By Joe McDiarmid
In part three of our Design Rule Checks blog series, we’ll dig deeper into the Component Terminals Not Connected DRC. This DRC is exceedingly important because it helps reduce one of the most common sources of human error: forgetfulness. Everyone has been there – a silly goof brought on by a lack of caffeine, distractions in the middle of working, or just a plain accident. Sometimes these little mistakes can lead to something as benign, though annoying, as a lack of power to the device, or it won’t work because the grounding circuit isn’t complete. In any case, reducing the number of errors due to forgetting to connect wires or cables to your electrical components in the schematics is a good place to start ensuring that when it comes time to hit the “on” switch, everything that lights up does, and any alarm bells that should ring, do.
The Component Terminals Not Connected DRC scans the project and reports back any component symbols in the schematics that are not connected to wires, or have wires that are dangling “on air” and go nowhere. Both of these scenarios lead to an “open circuit”, and current will not flow to any of the devices on that circuit. Running this DRC will ensure that all your components have wires to all the necessary connections, and that those wires actually terminate either at a power source, another component in the system, or a ground. Often, dangling wires reported by the DRC are actually wires that need “From-to” arrows to indicate continuations of the circuit on other drawing sheets – so this DRC is an excellent check to make sure you don’t have any wires to nowhere. It’s also a great way to double check whether you’ve used (or deliberately left open) any connections on PLC’s or multi-pin components whose symbol might be spread across multiple sheets.
To activate the DRC, click on the Project tab and in the far right section titled “Reports” is the Design Rule Check icon. Click it and click Add in the upper left corner of the “Design Rules Manager” window. Find the “UnCablingPins_Metric” (or “_Imperial” depending on the projects units) report and make sure that the check box is filled. Click OK and then Generate Drawings in the “Design Rules Manager” window. Again make sure the checkbox for “UnCablingPins” is checked, and click OK.
The software scans the project, and generates the report in the Document List. A table showing the component tag, the connection point, and the location in the project then allows us to find, and if necessary correct, any of the open connections listed. Some we might deliberately want to leave open, perhaps for future connections, while others could be mistakes. Once we’re finished, the report can stay as a record of which connections were deliberately left open, or to document the connections a senior engineer needs to verify and check before the design can move forward.