Updating Relations When Units Are Changed

Some users maybe unaware that when you change a part’s units in Pro/ENGINEER, the relations may not update as expected. This will occur because the Pro/ENGINEER conversion does not take into account constant values in the relation equations.

There should be some unit dimension in the start part, whether it’s an offset coordinate system or a line of unit length (1) to be used in relations. This is necessary in the event that the part’s units need to be converted.

Take the case of a rectangle with the following relation in standard units with the following variables:

D4=20 (length of rectangle)

D3=D4-10 (width of rectangle)

This gives you a rectangle with a length of 20 inches and a width of 10 inches. If you retain the size but switch the units to metric, you end up with a rectangle with a length of 508mm (20*25.4) and a width of 498mm (508-10). The unit conversion does not convert the integer values in the relation.

If you define a coordinate system in the start part that is offset a length of 1, and name that offset dimension CONVERT or some similar name, you can use it in all relations to insure the conversions work properly. (To name the offset dimension, modify the offset coordinate system and select the offset dimension. When prompted for a new dimension, enter “convert,” and answer yes to the prompt, “Do you want to add this relation_d#=convert?”)

Using this variable, the above relations would be:

D4=20*CONVERT

D3=D4-10*CONVERT

Initially CONVERT takes on a unit (1) value. As the units are changed, it adapts to the change and keeps the relations intent.

Michael Gallagher is the MCAD software administrator at Motorola Broadband Communications Sector, located in Horsham, Pennsylvania, USA. He can be reached by e-mail at michael.gallagher@motorola.com.