Contact and coils
Contacts are basic graphic elements of the LD language. A contact is associated to a boolean variable written upon its graphic symbol. A contact sets the state of the rung on its right side, according to the value of the associated variable and the rung state on its left side.
Below are the possible contact symbols and how they change the flow:
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Parameters |
Description |
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boolVariable -] [- |
Normal: the flow on the right is the boolean AND between the flow on the left and the associated variable. |
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boolVariable -] / [- |
Negated: the flow on the right is the boolean AND between the flow on the left and the negation of the associated variable. |
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boolVariable -] P [- |
Positive pulse: the flow on the right is TRUE only when the flow on the left is TRUE and the associated variable changes from FALSE to TRUE (rising edge). |
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boolVariable -] N [- |
Negative pulse: the flow on the right is TRUE only when the flow on the left is TRUE and the associated variable changes from TRUE to FALSE (falling edge). |
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boolVariable -] /P [- |
Not positive pulse: the flow on the right is TRUE only when the flow on the left is TRUE and the associated variable does not change from FALSE to TRUE (rising edge). |
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boolVariable -] /N [- |
Not negative pulse: the flow on the right is TRUE only when the flow on the left is TRUE and the associated variable does not change from TRUE to FALSE (falling edge). |
Note: When a contact or a coil is selected, you can press the SPACE bar to change its type (normal, negated, pulse...).
Two serial normal contacts represent an AND operation. Two contacts in parallel represent an OR operation.
Coils are basic graphic elements of the LD language. A coil is associated to a boolean variable written upon its graphic symbol. A coil performs a change of the associated variable according to the flow on its left side.
Below are the possible coil symbols:
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Parameters |
Description |
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boolVariable - ( ) - |
Normal: the associated variable is forced to the value of the flow on the left of the coil. |
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boolVariable - (/) - |
Negated: the associated variable is forced to the negation of the flow on the left of the coil. |
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boolVariable - (S) - |
Set: the associated variable is forced to TRUE if the flow on the left is TRUE (no action if the flow is FALSE). |
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boolVariable - (R) - |
Reset: the associated variable is forced to FALSE if the flow on the left is TRUE (no action if the rung state is FALSE). |
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boolVariable - (P) - |
Positive pulse: the variable is TRUE when the flow on the left changes from FALSE to TRUE. |
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boolVariable - (N) - |
Negative pulse: the variable is TRUE when the flow on the left changes from TRUE to FALSE. |
Note: When a contact or a coil is selected, you can press the SPACE bar to change its type (normal, negated, pulse...).
Important notes: Although coils are commonly put at the end, the rung may be continued after a coil. The flow is never changed by a coil symbol.
Contact and coils |
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IEC 61131-3 Automation platform > IEC 61131-3 Programming Environment > Editing programs > Ladder Diagram (LD) Editor > LD - Diagram components > Contact and coils |
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