When you’re looking at real-time wind readings, it’s important to understand the proper measurement of wind speed. You may assume that wind gusts are causing fluctuations in the numbers, but that’s not always the case. Even constant wind might turn up as spikes in the wind speed and direction indicator.
Let’s discuss what may cause these fluctuations and how you can avoid erroneous readings.
The Resolution of Pulse Measurements
The resolution of pulse measurements is one count divided by your device’s scan rate.
There will be instances when your actual signal frequency happens to be between resolution steps. The constant input of signal will result in the readings “bouncing” when seen on the data logger. When you average these new values over some time, they will still be the same as real-time values. You simply divide one count by the averaging interval.
For example, a constant 0.5 Hz signal will appear to bounce up and down when you look at it on the wind speed indicators. If you take an average of these readings, it will still result in 0.5 Hz, correctly matching real-time values.
How Inaccurate Readings Happen
However, if you move the frequency up or down within the resolution step, the reading will form a sawtooth pattern. Take note that faster scan rates will appear to have bigger spikes.
Here is where the usual errors come from. Readings become inaccurate when scan rates are faster than the frequency.
Let’s say your wind speed and direction indicator has a multiplier of 0.50 m/s per Hz. If you overshoot your resolution at 10 Hz, you’ll have an error of 5 m/s. This means if you just base your data on raw readings, you’ll be reporting erroneously by up to 5 m/s.
Always Take Averages
The takeaway is to be aware of the resolution of your measurements and how it can affect real-time readings. Always take averages of multiple readings when you suspect that there may be inaccuracies in your data logger. By doing this, you’ll ensure that your data is as accurate as possible.
Make Sure to Only Use High-Quality Equipment
It always helps that you also use high-quality wind speed and direction instruments when you’re out in the field. You can’t settle for something that will falter when you need it the most. If you’re looking for high-quality gauges and anemometers that will ensure accurate readings, contact Comptus today. We can talk about our products or provide more information tailored to your needs.