Davis VP2 - add ons

[steve]

[Paul C]

Steve - and I will make sure he does pay, Co Durham isnt far !

Solar Reading currentluy 0 w/m2
Max Today 962 w/m2

[hailstone]

Don't worry Paul, my word is my bond.
Like you I wish to collect authentic data or it is a sheer waste of my time otherwise.
I am a member of RMetS and was given your name to ask you if you new of a supplier of the slide rules you use to calculate the Dew Point from the readings of the Dry & Wet bulb thermometers. My 101 year old mother accidently through out my slide rule and I find it a bit of a chore to use the calculator from the internet web site every day at 9 zulu time. I find the Davis rain data a bit dodgy also compared with the Snowdon Raingauge possibly as much as 5 or 6 mm differance in 25 mm of rain. It may be due to the fact that I am using the mm converter on the balance and 0.2mm is not calculating acuratetly over an accumilated record of rain period. I have taken into account the Weatherlink software is from midnight to midnight. The beauty of Steve's Cumulus is it can be set to 9 zulu time as required.
CU.
Hailstone.
G0HJX.

[Paul C]

You can always adjust the raingauge if its under reporting. I have slightly adjusted mine last year and now the readings are very comparable. YES there is always a slight difference but not enough to worry me. 5-6mm over 25mm would concern me though.

[hailstone]

Thanks for the info Paul.
If my bucket is under recording I presume I will have to take some plastic away from the adaptor. Very fine tuning needed there then.
Dr D Wheeler from Sunderland, the RMetS regional rep gave me your name Paul to contact and see if you knew of a retailer who still sells the Slide Rule to work out Dew Point. You have not commented on my query.
Hailstone.

[Paul C]

If you take the rain collector off ( black gauge bit) underneath the two typing buckets are two small screws. These can be adjusted up and down. See page 14 in the VP2 integrated sensor suite manual. Try a very small turn at a time and leave it for a few days to see if the raingauge measures up to you standalone one. There maybe some further instructions in the manuals but I cant it at the moment.

Slide Rule - I dont have one. I rely on Cumulus and Weatherlink to provide the dewpoint. I submit wet and dry bulb readings to the Met Office but I do not calculate a dewpoint.
Will check my Meto Books and see if there is a chart in there. I thought it was a touch complicated, I think your high about sea level and air pressure come into aswell (dont quote me on that)

EDIT RE SLIDE RULE - http://www.paint-test-equipment.co.uk/index.php?id=19

Paul

[hailstone]

Mmmmmmm, page 119 of the Handbook reads...."For synoptic reports dew-point can be obtained from the slide-rule or from the booklet Dew-point tables for screen readings, degrees Celsius."
Again on page 133 it says dew point can be obtained when using aspirated psychrometers is obtained from tables in Hygrometeric tables Part III.
It was my slide rule my mother disposed of.
I have contacted the Met Office and these tables are no longer published. That's progress I suppose.
I was extremely lucky to obtain the very last pack of Metform 4237 Charts for the Barograph, in the store at Exeter. Because it was the very last pack of charts, I was presented with them for free with a complementery slip. It goes without saying I will not use these charts. They are now part of Meteorlogical history. The same goes for the Cambell-Stokes charts.

Will have a go at altering the magnet hight at a later date when I have a more accurate archive of rainfall for my area. The La Cross WS 2-550 rain gauge is set at exactly the same hight and only one and a half meter away from the Pro 2 and these readings only differ from the Snowden by 0.01 mm. I can not read the Snowden to this accuracy with the measure so that's good enough for me. I aim to get the Pro 2 as near as possible to this in the 0.2 mm steps.

Thanks again Paul and by the way, I have not yet had enough time to assess for myself Steve's Cumulus and it will only be a usefull tool when the Pro 2 querks are ironed out. By then I could cross his palm with silver.
Hailstone.

[hailstone]

Mmmmmmm, page 119 of the Handbook reads...."For synoptic reports dew-point can be obtained from the slide-rule or from the booklet Dew-point tables for screen readings, degrees Celsius."
Again on page 133 it says dew point can be obtained when using aspirated psychrometers is obtained from tables in Hygrometeric tables Part III.
It was my slide rule my mother disposed of.
I have contacted the Met Office and these tables are no longer published. That's progress I suppose.
I was extremely lucky to obtain the very last pack of Metform 4237 Charts for the Barograph, in the store at Exeter. Because it was the very last pack of charts, I was presented with them for free with a complementery slip. It goes without saying I will not use these charts. They are now part of Meteorlogical history. The same goes for the Cambell-Stokes charts.

Will have a go at altering the magnet hight at a later date when I have a more accurate archive of rainfall for my area. The La Cross WS 2-550 rain gauge is set at exactly the same hight and only one and a half meter away from the Pro 2 and these readings only differ from the Snowden by 0.01 mm. I can not read the Snowden to this accuracy with the measure so that's good enough for me. I aim to get the Pro 2 as near as possible to this in the 0.2 mm steps.

Thanks again Paul and by the way, I have not yet had enough time to assess for myself Steve's Cumulus and it will only be a usefull tool when the Pro 2 querks are ironed out. By then I could cross his palm with silver.
Hailstone.

[Paul C]

Where abouts are you in County Durham, is your data on line ?

[beteljuice]

Strange, if you are saying that 25mm 'real' is being reported as 20mm, that would be the same effect as having the inch magnet arrangement, but the console set to mm.

Regarding screw adjustment, a little 'iffy' - if you can adjust the screws 'up' so that the spoons don't fully empty on a tip (but can still see-saw) then you can compsenate for some undermeasure, but of course, after a dry spell, the first two tips will be ever so slightly light.

[Paul C]

Strange, if you are saying that 25mm 'real' is being reported as 20mm, that would be the same effect as having the inch magnet arrangement, but the console set to mm.

Regarding screw adjustment, a little 'iffy' - if you can adjust the screws 'up' so that the spoons don't fully empty on a tip (but can still see-saw) then you can compsenate for some undermeasure, but of course, after a dry spell, the first two tips will be ever so slightly light.

Good point first sentance

[beteljuice]

I was thinking what possible effect sheilding the magnet would have on the measurement ?

Of course it doesn't ! - the magnet happens to be on a cantilever to the see-saw balance, all they are doing is adding a little extra weight so the spoons tip on a smaller measure.

So ... as you are already under measuring, you could try removing the mm 'adapter' (As it looks this strangely should put you 'near enough'), but if that becomes an over measure, start adding a bit of blu-tack or similar.

To calibrate, just take a reference amount of wet stuff from your other gauge and tip SLOWLY into the bucket.

[hailstone]

Thanks for your very constructive advice lads.
As I am only in this residence as long as my 101 year old mother is alive, I have no intention of publishing weather info on a web site. Besides, if the info is not accurate, who will be kidding who? I just wonger how many Vantage Pro 2 stations throughout the world are fixed to a pole on Joe Blog's privy roof and is subjected to all sorts erroneous readings but are added to the NOAA yearly statistics. Over the course of time the figures will err greatly and show a false picture of what the weather is realy doing.
I rest my case.
Hailstone.

[hailstone]

Beteljuice my friend,
You can not use the H20 from the Snowdon rain gauge and use this calculated volume to calibrate any other rain gauge that differs from a 5" diameter collecting tube. The Pro 2 has a collector of 8 1/4" dia. so it collects a differant volume of H20 to the Snowdon per mm calculated. The Pro 2 is only rated at 4% accuracy anyway so is it realy OK to use this AWS to calculate the worlds rainfall. I think not. On 31st December I know that I may be + or - 4% of the figure shown as the total yearly rainfall despite my best attempts to make it fall in line. If all AWS's are under rating the rain value like the Monday morning assembled beasty that I have, we may not have the time to build an Ark after all.
The only redeaming feature the Pro 2 has for me to date is the thermometer probes. I calibrated 4 of these probes using a double sheathed Met Office approved thermometer as the master in a brine bath of ice cooled water. All 4 probes read exactly the same temperature to the 2 nd decimal place.
With the fan asperated ISS I am happy to record the Screen temp. Grass minimum, Bare-soil minimum, Concrete-slab minimum and the soil temperature at 100 mm depth and know that I am not telling porkys.
One more thing about the Wireless Vantage Pro 2. Last month after a thunder storm the Wind Vain heading on the Consle had flipped 120 degrees from true North.
I had to reset the Console bearing back to North so be in line with the arm of the unit mounted on the mast. A shot of electro magnetic energy can corrupt the Console reading.
Let nothing you dismay.
Hailstone.

[beteljuice]

In answer to your question !

Both RMetS and ebay have a Mk5 sliderule available: http://cgi.ebay.co.uk/Vintage-Blundell- ... 286.c0.m14

However; for the same bucks you may consider: http://cgi.ebay.co.uk/Brand-New-Compact ... 286.c0.m14

Probably won't won't measure up to your standards , but you get a new sliderule !