Andrew Groff
Guest
A
NO & NC
The way I have been explaining the normally open/normally closed in PLC land is a simple true and false statement.
The NO is TRUE if power is going through the discrete device. It is FALSE if no power through the device.
The NC is TRUE if no power is running through the discrete device. It is FALSE if there is power running through the device.
To show the point, a hard wired start-stop station is drawn. Then go through how it will be programmed into the PLC. They see that the stop button in the hard wired example is a NC switch but shown as a NO in the PLC program and wired to a discrete point on the input card.
So far I have had real good luck with this example.
Andrew T. Groff
The way I have been explaining the normally open/normally closed in PLC land is a simple true and false statement.
The NO is TRUE if power is going through the discrete device. It is FALSE if no power through the device.
The NC is TRUE if no power is running through the discrete device. It is FALSE if there is power running through the device.
To show the point, a hard wired start-stop station is drawn. Then go through how it will be programmed into the PLC. They see that the stop button in the hard wired example is a NC switch but shown as a NO in the PLC program and wired to a discrete point on the input card.
So far I have had real good luck with this example.
Andrew T. Groff
