A design diagram refers to a particular kind of circuit design which utilizes standard electrical/electronic symbols instead of pictures to show how a circuit (or a part of it) works. Below is a typical 3-wire motor controller circuit employing a normal momentary stop - start pushbutton station utilizing a schematic diagram. (Momentary this means the button/switch you activate will go back to its default position once you physically let go of this, typically by a spring which compels the button/switch to get this done.)
Think of it in this way; a circuit diagram is any kind of diagram which demonstrates how a circuit operates where the principal purpose is that the appropriate wiring of elements and their relationship to each other rather than physical place relative to one another or intending prototypes. Nevertheless, in some applications Assessing diagrams can be difficult so do this as overall information. I've found this is particularly true when working with much more complicated circuits and electronics. I'm going to use a more straightforward but average industrial circuit because these circuit setups are exactly the same, but where it is possible to observe how each kind of diagram shows the function of the circuit in their own manners.
Here is another schematic diagram showing the same circuit, components and connections and it appears different but they fall into precisely the identical category.
Pictorial design diagrams, or pictorial circuit diagrams are basically the identical thing with exactly the exact identical purpose, however they use pictures of components within the circuit rather than symbols. Again, here is the exact same exact circuit (virtually except a control transformer was included and they're utilizing conductors L1 and L3 rather than L1 and L2.
Right, much less clutter? I've got enough information in each of these diagrams to know exactly what this circuit does and also where to start looking for issues. Hope that this helps. ( Note: do not confuse circuit or schematic diagrams together with wiring diagrams; wiring diagrams will usually show pictures of elements such as the pictorial, and the way the whole or portion of a circuit has been wired. The difference is that wiring diagrams generally put an emphasis on actual physical location of necessary elements relative to each other that essentially tell a layman Just What to do about the wiring. )
Following is a version of a design diagram known as a ladder diagram. The primary point of this diagram will be to show the logic (speaking to electrical control) of a circuit board. This diagram is the one I mostly encounter in my line of work, and it's extremely effective for troubleshooting problems or learning how a circuit functions. Some frequencies are so huge that most kinds of schematic diagrams need to be read in increments from novel form (usually with coded numbers so information can be easier found). Again, here is the identical specific circuit as the first two, however looking at it in ladder form.