The Multiplexer function block selects one input out of a number of inputs. You select the input by operator action or by logic from another function block. You can use the Multiplexer function block to select one out of several transmitter values as shown in the following figure:
Figure: Multiplexer function block diagram example
In this example, the SELECT_NEXT_GOOD parameter is set to True. IN 1 is the value of transmitter A and IN2 is the value of transmitter B. IN3 is the average of the two. Normally, the output (OUT) would be the value of IN3 in this case, because SELECTOR equals 3. Suppose transmitter A fails, causing the status of IN1 and IN3 to be Bad. Because SELECT_NEXT_GOOD is True, the selected output will be the value of IN2.