# Questions tagged [measurement]

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### Is fft2 in MATLAB unitary? Some differences happen

I meet a problem when implementing fft2 in MATLAB. The question is I try to simulate the realistic measurements $Y = |FCXF^H|^2$ - the intensity of Fourier domain of object $X$, where $F$ denotes ...
20 views

### Direct path and reflections of ultrasound transmission

I am using the following system: Ultrasonic chirp signals with central frequency 100kHz are being transmitted using ultrasonic sensor. After the transmission through the medium(air/solid/liquid/...
21 views

### Oversample or undersample correlated noise?

I wish to measure nontrivial (non-Gaussian) broadband current noise for its distribution and power spectral density. The noise is amplified (with transimpedance amplifier) with some characteristic ...
31 views

### How to determine number of observations based on measurement frequency?

So I'm working on a problem where I'm measuring a signal with two different instruments -- one is a low frequency measurement system (1 Hz), and the other is a high frequency measurement system (200 ...
79 views

### Phase measurement with FFT for DMM Keithley 7510

I am currenly working on a measurement driver for the DMM Keithley 7510. I implemented a harmonics measurement using FFT (from MathNet library). First I simply sample my input voltage signal and ...
677 views

### Measuring non-planar objects in image

I'm working on a computer vision application (using openCV) and the goal is to measure the width of an object before/after it falls on a container. So after the fall its position will be random, ...
35 views

### Measuring THD using consumer sound card

I am trying to measure (estimate) THD of an audio path using a consumer sound card. The idea is that I do two measurements, one without the system being measured in the path and one with it: ...
280 views

### How to calibrate a signal with respect to frequency

I have recordings from accelerometers (non-flat response with respect to frequency) and I'd like to convert my voltage time series into acceleration values. Is there a standard method for doing this? ...
75 views

92 views

### Calculating Transfer Functions From Harmonic Distortion Percentage

Hi I am working on emulating a piece of analog audio equipment and would like to be able to create a transfer function based on the measured percentages of harmonic distortion. I know that harmonic ...
334 views

### How to calculate the entropy of random normally distributed samples?

I have a hardware device that outputs a normal distribution of readings. It's (fitted) parameters are mean = 35 units, std.dev. = 8 units and I read the values as 8 bit integers. I'm trying to ...
98 views

### Filter results from force measurements

I was provided with several force measurements. Precisely: The vertical compression force exerted from the milling tool on a working peace. The plot of the force looks reasonable and of course it ...
157 views

### Digital filter for sharp impulse in data

I am looking for an algorithm or a filter to remove sharp peaks from my data. I am collecting raw data after every 1 second from an sensor through an ADC. The ADC has an internal FIR filter. I use ...
210 views

### Estimating confidence intervals for the mean value

Say I conducted a numerical experiment -a time-dependent fluid simulation- and extracted a time-series of some variable. It looks like this: As a result of the simulation, I am supposed to report the ...
671 views

### Adjustment of window length with sliding/moving RMS method for frequency drifts

I'm using a sliding RMS mechanism to compute RMS of a signal, i.e. with a window size of N, I add the squared value of the new sample $x[n]$ to the running total while deducting the squared value of ...
6k views

### How to detect “fast” changes in signal processing

I'm working on a project where we measure the solderability of components. The measured signal is noisy. We need to process the signal in real time so that we are able to recognize the change that ...
1k views

### Measuring signal phase difference between receivers

I am working on a project which aims to locate a transmitter. I consider doing this using several receivers and measuring the phase differnces between them. My problem is that arduino measures once ...
48 views

### How does the error in azimuth angle vary as one moves away from the boresight direction of a radar

My question is basically same as the title. I am trying to find a mathematical model which provides the error, $d\theta$, in azimuth angle($\theta$) as one moves away from the boresight direction of ...
45 views

### Parameter estimation from a measure

I'm doing an exercise where, given a data sample taken from a physical measure, I have to estimate the parameters of the measure where samples $x_i$ are described by the equation:  x_i = A \sin(2\pi ...
78 views

### SNR problem with different sampling rates using innerproduct

I'm trying to measure the amplitude of a sinusoidal component in a noisy signal. Since the signal frequency is known beforehand, I'm calculating scalar product with a sine and cosine base function ...
71 views

### Why is the term deconvolution used more for signals and not so much (or at all) for systems?

Wikipedia defines mathematical deconvolution here, and with the examples given and my experience, what I've read over the years is that deconvolution is used to determine an input signal provided a ...
374 views

### Measuring amplitude of a spectral component

I'm trying to measure the amplitude of a spectral component in a signal. The component's frequency is always known beforehand. I take a given number of samples, apply the flattop window to reduce ...
219 views

### Best reference for object size estimation in an image

I'm working on a project where I need to measure the size of a 2D object on a flat surface from an image. I have total freedom to create a reference with any shape and size. The camera I am using is ...
34k views

### Determining the mean and standard deviation in real time

What would be the ideal way to find the mean and standard deviation of a signal for a real time application. I'd like to be able to trigger a controller when a signal was more than 3 standard ...
528 views

### Sampling and zero crossing

I am sampling a sine wave of 50Hz(stepped down from 230V) at the rate of 500KHz. For identifying disturbances in the wave, i was thinking of comparing a cycle of incoming sine values with reference ...