Circuit and related diagrams

Circuit and related diagrams

Circuit diagrams are used to show the functional relationships between the components in an electric or electronic circuit. The components are represented by symbols and the electrical connections between the components drawn using straight lines. It is important to note that the position of a component in a circuit diagram does not represent its actual physical position in the final assembly. Circuit diagrams are sometimes also referred to as schematic diagrams or schematic circuits.

Figure 2.28a shows the circuit for an electronic filter unit using standard component symbols. Figure 2.28b shows the corresponding physical layout diagram with the components positioned on the upper (component side) of a PCB. Finally, Figure 2.28c shows the copper track layout for the PCB. This layout is developed photographically as an etch-resistant pattern on the copper surface of a copper-clad board.

The term `wiring diagram' is usually taken to refer to a diagram that shows the physical interconnections between electrical and electronic components. Typical applications for wiring diagrams include the wiring layout of control desks, control cubicles and power supplies. Wiring diagrams are directly related to circuit schematics (circuit diagrams). As an example, architects use circuit schematics to show the electrical wiring and components inside a building or plant. They will also provide installation drawings to show where the components are to be sited.

In addition, they may also provide a wiring diagram to show how the wires and cables are to be routed to and between the components. The symbols used in architectural installation drawings and wiring diagrams are not the same as those used in circuit diagrams.

Schematic circuit diagrams are also used to represent pneumatic (compressed air) circuits and hydraulic circuits. Pneumatic circuits and hydraulic circuits share the same symbols. You can tell which circuit is which because pneumatic circuits should have open arrow heads, while hydraulic circuits should have solid arrowheads. Also, pneumatic circuits exhaust to the atmosphere, while hydraulic circuits have to have a return path to the oil reservoir. Figure 2.29 shows a typical hydraulic circuit.

Just as electrical circuit diagrams may have corresponding installation and wiring diagrams, so do hydraulic, pneumatic and plumbing circuits. Only this time the wiring diagram becomes a pipework diagram.