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Hello RL,

Please try my example to see and understand my point.

Files > Temp > z_from_FFT_with_noise.asc

Run the TRAN simulation.
Plot V(z2) and I(V2)
FFT of V(z2) and I(V2) with 1048576 points
-> plot FFT of V(z2)/FFT of I(V2)

Best regards,
Helmut


--- In LTspice@..., legg@ wrote:

--- In LTspice@..., "Helmut" <helmutsennewald@> wrote:

--- In LTspice@..., legg@ wrote:

Given a plot of a pink or white noise voltage, and a synchronized plot of the current induced in a partially reactive load -

Will the 'normalized' ratio of the FFT plots be an indication of Z?

I'm looking at the low frequency end of the FFT, to avoid sampling issues. By normalized, I mean that 1 volt would produce 1 amp with both plots resolving to 0dB at the minimum sampled frequency (the load being partially inductive in this example).

It seems much too simple......

RL

Hello RL,

It will only work when you filter the FFT-output, but the
the FFT-results can't be filtered in LTspice. Thus you have
to export the FFT-data and process them in an external program.
This method only work with a linear system and it's precision
may be somewhat limited due to group delay variation.

Best regards,
Helmut

Filter the FFT results? The source is, ideally, uniform in amplitude across the band; so ideally the FFT would be a flat (or at least a straight) line.....What does filtering an FFT output entail?

I am looking at a pink noise source that has been prefiltered to include only a decade or two, so a few assumptions can be made about any FFT output registering outside this region.

With both V and I being monitored synchronously, there are a hell of a lot of variables being weeded out, but the sample duration is limited and the resolution is fairly course (~8bit 2500 data points per variable). So even if the calculated Z were valid, it'd be a crude approximation at best. I'll post a few plots in temp to show what the results actually look like.

The Z in this case is a loudspeaker transducer coil, so it's static characteristics are fairly easily obtainable using a simple swept tone. Given the signal processing capabilities that are falling into our laps with LTspice and even the most modest digital scopes these days, some questions go begging for an answer.

I was also concerned about phase relationships and delays, hence the curiosity about the actual spot 'Z' produced by the calculation. If R is known, then the phase could be intuited. If L is independent of temperature, then a new R value could theoretically be winkled. If other things are known, then phantom R/L/C quantities, or functional shifts in the same could also be evaluated. It's probably already standard practice, somewhere, DSP101 or something FAIK.

As with any 'new' tool, there are applications that don't jump out at you, or get their own chapter in the manual. Knowing the limits could save some time fiddling about - so a reference or pointer could be worth a thousand words.

Doing this again, with a source that had an unpredictable frequency content......could be a very non-invasive sensing method that costs only software, which, as everyone knows, is free......(insert smiley face here).

RL

--- In LTspice@..., "beaudoin.christopher" <beaudoin.christopher@> wrote:

I am modelling a voltage noise source by defining the noise source with a PWL file. The circuit is very basic (two resistors no L's or C's) and I have setup a transient analysis using the time step equal to the time increment in the PWL file. In doing this, what I am finding is that the transient analysis is somehow modifying the statistics(I'm guessing by integration/interpolation)of the random signal defined in the PWL file. For this reason, I'd like to gain a better understanding of what this transient analysis is doing in this very simple case. For example, are there are time constants implicit to the solver that I should be aware of such that I should not expect to achieve a steady state case until some time "Tsteadystate" even if there are no Ls or Cs in the circuit? Any understanding you can offer would be greatly appreciated.

Best Regards,
Chris

Hello Chris,

LTspice dynamically changes the time step. You should simply
a small maximum time step in the .TRAN command. This ensures
that nothing will be lost. LTspice does a linear interpolation
between your defined PWL data points.

LTspice uses data compression by default when it saves the
results of the simulation. If you you want the best result,
you should disable data compression in this case. Please add
the following SPICE-directive to your schematic. It will
switch off data compression.

.options plotwinsize=0

Best regards,
Helmut

--- In LTspice@..., "bcapaldo" <bcapaldo@> wrote:

Maybe this question was already asked but I cannot find an
example, but is it possible to generate a signal like
A/t + t/B where A and B are two generic constant and t
is the simulation time?
thanks

Hello,

There are arbitrary sources Bv and Bi. Their symbol is bv and bi.
The time is "time" in the formulas.

V=A/(time+small_const) +B*time

You can't divide by 0 at time=0. Thus you have to add a small
number.

Also look at the help pages of B-sources for the possible
functions like sin, exp, if, ...

Best regards,
Helmut

What is wrong with the statement? Do you find practical applications
where a fixed DC voltage is applied, in the conducting direction,
between base and emitter of a bipolar transistor?

Helmut I have a question for you along this line if I may. I tried what you said but cannot change any thing at all in Select component dialog box. If I should start another thread just say so but my question is along the same line of this thread. How do I change that line in LTspice. I get nowhere with that dialog box.
Best Kevin


________________________________
From: Helmut <helmutsennewald@...>
To: LTspice@...
Sent: Tuesday, July 30, 2013 2:23 PM
Subject: [LTspice] Re: "Missing schematic(s) of the hierarchy" error



??


--- In LTspice@..., "nikkotel" <nikkotel@> wrote:

I'm trying to work hierarchically, so I created a low level schematic (myblock.asc), created a symbol (myblock.asy) for that schematic, and saved both of them at C:&#92;Program Files&#92;LTC&#92;...&#92;lib&#92;sym to be able to access the symbol when bringing components.
However, when I place that symbol in top level schematic, I get an error of missing schematic(s) of the hierarchy. If I save the top level schematic at the same folder as the low level, i.e. at e C:&#92;Program Files&#92;LTC&#92;...&#92;lib&#92;sym, there is no error and everything works fine.

However, I'd like to save my top level schematic at another folder, so I probably need to point LTSPICE to low level schematic location... I tried to place a SPICE directive ".include C:&#92;Program Files&#92;LTC&#92;...&#92;lib&#92;sym&#92;myblock.asc", however, it didn't work.

Please advise
Thanks a lot

Hello,

You have to save the symbol and the schematic in the folder
of your top-level schematic.

Now here comes what you missed.
You can add a symbol from the folder of your top-level schematic.
Therefore open the "Select component" dialog. Then change the
folder in "Top Directory" to your schematic folder. Now you see
all the components(.asy) in your top-level directory.

Best regards,
Helmut

--- In LTspice@..., "Helmut" <helmutsennewald@> wrote:

--- In LTspice@..., legg@ wrote:

Given a plot of a pink or white noise voltage, and a synchronized plot of the current induced in a partially reactive load -

Will the 'normalized' ratio of the FFT plots be an indication of Z?

I'm looking at the low frequency end of the FFT, to avoid sampling issues. By normalized, I mean that 1 volt would produce 1 amp with both plots resolving to 0dB at the minimum sampled frequency (the load being partially inductive in this example).

It seems much too simple......

RL

Hello RL,

It will only work when you filter the FFT-output, but the
the FFT-results can't be filtered in LTspice. Thus you have
to export the FFT-data and process them in an external program.
This method only work with a linear system and it's precision
may be somewhat limited due to group delay variation.

Best regards,
Helmut

Filter the FFT results? The source is, ideally, uniform in amplitude across the band; so ideally the FFT would be a flat (or at least a straight) line.....What does filtering an FFT output entail?

I am looking at a pink noise source that has been prefiltered to include only a decade or two, so a few assumptions can be made about any FFT output registering outside this region.

With both V and I being monitored synchronously, there are a hell of a lot of variables being weeded out, but the sample duration is limited and the resolution is fairly course (~8bit 2500 data points per variable). So even if the calculated Z were valid, it'd be a crude approximation at best. I'll post a few plots in temp to show what the results actually look like.

The Z in this case is a loudspeaker transducer coil, so it's static characteristics are fairly easily obtainable using a simple swept tone. Given the signal processing capabilities that are falling into our laps with LTspice and even the most modest digital scopes these days, some questions go begging for an answer.

I was also concerned about phase relationships and delays, hence the curiosity about the actual spot 'Z' produced by the calculation. If R is known, then the phase could be intuited. If L is independent of temperature, then a new R value could theoretically be winkled. If other things are known, then phantom R/L/C quantities, or functional shifts in the same could also be evaluated. It's probably already standard practice, somewhere, DSP101 or something FAIK.

As with any 'new' tool, there are applications that don't jump out at you, or get their own chapter in the manual. Knowing the limits could save some time fiddling about - so a reference or pointer could be worth a thousand words.

Doing this again, with a source that had an unpredictable frequency content......could be a very non-invasive sensing method that costs only software, which, as everyone knows, is free......(insert smiley face here).

RL