The And function block is used to determine if all the selected discrete inputs are True. You can use the And block to stop a process in an emergency when one or more emergency stop conditions are met.
You can also use the And function block for an interlock condition to be sure a pump runs only when the feed valve is open and the level in the feed tank is above a minimum value. The valve and level transmitter values can be inputs to the And function block. The And block would send a signal to run the pump only when the two requirements were met. The resulting signal could be sent to a Discrete Output (DO) function block for additional processing, as in the following example:
Figure: And function block application example
