Topic: Wildly Inaccurate Rain Readings - Solved (Faulty ISS electronics)

[melmerby]

Hi all
This is my first post.
I'm located in Worcestershire in the UK

I have had a VP2 wireless since May 2011, without a problem except a failed back up battery in the ISS.

Over the Christmas period just gone the Rainfall readings showing on the console became totally erratic and unpredictable.
e.g. I would get a rainfall reading of 281mm/hr when it is not raining at all and at other times when it was raining - nothing.
The ISS reading on the data stream is always 100 and no other parameter is affected.

I checked the buckets and cleaned the connectors in the ISS and checked the battery, which was fine.
This made no difference to the erroneous readings.

I contacted Davis support and the reply suggested I change the station ID
This is the reply:
"Change the station ID


1. Put your unit is setup mode. Press DONE & MINUS at the same time. Let it sit here for ½ hour.
2. Make a note of the station number(s) listed on the screen. Note: If a Vantage Pro2 or Vantage Vue ISS has been installed in your area, its ID number may also be displayed.
3. We want to avoid these numbers. Choose a number that does NOT show up on the screen.
4. Press DONE to move to the next screen
5. Press the < and > keys to select the transmitter ID. Step through ALL stations and set ot OFF (use the minus key to turn a station off). When you select a transmitter ID, the ID number is displayed on the screen as well as the current configuration.  Turn ON the station you want. Press the + and - keys to toggle console reception of signals from transmitters using that ID on and off.
6. Press GRAPH to change the type of station assigned to each transmitter. Scroll through the station types - ISS, TEMP, HUM, TEMP HUM, WIND, RAIN, LEAF, SOIL, and LEAF/SOIL - until the correct type appears.
7. Press DONE to move to the next screen.
Press DONE for 2 seconds to Exit"

I sent a reply to that e-mail, asking whether they thought it likely that the station was being affected by interference, I got no reply.

However by the time the original reply had been received the station had reverted to normal, so I did nothing.
Today it has started doing the same thing, again all other readings are fine and the ISS reads 100.

Any suggestions?
Sorry for the long first post!
Cheers

Keith

[racer3]

Most likely the reed switch under the tipping buckets.

[johnd]

https://www.manula.com/manuals/pws/davis-kb/1/en/topic/fixing-rain-gauge-faults

[melmerby]

Hi Guys, thanks for the replies.

Having worked with reed switches as part of my employment (now retired ) I would not expect to get such a consistent error.
See this snip just taken:

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Cheers

[johnd]

Having worked with reed switches as part of my employment (now retired ) I would not expect to get such a consistent error.

Well until you do some checks as suggested you won't know. There are ways that a reasonably consistent rate could be generated artefactually, eg 24mm/5mins is 120 tips/interval (assuming a 0.2mm tip) or about one tip per wind message on channel #1. I'm not sure exactly how that might come about but just saying that there could be explanations for certain numbers popping up. It could also reflect a SIM board fault - probably not but without more clues it's impossible to say. How old is the ISS?

[melmerby]

Hi John
It's 9½ years old, apart from the ISS battery failure about 3 years ago no problems with the ISS.

Today the odd readings suddenly started but it wasn't raining at all at the time.
They started at 1220 until 1425 and again at 1525 and stopped at 1715. (then a few more this evening.)

This is what the expanded strip chart from that period looks like:
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Re reed switches:
I would expect contact bounce to give extra readings when rain is being recorded, not when it's dry.
I wonder what would a stuck reed do to the readings? (A common failing of reeds.) But it would still need to operate before it could stick.

Cheers

Keith

[Waimarie]

I had a similar problem with an older  FineOffset station.  Turned out to be a combination of wind and the gauge "wobbling" on its mount. slightly.  My fix was a simple move to a more sheltered spot and securing the mount to an immovable object.  It lasted until the station died last year.

[melmerby]

Hi there
I don't think wind is a problem as it has done it sometimes when it is still.
It's also fixed to a 100mm/4" square concrete post, which doesn't deflect when I lean a ladder against to inspect the ISS.

Cheers

Keith

[melmerby]

No more suggestions anybody?

A point that might be valid (it happened today)
I had three high rain rate readings on the trot but no rain was recorded in that period.

I'm convinced that it is:
a) not interference from another station, else why are no readings apart from rain affected.
b) not the reed switch as why would I get high rain rates with no rain actually recorded.

Is that a reasonable assumption?
If so I think a new main unit for the ISS is required.

[racer3]

I would still change the reed switch before a new ISS. You never know, stranger things have happened.

[johnd]

No more suggestions anybody?

Well, TBH you've been given some pointers but don't seem to be following them up. So is there any sign of moisture in the RJ11 socket on the SIM board or cable damage? What happens if you leave the  rain gauge unplugged for a few days? Is the spurious rainfall still there or not?

This seems to be one of those scenarios where there's no unambiguous way of diagnosing the fault at long distance. Personally I'd probably buy one of the new (replacement) tipping spoon mechanisms - there's a good chance that will fix the problem but no-one can offer any guarantees.

[melmerby]

Hi John
As I said in the first post, I cleaned the connectors, (suspecting possible moisture/corrosion/anything else), although there was nothing to be seen.
I also cleaned and checked the buckets as once I found a spider had included it as part of it's web!

I will try your suggestion of unplugging it for a while.

It's a pity it's not an on/off fault as it can be OK for anything from a few days to 6 weeks and then starts playing up again.
The weather doesn't seem to affect it. dry or wet, windy or not.

Cheers

Keith

[CW2274]

I will try your suggestion of unplugging it for a while.

This. If it quits the false reports then you'll know that the problem lies between the tipping mechanism and the RJ11. Personally, I think you've somehow developed a short which mimics a reed switch hence the all-or-nothing reports. Of course, I could be completely wrong...

[melmerby]

Right.
It was playing up again this morning so:

I unplugged the rain jack and checked out the reed using my Fluke DMM on ohms
Unoperated the reading is unmeasurably high, operated it is virtually zero and switches between the two without hesitation.
I checked the condition of the connecting lead and it looks fine.
I checked the contacts on the jack and the socket, they still didn't look too bad, no moisture and no obvious tarnishing.
I decided to do a thorough clean using a lubricating switch cleaner and was surprised how much muck came off the contacts.
I've now put all back together.

It's now gone about 6 updates without any silly readings.
If it starts playing up again I will unplug it and see what happens

Keith

[melmerby]

I have been going back through the recorded rain rates from when it started about a week before Christmas to try and find a pattern
These readings stand out as being totally illogical (a period when it was raining steadily, each period typically read 0.2 mm or 0.4 mm of rain but the actual rain rates logged are all over the place):
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How can a recording period when no rain was recorded have a huge rain rate?

[dalecoy]

How can a recording period when no rain was recorded have a huge rain rate?

Interesting question...........

I also notice in your Reply #3 that there are times when the amount of rain DECREASES between periods. 

Software (small corruption) could cause this - I'm not sure what software you are using (probably Weatherlink?), but making sure you are using a recent version would be a good thing to do.  And, if so, then reloading (to make sure that it's a clean copy) would be good.

In terms of hardware: 
A.  What do the console diagnostics look like?  In particular, reception diagnostics.
B.  Unlikely to be interference, but just to be sure, changing the channel being used (ID) would be reasonable.

[melmerby]

Hi Dale
I'm using Weatherlink 6.0.5. The last stand alone version for Windows.
However these silly readings are also on the VP2 Console.

I have started a regime of Unplugging the rain lead for 24hrs, then replacing it for 24 hrs, to see whether I can determine where the fault lies.
So far one day unplugged, one day plugged, both fine.

EDIT
I checked Diagnostics for the 24hr period and the figures were all good (noise was 10, good packets were 99%, nothing else of note)

[dalecoy]

Hi Dale

However these silly readings are also on the VP2 Console.

Oh.  Well, given that (new?) information, it eliminates software. [Other than the ISS firmware, which is really difficult to "reset"]

So, perhaps the VERY LOW probability of very-selective RF interference -- I think it would be interesting to change the Station ID (channel), just to eliminate that. 

[melmerby]

This morning with the rain tippler connected as it has been since yeaterday, whilst in steady rain, nothing was recorded and then I got a one off 281mm/hr reading then nothing again.
(the collector isn't blocked, so not a sudden rush of readings)

Keith

[johnd]

You seem to be hoping that someone will have a flash of inspiration and be able to pinpoint the problem at long distance. Someone may be able to jump in and prove me wrong, but I'd suggest that it's not a problem amenable to that sort of deductive analysis. It is a rare issue with odd symptoms but that could have one of several causes from reed switch through to the console, though most likely it's in the ISS somewhere. I do think the only way you're likely to resolve it is to start swapping out parts.

TBH an ISS that is around 10 years' old is probably heading towards the end of its useful life and it may be time to think of replacing it. But if you don't want to go down that route then replacing just the tipper mechanism as a start (or even just the reed switch), as previously suggested, would be a start.

[Tornado12]

replace the tipping bucket. Its not that expensive. I wouldnt waste all this time trying to find out why its wrong, just start replacing parts until it goes away. The unit is 9 years old I believe I read, so thats not a bad life. Get the new tipping spoon and upgrade it at the same time. If problem persists on a new tipping spoon or bucket, then replace the ISS.

[melmerby]

At last I have (I hope!) the definitive answer: 
The unit is giving silly readings at the moment and the tipping mech is unplugged.
So it looks like a new electronics unit is required.

The plastic on the unit's cover is also showing signs of sun degradation so I think a whole new ISS suite might be the way to go.
As has been pointed out it is approaching 10 years old.

I assume the VP2 console will last a little longer?

Cheers

Keith

[dalecoy]

If you would like to try one more thing - without any expectation that it will fix the issue:
Remove the battery from the ISS.
Cover up the solar panel with something that's opaque - light-tight.
Leave it set up that way for an entire day (completely draining the supercap).  Make sure the console is not receiving.

Now, remove the Console batteries, and unplug external Console power. 
Remove the Weatherlink adapter, wait a minute, and plug it back in.
Restore Console power.

Put the ISS battery back in.  (and uncover the solar panel).

That should restart the ISS firmware, as well as the other electronics in the ISS, and the console firmware.

It's probably a futile exercise, but....................

[Tornado12]

If you would like to try one more thing - without any expectation that it will fix the issue:
Remove the battery from the ISS.
Cover up the solar panel with something that's opaque - light-tight.
Leave it set up that way for an entire day (completely draining the supercap).  Make sure the console is not receiving.
Put the battery back in.  (and uncover the solar panel).

That should restart the ISS firmware, as well as the other electronics in the ISS.

It's probably a futile exercise, but....................

Or you could just unplug the solar panel from the board - no need to cover it up.

The issue sounds like a short to me. Could be a hairline crack in a soldered node on the board somewhere. Ive done some soldering and used to work with radios back years ago. Lots of wierd things happen when board circuitry breaks down, and its near impossible to locate unless you want to go voer the entire PCB with a strong magnifying glass, and even then it may not be found. had a garage door motor start going nuts one day. I took it all apart, took the board out, actually managed to find the bad solder point - one dab of solder fixed it. This could also be the case that a little bit of water found its way into the ISS and has actually caused a failure on the board. I would just replace the ISS and be done with it. You got 9 long years out of it, thats not bad at all for something that spent all that time in the weather.

[CW2274]

I assume the VP2 console will last a little longer?