LD Element ‘Contact’¶

Symbol: , in the editor

The element is available only in the LD editor.

A contact passes on the signal TRUE (ON) or FALSE (OFF) from left to right until the signal finally reaches a coil in the right-hand part of the network. For this purpose a boolean variable containing the signal is assigned to the contact. To do this, replace the placeholder ??? above the contact with the name of a boolean variable.

You can arrange several contacts both in series and in parallel. In the case of two parallel contacts, only one needs to obtain the value TRUE in order for ON to be passed on to the right. If contacts are connected in series, all of them must obtain the value TRUE in order for ON to be passed on to the right by the last contact in the series. Hence, you can program electrical parallel and series connections with LD.

A negated contact forwards the signal TRUE if the variable value is FALSE. You can negate an inserted contact with the help of the command FBD/LD/IL ‣ Negation or insert a negated contact from the Tools view.

If you place the mouse pointer on a contact with the left mouse button pressed and with a network selected, the button Convert to coil appears in the network. If you now move the mouse pointer onto this button, still with the mouse button pressed, and then release the mouse button over this button, CODESYS converts the contact into a coil.