Humidity Temperature on my Davis Vantage Vue

[raul_sbd]

I have had my Davis Vue for nearly 2 years now I use it with Weatherlink without problems. Today I experienced a reading of -42 degrees on cumulus and when I went to the console it was showing lines on the external temp and 0% ext humidity.. Very annoying and frustrating.. It was a very expensive weather station and OK today has rained a lot in Manchester but I don't think this is a reason for this to happen.

Does anyone experienced the same problem?? Does it mean I will need a new T/H sensor? If so.. Where I can get a replacement at a reasonable price and will it be very difficult to replace the sensor?..

Thanks in advance for your replies!

[steve]

Large negative temperatures with a VP2 are a sign that the sensor has failed or is failing - I know this from experience having had mine fail four or five times (I've lost count now) in nine years. I assume the same is true of the Vue, but I know little about the Vue so can't give any specific advice myself.

[raul_sbd]

Thank you very much Steve!!

This morning is back to give me accurate readings.. But not sure how long it's going to last hopefully doesn't fail more.. But then Steve what u did when ur TH sensor failed the 4 times.. Did you replaced for a new one? If so how much and where I could buy it? Is it very difficult the replacement diy?

Many thanks

[steve]

Yes, I replaced it with a new one. But as I said, mine is a VP2, I don't know anything about changing the sensor on a Vue.

[raul_sbd]

I believe is about the same as the iss looks the same on both models.. Was it v expensive and hard to replace? Where did you purchase it the new sensor?

Thanks again Steve

[steve]

I'm confused. The Vue ISS:

VueISS.jpg

looks nothing like the VP2 ISS:

VP2ISS.jpg

But anyway, on the VP2, replacing the sensor was quite easy. The cost for the VP2 sensor is about £150 in the UK or somewhat less if you are prepared to have one sent from the US. When it failed again recently, I decided to buy one from forum user "belfryboy" to see if his would last longer than the Davis one. Price was £59 including postage.

[BigOkie]

I'm confused. The Vue ISS:

VueISS.jpg

looks nothing like the VP2 ISS:

VP2ISS.jpg

But anyway, on the VP2, replacing the sensor was quite easy. The cost for the VP2 sensor is about £150 in the UK or somewhat less if you are prepared to have one sent from the US. When it failed again recently, I decided to buy one from forum user "belfryboy" to see if his would last longer than the Davis one. Price was £59 including postage.

Just curious Steve. Do you know why you have such a high failure rate? Is it your location by the sea? I'm just wondering so I can anticipate if mine will go out (being land locked in the southern plains of the US probably is not hard on the sensors I would guess).

[steve]

Yes, Davis say it is because of my coastal location. Here's a quote from an email from them: "Salt & Moisture are the nemeses of our sensors. They last longer in dry, arid environments.". They suggested I could prolong the life of the sensor by partially covering the radiation shield with "Glad Wrap and Scotch Tape". I declined that suggestion.

Dave Wheeler, a meteorologist who lives on another island about 30 miles from me, has had a similar failure rate. The last time I looked, he had given up replacing his.

[RayProudfoot]

I believe is about the same as the iss looks the same on both models.. Was it v expensive and hard to replace? Where did you purchase it the new sensor?

Thanks again Steve

Raul,

Why not contact either your supplier or alternatively this site has a replacement sensor. Fitting will obviously be extra but give them a call. http://www.weatherspares.co.uk/davis-va ... -323-p.asp

[prodata]

If I might offer a couple of comments:

Davis do not make modern digital T/H sensor elements themselves - it's a highly specialist job to make that sort of chip. Instead, as many will know, Davis buy in the relevant T/H sensor elements from a specialist manufacturer and, while Davis don't disclose this, it's virtually certain that the maker is a Swiss company called Sensirion and, in particular, the SHT11 chip is used. To what extent Sensirion are the only or at least the dominant maker of such chips in the mid price range I don't know, but it's a make that is widely used by AWS makers. Davis then incorporate this chip in their own T/H sub-assemblies. There may not be many alternatives in the right price range.

While it's easy to make a sealed temperature probe with a long service life, the same is not true of RH. As far as I can see, the only way (short of reverting to eg wet and dry bulbs or more sophisticated sensors like a chilled mirror hygrometer) that RH can be sensed is to use a sensitive active surface whose properties change when exposed to humid air. It's almost inevitable that this surface is going to be vulnerable to ageing, pollution (including eg microscopic salt spray in the air) etc and so it's unsurprising that T/H sensors of this type have a finite service live, though how long will vary with circumstances, climate and environment. I do know that some high-end AWS makers that use Sensirion-type sensors recommend replacing the sensor every 2 years - that sounds like overkill to me and many eg VP2 T/H sensors last far longer than that but it is recognition of the finite service life.

The Davis T/H sub-assemblies are different (ie not interchangeable) between Vue and VP2 and indeed between earlier and later Vue models.

There are two reasons that VP2 T/H sensors start to become faulty. One is an intrinsic issue with the Sensirion sensor. The other is to do with the design of the sub-assembly and circuit board that carries the sensor element. In earlier VP2 stations (let's say 2007-2010 especially) field experience eventually showed that the sub-assembly design wasn't fully optimal and its design was gradually refined. We're now up to revision J (marked on a label on the sensor) which has been out for maybe 2-3 years now, possibly a little longer.

Rev J sensors have a substantially improved service life and few such sensors now seem to fail for reasons other than issues with the Sensirion sensor element. So for anyone who might have given up on replacing the T/H sensor a few years back before Rev J became available might want to try using a Rev J one. Ultimately, the sensor element will still have a finite life, but 5 years is a common experience unless the AWS is sited very close by the sea or in a very damp and exposed location that allows the sensor element to get flooded with wind-blown rain.

[mcrossley]

I still don't understand why Davis do not put the sensor behind a Gortex type membrane as Sensirion recommend for harsh environments. Sensirion even sell a chip enclosure for that purpose. Davis use a course mesh which is no potection against fine particulates.

[steve]

Rev J sensors have a substantially improved service life and few such sensors now seem to fail for reasons other than issues with the Sensirion sensor element. So for anyone who might have given up on replacing the T/H sensor a few years back before Rev J became available might want to try using a Rev J one.

That's interesting - looking at my records, I can see that when my previous one failed in late 2012, I managed to persuade McMurdo to replace it FOC (as the previous paid-for replacement lasted a very short time, six months I think), and that one failed after just over two years (replaced by the belfryboy version earlier this year).

The one from McMurdo in 2012 is still sitting on my desk, and I can see that it's a Rev C dated 2009. So perhaps a later revision would have lasted longer.

[prodata]

I still don't understand why Davis do not put the sensor behind a Gortex type membrane as Sensirion recommend for harsh environments. Sensirion even sell a chip enclosure for that purpose. Davis use a course mesh which is no potection against fine particulates.

That's fair comment and I don't know either is the response. Maybe slower response times might be one answer or, of course, cost - not saying that either is a seriously valid reason, just guessing at possible justifications. I can primarily only see things from the support side - design decisions are something that's entirely done within Davis and pretty much a closed book.

[mcrossley]

I still don't understand why Davis do not put the sensor behind a Gortex type membrane as Sensirion recommend for harsh environments. Sensirion even sell a chip enclosure for that purpose. Davis use a course mesh which is no potection against fine particulates.

That's fair comment and I don't know either is the response. Maybe slower response times might be one answer or, of course, cost - not saying that either is a seriously valid reason, just guessing at possible justifications. I can primarily only see things from the support side - design decisions are something that's entirely done within Davis and pretty much a closed book.

They could see it as an opportunity, and sell a 'harsh environment' sensor for a little more money - or reduce the price of the standard sensor a little

[prodata]

They could see it as an opportunity, and sell a 'harsh environment' sensor for a little more money - or reduce the price of the standard sensor a little

TBH it's enough of a nightmare at present with the introduction of the VP2 variants with the SHT15 sensor - I wouldn't want to encourage them to diversify the T/H sensor variants even further, not that they're likely to bite anyway I suspect.

But it's obviously an opportunity for someone to market a replacement screen for the T/H sub-assembly. I guess all it needs is for someone to find a way of sourcing the superior material and to secure it within the existing screen's pyramid structure, ie in place of the current fine mesh.