Weather Sensor Assembly p/n 80422
Imported by Argent Data Systems
Usage Notes
This kit includes a wind vane, cup anemometer, and tipping bucket
rain gauge, with associated mounting hardware. These sensors
contain no active electronics, instead using sealed magnetic reed
switches and magnets to take measurements. A voltage must be
supplied to each instrument to produce an output.
Assembly
The wind sensor arm mounts on top of the two-piece metal mast and
supports the wind vane and anemometer. A short cable connects the
two wind sensors. Plastic clips on the underside of the arm hold this
cable in place. Screws are provided to secure the sensors to the arm.
The rain gauge may be mounted lower on the mast using its own
mounting arm and screw, or it may be mounted independently.
Rain Gauge
The rain gauge is a self-emptying tipping bucket type. Each 0.011”
(0.2794 mm) of rain causes one momentary contact closure that can
be recorded with a digital counter or microcontroller interrupt input.
The gauge’s switch is connected to the two center conductors of the
attached RJ11-terminated cable.
Anemometer
The cup-type anemometer measures wind speed by closing a contact
as a magnet moves past a switch. A wind speed of 1.492 MPH (2.4
km/h) causes the switch to close once per second.
The anemometer switch is connected to the inner two conductors of
the RJ11 cable shared by the anemometer and wind vane (pins 2 and
3.)
Wind Vane
The wind vane is the most complicated of the three sensors. It has
eight switches, each connected to a different resistor. The vane’s
magnet may close two switches at once, allowing up to 16 different
positions to be indicated. An external resistor can be used to form a
voltage divider, producing a voltage output that can be measured with
an analog to digital converter, as
shown below.
The switch and resistor arrangement
is shown in the diagram to the right.
Resistance values for all 16 possible
positions are given in the table.
Resistance values for positions
between those shown in the diagram
are the result of two adjacent
resistors connected in parallel when
the vane’s magnet activates two
switches simultaneously.
Example wind vane interface
circuit. Voltage readings for a
5 volt supply and a resistor
value of 10k ohms are given in
the table.
Direction
(Degrees)
0
22.5
45
67.5
90
112.5
135
157.5
180
202.5
225
247.5
270
292.5
315
337.5
Resistance
(Ohms)
33k
6.57k
8.2k
891
1k
688
2.2k
1.41k
3.9k
3.14k
16k
14.12k
120k
42.12k
64.9k
21.88k
Voltage
(V=5v, R=10k)
3.84v
1.98v
2.25v
0.41v
0.45v
0.32v
0.90v
0.62v
1.40v
1.19v
3.08v
2.93v
4.62v
4.04v
4.78v
3.43v
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