How long is "IsRaining"

[Ken22]

I'm using an Ecowitt WS90 to trigger "LastRainTip" and "IsRaining" WebTags.

I think these are working properly.

My question is: How long does "IsRaining" stay on after the "LastRainTip" happens?

[mcrossley]

It depends!

If you are using the new IsRaining value that Ecowitt now send from the WS90, then I don't know the answer. You'll have to ask Ecowitt.

If you are using the Cumulus derived IsRaining then that stays set so long as the rain rate from the station is greater than zero.

[Ken22]

I asked Ecowitt and this is the answer I got. It may be of interest to others.
----------------------------
It adds up to the past 10 minutes of rainfall. So, if it stops raining after
10 minutes, the past 10 minutes will be shifted to 0, and then the rain rate
will be 0.

Rain processing is with a one-minute delay, so the total after 11 minutes
will be 0 for the rain rate.

Ecowitt Support Team

[mcrossley]

Did you ask them about the new flag on the WS90, they have named it "srain_piezo"?
(which I assume is short for "start rain piezo")

[Ken22]

Did you ask them about the new flag on the WS90, they have named it "srain_piezo"?
(which I assume is short for "start rain piezo")

I did not know about "srain_piezo" so I could not have asked. I also don't really care about when the rain started. I believe that I'm getting all the information I need from "IsRaining", "rrate" "rfall", and "LastRainTip". The HP2560 display shows how long the current "Rain Event" has been going on. This is interesting to me at times, but I don't need it on my web page.

[freddie]

Did you ask them about the new flag on the WS90, they have named it "srain_piezo"?
(which I assume is short for "start rain piezo")

I did not know about "srain_piezo" so I could not have asked. I also don't really care about when the rain started. I believe that I'm getting all the information I need from "IsRaining", "rrate" "rfall", and "LastRainTip". The HP2560 display shows how long the current "Rain Event" has been going on. This is interesting to me at times, but I don't need it on my web page.

It's a flag, so it won't be telling you when the rain started. It will tell you whether or not it is raining - which is exactly what you are looking for, isn't it?

[Ken22]

It's a flag, so it won't be telling you when the rain started. It will tell you whether or not it is raining - which is exactly what you are looking for, isn't it?

I'm using the "IsRaining" WebTag in Cumulus which seems to be working (I'm waiting for rain for a final test).

How would this be different?

[Ken22]

I did some searching for "srain_piezo" and found this:

in the customized server post string, the observation will show as srain_piezo
it can have the status “1” - raining or “0” - no rain
status 1 will be reset to 0

a. once the top is dry, or
b. after the amount of water on the top has remained unchanged for two hours

Is the "srain_piezo" available as a WebTag? If so, I can experiment with it.

[freddie]

The cumulus tag relies on a measurable amount of rain falling to cause bucket "tips" which result in a rainfall rate measurement being recorded. This means that when it is raining, but not hard enough to result in a rainfall rate being recorded, then the cumulus tag will tell you that it isn't raining when it actually is.

With Ecowitt's piezo sensor, I believe this will detect the presence of raindrops falling and striking the sensor regardless of whether there are enough to cause a rainfall rate to be recorded.

In summary, the piezo sensor flag will better represent reality (i.e. indicate that it is raining) than the cumulus tag.

[packman2008]

a. once the top is dry, or
b. after the amount of water on the top has remained unchanged for two hours

That challenges my understanding of how piezo rain sensors work. I always understood they measured the impact of rain drops on the sensor, i.e. counting how fast the drops hit and their size (based on the strain level generated by each impact) to calculate how much rain is falling. Have Ecowitt found a different way to do it?

[mcrossley]

In summary, the piezo sensor flag will better represent reality (i.e. indicate that it is raining) than the cumulus tag.

It should certainly trigger much sooner at the onset of lighter rain. When it stops indicating is a little less clear.

On the subject of clarity. If the station supports it, you can configure the Cumulus IsRaining flag to use the Ecowitt piezo sensor flag rather than the rainfall rate.

a. once the top is dry, or
b. after the amount of water on the top has remained unchanged for two hours

That challenges my understanding of how piezo rain sensors work. I always understood they measured the impact of rain drops on the sensor, i.e. counting how fast the drops hit and their size (based on the strain level generated by each impact) to calculate how much rain is falling. Have Ecowitt found a different way to do it?

Same here. The tops of the sensors are rather flat (even with the addition of the controversial "slope" they have added to later builds of the WS90), so water is always likely to collect on it.

But nobody should buy a WS90 and expect it to measure rainfall accurately. If I had one (I have a collection of WS80s at the moment - a better sensor in some ways), I would only use the rainfall for the IsRaining detection.

[freddie]

When it stops indicating is a little less clear.

I would imagine it would be a time offset from the last drop detected (i.e. 5 mins?) but, like you say, it isn't clear.

But nobody should buy a WS90 and expect it to measure rainfall accurately. If I had one (I have a collection of WS80s at the moment - a better sensor in some ways), I would only use the rainfall for the IsRaining detection.

Exactly how I would use it