TheSkySearchers

I have been using a wet-leaf water sensor to detect rain, in order to auto-close my dome if the weather tanks. It is reliable and sensitive, and it responds instantly. It is too sensitive, as it turns out, because it triggers on dew. I don't need dew protection, since I have a solid-tube Newtonian in a dome. So I am looking for a rain detector that discriminates between rain and dew.

I have had recommendations of the RG11 from Hydreon, and the M152 from Kemo. The simple solution of putting a heater under the wet leaf sensor turns out not to be competitive with these units. The Kemo unit is basically that, pre-assembled.

The down side of the Kemo unit is that it comes from Germany, and covid-19 has totally messed up transatlantic shipping. It could take months to get here. On the other hand, its performance is what I want. The Hydreon unit is high-tech. I have seen its sensitivity and response time questioned.

So, any other recommendations? Any opinions about the options I have mentioned? Thanks.

How about https://octopart.com/m152-kemo-47247821

Octopart, Inc.
29 West 38th St.
14th Floor
New York, NY 10018

Useful link. Thanks!

Just in case you have not looked at these Arduino options Kathy.


As I said in my other post I know nothing about Arduino so this may be way off base.

Thanks, Alex. That is pretty much what I have now. It doesn't distinguish between rain and dew. It only sees wet or dry.

Any way to mitigate just the dew, such as putting the sensor in the bottom of a short acrylic or aluminum tube and putting a dew strap around the tube. Having a short tube (2” or so) the rain would still reach the sensor.

ic_1101 wrote: ↑Mon Nov 09, 2020 4:56 pm Any way to mitigate just the dew, such as putting the sensor in the bottom of a short acrylic or aluminum tube and putting a dew strap around the tube. Having a short tube (2” or so) the rain would still reach the sensor.

Interesting idea, and it would probably work. However, I am not set up for dew heaters; I don't really need them with a solid-tube Newt in a dome. Getting set up with the straps and power controller would cost more than a good rain detector. I think I will order the Kemo unit.

They have these things for automated sprinkler systems.

https://cheapsprinklers.com/products/ra ... 20%2422.98

Update. I eventually went with the Hydreon RG-11 unit. I received it a couple of months ago, and was able to engineer a mounting bracket for it. But the weather was too cold to wire it up until yesterday.

We had a little sprinkle overnight, just enough that you could see individual drops of rain on the otherwise dry deck. I checked, and the RG-11 was reporting rain. Yay!

Just to be safe ("She who laughs last made a backup."), I kept the wet-leaf sensor. I have a switch now that selects between rain sensing (RG-11) and dew sensing (wet leaf), as well as a power switch to disable both sensors if I am getting nuisance detections.

Ah that is cool. I did not even know an 'optical' rain sensor existed!

Probably real important to keep it clean though.

UlteriorModem wrote: ↑Fri Mar 12, 2021 4:17 pm Ah that is cool. I did not even know an 'optical' rain sensor existed!

Probably real important to keep it clean though.

If it's dirty enough to need cleaning, it probably hasn't rained in a while. Conversely, if it is raining, it is self-cleaning.

Here in the deep south this time of year it only takes one day to get a thorough coating of pollen!

Kathy, That unit is the one I think NexDome resells. You started your search around the time I retired (finally). Now my wife and I are about to move into a new home with a good backyard(clear views 360 Bortle 5). I always had plans for an OB so I was looking around back then when I found it at Rainsensors.com . Still have plans but a moderate stroke and a grand mal seizure have modified them somewhat ( never giving up). Anyway, congrats on finding the solution. GCG

I've ordered a NexDome with the rain sensor. How does it react to frost? Wouldn't that be similar to rain on the small dome?

Lenny wrote: ↑Sat Jun 19, 2021 3:41 pm I've ordered a NexDome with the rain sensor. How does it react to frost? Wouldn't that be similar to rain on the small dome?

I haven't yet had mine operational through a winter, so I don't know how it reacts to frost. It might or might not detect it. And it might depend on the device settings. It includes a built-in dew heater, so that might prevent some frost.

If I record unexpected "rain" closures on frosty nights, I'll know it is detecting frost.

Re-visiting this thread after a few months of fairly intense use. Obviously, I still haven't used the Hydreon sensor in winter, but I did give it a good summer workout.

I initially had it set to "first drop" detection. The built-in dew heater was supposed to prevent dew, and for the most part, it did. However, the dew heater is only about 0.25 watts, and is not up to the challenge of heavy dew. I got a couple of nuisance dew detections that prematurely closed the dome on nights of heavy dew. To be fair, on those nights where it detected dew as rain, even my sky cam, with 2.5 watts of dew heat, got dewed over, while confirming that it was not in fact rain.

I have switched the RG-11's sensitivity to "light rain". That has prevented further nuisance detections, and it seems to respond well to actual rain.

Would it not be such a bad idea to button things up when the dewpoint is so high ?

UlteriorModem wrote: ↑Mon Oct 25, 2021 2:38 pm Would it not be such a bad idea to button things up when the dewpoint is so high ?

With a solid-tube Newt in a dome, dew is not really a factor inside the observatory. On the heavy dew nights, stuff outdoors was soaking, but the scope stayed dry.

KathyNS wrote: ↑Mon Oct 25, 2021 2:57 pm

UlteriorModem wrote: ↑Mon Oct 25, 2021 2:38 pm Would it not be such a bad idea to button things up when the dewpoint is so high ?

With a solid-tube Newt in a dome, dew is not really a factor inside the observatory. On the heavy dew nights, stuff outdoors was soaking, but the scope stayed dry.

Even a Cassegrain open at the top doesn't have any problem. I've had my Vixen VC200L outside on nights with water dripping off everything, finder completely dewed over but the VC200L optics are bone dry. I have never bought any sort of dew strap for it, and never will by the looks of it.
Joe

Hi Kathy,
I read this one originally, but never thought of following up on last winter's experience with the sensor until stumbling across this thread again.
How well did the Hydreon work in winter?