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Registered Member #538
Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181
Well actually I DID manage to do a parametric plot where the value of a resistor changes, but I'm having problems getting "readable" data from it. Seeing hundreds of voltage vs. time plots on top of eachother isnt really what I want, I'd like to see something like resistance vs. average signal amplitude or something. I fought and googled and fiddled but couldnt get anything like this. LTSpice HAS an integration thing, but it doesnt work for parametric plots, and even then you cant plot it, it just tells you the integral value. Is it possible to plot something like resistance vs. average signal amplitude in LTSpice and how do you do it?
I actually think I MIGHT have managed to get data for the measurement (values for resistance and integral of the voltage) in a text format by adding a ".MEAS" directive with the "INTEG" statement, but I have to write some script to scavenge the data off the file and arrange it so its suitable for plotting with gnuplot and make sure the data makes any sense. But this feels like a quite hard way to do something that I'd say is pretty important to get any useful data out of a parametric sweep o_O
Edit: Just realised I could also plot it with gnumeric, might be a tad easier.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I don't know about LTSpice, but I guess it has a tool similar to Microsim PSpice's parametric plots. In Microsim Probe, you could make plots with the parametric variable ("StrLen" in my simulations) as the X-axis, and anything you wanted as the Y axis. You just enter the name of your variable as the expression for the X-axis. Note the kinds of expressions I've used in the screenshot below.
As you can see from these expressions, you need to be rather careful about what you mean by "average". I've used the integral of the product of instantaneous voltage and current, to get energy, which you can divide by the simulation time clock to get a plot of average real power. Again in Pspice, never tried it in LTSpice :(
Registered Member #538
Joined: Sun Feb 18 2007, 08:33PM
Location: Finland
Posts: 181
Steve McConner wrote ...
I don't know about LTSpice, but I guess it has a tool similar to Microsim PSpice's parametric plots. In Microsim Probe, you could make plots with the parametric variable ("StrLen" in my simulations) as the X-axis, and anything you wanted as the Y axis. You just enter the name of your variable as the expression for the X-axis. Note the kinds of expressions I've used in the screenshot below.
As you can see from these expressions, you need to be rather careful about what you mean by "average". I've used the integral of the product of instantaneous voltage and current, to get energy, which you can divide by the simulation time clock to get a plot of average real power. Again in Pspice, never tried it in LTSpice :(
I've fiddled alot with LTSpice and it seems I cant plot anything else on the X-axis than time/voltage/current and cant put any mathematical expressions (other than basic mathematical functions like multiplication) in there. I guess I'll have to switch to PSpice, it has far superior plotting abilities. The main reason I'm using LTSpice is that I can make simulations run alot easier and its easier to use. With PSpice I always get transgression errors and "too small timestep" and all kinds of crap :P
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How to do parametric plots in SwitcherCAD/LTSpice?
