- Wind vanes determine the wind direction. The evaluation of the wind direction ensures the best possible position of wind turbines.
- It is essential that a wind vane covers an entire 360° degree radius, without a north gap.
- Cheaper wind vanes often have lower quality internal electro-mechanic fittings, which limit their life span, and a considerable north gap.
- Most wind vanes can be equipped with electronically regulated heating.
- Digital (TMR) and potentiometric (POT) wind vanes are available.
Wind Vanes TMR vs. Wind Vanes POT
Compared to wind vanes POT, digital wind vanes TMR are the winner on the technical perspective as well as on the commercial point of view:
- Digital (TMR) wind vanes are offered at a lower price than potentiometric (POT) wind vanes.
- Digital (TMR) wind vanes are subject to less mechanical wear than potentiometric (POT) wind vanes thanks to their solid state design.
- Digital (TMR) wind vanes do not have moving parts, except the bearings. Thus digital (TMR) wind vanes are more reliable and less susceptible to failure.
- Digital (TMR) wind vanes deliver more precise measurement values (see table below).
|Thies Compact TMR||± 1°|
|Thies Compact POT||± 2°|
|Thies First Class TMR||± 0.75°|
|Thies First Class POT||± 1°|
Measuring principle Wind Vane active POT
The angular position of the axis is scanned contactless by a magnetic angle sensor (TMR sensor, tunnel magneto resistance) via the position of the magnetic field. The sensor is operated in magnetic saturation, it can therefore be considered inert to external magnetic fields. The maximum output voltage is proportional to the supply voltage and therefore shows the same behavior as the wind direction sensor with a mechanical potentiometer.
The special feature of this type of circuit is a very low energy consumption, which is partly lower than for mechanical potentiometers. In comparison to a mechanical potentiometer, no wear does occur here. The output signal of the sensor is an analog voltage. This output voltage is in the range from 0V up to the applied supply voltage.
Due to the fact that the output voltage can be identical to the supply voltage, this sensor can be used as a replacement for previous sensors with a mechanical potentiometer.
When changing from a sensor with a mechanical potentiometer to this device, the parameters supply voltage and supply current must be observed. They must fulfill both requirements. If the wind vane is supplied over one output of the data logger, its minimum supply voltage will have to be obeyed or a suitable external voltage supply will have to be selected.
Deadzone is only to be found by potentiometer wind vane, but not by TMR wind vane.
Potentiometer (POT) wind vane
Potentiometer wind vane uses as sensing element a potentiometer with typically 10 kOhm or 2 kOhm.
A potentiometer is a resistance with a value in a linear relation to the angle of wind vane.
So with resistance (359°) = 10 kOhm by 359°, so by an angle alpha, Resistance (Alpha) = 10 kOhm *Alpha/359.
So clearly by an angle close to 0°, the resistance is close to 0 Ohm. This means you have a short circuit.
To avoid a short circuit, cheap wind vane give no value in the dead band (usually from 355 to 5°).
This means you have
- only 97% data availability from 5° to 355°) and
- no data from 355° to 5°.
TMR wind vane
TMR wind vane are not using a potentiometer as sensing element, but the “Tunnel magneto Resistance “ effect.
And behind that, a processor evaluating this TMR effect. There is no issue with short circuit around 0°, so there is no need for a deadband to protect from short circuit.