Temperature compensated linear wind energy meter

Rising fossil fuel prices and fears of global warming have increased interest in renewable energy sources and have also brought attention to supporting and demonstrating instrumentation. This design responds to this trend by enabling direct and convenient measurement of an important renewable energy source: wind energy. It facilitates a quick and simple initial assessment of potential wind turbine sites and features a wind speed transducer consisting of an optically detected vane anemometer and a temperature sensor consisting of a diode-connected transistor (Figure 1). These components are connected to a digital/analog hybrid circuit that together provide real-time, linear, temperature-compensated readings of wind energy density.

The potential energy of wind power is: × air density (kg/m3) × air velocity (m/sec)3. Therefore, to calculate this value, it is necessary to estimate the air density (air density is inversely proportional to absolute temperature), measure the air velocity and calculate a cube.

Below are the details of the wind energy meter. Q1, connected as a diode, has a base-emitter voltage of about 600 mV and a temperature coefficient of –2 mV/°C at 25°C (298K), with a bias current of 550 A. Therefore, Q1 is a voltage reference that tracks the relationship between air density and temperature. According to the ideal gas law, the relationship between air density and temperature is: –0.3%/°C. At the same time, the optical sensor O1 works with a rotating anemometer impeller to provide a frequency proportional to the wind speed: FW=10 Hz/(m/s). Thus, the conversion of VQ1 and FW to an output signal of 1mV = 1W/m2 is a function of the third-order X×Y×Z product of three cascaded CMOS switch FVC (frequency-to-voltage converter) charge pumps S1, S2, and S3.

FVC S1/IC1A produces a negative voltage of –0.17×VQ1×FW; FVC S2/IC1B produces V2 = –V×FW = 0.17×VQ1×FW2; and FVC S3/IC1D produces –V3 = –0.17×VQ1×FW3. Finally, differential converter IC1C offsets and scales –V3 to an output of VOUT = 0.42×VQ1×FW3 = 1V/(kW/m2).

A wind meter can be easily calibrated with a car by driving it at a constant speed of 18.6 m/s = 41.5 mph = 66.8 kph on a windless day. The anemometer is exposed to the outside airflow, and the calibration potentiometer is adjusted to make the output voltage 4V. If you want to obtain better accuracy, you can calculate the output voltage according to the following formula adapted to the actual air density: VOUT = 1.14V × air pressure mbar / (273 + ambient temperature in Celsius). 0 0 (Please comment on the article)