MP3 - Time domain techniques and frequency analysis for condition monitoring Flashcards
Time domain techniques
What are the part of th signals
How can I save this value?
You have the samples on time but what about the amplitude (analogue value), how to save the amplitude of 1.2. This should be save digital, on a computer???
How to save the the analogue value of the amplitude on the computer, by means DIGITAL?
The measurement you have to save it digital on the computer, so it depends on the bytes that you measurement system can safe
Dynamic Range
The dynamic range of the input signal is less straightforward, because the lower limit is determined by the amount of noise in the analog waveform, which could be influenced by environmental conditions or the gain setting of a variable-gain amplifier that precedes the ADC. If the reference voltage imposes an upper limit of 2.5 V and the noise floor is 1 mV, the dynamic range is 2.5/1×10–3 ≈ 68 dB.
What is the RMS value
Is the quadratic mean of a voltage signal. the root mean square has to be taken because the sinusoidal signal varies in the time
What is the sampling theorem, what is this saying, what you want to achieve with correct sampling
When you fullfill this condition you can represent the ANALOGUE SIGNAL ENTIRELY.
* If the samling theorem is fulfilled before sampling, then x(n) is an exact representation of the analog signal
* The signal contains all information of the analog signal
What are the consideratinos when sampling?
- Signal has to be band-limited beofre sampling (antialiasing filter).
- Oversampling. Sampling higher than niquist freq
- Resampling.
- Mostly we use 0 to max freq to
Why shoud we filtering?
Why filtering?
* Certain frequency range of signal not relevant
* Erroneous part of signal
* Adjusting the signal
* Representing the signal
How to filter?
* Create a frequency response function
* Analog vs digital
Filters: Integration and differetiation??
When do we need to integrate.
Which kind of filters?
To integrate you need to filter the signal
What is the intuitive method
Discrete Fourier Transform
A peridodic function in the TIME DOMAIN result in a DISCRETE function in a Freq Domain==>Series function
How do you want to increasse your frequency resolution?–How to solve the leakege problem
By increassing your meassurement time.–by ussing a window
What is de Nyquist theorem? why is needed? and what is the sample frequency
How fast you have to measure or sample to reconstruct this signal.–to represent the function or signal, you have to sample a twice it sample frequency–>you must sample at twice the highest frequency present
What is aliacing and when you get that phenomena.
How to eliminate aliasing
When you sample at lower frequency than Nyquist, you get aliasing. The problem is that you lose information about the original signal
The aliasing can be removed by prefiltering
What is kurtosis
Kurtosis is a statistical parameter used to characterize a signal. In essence it provides a measure of the “peakedness” of a
random signal. Signals that have a higher kurtosis value have more peaks that are greater than three-sigma; that is, peaks
that are greater than three times the RMS value of the signal.
What is the SAMPLING PROCESS.
In which domein is described.
What is the sample and hold operation
What is the Uniform sampling theorem
(1) A band-limited signal of finite energy with no frequency components higher than W Hz is completely described by specifying the values of signals at instants of time separated by 1=2 W sec.(Niquist Rate)
(2) A band-limited signal of finite energy with no frequency components higher than W Hz may be completely recovered from a knowledge of its samples taken at the rate of 2 W (Niquist Interval) samples/sec.
