Flow Switch

Written by Jerry Ratzlaff on . Posted in Flow Instrument

A flow switch provides a discrete input to the PLC. The flow switch is typically used as a method of control in tanks, vessels, pumps and other types of process equipment.

  • Abbreviated as FS

Note that like apressure switch, a flow switch is different than a flow transmitter in that a flow switches sole function is to provide a binary TRUE or FALSE into the PLC. This approach simplifies programming.


Flow switches can be solid state or electro=mechanical.  They can be mass flow switches or volumetric flow switches and measure gas or liquids.  

Configuration and Alarms

Alarms in the PLC can be:

  • Flow
    • High - FSH
    • Low - FSL
    • High/Low - FSHL