Thanks to the excellent WX information on the Davis Vantage Pro anemometer, I have been able to repair the original ‘Mk 1’ anemometer that my son (whose weather station it is) had to discard 3 years ago when it stopped working. He had to replace it with the later Mk. 2 version (with a detachable anemometer cup spindle unit), since the Mk. 1 was no-longer available, but this replacement anemometer has now also stopped working. Now, however, thanks to the information sheets, he can replace it with the repaired Mk. 1 unit.
Some comments on your Mk. 1 Davis VP information sheets
In the UK, both the anemometer is fitted with a 4-wire, flat ASDL2 cable with an RJ11 (4-pin) plug, though wired just as the information sheets show. A 6-pin plug is not used.
Although the anemometer unit cannot be taken apart easily, the direction potentiometer can be prized out fairly easily after cutting out the 4 ‘stakes’ round the edge of the plastic disk it’s mounted on. I think they’re made by melting the plastic locally with a hot punch, but the joints so formed can be detached with a sharp-pointed knife. The black and red wires from the reed switch are just long enough to allow the potentiometer to slide right out. But before you try to do this, the cable must be released so that it can slide freely through the mounting tube (by removing the flattened tubular plug/cable clamp at the bottom end of the tube - use a wood screw screwed into the plug to remove it). When replacing this cable plug, make sure the flattened part is parallel to the clamp screw that goes through the tube so that it holds the cable well away from the screw thread.
Neither the Bourns 6639 potentiometer listed as a spare (nor its Vishay 357B0203MAB251S22 equivalent) have the extra ‘spare’ terminal for the black wire, but one can be stuck on with epoxy to provide a support if necessary. The genuine Davis potentiometer is clearly a ‘special’. If you do need to replace the potentiometer, however, the potting compound round the 4 terminals on it is soft and easily cut off. In the UK, both replacement potentiometers are off-the-shelf from RS Components.
Mk. 2 version
My son’s Mk. 2 anemometer has developed an unusual fault. The wind-speed indicator works perfectly, as does the wind vane - in all compass directions except W, when it continuously indicates N. I think this can only be a potentiometer fault - presumably, for some reason, the slider isn’t making contact with the track in that position - possibly a speck of dirt - so, (in spite of the 909 ohm resistor?) the green wire ‘sees’ 0V, indicating N. I’m hoping the circuit is basically similar to that of the Mk. 1 unit, so that this logic works!
Does anyone have any other explanation for this behaviour or more information about the Mk. 2 anemometer? It would be a great help!
Thanks,
Tony Pennell.
Incidentally, the bearings on the anemometer cup spindle are much easier to replace on the Mk. 2 version! As with the Mk. 1 version, replace both ball bearings. SKF is good!