One area you did not address in the article, "Electrical Schematic Software Automates Wiring, Panel Design" (CE, Aug. '99, p. 47), is usefulness of the resulting schematic for troubleshooting. Every implementation of schematic drawing software seems to make designing and building the control equipment easier at the expense of troubleshooting and repair to the end-user.

The main example of this is that PLC I/O points are invariably grouped by module rather than floating individually where needed to allow the schematic to have a logical flow. A primary requirement for a useful schematic ladder diagram, as far as I am concerned, is that it follows a logical flow, keeping all logically related devices together, regardless of their physical location or PLC connection. The only exception is separating of the power (motors, etc.) portion from the control portion of the schematic. The system is only built once and it is diagnosed and repaired, using the same documentation, many times throughout its useful life. It is more important that it be easy to troubleshoot and fix than that it be easy to design and make. For some systems, downtime can cost $100,000 per hour or more.

Does anyone make AutoCAD add-ins for making schematic ladder diagrams that incorporate this end-user (troubleshooting) focus? I also need easily implemented flexibility in such a package to accommodate other existing standards. We make glass parts for picture tubes (CRTs).

Steve Alton, design engineer, Techneglas Inc., Columbus O.