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 gauges 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 vanes 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 vanes magnet activates two switches simultaneously. Direction Resistance Voltage (Degrees) (Ohms) (V=5v, R=10k) 0 33k 3.84v 22.5 6.57k 1.98v 45 8.2k 2.25v 67.5 891 0.41v 90 1k 0.45v 112.5 688 0.32v 135 2.2k 0.90v 157.5 1.41k 0.62v 180 3.9k 1.40v Example wind vane interface 202.5 3.14k 1.19v circuit. Voltage readings for a 225 16k 3.08v 5 volt supply and a resistor value of 10k ohms are given in 247.5 14.12k 2.93v the table. 270 120k 4.62v 292.5 42.12k 4.04v 315 64.9k 4.78v 337.5 21.88k 3.43v