Poor documentation is a common complaint lodged against control system designers. Good documentation is developed as a project progresses. Many engineers will leave the documentation to the end of a project as an afterthought. But, by that point many of the details have been forgotten. So, it takes longer to recall the details of the work, and the report is always lacking.
A set of PLC design forms are given in Figure 30.1 Design Cover Page to Figure 30.1 Ladder Logic Page. These can be used before, during and after a controls project. These forms can then be kept in design or maintenance offices so that others can get easy access and make updates at the controller is changed. Figure 30.1 Design Cover Page shows a design cover page. This should be completed with information such as a unique project name, contact person, and controller type. The list of changes below help to track design, redesign and maintenance that has been done to the machine. This cover sheet acts as a quick overview on the history of the machine. Figure 30.1 Project Note Page to Figure 30.1 Project Diagramming and Notes Page show sheets that allow free form planning of the design. Figure 30.1 IO Planning Page shows a sheet for planning the input and output memory locations. Figure 30.1 Internal Memory Locations Page shows a sheet for planning internal memory locations, and finally Figure 30.1 Ladder Logic Page shows a sheet for planning the ladder logic. The sheets should be used in the order they are given, but they do not all need to be used. When the system has been built and tested, a copy of the working ladder logic should be attached to the end of the bundle of pages.
These design sheets are provided as examples. PLC vendors often supply similar sheets. Many companies also have their own internal design documentation procedures. If you are in a company without standardized design formats, you should consider implementing such a system.