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The Nyquist frequency is equal to half of the sampling rate (number of measurements per second) — 
In the case of RULA vibration controller and data acquisition system RL-C21M, the maximum sampling rate of the device is 216 kHz — this means the Nyquist frequency is equal to 108 kHz. The Nyquist frequency will decrease together with the sampling rate.
The principle of Nyquist frequency helps engineers design ADC and DAC converters and set appropriate sample rates. And this is not just about converting signals from continuous (analog) to discrete, but also when you want to reconstruct a smooth, continuous signal from a set of discrete data points.
To further emphasize the importance of this principle, let’s consider what is going to happen if we ignore it. If a signal is sampled at a frequency less than twice its highest frequency 
, two phenomena called 'aliasing' and ‘distortion’ occur.
Aliasing is the effect that happens when high-frequency information is incorrectly identified as low frequency — it's similar to the effect seen in films where wheels or helicopter blades appear to be turning backward.
Aliasing is generally undesirable because it introduces errors or distortions that are not present in the original signal.
This is why, in practice, an anti-aliasing filter is used before the sampling process to remove frequencies above the Nyquist frequency (half of the sampling rate), thereby preventing aliasing.
The addition of filter is the reason why the sampling rate is usually chosen in the range of 
. With this in mind, the maximum frequency RL-C21M can measure is 80 kHz.
The figure below is an example of bandlimited signal and frequency aliasing.
1) Fmax < 1/2Fs. Signal without any artifacts
2-3) Fmax = 1/2Fs. Different phases of sampling frequency
4) Fmax > 1/2Fs. Signal aliasing. New frequency = Fs - Fmax
If you have further questions about the concept or would like a consultation on choosing a suitable data acquisition system for your task, please contact us in any convenient way:
contact@rula-tech.com
+371 6610 2166
