Why do I need a cloud sensor?

[old_eyes]

Following on from @steppenwolf's 'unattended' observatory thread I have been doing some thinking and sketching on paper waht the various inputs and outputs would be for the different conditions (especially error conditions) in my ROR observatory. I have also been playing around with Voyager as the control software, and have got the basic operation of a sequence working.

My goal is not for completely remote operation with full automation, but to be able to leave it running whilst I go to bed feeling relatively confident that it would shut up shop in a safe way if anything untoward happened.

I see that a lot of people use devices like the AAG Cloudwatcher to measure cloud cover and detect rain. I am not sure why you need both.

Clearly the main risk to the observatory is that it is open when the heavens open and the rain arrives. So I see the need for rain sensing. Clearly, I want the automation to stop the sequence, park the scope and close the roof if it starts to rain. However, Voyager is capable of attempting to resume a sequence (or of taking any other programmed action) in response to any defined failure condition, such as guiding, focus or platesolving. In fact, I have watched it doing this when I was dozing in the warm room (just resting my eyes!) and some cloud swept across the target area. It reacquired the target and guiding after a few minutes and carried on. I wasn't expecting it and hadn't planned for it, it just happened.

Since such brief attacks of cloud are frequent where I live, even on a 'good' imaging night, it does not make sense to go through closing the roof and making the scope safe every time cloud interrupts the sequence. Would it not be better to allow Voyager to attempt to continue with the plan until it starts to rain?

Some have said that since cloud is a necessary conditionfor rain, it makes sense to monitor cloud and be prepared. But cloud does not inevitably lead to rain.

Am I misunderstanding what people are doing? Is it that the delay between detecting rain and closing the roof is to long for the safety of the equipment? Genuinely interested in the reasons people chose cloud as well as rain sensing.

[Gina]

Conversely to cloud not necessarily meaning rain I have known it to rain when there hasn't been any cloud overhead, often accompanied by a rainbow!

[steppenwolf]

27 minutes ago, old_eyes said:

I see that a lot of people use devices like the AAG Cloudwatcher to measure cloud cover and detect rain. I am not sure why you need both.

You need both so that you can make use of the varying levels of cloud (Cloudy and Overcast). 'Overcast' means that the session is likely over whereas 'Cloudy' could mean a passing cloud so hold tight as all is not lost. Rain means that the 'Overcast' has well and truly setting in OR that darn single cloud has let go the wet stuff, close down immediately!

Voyager will indeed allow a recovery from a suspend or a complete exit but having those two levels of 'hold fire' can be very useful.

The AAG CloudWatcher unit is very good indeed but in my experience, the 'Cloudy' level is very much a moveable feast and the thresholds change throughout the seasons adding to the grey area. With this in mind, I tend to set cloudy as a non-event and let 'Star Faded' or other Guiding failures dictate what happens under these conditions.

37 minutes ago, old_eyes said:

Would it not be better to allow Voyager to attempt to continue with the plan until it starts to rain?

I tend to hope that 'Overcast' will make that choice for me long before the rain starts! In several years of operations, I have (thankfully!) never got my equipment wet using this strategy.

[old_eyes]

Yes I can see that an "ooh, it's getting pretty murky!" signal could be a useful warning. So you don't bother with the 'cloudy' level and allow the stronger 'overcast' message to trigger the programmes "oh [removed word]!" events?

[old_eyes]

1 minute ago, old_eyes said:

Yes I can see that an "ooh, it's getting pretty murky!" signal could be a useful warning. So you don't bother with the 'cloudy' level and allow the stronger 'overcast' message to trigger the programmes "oh [removed word]!" events?

Isee the forum censor has made my extremely mild cursing look much worse than it actually was!

[steppenwolf]

1 minute ago, old_eyes said:

Yes I can see that an "ooh, it's getting pretty murky!" signal could be a useful warning. So you don't bother with the 'cloudy' level and allow the stronger 'overcast' message to trigger the programmes "oh [removed word]!" events?

Currently, yes, that is what I do and it works very well for me although if I had greater confidence in the accuracy of the 'Cloudy' setting, I would consider using that but I don't have that confidence!

[steppenwolf]

1 minute ago, old_eyes said:

Isee the forum censor has made my extremely mild cursing look much worse than it actually was!

That is an automated correction and normally it gets it right but there have been some amusing corrections in the past!

[DaveS]

I have an AAG Cloudwatcher and Talon roof automation system incoming for my oby. It will be interesting to see how they interface with the ASA software.

[Steve 1962]

Hi @old_eyes

I've just read your post - and thought I might add my two penny worth.

I'm not sure about Voyager, but SGPro, which I ran with when I had my observatory just used an ASCOM Safety_Monitor device (e.g. the Aurora that I've just sold). 

The ASCOM Safety_Monitor feature only provides an Is_Safe (from memory) flag which is either true or false - depending on parameters which are set by the user through the ASCOM driver in the safety device itself. In the Aurora case (again from memory) this is a combination of cloud, rain and lightness and this is all that my driver does - safe or not? Yes or No!. The Aurora also has a set of relay contacts which I understand provide a "hardware alternative" to  the Is_Safe software flag.

The ASCOM Environmental Conditions feature could provide you with data such as sky temp, ambient temp, rain, lightness etc. but I never got around to writing a driver for this use of the Aurora. Sorry!

Again, I'm not sure how Voyager works but you might find this interesting....http://www.dehilster.info/astronomy/ascom-safetymonitor-hub.php

Hope that helps

Steve

 

[old_eyes]

Thanks Steve. Very interesting.

 

[laser_jock99]

Do the rain detectors detect snow? I left my gear going once and came back outside to a near blizzard!

Edited May 6, 2020 by laser_jock99

[sloz1664]

12 hours ago, laser_jock99 said:

Do the rain detectors detect snow? I left my gear going once and came back outside to a near blizzard!

That's where the AAG Cloudwatcher's "cloudy" setting would have come in handy.

Steve

[old_eyes]

On 06/05/2020 at 22:46, laser_jock99 said:

Do the rain detectors detect snow? I left my gear going once and came back outside to a near blizzard!

Many claim to. They have heated surfaces to prevent dew and to dry quickly when it stops raining. So will quickly form a thin layer of water when snow falls.