--- title: "Flow Rate Sensors & Monitoring | Aethair" description: "Flow rate is the volume of water or fluid passing a point in a given time. 1 sensor that measures it." url: https://aethair.io/parameters/flow/ --- Measurements · Fluid / Level / Flow # Flow Rate Also known as flow meter, discharge measurement, flow 1 Volumetric flow rate (open-channel or pipe). [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Flow Rate Monitoring](https://aethair.io/build/?params=flow) At a glance — Fluid / Level / Flow 1 way to measure it - **Thiamis** 1 external instrument What it is ## What is flow rate? Flow rate is the volume of water or fluid passing a point in a given time. It is expressed in liters per second, cubic meters per hour, or cubic meters per second, depending on the setting, which is why it carries no single fixed unit. It is the quantity that answers "how much is moving," and it falls into two broad situations that are measured very differently: **open-channel flow**, where water runs with a free surface in a river, drain, or flume, and **full-pipe flow**, where fluid fills a closed conduit under pressure. In both, flow is the product of how fast the fluid moves and the cross-sectional area it moves through, so it is intimately linked to velocity and to water level. Because it quantifies the actual quantity delivered, discharged, or abstracted, flow rate is the central variable in water supply, wastewater, irrigation, and process monitoring. Flow is the number behind most water compliance and management: withdrawal permits cap how much may be taken, discharge permits limit what may be released, and both are enforced on measured flow. In wastewater and drainage, flow reveals infiltration, storm response, and the loading on treatment plants. In irrigation, it confirms that crops receive the intended amount, and in industry it governs process dosing, cooling, and billing. A concentration measurement (of a pollutant or nutrient) only becomes a load, the mass per unit time that matters environmentally, when multiplied by flow. For utilities, regulators, irrigators, and process operators, flow is therefore the accounting and compliance variable, and pairing it with quality data is what turns concentrations into loads. How it is measured ## How Flow Rate Is Measured The method depends on the setting, and all use professional sensors logged on a Thiamis gateway. In **open channels**, flow is commonly derived from water level over a calibrated **weir or flume** using a known level-to-flow relationship, or measured directly by the **area-velocity** method, which combines a velocity sensor with the flow depth and channel geometry. In **full pipes**, **electromagnetic** meters sense the voltage a conductive fluid generates as it moves through a magnetic field, and **ultrasonic** meters use transit-time or Doppler techniques to gauge velocity across the bore. Each requires correct installation and calibration to the specific site. An instrument on Thiamis 1 A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account. ### Placing flow sensors Good flow measurement needs a well-conditioned location: a straight, uniform run of channel or pipe, free of bends, steps, obstructions, and backwater close to the sensor, so that the flow is stable and representative. Weirs and flumes must be installed to their design geometry and kept clear of silt and debris that would distort the level-to-flow relationship; area-velocity sensors are placed where the velocity profile is regular. In pipes, the meter is sited with the required straight lengths upstream and downstream and, for many types, kept full and free of trapped air. ### Every device and option that measures Flow Rate 1 | Device / option | Type | Base platform | Measures | | - | - | - | - | | [Parker Velcon](https://aethair.io/sensors/parker-velcon-fluid-fuel-quality/) · FDPM MK II, FDPM | Fluid & Fuel Quality | Thiamis | Flow Rate [Fluid Differential Pressure](https://aethair.io/parameters/differential_pressure_fluid/) | [Configure Flow Rate Monitoring](https://aethair.io/build/?params=flow) Where it is monitored ## Solutions That Monitor Flow Rate Each one links to the solution page showing what that industry measures it for. ### [Hydraulic & Fuel Cleanliness](https://aethair.io/solutions/industrial-fluids/) Often added ISO 4406 oil cleanliness and aviation fuel ### [Hydrology, Level & Flow](https://aethair.io/solutions/hydrology/#measure-flow) Often added Flow, the volume of water moving past a point per unit time, quantifies rivers, channels, and discharges for water-resource management, flood modeling, and compliance. Related ## More in Fluid / Level / Flow [Water Level / Depth](https://aethair.io/parameters/water_level/) [Water Pressure](https://aethair.io/parameters/water_pressure/) [Volume (totalized)](https://aethair.io/parameters/volume/) [Fluid Differential Pressure](https://aethair.io/parameters/differential_pressure_fluid/) [Fluid Particle Count (ISO 4406)](https://aethair.io/parameters/particle_count_fluid/) [Velocity](https://aethair.io/parameters/velocity/) Questions ## Flow Rate FAQ What is the difference between open-channel and pipe flow? Open-channel flow runs with a free water surface, as in a river or drain, and is usually derived from water level over a weir or flume or by the area-velocity method. Pipe flow fills a closed conduit under pressure and is measured directly by electromagnetic or ultrasonic meters. The two settings need different sensors and installation. How does the area-velocity method work? It measures the average velocity of the flow and multiplies it by the wetted cross-sectional area, which is found from the measured depth and the known channel shape. Because it combines velocity and level, area-velocity works where a fixed weir or flume is impractical, including in channels that sometimes surcharge. How are flow, velocity, and volume related? Velocity is how fast the fluid moves, flow is that velocity multiplied by the cross-sectional area (the volume per time), and volume is flow accumulated over time. Measuring velocity and depth gives flow, and integrating flow gives the total volume delivered or discharged. How do I monitor flow? Pair a Thiamis gateway with the sensor suited to your setting (a level sensor on a weir or flume, an area-velocity sensor, or an electromagnetic or ultrasonic pipe meter) for continuous flow logging. Use the configurator to combine flow with water level, velocity, and totalized volume for a complete hydraulic station.