Types of Flow Meter
The two types of Flow Meter, Transit Time (Time of Flight) and Doppler, are both available in a clamp-on meter style with transducers which are used to detect and then measure flow rates from the outside of the pipework, without any interruption to flow or process.
What Are Doppler Flowmeters?
These ultrasonic flow meters are designed to measure the flow of a liquid where it contains sound reflectors such as bubbles of gas or suspended solids. The monitor the flow in difficult applications such as effluence pipes, chemicals or very viscous fluids.
They use reflected ultrasonic sound to measure fluid velocity. By measuring the frequency shift of the ultrasonic source, the received and the carrier, then the relative motions are measured. This frequency shift is called the Doppler Effect.
What are the advantages of a Doppler Effect Flow Meter?
These meters are useful as they can work where other flow meters can’t. This could involve slurries, aerated liquids or fluids that might contain both small or large amounts of suspended solids.
The Doppler meters will not obstruct the flow as they can be installed outside of the pipework. They can therefore be corrosion resistant and are very energy efficient with a relatively low consumption of power.
There are however some disadvantages, mainly that performance will be dependent on the physical properties of the liquid (sonic conductivity, density and flow profile). Unlike other acoustic flow meters, these meters are affected by sonic velocity changes in the liquid. So the meter is very sensitive to temperature and density changes, this sometimes makes them unsuitable for extreme accuracy when it comes to measurement applications.