EEVblog® Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: Evan.Cornell on January 27, 2018, 04:46:30 pm
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If I have data describing a complex impedance (say, 100 data-points of magnitude & phase at various frequencies) collected from a RLC / impedance analyzer, is it possible to insert that into simulation program for analysis in a larger system?
I am currently familiar with TINA-TI, so being able to use that program would be ideal, but if anyone knows how to do such a thing in other (preferably free) tools, that would be extremely helpful.
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If you have the frequency response (or time domain response) from the network, you can then use multiple methods to generate a transfer function in the laplace domain (s-plane).
A common method is design by bode plot, where the magnitude and phase response is observed and a transfer function is generated usually in zero, pole and gain form.
Once a transfer function is determined, it can be realised by either passive or active networks. A good example of this is a pure-integrator implementation.
If you're looking for a specific process, here is a good example with matlab: http://au.mathworks.com/help/ident/examples/frequency-domain-identification-estimating-models-using-frequency-domain-data.html?prodcode=ID&language=en (http://au.mathworks.com/help/ident/examples/frequency-domain-identification-estimating-models-using-frequency-domain-data.html?prodcode=ID&language=en)
How complicated is the bode plot? (how many poles and zeros?)
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To add some more information, I have found out that TINA-Industrial is required to directly take impedance measurements into simulations. So, for free simulators, it does look like fitting the data to a lumped-element model is the best method for simulation.
See screenshot attached for shape of impedance data that I need to model.
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See screenshot attached for shape of impedance data that I need to model.
Would you be willing to share the data in CSV format? I would gladly have a go at modelling the transfer function.
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Please find attached. I would be most grateful if you could share your process for fitting model to the data, as I'm going to have to repeat this process in the future..
Thanks,
Evan
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Awesome, I will give it a show tomorrow morning as it is 2AM and brain no function |O
One thing that I glossed over is to mention 2 port network parameters and how they are essential if you want to correctly model/analyse a system.
I'm going to assume that the data given is the Z11 parameter (i.e. the impedance "looking into" the input). (and before people yell at me, im approximating Zin = Z11, bad i know)
This is the case for a passive network with a single input, I am assuming this as the vertical axis in your plot has the unit of ohms.
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This data was taken by hooking up the test leads of B&K 891 RLC meter to the two leads of the device under test, and getting impedance magnitude data (in ohms) and impedance phase data (in degrees).
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Keep in mind that the impedance will vary greatly with what's on the other side of that... piezo transducer, if I had to guess. :)
Indeed it doesn't seem to be all that well matched, for how strong the main resonance is, and it also seems to be in a bit of a cavity, given the higher modes (not quite harmonics). Pretty typical for air, I suppose.
The equivalent circuit will be, more or less: a capacitor (the terminal capacitance of the device), with branches in parallel. Each branch is a series RLC, resonant at whatever frequency. This should give you enough info to start playing around. Though it's not all that easy to adjust; that's why I wrote this:
https://www.seventransistorlabs.com/Calc/Filter1~.html (https://www.seventransistorlabs.com/Calc/Filter1~.html)
(Hover over the schematic elements to view tooltips, transform, change, add or remove stages. Set unused components to near-zero or near-infinite. Click and drag values to adjust in real time.)
Tim
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The last time I played with piezo transducers I used a lumped model and calculated the values by using the characteristics from the datasheet. There is a lot of good info out there on how to do this. See the attached PDF.
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So a single RLC || C model (Butterworth VanDyke) doesn't really capture the phase information properly in the frequency region I care about (25-35kHz).
So I am back to wondering if there are any SPICE tools that can take in a list of impedance data points to run AC sweeps. Any ideas?
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I guess I would use LTspice. If I wanted to find out if it can be done, I would join the Yahoo LTspice group because there are some VERY knowledgeable people over there. Be aware that there are two LTspice groups on Yahoo. One is a user forum and the other is a repository for files.
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Many simulation programs have an ability to load and use S-parameters files. They would have a S-parameter component, you load your S-parameters file in it and use the block as any other component to set up an analysis. Look for such component in your favorite simulation program.
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I have a list of impedance values (polar or rectangular format possible) taken at various frequencies. How would I go about converting this into s-parameter file?
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Look for Touchstone file format, there are different data representations that can be used to create a file out of your data.
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Any free SPICE simulators that can read in touchstone files and do AC sweeps?
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Can't B-sources (http://ltwiki.org/index.php5?title=B_sources_(complete_reference)) do this with LTSPICE?