Understanding the Function of a Schematic Diagram
In the realm of electrical engineering, international standards play a crucial role in ensuring consistency and clarity in the representation of electrical circuits. Two primary standards govern the use of schematic symbols: IEC 60617 and ANSI Y32.2 (also known as IEEE Std 315).
IEC 60617, an international standard, defines graphical symbols for electrical and electronic diagrams. It is widely used for the representation of various electrical components such as wires, batteries, resistors, transistors, oscillators, and more. This standard aims at ensuring a consistent and clear representation across international engineering and technical documentation. Symbols from IEC 60617 are commonly found in industrial control panels, electrical schematics, and electronic circuit diagrams.
On the other hand, ANSI Y32.2, also known as IEEE Std 315 or CSA Z99, provides graphic symbols for electrical and electronics diagrams and covers both basic components and complex devices used in circuits. Its use is more prevalent in the United States and aligns with IEEE standards for symbols, including those for logic functions common in digital electronics.
While both standards cover a wide variety of components, there are variations and minor disagreements between them. Engineers sometimes need to be aware of the exact standard used on a schematic to avoid confusion.
IEC 60617 includes symbols for specific functions like oscillators and logic functions and defines usage rules such as placing frequency values next to oscillator symbols. This standard serves as a basis for national or application-specific adaptations, such as the now-withdrawn Australian Standard AS 1102, based on IEC 60617. Industry-specific symbol sets like JIC symbols exist, but IEC 60617 and ANSI Y32.2 remain the primary international and US standards for schematic symbols.
IEC 60617 is the more globally recognized standard, especially outside North America, whereas ANSI Y32.2 is more common in American contexts. The American National Standard Institute (ANSI) has issued the standard ANSI Y32 for schematic symbols, which is aligned with IEC.
In a schematic diagram, every symbol represents a component, such as a resistor, battery, or light-emitting diode (LED). Each symbol needs to have its own unique designator for easy identification. Components are differentiated by their specific properties, such as capacitance for capacitors (expressed in farads), inductance for inductors (expressed in Henrys), resistance for resistors (expressed in ohms), and potential difference (voltage) for batteries (expressed in volts).
To make the schematic diagram more legible, the nets are labelled with their names rather than drawing lines to show the connectivity. Nodes help identify the connection among wires intersecting a point, and the absence of a node means two separate wires are just passing by without any electrical connection.
A schematic diagram defines the logical connections between components on a circuit board, showing how the components are electrically connected. Schematic nets define how components are interconnected in a circuit, with the line between the two interconnected components called a net.
The international system of units (SI) is used for values on schematic diagrams to avoid filling circuit diagrams with long, repeating strings of zeros for values. The title block on the lower right corner of the first sheet should display the title, part number, revision (if any), and other relevant information. Pin numbering is made to ensure the connections shown in the schematic end up connected properly by copper on the PCB.
Sheet connection symbols should always be placed on the extreme left edge or extreme right edge of the page. To make the schematic diagram more understandable and organized, design schematic sections in functional blocks. Additional attributes can be given to the symbols, such as power ratings and tolerances.
In complex circuits, it is recommended to assign a name to nets. The nets with the same name are assumed to be connected. This practice simplifies the understanding of the circuit's flow and aids in troubleshooting.
In summary, these standards ensure uniformity and clarity in electrical diagrams internationally, with IEC 60617 serving as the main global reference and ANSI Y32.2 covering US-centric practices. Differences exist but are generally reconcilable through proper referencing.
Data-and-cloud-computing technology plays a significant role in the digital representation and storage of electrical engineering information, including schematic diagrams. These diagrams, based on international standards like IEC 60617 and national standards such as ANSI Y32.2 (also known as IEEE Std 315), utilize a set of standardized graphical symbols for electrical and electronic components.
