What is a Flow Sensor?

A flow sensor (more commonly referred to as a “flow meter”) is an electronic device that measures or regulates the flow rate of liquids and gasses within pipes and tubes. Flow sensors are generally connected to gauges to render their measurements, but they can also be connected to computers and digital interfaces. They are commonly used in HVAC systems, medical devices, chemical factories, and septic systems. Flow sensors are able to detect leaks, blockages, pipe bursts, and changes in liquid concentration due to contamination or pollution.

Flow sensors can be divided into two groups: contact and non-contact flow sensors. Contact flow sensors are used in applications where the liquid or gas measured is not expected to become clogged in the pipe when it comes into contact with the sensor’s moving parts. In contrast, non-contact flow sensors have no moving parts, and they are generally used when the liquid or gas (generally a food product) being monitored would be otherwise contaminated or physically altered by coming into contact with moving parts.

Vortex flow sensor.
Vortex flow sensor. (Automation Forum)

The two most common types of contact flow sensors are vortex and mechanical flow sensors. Vortex flow sensors are comprised of a small latch (known as the “buff body”) that flexes back and forward when coming into contact with a flowing liquid or gas. The differences in pressure (i.e. the vortices) generated by the latch are measured to determine the flow rate. Mechanical flow sensors use propellers that spin at a rate that is directly proportional to the flow rate. Mechanical flow sensors can also be controlled to cause the flow rate to increase or decrease.

Ultrasonic flow sensors are the most popular type of non-contact flow sensor. Ultrasonic flow sensors send pulses of high frequency sound across the flowing liquid or gas medium. These sensors measure the time between the emission of the sound and its contact with the sensor’s receiver to determine the flow rate of the gas or liquid.