Tutorial: Repairing an Anemometer in the WeatherRack
By Roger Slocomb 2/14/2018.
Editors Note: We are pleased to publish Roger’s excellent tutorial on repairing the reed switch in the SDL WeatherRack Anemometer. Thank you Roger.
I purchased my Switchdoc Grove Weather Pi Weather Station about a year ago. The anemometer which came with it had worked initially. As the vane cups would spin, I would get indication of wind speed. I really didn’t know how these worked, so this has been a fun little adventure into something new. I was having trouble deploying the weather kit because of family issues and vacations. When I got back to it, I discovered that the anemometer was not working anymore. It appears that either the magnet might have fallen off or that the reed switch was not working correctly. I determined by the steps below that the reed switch was probably the issue.
To check for the broken reed switch, I used an old phone wall jack. I plugged the anemometer into the phone jack. I connected the VOM meter (ohm mode 200 ohm setting) to the phone jack wires. then spun the cup spindle slowly.
A good reading should be 0 ohms and then almost infinity. My ohm meter read (0 to 0.5) ohms and then read 1.8 ohms. The switch must have gotten stuck to an almost the closed position.
Description of the Anemometer:
The 3 cup Anemometer that is supplied by SwitchDoc is supplied by the same company that supplies Argent Data Systems. SwitchDoc Labs does not sell replacement parts, but you can get the Anemometer separately at https://www.argentdata.com/catalog/product_info.php?products_id=175. At the time of this article they cost around $15.00 plus shipping.
The 3-cup anemometer consist of 3 cups mounted on a rotating spindle top. Under the top which is friction mounted to a nice bearing is a permanent cylindrical magnet. As the spindle rotates it actuates a proximity reed switch. This reed switch is located inside the bottom half enclosure of the anemometer assembly. The reed switch is soldered to a circuit board and securely mounted with screws to the bottom assembly.
As the top spins so does the permanent magnet and causes the reed switch to open a contact and close a contact.
More info on Anemometers: https://en.wikipedia.org/wiki/Anemometer
Editors Note: Check out Dr. Shovic’s talk on anemometers in his “weather week” talks here:
Here is what my Anemometer looks like:
Under the cup spindle you will find the permanent magnet and the inner cylinder that friction fits over the bearing mounted on the lower housing. To get the spindle off, you can use your bare hands to work it back forth. I would not suggest using a screw driver, because it might damage the spindle. You might be able to use a wide putty knife. My hands worked just fine. Be careful to not bend or damage the cups.
This is the top of the lower housing with the bearing attached to it.
This is the bottom side of the lower housing. This is the side that attaches to the weather mast. You will notice 3 screws on the bottom. Also, the wires that go to the wind vane exit at the bottom of the lower housing.
Once you remove these three screws you will see that the wire is tied in a knot. This is done to offer strain relief protection to the soldered wires inside the cavity.
Strain relief and fiber shield are seen below after the bottom cover is removed:
Once the fiber disk is removed you will see a circuit board. This is where the sensing wires and the reed switch are mounted (this picture is after I replaced the reed switch with the new SOWAY encapsulated reed switch.
The second picture is the circuit board removed with the broken reed switch. You remove the two screws and pull the whole circuit board out of the lower case.
So, unsolder the old reed switch and solder in the new reed switch.
The reed switch I used was an encapsulated reed switch made by Soway. I purchased mine from 123electronics on Amazon. I, also, found them at Sparkfun.
You might want to test the reed switch with a magnet and ohm meter before reassembly.
Figure 1. Re-assemble by remounting the circuit board and securely tighten screws.
Figure 2. Put fiber cover back on, re-tie strain relief knot.
Figure 3. Re-mount bottom cover and tighten screws.
Figure 4. Put the cup and spindle back the housing top bearing if you took this off. It is not necessary to remove this part if you are certain it is the reed switch. I guess the magnet could fall off.
Testing the anemometer:
I tested the anemometer initially with an old phone jack with an RJ11 connector and a VOM meter. Then I connected it to the wind direction vane and did a test spin with the Grover Weather PI.
An O-scope would be able to measure fast spinning. The digital VOM is not fast enough to show the switching. It only checks very slow rotation. You would need a VOM meter with an analog needle style meter to see the switch working at higher speeds.
The Question of Accuracy:
Final testing of this fix will require checking known wind speeds with the anemometer connected to the weather station. My worry is that the Soway reed switch sensitivity may affect its accuracy. I cannot find the sensitivity spec on the Soway manufacturers documentation. This may not be an issue at all, but it should be checked for accuracy.
Question of Economics:
Another thing that I considered was replacing the whole anemometer at the cost of $15.00 plus shipping.
The reed switch glass replacement is $1.94 to $6.00. The encapsulated reed switch is 3.50 to $6.00. Don’t forget shipping. If you purchase 2 or more reed switches then over time it be worth it over purchasing a new one. I didn’t account for my labor time either. It’s more fun fixing it yourself.