Once a simulation is finished, it is possible to “right click” signals available for ploting and a dropbox of is offered.
What do the measurements are about?
I assume that most measurements are self-explanatory.
And what about this: Schematic Editor | 8.0 | English | Documentation | KiCad?
To check it out, for example do a transient simulation of a 1 kHz sine wave with amplitude 1 V for 10 ms.
You have the average, minimum, maximum, rms, peak-to-peak, time where min is found, time where max is found, and the integral over the area, most of them measured from time tstart (typically 0) to time tstop.
Fourier is a bit special, you see the voltage at various frequencies.
The measurement results are
AVG V(/in) 11nV
MIN V(/in) -1000mV
MAX V(/in) 1000mV
RMS V(/in) 710mV
PP V(/in) 2.0V
MIN_AT V(/in) 3.7ms
MAX_AT V(/in) 3.2ms
INTEG V(/in) 3.0nV.s
If you are interested in more details, look at the text output window of the simulator:
meas TRAN meas_result_0 AVG V(/in)
meas_result_0 = 1.142833e-08 from= 0.000000e+00 to= 1.000000e-02
meas TRAN meas_result_1 MIN V(/in)
meas_result_1 = -9.995446e-01 at= 3.745196e-03
meas TRAN meas_result_2 MAX V(/in)
meas_result_2 = 9.995446e-01 at= 3.245196e-03
meas TRAN meas_result_3 RMS V(/in)
meas_result_3 = 7.07107e-01 from= 0.00000e+00 to= 1.00000e-02
meas TRAN meas_result_4 PP V(/in)
meas_result_4 = 1.999089e+00 from= 0.000000e+00 to= 0.000000e+00
meas TRAN meas_result_5 MIN_AT V(/in)
meas_result_5 = 3.745196e-03 with= -9.995446e-01
meas TRAN meas_result_6 MAX_AT V(/in)
meas_result_6 = 3.245196e-03 with= 9.995446e-01
meas TRAN meas_result_7 INTEG V(/in)
meas_result_7 = 2.95987e-09 from= 0.00000e+00 to= 1.00000e-02
Fourier analysis for v(/in):
No. Harmonics: 10, THD: 2.89235e-12 %, Gridsize: 200, Interpolation Degree: 1
Harmonic Frequency Magnitude Phase Norm. Mag Norm. Phase
-------- --------- --------- ----- --------- -----------
0 0 -4.8495e-15 0 0 0
1 1000 0.999735 1.02971e-05 1 0
2 2000 1.09111e-14 98.5898 1.09139e-14 98.5898
3 3000 7.92418e-15 107.185 7.92629e-15 107.185
4 4000 5.03218e-15 178.873 5.03352e-15 178.873
5 5000 1.13776e-14 -65.755 1.13806e-14 -65.755
6 6000 6.2389e-15 20.6478 6.24056e-15 20.6478
7 7000 1.32601e-14 169.96 1.32636e-14 169.96
8 8000 9.19981e-15 -120.5 9.20225e-15 -120.5
9 9000 1.41463e-14 19.565 1.415e-14 19.565
Descriptions are to be found in the ngspice-42 manual in chapter ‘15.4 Measurements after AC, DC and Transient Analysis’ and for the Fourier command in chapter 15.6.4 .FOUR: Fourier Analysis of Transient Analysis Output (unfortunately not very detailed).
Fourier results: 0 (dc) is at about 1e-14, quasi 0. 1. harmonic (1k) is 1, all others are again 0. O.k. we have a 1KHz sine wave, only faint noise at higher harmonics.
Sorry, but your assumptions fall short when the only analisys done was an AC sweep.
Have you an explanation for what the measurements are about in this case?
The exported line for the spice simulation was:
.ac dec 10 10 100k
If I look at the RMS(I(R1) in the text I find the line:
meas AC meas_result_0 RMS I(R1)
meas_result_0 = 9.81216e-05 from= 1.00000e+01 to= 1.00000e+05
Does it makes sense to have a single value for a range of frequencies spanning four orders of magnitude on a RC low pass configuration?
I don’t see any assumptions. My suggestions are real.
It is great that you come up late with an example.
No, the RMS measurement on an ac simulation probably does not make any sense. But it is up to the user to decide if a measurement is reasonable or not.
Dear @holger,
You started your reply with:
I assume that most measurements are self-explanatory.
I’m glad we converged about the “not so self explanatory” for the case of AC sweeps.
OTOH some examples of the Ngspice 42/43 manual show there is an opportunity for enhancement of the UI in Kicad, as it is possible to ask for measurements at specific frequencies, or obtain a vector of the selected measuments, which IMNSHO makes a lot of sense.
Together with a max() function type on the vector it would allow to quickly find the maximum stress in a given component, I find it very useful!
HTH
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