P&ID and Machine Design
The process industry has used P&ID (Piping and Instrumentation Diagrams) for many years as a method of describing the relationships between piping, instrumentation and system components. Usually this is applied to chemical, batching or fluid transfer projects and is nearly unknown in the industrial machinebuilding industry. Larger engineering firms such as Bechtel, Parsons or CH2M Hill however are very dependent on this type of system representation though they don’t deal with production machinery and discrete logic as much.
In my experience dealing with various machine building companies and integrators there is no single drawing or design system that easily allows mechanical and controls designers to exchange conceptual information quickly during the pre-design phase of discussing machines. 3D “cartoons”, timing diagrams and CAD or hand sketches (often on napkins) are exchanged between engineers and then often discarded after the machine design has been firmed up. In my previous controls oriented company we had developed a shorthand of circles, X’s and various letters to depict the mechanical layout and electrical/controls interfacing of a machine. This was usually done on graph paper and used to generate a rough I/O count and name the actuators and stations of the machine before design began. This technique varied from team to team and was never really formalized.
P&ID drawings do not lend themselves as well to discrete machine design. There are hundreds of symbols for flow oriented devices but components such as photoeyes, proximity switches, motor starters and relays are either very generic or not used at all. Determining whether a sensor is a through-beam or retroreflective photoeye or an inductive proximity switch is usually not possible just by looking at the diagram.
Wouldn’t it be nice if there was some kind of common language or set of tools that could be used across disciplines that was appropriate for machinery? I would propose that the P&ID system would be a good starting point as it has a good numbering system, a large set of already developed symbols and widespread use in industry. The only remaining piece of the puzzle that would need to be elaborated upon are the devices described above and some modification of the numbering system. Safety devices such as MCRs and light curtains would need to be represented and a bit more commonality and formalizing of the system would need to take place. Currently the larger engineering companies each have their own slightly different sets of symbols. A software package that incorporates a standard set of symbols and numbering sytem but could be modified to add symbols would be very useful.
If anyone knows of such a software package please let me know. If one doesn’t exist I am interested in collaborating with an enterprising programmer to develop one as a commercial enterprise. It always helps to have the right tools!