About the . . . .

Wackado Weather Station

The Wackado Weather Station is controlled by a Hitachi 6303 microprocessor datalogger.   The datalogger can receive both analogue and digital signals.  The datalogger collects measurement readings in real time from each of the weather sensors.  These measurements are captured every 10 seconds and stored.  At the end of a specific time period the datalogger summarises the measurements (ie. max or min, average or total) for each sensor and downloads the information to a Desktop PC (normal computer).  The Desktop PC processes the data by sorting and totalling the information as it is received.   This is done by using database software.  The database calculates the results and produces "web" pages for all to see. 

Measurements collected by the datalogger are broken up into three distinct time periods.  Every 15 minutes measurements for wind speed and direction, temperature and humidity are collected.   The measurements include the average wind speed and maximum wind speed, average temperature, a sample wind direction and average humidity over the 15 minutes.  The second time period records the total rainfall over an hour. The third time period records the maximums and minimums experienced over the last 24 hours for wind speed, temperature and humidity.  Rainfall is totalled for the 24 hour period from the hourly readings.

The sensor instruments used to collect the weather data are fairly accurate and the datalogger quite precise in its readings.  Readings to 5 decimal places are available, however in most instances this is trivial.  The temperature and humidity sensor uses a capacitive-resistive measurement.  Temperature can be measured from -40 deg C to +60 deg C with an average accuracy of +- 0.5 deg C.  Relative Humidity can be measured between 10% to 90% with an average accuracy of 2.5%.  However measurements above 90% can be misleading at times and accuracy falls away.

Wind Speed is measured using hemispherical cups (Anemometer) which rotate a magnet on the end of a rod near a coil (a resistive transducer).  This produces an AC signal which is proportional to the frequency of rotation of the cups.  Accuracy should be within 0.5 metres per second.  The measurement range is from 0 to 50 metres per second.  Wind Direction is measured using a Wind Vane.  The Wind Vane uses a precision potentiometer (resistor) which rotates outputting an analog DC voltage proportional to wind direction (angle).

Last of all are Rainfall measurements.  These are collected by a Tipping Bucket Rain Gauge.  The Rain Gauge has two small buckets arranged like a see-saw.  The buckets tip threshold is 0.2mm of water.  Each tip activates a "reed" switch which signals a pulse count to the datalogger.  The Rain Gauge can measure up to 500mm/hr.  Accuracy is better than 2% at 100mm/hr.

 

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