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Re: .MEAS Failure

 

I don't have a video card.
Mine is on the motherboard.
Intel UHD Graphics 750.

Sent:?Tuesday, February 25, 2025 at 5:21 AM
From:?"Tony Casey via groups.io" <tony@...>
To:[email protected]
Subject:?Re: [LTspice] .MEAS Failure
On 25/02/2025 10:53, eewiz via groups.io wrote:
I have 136GB free space on the drive where the .RAW file grows.
I did have Mark Data Points turned on which makes the plot window render many times slower.
?
Also, I can crash the plot window, taking LTspice 24.0.12 along with it, whenever I wish.
See
Close a window that overlays the plot window, as the plot window is rendering, and poof, there goes LTspice.
The plot window crashing is nothing new to me.
?
I agree also that increasing numdgts was not the cause of the crash.
Ah, OK. I seem to remember this issue might also be dependent on the graphics card/driver. There are also message threads from many years ago, before V24, that certain (Intel) CPUs were more susceptible to crashes. Helmut documented which types were most problematic, but I can't find that right now.

--
Regards,
Tony

Re: .MEAS Failure

 

Tony, I was not out to prove that 2.000000000 volts never happens.
I was out to prove that 2.000000000 volts did not happen in my case.
So that I could therefrom propose that the test ".MEAS = something FALL=1" in my case does not test for equality to something because that something does not exist.
Until someone can show me proof of interpolation to obtain the .MEAS result in my case, I will assume that it is actually doing the more efficient test for a value that was more than something and now has become less than something.
?
When it comes to plotting, that's a different story.
If your pixels are a certain size and your two data points span more than two pixels then interpolate to find the missing pixel coordinates.
But would you interpolate 100 new coordinates if you know you only have to locate 14 pixels between the given data points.
No, that would be inefficient to crank an interpolation a 100 times to fix the coordinates of 14 missing points.
?
The same logic applies to using interpolation at all, when the task at hand is to analyse the data stream to find any data value greater than something followed by any data value less than something.
That simply requires if(X <= something && priorX >= something) to be true [C syntax not precisely correct] which is considerably simpler than interpolation.
How would you know how many times to turn the interpolator crank to find if any interpolated point could be found that was exactly 2.00000000 volts so that it could be compared for equality to 2.
?
I predict that the .MEAS statement never tests for equality.
Even in this example from the help file, I posit that:

.MEAS TRAN res2 FIND V(out)*I(Vout) WHEN V(x)=3*V(y)

Print the value of the expression V(out)*I(Vout) the first time the condition V(x)=3*V(y) is met. This will be labeled res2.

Does not ever test that V(x) becomes exactly equal to 3*V(y).
It does this; "if((V(x) <= 3*V(y) && priorV(x) >= 3*V(y) || (V(x) >= 3*V(y) && priorV(x) <= 3*V(y)))" == true" then it would be known that the data has passed through the point 3*V(y) without ever having to resort to a test of equality between floating point numbers.
?
All for now
?
Sent:?Tuesday, February 25, 2025 at 4:28 AM
From:?"Tony Casey via groups.io" <tony@...>
To:[email protected]
Subject:?Re: [LTspice] .MEAS Failure
On 25/02/2025 08:53, eewiz via groups.io wrote:
Yes, I agree.
Rather than assume such was true, I sought to prove that in my case there actually was no 2.0000000000 volts.
In general, it is usually impossible to prove the non-existence of something.
Therefore the effect, however it may be accomplished, is to print the time at which the next sample found is LESS-THAN 2 volts.
?
Wouldn't it be a phenomnal waste of processor time to interpolate between points, following the resultant curve, to find a point on that curve that is exactly 2.0000000000 volts when simply looking for the first value of data less-than 2 volts provides the same result.
Hardly a phenomenal waste of processor power. Linear interpolation between two points is a trivially simple operation. The .MEAS already finds the last data point before, and the first data point after the target is reached. Interpolation means you always get a more accurate answer even when not using very small values of maximum timestep, with very little overhead.
?
Regardless of how it is accomplished, the end result of using FALL=1 is to print the time at which the first data value less-than 2 is found.
This is obviously not true. The end result of using FALL=1 is to print out the interpolated value.

The reason why you found that apparently two points at the same time had two different voltages is due the printed precision of the time points. The time points are printed in single precision in the logfile. You can get double precision by adding .option measdgt=15. This is true whether or not you also use .option numdgt=15.

For example, to find the first falling value of 0, I added:

.MEAS T1 when V(test)=0 fall=1

..when analysing a 0.999Hz sine wave with .TRAN 1.1. By default the logfile was:
?
LTspice 24.0.12 for Windows
Circuit: * C:\users\tony\Desktop\LTspice\_Temp\Eewiz\MEAS_example.asc
Start Time: Tue Feb 25 10:09:09 2025
solver = Normal
Maximum thread count: 32
tnom = 27
temp = 27
method = modified trap
Direct Newton iteration for .op point succeeded.

t1: v(test)=0 AT 0.500501

Total elapsed time: 0.054 seconds.

After adding .option measdgt=15:
?
LTspice 24.0.12 for Windows
Circuit: * C:\users\tony\Desktop\LTspice\_Temp\Eewiz\MEAS_example.asc
Start Time: Tue Feb 25 10:10:33 2025
solver = Normal
Maximum thread count: 32
tnom = 27
temp = 27
method = modified trap
Direct Newton iteration for .op point succeeded.

t1: v(test)=0 AT 0.500500582598

Total elapsed time: 0.044 seconds.
Note: this option is sticky. It remains active for the session (until you close and restart LTspice), even if it is removed. Whether this is intended or not is not known. AFAIK, it is not documented.
?
--
Regards,
Tony`
Re: Create symbols.

 

Ok, gracias, lo investigaré.
Re: Create symbols.

 

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On 25/02/2025 12:26, Tony Casey wrote:
If that doesn't work, there is a recent PDF version of the Help in the Files section of the group's website: LTspice Manual. You could download it onto your Desktop.
I mistakenly linked to an older version, but I don't think it had changed much. Newer version: LTSPICE_Manual

--
Regards,
Tony
Re: Create symbols.

 

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On 25/02/2025 12:09, j.bernabe1 via groups.io wrote:
The F1 key does work, a window opens, but nothing of what you're telling me appears
Help > Schematic Capture > Creating New Symbols ?
For V17, the Help has an additional heading:

Help > LTspice > Schematic Capture > Creating New Symbols

If that doesn't work, there is a recent PDF version of the Help in the Files section of the group's website: LTspice Manual. You could download it onto your Desktop.

--
Regards,
Tony
Re: Create symbols.

 

The F1 key does work, a window opens, but nothing of what you're telling me appears
Help > Schematic Capture > Creating New Symbols ?
Re: Create symbols.

 

?
I'm using version 17.0.37.0
Re: Create symbols.

 

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On 25/02/2025 11:44, j.bernabe1 via groups.io wrote:
He abierto la ayuda con F1, pero la ventana que se abre, no contiene nada.
What version of LTspice are you using?

The F1 key works on V17.1, V24.0 and V24.1. If you're using one of those and it doesn't work, your installation may be missing the help file.

--
Regards,
Tony
Re: Create symbols.

 

He abierto la ayuda con F1, pero la ventana que se abre, no contiene nada.
Re: Create symbols.

 

For example, I've opened (opamp2), how can I associate it to the library or file (. lib or . sub) ??? and how do I match the pins with their true function ??
Re: Create symbols.

 

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On 25/02/2025 11:34, j.bernabe1 via groups.io wrote:
Help?? where?? in this channel?? Or in LTSpice
The LTspice Help. Just hit the F1 key.

Haven't you ever read the Help?

--
Regards,
Tony
Re: Create symbols.

 

help topics
About Ltspice
show change Log..
?
I don't have what you're telling me,
Help > Schematic Capture > Creating New Symbols ?
?
?
Re: Create symbols.

 

Help?? where?? in this channel?? Or in LTSpice
Re: Create symbols.

 

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On 25/02/2025 11:28, j.bernabe1 via groups.io wrote:
Can I remove it from the rectangle and load the symbol for a comparator from a library?
No, the symbol editor lacks many of the features of the schematic editor. You cannot drag items from one symbol into another, like you can with schematics.

--
Regard,
Tony
Re: Create symbols.

 

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On 25/02/2025 11:17, j.bernabe1 via groups.io wrote:
Thanks for answering
That's what I'd like to do..
Find a symbol that looks more like a comparator.
My question is, where do I look for it??' within Ltspice??
And if I find one, how can I associate the appropriate PINS to my comparator?
If your comparator has 5 pins, you can start with the LTspice opamp2 symbol.

The most important thing is for the symbol pin order to match to the order in the .subckt line. The pin names do not have to match. If they match, then you only have to change the opamp2 symbol's value to match the .subckt name, and you're good to go.

But, honestly, if you can draw schematics, you can also draw symbols. It's not hard, and once you have had a little practice, you will never use auto-generated symbols again, and we will all be glad.

Did you look in:

Help > Schematic Capture > Creating New Symbols ?

--
Regards,
Tony
Re: Create symbols.

 

Can I remove it from the rectangle and load the symbol for a comparator from a library?
Re: .MEAS Failure

 

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On 25/02/2025 10:53, eewiz via groups.io wrote:
I have 136GB free space on the drive where the .RAW file grows.
I did have Mark Data Points turned on which makes the plot window render many times slower.
?
Also, I can crash the plot window, taking LTspice 24.0.12 along with it, whenever I wish.
See
Close a window that overlays the plot window, as the plot window is rendering, and poof, there goes LTspice.
The plot window crashing is nothing new to me.
?
I agree also that increasing numdgts was not the cause of the crash.
Ah, OK. I seem to remember this issue might also be dependent on the graphics card/driver. There are also message threads from many years ago, before V24, that certain (Intel) CPUs were more susceptible to crashes. Helmut documented which types were most problematic, but I can't find that right now.

--
Regards,
Tony
Re: Create symbols.

 

?
Thanks for answering
That's what I'd like to do..
Find a symbol that looks more like a comparator.
My question is, where do I look for it??' within Ltspice??
And if I find one, how can I associate the appropriate PINS to my comparator?
Re: Create symbols.

 

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On 25/02/2025 10:29, j.bernabe1 via groups.io wrote:
Good morning, I have a question about symbols.
Could a symbol be automatically generated from a (.lib) or (.sub) file??..
In this case it would be a comparator.
?
If so, how could I generate it?
Yes, symbols can be automatically generated from any text file containing a valid .subckt. It doesn't matter what the name of the file is. It can be a .lib or .sub file, but it doesn't have to be.

The procedure is simple.
  1. Open the file in LTspice. this most easily done by dragging the file from Explorer into LTspice.
  2. Right-click with the mouse on the .subckt line.
  3. From the drop-down menu, choose Create Symbol.
  4. Save.
Whether this is a good idea, or not, is another matter. You will get a rectangular box with the correct pin names, but not necessarily in appropriate places. Nobody will know for sure what kind of component it is. You could delete the box and draw a proper comparator outline, for example, and re-arrange the pin positions. But many people don't bother, and it is often difficult to figure out what a schematic does that uses them.

So, here are some alternatives:
  1. Look for an LTspice standard symbol that is appropriate for the type of component.
  2. If it also has the correct pin configuration, use it with modification.
  3. If it doesn't you can make a copy of the standard symbol, and edit it to have the correct pin configuration.
  4. Draw a new symbol from scratch.
--
Regards,
Tony
Re: .MEAS Failure

 

Hi Tony,
?
I have 136GB free space on the drive where the .RAW file grows.
I did have Mark Data Points turned on which makes the plot window render many times slower.
?
Also, I can crash the plot window, taking LTspice 24.0.12 along with it, whenever I wish.
See
Close a window that overlays the plot window, as the plot window is rendering, and poof, there goes LTspice.
The plot window crashing is nothing new to me.
?
I agree also that increasing numdgts was not the cause of the crash.
?
All for now
Sent:?Tuesday, February 25, 2025 at 3:54 AM
From:?"Tony Casey via groups.io" <tony@...>
To:[email protected]
Subject:?Re: [LTspice] .MEAS Failure
On 25/02/2025 06:59, eewiz via groups.io wrote:
.options numdgt=15. caused the plot window to crash at the end of simulation as it was rendering.
That plot window crash took LTspice 24.0.12 down with it.
I will restart and try again.
?
On the next try the .meas result was:
.meas TooLow1 FIND V(XSW11:X1:Qc,XSW11:X1:Qe) WHEN V(XSW11:X1:Qc,XSW11:X1:Qe)=2 FALL=1
toolow1: v(xsw11:x1:qc,xsw11:x1:qe)=2 at 0.00804695
AND
.meas TooLow2 FIND V(XSW12:X1:Qc,XSW12:X1:Qe) WHEN V(XSW12:X1:Qc,XSW12:X1:Qe)=2 FALL=1
Measurement "toolow2" FAIL'ed
?
TooLow2 saw no point that fell below 2V on the XSW12 signal, so it reported "Measurement "toolow2" FAIL'ed".
Both syntax error and, failure to find the measurement specified, produce the same "Measurement "toolow2" FAIL'ed" error message.
Isn't that a fine kettle of fish.
?
Subtracting 8ms from the start and stop values on the abscissa saw the plot window simply stop rendering in mid-redraw.
I am not going to burn any more time divining how LTspice works.
I will now move on to more productive efforts.
?
In my case ".options numdgt=15" broke 24.0.12.
The .raw file for the run is 11.5GB.
This suggests that LTspice might have crashed because you ran out of disk space. I have never seen crashes upon invoking double precision, but I have when running out of disk space.

--
Regards,
Tony
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