Types of Ultrasonic Flow Meters Ultrasonic flow meters are generally categorized into two main types based on how they measure flow:
- Transit-Time Ultrasonic Flow Meters (also called Time-of-Flight) How it works: Measure the time difference between ultrasonic signals sent with and against the flow direction. Best for: Clean or slightly contaminated liquids with low particle or bubble content. Subtypes: Clamp-on (non-intrusive, mounted on outside of pipe) Inline (transducers embedded in the flow tube) Insertion (probes inserted into the pipe wall)
- Doppler Ultrasonic Flow Meters How it works: Measure frequency shift (Doppler effect) of ultrasound reflected off particles or bubbles in the fluid. Best for: Dirty or aerated liquids containing suspended solids or gas bubbles (e.g., wastewater, slurries). Usually clamp-on or insertion types. How Ultrasonic Flow Meters Work (Basic Principle) Transducers emit ultrasonic pulses through the fluid. In transit-time meters, two transducers send and receive signals both upstream and downstream. The signal travels faster with the flow and slower against the flow. The time difference is used to calculate flow velocity. In Doppler meters, an ultrasonic signal bounces off particles or bubbles in the fluid. The change in frequency of the reflected wave is related to the flow velocity. The flow velocity is multiplied by the pipe’s cross-sectional area to get volumetric flow rate.