A Negative Transition Contact gives a single one-shot pulse when its reference address falls from ON (logic 1) to OFF (logic 0). A Negative Transition Contact is registering the fall in status from ON to OFF.
A Negative Transition Contact condition can be:
A computer ON/OFF button is an example of a Negative Transition Contact. The computer is ON.
If you push the ON/OFF button in without releasing it - the computer will not shut off. Only when you release the button will the system register a change in status from ON to OFF and the computer will shut OFF.
During the system scan, a Negative Transition Contact address is evaluated for a transition from ON to OFF. A transition allows power to flow through the Negative Transition Contact for one scan.
At the end of the one scan, the Negative Transition Contact is reset to OFF (logic 0). Only after the triggering signal turns from OFF to ON again is there the possibility for the Negative Transition Contact to be re-activated by the next falling transition from ON to OFF.
Decreasing the Number of Transitional Contacts