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A PLC main symbol is technically very similar to a conventional main symbol. The same procedure applies when you create one.

 

The appearance may however differ quite a lot. Here are few common ways of drawing PLC main symbols:

 

•Symbolically, more or less with a box and connection points for power feeding and other common connections.

•As a simplified illustration of the physical appearance of the PLC. Connection points are often included anyway.

•As a table header, adapted to be placed together with the PLC mirrors that are included in cadett ELSA upon delivery, also this with connection points included.

 

In the Example topic, you find descriptions of how conventional main symbols are created. PLC main symbols are created in the same way, except for the graphical appearance.

 

Distinguishing properties of a PLC main symbol include the following:

 

•It is a PLC.

•It has an index for reference to a suitable resource in the Catalogue.

•It typically have connection points, but it does not have to.

•It has a component type letter code that is used for automatic item designation generation. According to IEC750, D is closest to hand. IEC1346 leans towards K.

•It typically does not have a function code, but it still can have one.

•It typically does not have a cross-reference attribute, but it still can have one.

•The Resource Category and the Component Type Letter Code are often equal, but they do not have to be. Standard PLC main symbols are for example placed under 80.

 

The two figures below presents one example of how a PLC main symbol can be drawn, in this case like a table header.

 

 

The PLC main symbol in the figure above (LPM1) is part of the IEC1082 standard symbol library. It is defined as a vertical symbol in resource category 80.

 

In the figure below, the main symbol has been completed with a PLC mirror, in this case an eight channel digital output module with two connection points for each output.

 

 

The PLC mirror in the example above is part of the standard IEC1082 symbol library. The name of it is LP8DJ2 and it is defined as a horizontal symbol in resource category 823.