Difference between revisions of "Hints on using individual LTspice commands and things the Help Manual sometimes may not help you with"

From LTwiki-Wiki for LTspice
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.param
 
.param
  
One of the more confusing aspects of using .param (at least when I began using LT) was where and when do you use the curly barckets {} ?
+
One of the more confusing aspects of using .param (at least when I began using LTspice) was where and when do you use the curly barckets { } ?
  
Beginning with the simplest definition, LT doesn't require curly brackets  
+
Beginning with the simplest definition, LTspice doesn't require curly brackets:
 
+
.param res1 = 1000
.param res1 = 1000
+
This could be used to define a resistor of 1000 Ohms.
 
 
This could be used to define a resistor of 1000 Ohms  
 
  
 
However, in the real world, a parameter sometimes needs to be defined from other parameters.
 
However, in the real world, a parameter sometimes needs to be defined from other parameters.
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Without them - you can only nest (calculated) .param values, one parameter calculation deep.
 
Without them - you can only nest (calculated) .param values, one parameter calculation deep.
  
Going any deeper (where one calculation depends on another etc) will invite LTspice to complain with an error.
+
Going any deeper (where one calculation depends on another etc.) will invite LTspice to complain with an error.
  
  
  
'''Correct Method { doesn't pull errors }'''  
+
'''Correct Method (doesn't pull errors)'''  
  
<nowiki>
+
<nowiki>*</nowiki> Comment line : Calculate capacitance
*</nowiki> Comment line : Calculate capacitance
 
  
 
<nowiki>*</nowiki> -------------------------------------
 
<nowiki>*</nowiki> -------------------------------------
  
.param length = {3e-2}
+
.param length = {3e-2}
 +
 
 +
.param width  = {4e-3}
 +
 +
.param area = {length * width}
 
   
 
   
.param width = {4e-3}
+
  .param gap = {40e-6}
 
+
.param area = {length * width}
+
.param Eo = {8.85e-12}
 
+
.param gap = {40e-6}
+
.param Capa = { (Eo * gap) / area}
 
+
.param Eo = {8.85e-12}
+
.MEAS Capa_  PARAM Capa
 
 
.param Capa = { (Eo * gap) / area}
 
 
 
.MEAS Capa_  PARAM Capa
 
 
 
  
 
The answer (from the error log ) is:
 
The answer (from the error log ) is:
capa_: capa=2.95e-012
+
capa_: capa=2.95e-012
 
 
  
To see the results in LTspice  
+
To see the results in LTspice use the Error Log (a better name would have perhaps been ''Results Log'' or ''Output Log'')  
Use the Error Log (a better name would have been the results log)  
 
  
 
   
 
   
 
'''Incorrect method (pulls errors)'''
 
'''Incorrect method (pulls errors)'''
 
+
.param length = 3e-2  
.param length = 3e-2  
+
 
+
.param width  = 4e-3
.param width  = 4e-3
+
 
+
.param area = length * width
.param area = length * width
+
 
+
.param gap = 40e-6
.param gap = 40e-6
+
 
+
.param Eo = 8.85e-12
.param Eo = 8.85e-12
+
 
+
.param Cap =  (Eo * gap) / area
.param Cap =  (Eo * gap) / area
 
 
 
.MEAS Capa_  PARAM Capa
 
 
   
 
   
 +
.MEAS Capa_  PARAM Capa
  
 
Error:
 
Error:
Measurement "capa_" FAIL'ed
+
Measurement "capa_" FAIL'ed
 
 
  
The quickest way to check a calculation before you commit it to a library  
+
The quickest way to check a calculation before you commit it to a library is to create a section of text within the LT schematic. Set the text as LTspice directive (command), then run the schematic  
is to create a section of text within the LT schematic.  
 
Set the text as LTspice directive (command) ,  
 
then run the schematic  
 
  
  
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'''Suggestion:'''  
 
'''Suggestion:'''  
Set the Tools/Control panel/ Operation / Generate Expanded Listing  
+
Set the Tools/Control panel/ Operation / Generate Expanded Listing and tick (yes) to see a more comprehensive output listing - helps with debugging
and tick (yes) to see a more comprehensive output listing - helps with debugging
 

Revision as of 01:09, 10 August 2009

Add items as subpages (rather than details at this page level)


.Param and Curly Brackets

.param

One of the more confusing aspects of using .param (at least when I began using LTspice) was where and when do you use the curly barckets { } ?

Beginning with the simplest definition, LTspice doesn't require curly brackets:

.param res1 = 1000

This could be used to define a resistor of 1000 Ohms.

However, in the real world, a parameter sometimes needs to be defined from other parameters.

To get results and not pull errors within LT, it becomes useful to use curly brackets. Without them - you can only nest (calculated) .param values, one parameter calculation deep.

Going any deeper (where one calculation depends on another etc.) will invite LTspice to complain with an error.


Correct Method (doesn't pull errors)

* Comment line : Calculate capacitance

* -------------------------------------

.param length = {3e-2}
 
.param width  = {4e-3}

.param area = {length * width}

.param gap = {40e-6}

.param Eo = {8.85e-12}

.param Capa = { (Eo * gap) / area}

.MEAS Capa_  PARAM Capa

The answer (from the error log ) is:

capa_: capa=2.95e-012

To see the results in LTspice use the Error Log (a better name would have perhaps been Results Log or Output Log)


Incorrect method (pulls errors)

.param length = 3e-2 

.param width  = 4e-3

.param area = length * width

.param gap = 40e-6

.param Eo = 8.85e-12

.param Cap =  (Eo * gap) / area

.MEAS Capa_  PARAM Capa

Error:

Measurement "capa_" FAIL'ed

The quickest way to check a calculation before you commit it to a library is to create a section of text within the LT schematic. Set the text as LTspice directive (command), then run the schematic


Finding the measure results of a simulation Check your results in the error log Found from the toolbar : View/Spice error Log


Suggestion: Set the Tools/Control panel/ Operation / Generate Expanded Listing and tick (yes) to see a more comprehensive output listing - helps with debugging