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  January 12, 2005

  • Project proposal submitted and accepted.

  February 16, 2005

 

 

  • Specifications reviewed and accepted by AXYS.

  March 19, 2005

  • Working prototype of the smart sensor.

  April 1, 2005

  • Poster presentation at 4:00PM in the engineering lobby.

 

 

Conditioning Data

 

RM Young Wind Sensor

The wind characteristics (wind speed and direction) was acquired from the use of an RM Young Model 05103 wind sensor provided by the AXYS.  A detailed layout of the RM Young  is shown below.  The RM 05103 is a high-performance wind sensor that measures horizontal wind speed and direction. It uses a four bladed propeller to produce an AC sine wave signal with frequency directly proportional to wind speed. To measure direction, the wind sensor has a 10kΩ potentiometer which varies linearly with wind direction. 

 

RM Young 05103 Wind Sensor

 

Wind Speed

The propeller rotation of the RM Young 05103 produces an AC sine wave signal with frequency proportional to wind speed. This AC signal is induced in a stationary coil by a six-pole magnet mounted on the propeller shaft. Three complete sine wave cycles are produced for each propeller revolution.  Conditioning of this AC signal must be done to produce a signal that can be easily converted to a digital signal.  The generated AC sine wave is fed into the input of an operational amplifier to produce a square wave with the same period and therefore still proportional to the wind speed.  The period of the square wave can be calculated from the onboard asynchronous timer of the processor (PIC16F88).  The period is measured from the number clock pulses of the oscillator between two consecutively rising edges of the square wave. The number of clock pulses and the frequency of the oscillator are used to calculate the precise wind speed.  The wind speed can be determined from the following formulas.

 

Wind Speed vs Propeller RPM

m/s = 0.00490 x rpm

knots = 0.00952 x rpm

mph = 0.01096 x rpm

km/h = 0.01764 x rpm

Wind Speed vs Output Frequency

m/s = 0.0980 x Hz

knots = 0.1904 x Hz

mph = 0.2192 x Hz

km/h = 0.3528 x Hz

 

Wind speed circuit implementation

 

Wind Direction

The RM Young 05103 transduces wind direction by a 10kΩ precision conductive plastic potentiometer. With a constant voltage applied to the potentiometer, the output signal is an analog voltage directly proportional to wind direction angle. It is important to note that, while the sensor mechanically rotates through 360, the full scale electrical signal only rotates through 355.  Therefore external signal conditioning electronics must be placed accordingly.  When the potentiometer wiper is in the 5 deadband region, the output signal is floating and may show varying or unpredictable values. A deadband circuit was implemented to prevent these false readings. In this circuit the 10kΩ potentiometer was used as a variable feedback resistor of an operational amplifier and a 10kΩ resistor was placed on the negative input of the op-amp. This causes the output voltage of the op-amp to vary from 0 to -Vcc/2 with an input voltage of Vcc/2.  This voltage corresponds to a wind direction of 0 to 355.  As the potentiometer enters the deadband region the op-amp goes to open loop gain and the output voltage goes to -Vcc.  This analog voltage is then inverted and converted into digital data using the 10 bit analog-to-digital converter (ADC) of the processor. 

 

Wind direction circuit implementation with deadband compensation

 

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