Cumulus Support

steve wrote:I agree; I'm not trying to say that you should have expected yours to have failed by now - I don't think you should. I didn't expect to have had to replace as much of mine as I had to, even here.

Maybe Davis kit isn't as robust as we think. You certainly seem to have had some bad luck. Do you visit WxForum? Davis do seem to have a strong fan base there but there will inevitably be an element of home support.

I'm curious as to what people think can be improved on the latest versions of the Davis T/H and wind sensors (at least short of a complete technology change like moving to an ultrasonic anemometer, which brings its own set of issues).

The Rev J version of the VP2 T/H sensor is totally encapsulated other than the active surface of the Sensirion sensor itself, which can't be covered for obvious reasons. If there is failure of these Rev J sensors then I'm struggling to think what else could be done, other than for Sensirion themselves to improve their sensor's robustness, or Davis should switch to a different make of sensor (but there don't seem to be many options, at least in the price range of the Davis stations). Mounting the sensor upside down in the VP2, as Davis have been doing for a couple of years now (except in FARS models), reduces the possibility of water, especially salt water for more coastal locations, pooling on the sensor surface, which is one known cause of degradation. What further solutions can anyone offer for further improvements?

The anemometer is a slightly different proposition because it still obviously involves more mechanical parts. But the recent change to a solid-state speed sensor ought to give a significant improvement in MTBF and perhaps also a more consistent performance. It's too soon after the introduction of the solid-state version to have accumulated any meaningful stats, but Davis seem to have an expectation of an extended service life. I'm also aware of previous-version VP2 anemometers that continue to give good service for many years (I've got one here that must be 10-12 years old now and still seems to be functioning OK). But I know that other examples do tend to give up after 4-5 years and occasionally sooner.

Hi John,

Thanks for initiating a discussion on the Davis sensors. My T/H sensor is currently fine so I will keep my comments to the anemometer. I don't have an engineering background so my comments are those of the layman.

Let me start by posting the comments my friend made after inspecting my failed anemometer...

As you can see from the pictures the reason for the Cups "doin one" would seem to be due to the fracture in the retaining hub (shown on the shaft to allow you to see it) this I am surmising would be due to weathering form the previous loss of the cowl. The ensuing fracture would then allow the cups to fall down the shaft over time until finally falling off in a strong gust like on the evening they went walkabout.
You can probably diagnose this better than me John but the problem seems to have started some weeks earlier when the cowl at the bottom of the assembly came off exposing the shaft. That eventually fractured during last Wednesday's storm. From a layman's point of view I find this worrying. Is this how most anemometers fail? I would have expected the reed switch to be the weakest link - not the general assembly. As I said to Steve the UK doesn't have extremes like the US and I would expect the anemometer to last quite a bit longer than 4.5 years.

As for how much better the new model is only time will tell I suppose. The solid-state sensor will, I trust, last many years. But I also hope that the assembly is built to a higher specification.

I assume Davis still only provide a 12 month warranty for all their equipment? That's the legal minimum isn't it? A 3-4 year warranty would give me more confidence in their products and I do admit my confidence in their build quality has been affected. I will be writing to them to express my dissatisfaction at the structural failure of the unit.

John, I'd be interested to see the latest T/H cct board. Mine failed due to eventual moisture ingress under the black rubber Davis has used. If any of the cct board is exposed and it is the same (common) fibre type used before, then it will still be susceptible to moisture penetration eventually as fibre boards are not 100% water proof. If they switched to a fully glass fibre board it would be better.

Davis are using a cct board for three reasons that I can see:

1. To mount to the external decoupling capacitor the Sensirion chip requires on the power line.
2. To make the connection between the cable and chip.
3. To physically mount the assembly in the radiation shield.
EDIT: Add number 4.
4. Because they have always made them like this.

I have used the Sensirion module rather than the chip, this has the capacitor pre-mounted on a very small (tiny!) board, it is a couple of pounds more expensive than the bare chip.

I have connected the cable directly to module, then thinly 'potted' the cable, joint, and the module board area in epoxy, leaving only the sensor plastic body exposed. For mounting I have the module at right angles to the cable, and just use the P-clip to mount to whole lot in radiation shield - at the top hanging down.

My mk II version will then have the whole module enclosed in sealed vapour permeable membrane (similar to Goretex, but more porous for a better response time). This will keep out air borne salt in harsh coastal environments, and 'critters' everywhere else.

The Sensirion module is designed with a very narrow 'neck' between the sensor and the cabling area to keep down the thermal mass at the sensor, and also has a hole in the board where the humidity sensor is located to allow airflow from both sides. The Davis design has neither of these, the large cct board increases the thermal mass (and the ever increasing amounts of thick rubber they are applying make it even worse), and they mount the chip flat on a solid board blocking the access of air to the other side of the sensor. Lastly Davis only provide a 'critter' protection mesh, it does not prevent air borne contaminant penetration that a proper membrane would (in their application notes Sensirion do recommend using a Goretex membrane when using the sensor in harsh environments, and do supply a suitable housing with a membrane built-in).

So yes, I think Davis could improve the T/H sensor - they could even use the tighter specified version I have used which only costs a couple of pounds more. The question is would it be economically viable for them to do so.

I'm a relative newcomer to Davis equipment but I'm surprised at how much rotor vibration can be felt on mounting tube. Is any allowance made for balancing during or after manufacture?

Ray, the problem you've seen is with the older pattern of wind cups. For the past few years, the cups have been a stronger all-in-one moulding (ie the separate individual cups are no longer used).

This is an illustration of the incremental updates to the Davis stations that happen on a frequent basis. Although the VP2 as a model has been out several years' now, the detailed design is still being developed year on year and the current examples are enhanced in several respects from those of even a year or two back. But this isn't necessarily obvious in the marketing and sales material unless you're an expert in reading the Mfg Codes that Davis use (the revision letters that Davis use in these codes do give important clues, but even then aren't the whole story, eg the current anemometer is still known as a 6410 anemometer even though the latest version is significantly enhanced).

A change to eg a formal 2 year warranty is something that dealers have been lobbying for for quite a while. It actually there informally in many cases, ie genuine failures in Year 2 of ownership are usually handled sympathetically, but I know that's not quite the same as a formal 2 year warranty. I suspect the core problem is that Davis is a US company and that 1-year warranties are the norm in the US (no doubt someone will correct me if this statement is significantly in error). It's difficult then for overseas service centres to offer a warranty that's not then backed up by Davis centrally. What needs to happen is - being parochial for a moment - for the UK parliament to enact the existing EU legislation that supports 2-year warranties for electrical goods (which isn't currently the case). But the political climate obviously isn't going to favour that at present. But if that were to happen then don't be surprised to see a slight price rise.

Hi John,

So it seems it's a case of continuous improvement and the customer doesn't know which version he's getting. I know the VP2 had been out for a couple of years before I bought it (Apr 2009) so you might have hoped any early flaws had been ironed out by then. Was it just the wind cups or the whole assembly they modified.

I'm still a bit miffed because something actually dropped off causing the eventual failure of the unit. How could a design be so bad that something just drops off? The retaining hex bolt was certainly tightened enough. Could it be over-tightened? Might that have caused it?

Maybe when Davis have more confidence in their products they will extend the warranty beyond 1 year with enough dealer's pressure. I know the stations can be placed in extreme weather areas so it's a difficult one for them to call. Maybe when the VP3 comes out they might have more confidence.

Thanks for your input, much appreciated.

RayProudfoot wrote:So it seems it's a case of continuous improvement and the customer doesn't know which version he's getting.

That makes it sound like Davis are deliberately setting out to mislead, which isn't the case. They're simply not good at providing a public change-list of all the various enhancements that have been carried out (which they effectively do for eg the console firmware, shame they don't do the same for the hardware). If you buy from a reputable dealer then you should be reasonably sure of getting something close to the latest available version (there's inevitably some buffer stock in the supply chain, but good dealers try to minimise this effect).

I know the VP2 had been out for a couple of years before I bought it (Apr 2009) so you might have hoped any early flaws had been ironed out by then.

Identified early flaws had been ironed out. But some issues are only apparent over extended time (years).

I'm still a bit miffed because something actually dropped off ... Could it be over-tightened?

The fault you've seen is rare - it's not a systemic issue. Yes over-tightening is one possible explanation.

Maybe when Davis have more confidence in their products they will extend the warranty beyond 1 year with enough dealer's pressure.

The pressure won't come from distributors in general. What will/would make a difference (in the UK) is the point I mentioned - ensure that EU law is fully implemented in the UK.

prodata wrote:That makes it sound like Davis are deliberately setting out to mislead, which isn't the case.

That was certainly not what I was suggesting. I think your next sentence sums them up.

They're simply not good at providing a public change-list of all the various enhancements that have been carried out (which they effectively do for eg the console firmware, shame they don't do the same for the hardware). If you buy from a reputable dealer then you should be reasonably sure of getting something close to the latest available version (there's inevitably some buffer stock in the supply chain, but good dealers try to minimise this effect).

Perhaps they don't consider it important to keep the hardware changes in the public eye. Having bought from a reputable dealer I have every confidence I bought the latest version available.

Identified early flaws had been ironed out. But some issues are only apparent over extended time (years).

Fair point. Let's hope the latest model doesn't need any further work.

The fault you've seen is rare - it's not a systemic issue. Yes over-tightening is one possible explanation.

Well they do tell you to ensure the bolt is very tight. I would be disappointed if it was overtightened but I'll probably never know.

The pressure won't come from distributors in general. What will/would make a difference (in the UK) is the point I mentioned - ensure that EU law is fully implemented in the UK.

I won't hold my breath.

Mark: Only just had a chance to respond to this part of the thread. Thanks for a typically well-informed post and you clearly know far more about the details of PCBA construction than I do. But a couple of comments:

The current Davis T/H PCBA revision is Rev J which is shown as the last letter on the Part No on a label on the underside of the sensor (ie 7346.166J). The board (presumably layout) revision is Rev CO or perhaps C0. I don't know enough about what the different boards look like to know whether it's fibre or glass. The overmoulding (or encapsulation or whatever the correct word is) is substantially more extensive than on previous revisions. It still does not cover the complete PCBA, ie including all edges, but there are only about one and a half edges remaining unprotected (which presumably Davis judge to be far enough away from any tracks not to represent a significant weakness in design). Looking at the black moulding on these latest units I have to say that it does look thicker and more thoroughly/professionally applied than on older T/H boards. As a layman it's difficult to imagine that there could be any moisture penetration below the moulding, but I'm clearly no expert.

Comments on detailed sensor construction etc noted. You obviously don't anticpate that the goretext type membrane is going to slow down the response time significantly (even after compensation for the lower sensor element mass)? Do you think that there's any actual difference between the different Sensirion part numbers (ie differing in nominal accuracy but of the same sensor type). I rather got the impression that they were just different selections from the same production run. So even the cheaper sensor could be just as accurate provided it was properly calibrated. But I'm with you - for any station that I'm designing, it's difficult not to automatically opt for the best available sensor for the sake of £2-3.

prodata wrote:You obviously don't anticpate that the goretext type membrane is going to slow down the response time significantly (even after compensation for the lower sensor element mass)?

I'm not sure until I try it , I plan on creating a small cylinder of material say 1cm in diameter to enclose the sensor. The amount of air that contains should have minimal effect, and the membranes are pretty thin and allow a surprising rate of air flow - if I can can get the right material.

I have as spare SHT75 hooked up to a RaspberryPi to continuously readout the data - those things react extremely quickly to humidity changes, you just have to breath out near the thing for the humidity to shoot up within a second.

As an aside, that sensor had started reading low on the humidity when outdoors on the ISS, so I swapped it for another one. I followed the Sensirion documented method of washing the sensor in distilled water, followed by a drying cycle. That cleared the contaminants and it reads accurately again. This is one reason I want to encase the sensor in a membrane, I don't want to have to repeat that process, or have the sensor readings drift unbeknown to me.

Anyway this is bit off topic for Ray's original problem.

To comment on the improvements of the anemometer over the last few years, I have personally seen a few which are:

1) The drip rings on the anemometer are now integrated rather than separate - less likely to get water ingress between the rings.
2) As mentioned by John, the wind cups are now a completely moulded so less likely to fall apart as in the case of the original poster.
3) The vane was weighted with a more substantial brass tip to give a more stable direction in stronger gusty winds.
4) The sensitivity of the 2013 anemometer was increased reading as low as 1mph and up to 200mph.
5) The reed switch and magnet mechanism have been replaced in the 2013 with the solid state measurement system - reed switches always ended up sticking.
6) 2013 the removal of the magnet from inside the wind cups near the spindle, someone mentioned vibration issues earlier on, and this little weight could of contributed to their problem. Make sure you check replacements are with/without magnet if you're replacing them peeps
7) Change of plastic moulding to something a bit more aerodynamic where the cups and vane are mounted on the arm.

So little changes, but all under the same model number and no doubt all to improve the design. I suspect that a VP3 if launched in years to come will probably stick to the same anemometer / vane design if these changes are seen to work over the long term without adverse design problems.

I have sent an email to Davis Customer Service this morning. I have copied ProData in so John is kept informed. Fingers crossed for a favourable outcome.

I appreciate I am very late in keeping you updated on my failed anemometer 10 months ago.

I did write to Davis (2 sources) about the failed anemometer and got the brush off initially with Davis saying it broke US Law for them to send me replacement cups free of charge. I challenged this and had another email a couple of days later asking for my home address.

Some time later I received not one but two sets of wind cups. I guess something got duplicated in their customer service department. Anyway, I was quite pleased with myself for persisting.

A couple of months ago my friend in Flixton ordered two spare VP2 sets of kit using a US-based relative. New rain gauge (with anti-bird plastic spikes), ISS shields, temp & humidity sensors and another anemometer for around £140 including import duty. Big saving on UK prices.

And the new anemometer has been working just fine since last December.