If you want to activitate a switch when the RPM reaches a certain value, then you can use the PULSEFREQUENCY function to measure the incoming pulse rate and make a decision:
E.g. IF PULSEFREQUENCY(1) > 1000 THEN
SETIO OUT1
ELS
CLRIO OUT1
ENDIF
This is the unique capability of M-series PLC's "Ladder+ BASIC" command and not available to ladder logic only PLCs such as the H-series or E10 and certainly not applicable to other makes of PLC.
