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To have reliable results I've set the potentiometer to max resistance, so I need about totally 15 MOhm .
I suppose that the upper shift of r.h. is not linear for all the values of r.h.
Other thing, partially inserting the shield on the thermohygrometric sensor, the temperature record is lower than totally inserting it...and facing the thermal sensor to nord.

Regards.

Stefano

Hi all,
FINALLY SOLVED!

I've removed all the resistors, I experienced that the best way to resolve the problem about the humidity sensor is to move the sensor from the printed board.
I've do it with two short (each about 2 cm long) between the sensor and the printed board.
Care with the solderer.
Bye

Stefano

Hi guys,
today the humidity has reached 99%, so I can say definitively that the solution of distancing the sensor from printed board, without resistors, is good.
Bye.

Stefano

As a new member to the forum I have just been reading this thread and noticed that the %RH on my WH1080 was also reading very low.

Checking against another digital RH meter I have I found that the WH1080 was reading 71% when the other more reliable one was reading 85%.

As I only took delivery of the WH1080 last week, and it's under guarantee, I am loath to modify it at present; although as a retired Radio and Electronics Engineer it would be no problem adding the pot and resistors.

I have reset the multiplier in Cumulus to x1.22 which brings it into line with the other digital stand alone monitor but will have to see if it tracks OK when the humidity is low and perhaps have to juggle with the offset and multiplier to get it to read correctly.

I guess with such a cheap unit like the WH1080 one must expect errors but that does seem to be an awful lot out of calibration.

One thing I need to point out is that if you are adding high value pots and resistors to the sensor board you really need to spray them when calibrated (and in dry conditions) with an acrylic lacquer, as high value components can be effected by high humidity, and you are in effect adding another high value resistor across the components.

Mike.

As a matter of interest, how accurate is your digital RH Meter?
Auckland regularly goes to 100% when the water is materialising in front of your face and my 1081 has only ever gone to about 97% and I am happy with that as RH meters could commonly be plus or minus 10%.
Fine Offset website shows "Humidity range: 10% to 99% (1% resolution)", but in my experience, I find that very hard to believe.
As you say, high resistors, a bit of dust and water vapour cause havoc

Hi Terry, I did check the digital RH meter against a whirling hygrometer and it's fairy accurate.
The sensor in the remote system seemed to be miles out, reading about 10% low.

Fine Offset website shows "Humidity range: 10% to 99% (1% resolution)", but in my experience, I find that very hard to believe.
Yes me too judging by the posts on this thread! Most meters take a while to stabilise when RH changes rapidly as well so you have to take this into account too. Perhaps we should go back to the Wild Oats seed, LOL!

We should get some rain later today so that will be a good test.

Only high speck RH meters would be accurate to 1or 2%. The sensors alone for these are near to a £100 each; one of my farmer mates bought one a few years back.

I've found most RH meters to be poor comparing them to the high spec ones; but at such a cheap price I suppose they give you an idea. It's good that Culumus gives you the option of offset and multiplier which is lacking in EasyWeather.

Will see how I get on when it rains; should give me a reasonable cabibration.

Mike.

I have three weather stations Davis VP2 close to me, within the radius of 3 km.
After the last modification, the easiest to do, my station is aligned with these also for u.r. .
For my station the gap was not linear, so the correction made by cumulus has been good for high values of moisture but bad for others.

Bye

Stefano

taddeus wrote: For my station the gap was not linear, so the correction made by cumulus has been good for high values of moisture but bad for others.

Bye

Stefano

It should be possible to adjust the scale by use of the multiplier and offset and get it roughly right, but it may take a bit of time juggling the two settings.

Mike.

Found some interesting articles on Hygrometers on the Web.
It would appear that the expensive units, around £200+, are only +/-2% RH; cheaper ones much worse.
I guess there are more accurate laboratory instruments at BPL and similar places, but beyond our reach.

There is an interesting page on calibrating hygrometers here...
http://ezinearticles.com/?Stop-Mold!-Us ... &id=602308

Various salt and chemicals wetted and put with the hygrometer (or WH1080 transmitter unit) in a plastic box.
Although the WH series transmitter units have no adjustments (without modifying it) it could be recalibrated via the option in Cumulus.

Mike.

Whilst not adding much to the previous posts noting mods for accuracy, I have just noticed on mine (Watson 8681) quite a low humidity in relation with the other stations in my area. I have always assumed to humidity to be OK, seemed to track others quite well and has no problem reaching 100% when the village is in the clouds. Late last week I moved the sensors to quite an exposed position and I'm now noticing accuracy improvements in some areas and reductions in others

As I write it is absolutely lagging it down with 5mm/hr rainfall and winds of 28mph, but my humidity is showing only 58%, and I would have expected higher. Other stations in the area are showing humidity of 94% to 99%, but have nowhere near the high wind speed. Is the wind speed making the humidity appear lower??

Many thanks in advance to those who may be able to answer.

Hi Mike,

Well mine is showing 96%, which seems to be a little low as it's chucking it down here as well in Cambs.

It does show a max of 99% when it's raining without a strong wind, so I think you've hit on something there.

At present I have an Offset of -1.00 and a multiplier of 1.10 which does seem to track roughly with another digital humidity unit I have. But humidity is a difficult thing to measure accurately without laboratory equipment so I guess that it can only be used as a guide.

I check with 3 RAF sites around here and they normally read all different. Two of them, Mildenhall and Lakenheath are only a mile or two apart and they are totally different...

http://www.weathercity.com/uk/gb/mildenhall/
http://www.weathercity.com/uk/gb/lakenheath/
http://www.weathercity.com/uk/gb/marham/

Make of that what you will.

Mike.

Thanks Mike.

I did check with Manchester Airport (http://www.wunderground.com/cgi-bin/fin ... 2.27472210) and that is showing high winds and a humidity of about 94% now - seems to have shot up from earlier this morning.

Just noticed that my wind speed is increasing a bit ( a couple of high all-time records indicated) and my humidity is now down at 54%. The humidity has been dropping since about 10pm last night night when it was about 85%, this looks to be tracking the barometric pressure which started dropping too around that time, in addition to the wind speed picking up too around 10pm. Maybe it is linked to barometric pressure and wind speed, or it is just a flaw with the FO stations.

I may have a look at the modifications to the sensor unit.

Mike, to be honest I wouldn't bother doing electronic mods to the sensor unit inside the transmitter box. You can achieve the same results with the multiplier and offset settings on Cumulus, and you won't invalidate any warranty you have. Adding a high value resistor (as has been suggested) across the sensor will only alter the range and offset the same as you can do with the calibration settings. Of course if you want to make the display on the console read correctly then that's the only way. I don't bother too much with the colsole readings as most of those are out compared with the ones I have calibrated on the Cumulus display.

The basic problem, I am pretty sure, is that none of the sensors are temperature, humidity and pressure compensated.
I guess that would push up the price considerably; and hence every one has an effect on the others re; calibration and accuracy.

It would be possible to write a formula for Cumulus or Cumulus2 perhaps which would take into account all the 3 readings and then compensate and display the result on the Cumulus display, but there may not be a common setting for all the users stations, although you could probably have a standard formula that improved most of the accuracy.
Perhaps Steve would give that option at some time in the future? Quite a job though. It would take weeks, or months of observations and checking tracking with external instruments.

My RH is now 94%.

Mike.

Hi Mike,

The only mods I was thinking of doing are the ones to drill holes in the sensor casing, and maybe move the sensor away from the PCB. There is no warranty on the unit as I bought it 2nd hand off eBay for 30 quid. Currently my RH is 54% and wind speed is 34mph. Maybe the wind blasting through the sensor screen is causing increased evaporation near the sensor and thus giving such a low reading?

I'm in agreement with you re adding more components, it is just as easy to add figures to the calibration settings in Cumulus - and additionally, I do not have any other equipment to provide a reference.

M.

Mike; your very low RH is quite strange; in rainy conditions it must be in the nineties. Mine reads 96% at the moment and we have the same sensors; although position could have something to do with it perhaps?
You could try one of those swinging hygrometers; a few around £10 on ebay last time I looked. They are not completely accurate but should give an accuracy of a few %.
I broke one of the thermometers in mine last week; have some spares but can't find them. It did compare OK with my other digital Thermometer/Hygrometer unit though.
Mike.