Measurement Principles of Liquid Flow Meters

The measurement principles of liquid flow meters vary depending on the type. Here are explanations for common types:

1. Electromagnetic Flow Meter?

Based on Faraday's Law of Electromagnetic Induction, when a conductive liquid (conductivity ≥5 μS/cm) flows through a pipe with magnetic field strength ?B? at velocity ?v?, an induced electromotive force ?E? (E = B·v·D, where ?D? is pipe diameter) is generated. By measuring ?E?, the flow rate can be calculated. Key features include ?no pressure loss?, ?suitability only for conductive liquids?, and ?insensitivity to temperature/pressure changes?.

2. Ultrasonic Flow Meter?

Uses the ?time-difference method?: Upstream and downstream probes alternately transmit ultrasonic signals. Fluid flow causes a time difference in signal transmission, which is used to calculate flow based on the relationship between time difference and velocity (Δt = 2Lv/c2, where ?L? is sound path length and ?c? is sound speed). Advantages include ?ability to measure corrosive/radioactive liquids?, but it is ?limited by temperature (usually ≤200°C)?.

3. Turbine Flow Meter?

Relies on fluid pushing turbine blades to rotate. The rotational speed is proportional to flow velocity, and a ?Hall sensor converts mechanical rotation into electrical pulse counts?, which are then converted into flow rate. ?Full-pipe installation and straight pipe requirements? must be observed.

4. Differential Pressure Flow Meter (e.g., Orifice Plate)?

Based on Bernoulli's principle, when fluid passes through a restriction (e.g., orifice plate), a pressure difference ?ΔP? is generated. Flow rate ?Q? is proportional to the square root of ?ΔP?. It has a ?simple structure but causes pressure loss? and is suitable for ?gases, liquids, and steam?.