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

Line 6: | Line 6: | ||

.param | .param | ||

− | One of the more confusing aspects of using .param (at least when I began using | + | 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, | + | 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. | ||

Line 19: | Line 17: | ||

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 | + | '''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 gap = {40e-6} | |

− | + | ||

− | + | .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'') |

− | |||

'''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 | ||

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 | ||

Line 87: | Line 75: | ||

'''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 00:09, 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