Homebuilt magnetically damped wind vane with optical sensor

[Gina]

I've mentioned my attempt at a magnetically damped wind vane elsewhere (in the Fine Offest sub-forum I think), but since this has little to do with FO stations I'm starting a new thread here. I'll post details with diagrams and photos shortly but I now have some interim results from a temporary mounting where it will be going - 7m above ground and about 2-3m above nearby shed roofs.

Comparing visual results with an FO vane at 6.3m above ground a bit further from the sheds and bungalow, the new damped vane deviates less than half as much from it's average direction as the FO one. Now I know they are in different positions and wind conditions will be a bit different but I thought I'd post my first results with the new vane at a decent height. I will be doing more rigorous tests in this new location with both the FO unaltered vane and later with an undamped vane of basically similar design. I guess I might just replace the magnet with a non-magnetic counterweight and test that. The new vane is considerably bigger and longer than the FO and that might be the main cause of the improvement I appear to be seeing. Without the damping I could produce a more compact and lighter wind vane sensor.

Ideally, the best testing would be with the different vanes in the same location at the same time, which of course, is impossible. Two vanes on the same pole one above the other might be the nearest practical arrangement. I'm giving it some thought. Meanwhile I'm working on the finishing touches to my mast head mounting, waterproofing that and the wind vane and a new homebuilt anemometer which will be mounted above the new vane.

[Gina]

Here's a cross-section of the new wind vane showing the damping magnet and optical sensors. The magnet produces eddy currents in the aluminium saucepan lid which causes drag on the magnet when it moves - the faster it moves, the more drag. The encoding disc interrupts light from the LEDs to the photo-transistors. Since the two most significant bits of the Gray code are the same but displaced by 90 degrees, one encoder track can be used for both if the sensors are displaced by 90 degrees. This makes for a smaller encoder. The 3 main optical sensors are shown in the main diagram and the single one - offset by 90 degrees - in the inset.