Signals
- There are many different types of signals. The two main classification of signals are those that are deterministic and those that are nondeterministic. These may be subdivided as shown below:
- Deterministic
- For a deterministic signal the physical phenomenon can be represented by a mathematical relationship to a reasonable degree of accuracy.
- Periodic - pure sine wave
- Complex periodic - vibration signal from a petrol engine at idle.
- Almost periodic - microphone measurement close to diesel engine at idle.
- Transient - a swept sine wave, vibration signal from an engine that is increasing in speed, hammer force input modal excitation.
- Nondeterministic - random
- For a nondeterministic signal the physical phenomenon cannot be represented mathematically.
- Stationary - average statistical properties over a time interval of interest are constant e.g. interior noise of a vehicle driving at constant speed.
- Nonstationary - characteristic of a time series for which the distribution changes over time e.g. interios noise of a vehicle that is coasting down (decreasing in speed).
See also: Fast Fourier Transform, Power Spectral Density, Settling Time.
