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Cross section tool and impedance calculations

TH Designs

I ran into something the other day and have been working with tech support on, but thought I might get some answers here.

Four layer board, two inner layers set to planes (and shield) FR4 material.

In the Setup - cross section tool, when I try to calculate the trace width based on a given impedance and stack up, the impedance is always 60 ohms. For example, I open the cross section tool and select Show Single Impedance.  The default impedance shows as 60 ohms. If I try to change it to 50 ohms by manually editing the cell, it resets to 60 as soon as I click out of the cell.

If I try to change it by using the drop down boxes at the bottom of the window; Layer Type - Conductor; Material 1oz cu; Field set to - Impedance; Value Set to - 50; then select "Update Fields", nothing happens.

We tried multiple things yesterday. I even sent the board file to tech support and it works just fine for them (figures.....)

I tried it on a different computer at my home office and the impedance is displayed in exponential format, not in ohms.

A couple of screen shots:

  • TH Designs

    Another tid bit, I do get a warning saying the the default impedance and propvelocity values are being used.

    I don't know where these "defaults" are located or come from and neither did tech support. 

  • budnoel

    Interesting.  Keep us posted.  Thanks.

  • oldmouldy
    Where is you TEMP directory set to? The SI related stuff can be a bit picky about spaces in paths but, having said that, my TEMP is set to "docs and settings" in XP and it still calls the bem2d as expected. We have also tried a standard license and that calculates OK as well. You can also "just type" the numbers in the field, like "width" and the impedance will "just update".
  • oldmouldy
    OK, another thought. Any chance at all that the User Preference for the materials.dat locations has changed or that you have a custom, but incomplete, materials.dat in the local directory. Possibly the required values are not in the materials.dat being found and the calculations bail out from there. I have found that the first materials.dat found is used in isolation and not merged with other materials.dat files, so an incomplete one could potentially wreck things.
  • TH Designs

    oldmouldy said:
    Where is you TEMP directory set to? The SI related stuff can be a bit picky about spaces in paths but, having said that, my TEMP is set to "docs and settings" in XP and it still calls the bem2d as expected. We have also tried a standard license and that calculates OK as well. You can also "just type" the numbers in the field, like "width" and the impedance will "just update".

    OM,

    My temp path is C:\Users\Tom\AppData\Local\Temp.

    Either way of entering the numbers,  directly into the cells or using the update field cells at the bottom of the window, does not yield the correct results.

    Tom

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