#Coherence X instal software#

#Coherence X instal software#

I've performed a quick test measurement to demonstrate how the simple, naive method gets tripped up and to confirm that the Waveforms software currently doesn't seem to do any coherent averaging. For example in experimental modal testing this is used extensively. This makes it a very useful diagnostic tool indicating when the measurement can be trusted. is phase-coherent) will be retained, whereas the part of Y that is incoherent will get averaged over multiple measurements.Īnother very useful feature is that one can then introduce the so-called coherence function gamma that tells us how much of the measured response y is actually due to the stimulus x, as compared to noise or other unaccounted excitations. The part of Y that has a stable phase relationship with X (i.e. The crucial part happens in step 2), specifically in the numerator with the averaging of E = E. Using coherent averaging, we can however form a better estimate of the transfer function, by using only the part of the output Y that is coherent with the input excitation X: In reality, there will always be various additional noise sources, as shown below. If I understand the documentation correctly, then the Waveforms software implements exactly this, and gets the magnitude and phase of the frequency response function by calculating magnitude = |X/Y| and phase = (angle(Y)-angle(Y)). Here X and Y are the Fourier transforms of x(t) and y(t), as calculated by the FFT.

In the simplest, noiseless case we can measure the transfer function as follows:

Let me explain the motivation step by step. While the NA functionality has already proven quite useful, it is currently still missing one crucial feature: Coherent averaging The AD2 and ADP3x50 nicely fill this gap, which is why I recently bought a ADP3450, hoping to finally fill the void.įeature request: Coherent averaging for network analyzer At higher frequencies, there is of course the option of traditional network analyzers, but they often don't work all that well below 10 MHz, and the 50 Ohm input and output impedance is a big nuisance to interface with. Unfortunately, most FFT analyzers only seem to go up to 100 kHz at most, so not quite far enough for my applications. Traditionally, this kind of measurement would have been done with a two-channel FFT analyzer (such as the venerable HP 3563A control systems analyzer). There the AD2 and especially the recent ADP3X50 nicely fill a mostly unaddressed niche: Recently, I've started using the network analyzer capability of the AD2 extensively, measuring the frequency response of various devices both in open-loop operation, and in closed-loop configuration in order to fine-tune PI(D) controller parameters in-situ, with bandwidths reaching up to a few MHz. As a consequence, this has led my lab to buy a dozen or so ADs over the years.

However, what really makes it stand out for me is the Waveforms software, which simply works well, is modern and convenient to use, and reasonably open and extendable (unfortunately all of these three points are often sorely lacking in test & measurement equipment). The hardware is decent, well-documented and affordable (especially before the covid price hike). First, I want to congratulate you on the Analog Discovery kit & Waveforms software.