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Hi Nick
The principle weather monitor used is an AAG Cloudwatcher from Lunatico Astronomia. This has two (semi) independent methods of rain monitoring for observatory shutter control.
Normally, AAG software running on the observatory computer monitors the AAG hardware mounted on a pole adjacent the observatory where an I.R. sensor measures sky temperature to determine cloud coverage, a heated capacitive plate senses rain droplets directly and a light sensor detects sky darkness. I also installed the optional anemometer.
If user configured thresholds in the software for the I.R. sensor monitoring sky temperature are exceeded, water droplets fall on the capacitive plate, the sky brightens or high wind speeds are detected then the AAG software will issue a weather unsafe warning and the observatory management software (ACP) will initiate an observatory shutdown and issue a close shutter command to the dome controller.
The above actions depend on the correct functioning of the observatory computer which can never be 100% reliable, even with UPS backup, so the AAG Cloudwatcher also has an independent pair of potential-free relay contacts on a dedicated socket built into the hardware mounted on the pole. When the capacitive plate senses water droplets the relay contacts close and via a separate direct wire feed back the the dome controller, the dome controller will close the shutter independently of any computer command.
The dome controller itself, which is a Rigel System from Pulsar Observatories (UK), uses a ‘heartbeat‘ monitor. If for any reason the observatory computer ceases to respond to regular ‘Are You Still Alive?’ queries then the dome controller will close the shutter. Also, as the dome controller communicates with the battery powered shutter via wireless it also has a ‘heartbeat‘ monitor and should the wireless link go down between shutter and controller then the shutter will independently close after a short delay.
The capacitive water sensor plate in the AAG Cloudwatcher hardware is heated to prevent condensation, melt ice or snow and dry the plate when rain stops. Because of this, power consumption of the AAG Cloudwatcher is quite high so the AAG hardware is powered from the mains supply via an AC/DC convertor.
Due to local topography and coastal location my observatory is subject to gusting wind speeds exceeding 90 mph several times a year. Should the open dome shutter be facing towards the wind it is possible the dome roof would be lifted off as the Pulsar Observatories dome design does not use a captive suspension system for dome roof to dome wall coupling, the dome roof rests on support rollers with a short skirt providing lateral location. As the observatory is under full automatic control of ACP I installed the optional AAG wind speed anemometer with the rest of the AAG pole mounted hardware. ACP monitors the AAG Cloudwatcher wind speed sensor and either will not startup the observatory and open the shutter or will close the shutter and suspend operations should windspeed exceeed my user defined threshold, currently this is set at a rather low windspeed of approx 30mph.
In practice, the AAG Cloudwatcher is not infallible as far as the I.R. cloud sensor works. The user defined thresholds need constant tweaking as the seasons progress and upper atmosphere temperature conditions vary, otherwise clear sky conditions are reported cloudy and vice versa. I had been working on writing a program in C++ code that could read my local public and ATC airport weather stations to automatically update the AAG thresholds for the I.R. cloud sensor but have found that my nearest airports ATC weather reports usually stop when the airport closes for the night so this project has been shelved for now.
My AAG unit is from an early batch and I read that Lunatico Astronomia have changed the specification of the I.R. sensor on the current shipped units to improve the stability of the the I.R. sensors response to upper atmosphere temperature changes.
The AAG Cloudwatcher also now includes a humidity sensor though apart from recording and reporting purposes I’m not sure it serves much purpose in active observatory management unless you incorporate this into dew heater management for example.
The AAG capacitive plate water sensor, light sensor and I.R. sensor are reliable but do need regular cleaning to keep them free of bird droppings etc so location for access is important.
At the time I purchased the AAG Cloudwatcher I also bought the AAG Solo weather server with the intention of mounting the AAG hardware high on one of the house chimney stacks, communication between the observatory computer and the AAG hardware would have been via the Solo unit and the LAN network. In the end I abandoned this approach for several reasons, partly planning since the house is a listed building but mainly accessibility to keep the AAG hardware clean (I did start down the path of building a heated washer system based around a salvaged automobile high pressure headlamp washer), possible issues with heat plumes from the chimmneys causing misreading of the I.R. sensor and the inabilty to use the built-in direct connection rain sensor relay contacts. In the end I decided to keep things simple and mothballed the Solo unit for now and placed the AAG Cloudwatcher hardware on a pole, 2mtr above ground and 1mtr from the observatory wall where it can easily be cleaned and wired directly to the observatory computer.
The anemometer is not heated and has frozen twice this winter where snow has melted and refrozen around the base. In practice as my location is just a mile inland of the South coast this has not caused a problem since we rarely experience snow, freezing conditions and high winds simultaneously but I will add an external heater cup to the base of the anemometer at some time. As an engineer I feel I can do this easily and at a much lower cost than Lunatico Astronomia’s own optional anemometer with built-in heater.
The ambient light sensor will respond to moonlight or domestic light spill so threshold settings need carefull adjustment to avoid false readings and unnecessary observatory unsafe conditions shutdown or delayed opening. Orientation of the AAG hardware so that the I.R. sensor faces the prevailing weather direction is important though there is no reason why you can not mount the AAG hardware on a pole that can be rotated to face into the prevailing weather direction and adapt to seasonal weather patterns.
Looking back at the observatory weather records for the last year I can see that with an observing session under way the AAG Cloudwatcher I.R. sensor detected cloud and initated observatory shutdown and shutter closure before it began raining on 37 nights while the capacitive rain sensor detected water droplets even though no cloud was detected and initated shutdown on 8 nights.
I did preferentially consider the Boltwood cloud monitor from Diffraction Ltd over the AAG Cloudwatcher The stability of the sky temperature detection of the Boltwoods active thermopile compared to the passive I.R. sensor used in the AAG Cloudwatcher is an advantage plus the no-moving-parts anemometer of the Boltwood is a simpler and more reliable device but I felt the higher initial purchase price and long term running costs of the Boltwood are too excessive for a purely amateur observatory. With a finite life of the thermopile and degradation of the thermopile window by airborne salt and organic contaminants, given my coastal location and seagull – pigeon populations I would expect to have to return the Boltwood to Canada every three or four years for thermopile / window replacement.
William.
Grant.
I used to use medical rated versions of the Startech USB over Cat5 cabling extenders in medical imaging systems and have some experience with them.
In some circumstances they do work well but the achilles heel is that all the data from your four devices at the client end flows through a single USB 2 port at the host end and is therefore limited to 480Mbs split four ways. These devices work well where the total data throughput from all the client devices never reaches that 480Mbs limit and that all the devices are roughly balanced in data throughput.
Problems can occur where a modern large sensor CCD/CMOS camera hogs all the available bandwidth for thirty seconds or more while downloading to the host and regular polling of the mount by your observatory software can not occur, in some cases the mount will “time out“ and require a reboot to reestablish USB communication.
This problem with the main camera taking all the available bandwidth has been addressed to some extent with the latest manufacturers offerings that include an onboard memory buffer in the camera that allows for a reduced data rate on the USB link however at this time I have only seen this with USB 3 CMOS cameras.
It is also the case that you will most likely need many more than just 4 USB ports in the observatory as you will find as you progress along the automation route.
In my own observatory (dome) I have (up to, depending on OTA configuration) 12 USB ports in use, main camera, guide camera, fiter wheel, AO unit, mount, focuser, rotator, dew controller, dome controller, cloud/rain/wind monitor, UPS supply for the PC and observatory power switch controller.
Depending how far along the remote control/automation path you plan to go if you begin adding in plate solving and refined mount pointing/closed loop slewing plus an all sky camera, well, a single USB over Cat5 cabling extender just won‘t be sufficient, you could be looking at two or even three separate extenders and at that price you might as well use a dedicated laptop or PC in the observatory controlled remotely by TeamViewer or Microsoft Remote Desktop from a separate laptop/tablet/PC in the house.
In the past my observatory was controlled by a dedicated desktop PC, that blew up due to damp, the ATX power supplies of conventional desktop PC’s are not rated for use in a condensing atmosphere and one dreary damp November the computers ATX power supply let go and damaged several connected devices. This was replaced with a laptop powered by a weatherproofed 19v supply. The laptop worked well until the temperature fell below freezing where the RAM memory clocks would drift and the dreaded ‘Blue Screen of Death’ would appear as Windows gave up. That problem was resolved by placing the laptop in a ventilated cabinet on top of low voltage pet warmer pad that kept the laptop above freezing. Eventually when that laptop came to the end of life it was replaced by an industrial fanless sealed PC with specially rated components for use below freezing, this works perfectly but at a high price. This type of industrial PC was a priority for my observatory because it is run fully autonomously for much of the year with no one in attendance to step in and deal with failures.
From the house to the observatory I ran three Cat5 cables, two in use and one spare, a multicore cable that is used for the alarm and halon gas fire supression system and an armoured power cable connected back to the main house fuse box. One of the Cat5 cables connects to a network switch in the observatory, the other end to the house router. The second Cat5 cable connects to a second separate switch and a pair of surveillance CCTV cameras, one inside the oberservatory the other outside, both connected back to the main house alarm system. Wireless networking is just not reliable enough at my location, it was not an issue with distance so much as too many other users nearby using the same wireless channels plus a requirement by my house insurer that only wired CCTV networking was used as many ne’er do well’s carry wireless network jammers while engaged on their activities. Networking over the powerline was considered but a line interactive UPS in the observatory does not pass the signal downstream of the UPS and severely attenuates the signal upstream.
All the low voltage signal cables from house to observatory run in a single 90mm diameter plastic pipe, buried a metre below ground, with a couple of spare pull-through draw wires in case I need to add or replace in the future. The armoured mains cable runs in the same trench but buried a further 450 mm below the pipe carrying the signal cables to prevent mains bourne interference and comply with local planning rules where minimum depth for a buried mains cable was stipulated at 1.2mtrs below ground level. The mains supply is configured as a TT system, that is, only live and neutral leave the house protected by a dedicated RCD in the main house fuse box and a two metre earth rod was driven into the ground right next to the observatory connected to a single earth bus bar installed inside the observatory. All metal work, including the steel pier, and observatory device power supply earths run back to that single point to avoid possible earth loops. The observatory computer is protected and maintained by a line interactive UPS, the dome shutter is battery operated and its supply is recharged by a solar panel on the dome roof. In case of loss of communication between shutter and dome controller or PC failure the shutter closes automatically. As well as a cloud, wind and rain monitor talking to the observatory computer and initiating a shutter closure command, a separate, independent rain sensor on the observatory roof triggers a shutter closure irrespective of the observatory computer.
In use, the observatory is controlled by ACP software that I can log in to from anywhere via TeamViewer but apart from giving it a list of targets ACP is in control of all the observatory functions including turning off/on frost protection heaters and the dehumidifier, observatory startup and shutdown, weather monitoring and target sequencing, switching on the flats panel etc. At the same time I can log into the house alarm and security system via a browser and watch the live video stream from my security cameras. When a planned target observation is complete, however many hours, days, weeks or months that may take, ACP sends the folder of images over the internet to my dropbox account as well as an email notification for me to post process wherever I might be.
Some astronomers are reporting successful control of small observatories using ’micro’ or ’stick’ computers run ‘headless’, that is without monitor keyboard or mouse, mounted up on the OTA with an additional 12v powered USB hub and 12v power distribution bus. Usually these micro stick PC’s only have a couple of USB ports plus either a cabled network port or wireless LAN and Bluetooth. As long as the main camera is assigned one of the available USB ports alone while everthing else goes via the second USB port and hub they do seem to work. The slightly larger mini PC‘s usually have four USB 2 sockets and are still light enough to be mounted alongside the OTA for short cable runs. Communication and control is only via TeamViewer, Remote Desk Top, or similar, from another computer but with the ability to run a full version of Windows and very short USB cables to everything else bar the dome/roof which would probably need an active extension from the USB hub up on the OTA to reach. Though not very fast and small memory storage I have read they will run observatory software including plate solving quite successfully with a minimum of cabling running up the mount. If you are not planning a fully autonomous observatory and are happy to attend to switching heating/ventilation and dehumidifying on off plus flats panels as necessary and don’t require a cloud/rain/wind sensor or weather station then these little ’Micro Stick’ or Mini PC’s may offer you all you want.
Do remember to check with your insurance company, I found it impossible to get insurance cover for the observatory without providing the connection into the house alarm and CCTV systems, when you look carefully at the wording of many household policies high value items used outside the home are not covered if you are actually away from home and out of sight of the items while general outbuilding cover is limited to a fraction of the cost of a typical observatory, I also discovered that in the case you are underinsured the insurance company can refuse to payout anything in the case of a claim!
Rather a long reply but hopefully of some use.
William.
Ernst.
Visit the BASS Yahoo group, link below, register for group access and after your registration is approved you will be granted access to the hidden *Links* area under the *More* tab where you will find folder paths to the BASS downloads.
https://uk.groups.yahoo.com/neo/groups/astrobodger/info
Approval is usually immediate if you already have a Yahoo groups account, otherwise it may take a few days to be granted access after initial registration.
Visit the conversation boards regularly to check for download links to the beta software releases
William.
