Topic: WH40 0.5mm under compared to Davis

[Bashy]

Had some rain yesterday, some light, medium and heavy, the latter was a minute or so.

The Davis recorded 6.2mm and the WH40 recorded 5.7mm

To be fair, i don't know what the accuracy is, so is this normal or acceptable for the WH40?

[CW2274]

To be fair, i don't know what the accuracy is, so is this normal or acceptable for the WH40?

  How would you know? Has either gauge been truly calibrated? Without that, you're comparing one unknown against the other. Gotta have a control.

[Bashy]

My manual ties in quite nicely with the Davis.

[CW2274]

My manual ties in quite nicely with the Davis.

Then I guess we carry on. 

[Gyvate]

The WH40 is generally known for rather underreading and the WH65/WS69 rain bucket for overreading.
At low rain rates the WH40 comes close to the manual readings, but the stronger the rain gets, the more the underrreading (a systematic affair due to the funnel design).
But it depends a lot on the type of rain (drizzle, medium, strong, very strong ...) and the accompanying wind situation.
The same, by the way, for the WS90 haptic rain sensor.
While many report an overreading with the WS90, I could not confirm that in over 30 rain days - at two days it was overreading (reference two manual rain gauges) and otherwise generally underreading, and provided generally lower values than the WH40. (for the WS90 all five rain gains = 1.0) The usual observation of mine is WH65 > Manual > WH40 > WS90

[giusCB]

Had some rain yesterday, some light, medium and heavy, the latter was a minute or so.

The Davis recorded 6.2mm and the WH40 recorded 5.7mm

To be fair, i don't know what the accuracy is, so is this normal or acceptable for the WH40?

first to all, set the correct offset for the wh40 ( 1.022 ) and check if is on level

[Rover1822]

Gyvate, on the WS90, I'm having the same experience, I am finding that the WS90 seriously under reads with wind blown rain, rain at an angle. I've been having major winds here 25 MPH constant with gusts above that.

[Bashy]

Thanks guys and sorry for the late reply, re lower rain intensity, i certainly agree there, its pretty much neck and neck with the Davis and manual. Because my recent rain included various intensities and more so the heavy for around a minute is what caused the discrepancy seen i had my suspicions, i think its gets overwhelmed and perhaps been more suited to 0.2mm resolution? To be fair, i did have my reservations on the bucket size and on the cone size, i had a feeling it may see some performance related, I'm gonna say issues but that might be a bit ott...

Is the offset of 1.22 the done thing then? and it is 99.99% level, its only 2ft off the ground so very easy to see these things.

As a side note, i did add an old OS bucket debris shield, this lets in far less that the standard effort

The same, by the way, for the WS90 haptic rain sensor.
While many report an overreading with the WS90, I could not confirm that in over 30 rain days - at two days it was overreading (reference two manual rain gauges) and otherwise generally underreading, and provided generally lower values than the WH40. (for the WS90 all five rain gains = 1.0) The usual observation of mine is WH65 > Manual > WH40 > WS90

I would have expected differences with the haptic, still kicking myself for not checking to see if it was available lol

[Platokidd]

My wh40 is spot on with my Stratus.

[Rover1822]

When clean, so are mine 

Unfortunately, mine are also some kind of tree, seed, pollen bomb, debris magnet

Partly why I got the WS90

[Bashy]

I cant take the WH40 seriously anymore, not in heavy rain anyway,

Davis  180mm/hr 4mm
WH40 18mm/hr 3mm
WH40 lost 1mm in a 4mm event, the event lasted 5mins max

[Gyvate]

the WH40 is since long known for underreading in strong rains.
Due to the poor design of the funnel (too flat, too low edge) a lot of rain gets lost splashing off.

[horseflesh]

Why is the WH40 offset 1.022? I don't even see where to set that in the calibration controls.

At what rate does the WH40 start to fail? Where I live, 1 inch/hr is pretty heavy rain. Even 1.5 in/hr would look Biblical, haha.

[Rover1822]

Why is the WH40 offset 1.022? I don't even see where to set that in the calibration controls.

At what rate does the WH40 start to fail? Where I live, 1 inch/hr is pretty heavy rain. Even 1.5 in/hr would look Biblical, haha.

In VSView +, look under more/rain totals, not under more/calibration.
FYI, I don't use the offset as 99% of the time it  is within a few percentage points of my manual rain gauge, plus or minus (within the published error for the device). As using an offset (rain gain) for the WH40 means for all rain rates, I rather not use it.

[DelChard]

Why is the WH40 offset 1.022? I don't even see where to set that in the calibration controls.

At what rate does the WH40 start to fail? Where I live, 1 inch/hr is pretty heavy rain. Even 1.5 in/hr would look Biblical, haha.

In VSView +, look under more/rain totals, not under more/calibration.
FYI, I don't use the offset as 99% of the time it  is within a few percentage points of my manual rain gauge, plus or minus (within the published error for the device). As using an offset (rain gain) for the WH40 means for all rain rates, I rather not use it.

Another reason for not using is contained in post https://www.wxforum.net/index.php?topic=39166.
The post requires reading in its entirety, as there is a lot of confusion in the early stages.
My memory is that Ecowitt have attempted to correct the error within the gateway or console firmware.
However, the respective firmwares have all changed in the mean time?????

Re Bashy's issue. I also had an 18mm/hr event about 30 mins earlier.
My WS69 (which reportedly over reads) recorded 18.6mm/hr and 3.3mm total. My WH40 recorded 18mm/hr and 3.1mm total.
Both are within 10 feet of each other and 8 feet high (necessary to keep the canines from triggering a rain event)
A nearby (1/2 mile) davis station recorded less. (for what thats worth).