 weeks for batteries to come in stock with Davis NZ!

Apparently you're supposed to replace the fan motor & NiCad batteries every 2-3 years (mines been going almost 5 years). Must have missed that part in the manual!

[GrantK]

I've just replaced the second Temp/Hum sensor in my VP2 and got everything working again.  The station is now 5 years old and each of the Temp/Hum sensors has lasted almost exactly 2.5 years.  I noticed this time there is a new sensor available with the latest Sensiron SHT31 chip.  As noted on various webpages, this necessitated a calibration offset of -0.5C to get the correct reading.  It's no big deal and I would certainly rather have the later more accurate sensor, so I've ordered an extra spare to keep in stock for next time this happens.

As others have noted above, there have been some improvements in treatment of the PCB to hopefully make these sensors last longer.  Fingers crossed on that score...

While I had everything apart, I cleaned each element of the radiation shield and replaced the fan and NiCd cells which is recommended every 2 or 3 years.  Last time I did this, the fan lasted less than a year, so here's hoping this one is better.

[davidrg]

I had to do the same to my Vantage Vue back in April. The sensor lasted around 1136 days (9-FEB-2013 to 21-MAR-2016). Of course because all the electronics (besides the solar panel) in the Vue are potted you have to replace the whole lot as a single part - its not possible to just replace the temperature sensor PCB on its own. Cost around $250 IIRC so not as bad as I was expecting.

As an added bonus I discovered a huge ant colony in the ISS. There were so many I ended up just pulling the ISS to bits and leaving it all outside to let the ants move all their eggs out themselves over a few days. They'd slowly been re-purposing the potting for their own purposes too - stripping it off the PCBs and using it to block up all the holes in the ISS enclosure.

For the Vantage Pro2 at the bach I think I'll have to keep a spare Temp/Hum sensor PCB on hand so I can replace it in a single trip when it eventually fails in a year or two. How much did the replacement SHT31-based module end up costing?

[GrantK]

This is my one complaint with the Davis electronics enclosures -- they're just not ant-proof!

Fortunately, my ISS has never been invaded, possibly because it's on a metal pole which the ants don't like crawling up.  I've had 2 remote temperature stations and one remote anemometer transmitter enclosure invaded and both are on wooden poles.  In 2 out of 3 cases that meant replacing the transmitter board so next time I more carefully sealed up the cable openings with black windscreen sealant.  Even so, in one case the ants have got in again, although the transmitter board is still OK.  The square rubber grommets with a cross cut in the middle are a joke when it comes to keeping ants out!

USD 44.95 plus a bit of postage.  I've seen them advertised for much higher prices elsewhere.  If you like, I can PM the website address.  I'd rather not advertise the fact within NZ as the local distributor will probably get upset.