What are flow sensors?

Meet the Sensor: Flow Sensors

Flow sensors are electromechanical devices used to measure the flow of liquids, gases, or non-Newtonian fluids. Flow sensors use both mechanical and electrical subsystems to measure changes in the fluid’s physical attributes and calculate its flow. Optical gas flow meters use laser beams to sense the velocity of microscopic particulates in gases. Measurements can be expressed in terms of volume per time (e.g., liters per minute) or mass per time (e.g., kilograms per hour). Flow sensors convert the measurement into an electrical signal that can be monitored, recorded, and transmitted to other devices in a connected system to ensure optimal performance.

Flow sensors are essential components in systems that involve the movement of gases and liquids such as water, chemicals, oil & gas, food and beverages, or gaseous substances. They are used in applications as diverse as automobiles, manufacturing facilities, municipal water treatment plants, medical equipment, heating and cooling systems, and agricultural equipment

TE Connectivity offers a variety of flow sensors for applications that require fluid control, monitoring, and leak detection.

The Connector Connection

Flow sensors are typically installed using a threaded, push-on, or other connection. Some flow sensors are integrated into IoT measuring devices using M12 connectors.

Two types of flow sensors and how they operate

There are two commonly specified types of flow sensors, differential pressure flow sensors and mass flow sensors.

Differential pressure flow sensors are the most commonly used type of flow sensors. They calculate the pressure of the fluid at two varying velocities. In most differential pressure flow sensors, a single pressure sensing node is positioned on the edge of the flow path of a fluid. A nozzle or change in diameter of the flow accelerates the fluid, which is measured again at a higher velocity. Once the sensor determines the difference in pressure between the two points of measurement, the Bernoulli equation can be used to calculate the fluid velocity and overall flow. A fluid’s velocity is directly related to the fluid’s pressure, per the Bernoulli equation:

dp=(density*velocity^2)/2

Accurate measurement depends on controlling several variables. Differential pressure-based flow sensors can be used to “interrupt” the piping as a control measure. Different types of sensors utilize the differential pressure methodology, such as Venturi tubes, Rotameters, Orifice plates, and Pitot tube arrays. These sensors vary in accuracy and system pressure loss.

Amphenol’s Coolant Leak Detection Sensor, available from DigiKey, is used in EV battery packs to detect moisture leakage via a change in the resistance value of the sensor.

Thermal mass flow sensors are used in gaseous, low-flow applications like semiconductor manufacturing, where accuracy is paramount. This type of sensor utilizes a fluid’s thermal properties to measure flow. A thermal mass flow system uses a fluid’s propensity to absorb thermal energy and measures the amount of energy in the fluid using one of two systems. The first system uses a heating element with a thermal sensing element. The fluid absorbs energy from the heating element and the sensor measures the fluid to determine how much energy it absorbed. In the other system, the temperature is kept at a fixed level by the heating element. As the fluid absorbs energy, it cools the heating element, which then requires more energy to maintain the fixed temperature. The amount of energy that the heating element needs to maintain the constant temperature is used to calculate the flow.

The velocity of the fluid in both methods is directly related to how much energy it absorbs. A slower flow requires more time for the energy to transfer from the heating element to the fluid. A faster flow needs less time. Thermal mass flow sensors are calibrated for specific gas purity levels, making them suitable for sensitive applications such as pharmaceutical manufacturing.

*Non-Newtonian liquids are unique substances that do not conform to Isaac Newton’s law of viscosity. Their viscosity changes — that is, they become thicker or thinner — when force or stress is applied or when time elapses. Examples include paint, cornstarch-and-water mixtures, and ketchup. In other terms, shear-thinning fluids become less viscous with increased force (like paint). Shear-thickening fluids become more viscous under stress (such as cornstarch and water). In contrast, the viscosity of Newtonian fluids is influenced only by temperature and pressure, not on the forces acting upon it. These fluids fall under the branch of physics known as rheology, which examines how forces impact fluid flow.

Read Flow and Pressure Sensors 101 by Mouser Electronics

Design Notes 

Material specifications: Flow sensors are ruggedized components that are designed to withstand constant submersion and exposure to potentially corrosive substances. They feature a robust housing, available in a variety of materials that correspond with the needs and requirements of the application and specific fluids to be measured. They are typically available in plastic, brass, or stainless steel, as well as specialized materials such as bronze, Hastelloy, tantalum, or titanium for industrial applications that involve hazardous substances. Some manufacturers supply explosion-proof sensors that meet ATEX and IECEx requirements.

Markets and Applications 

Test & Measurement, Automotive, Medical, Industrial, Transportation,

Oil & Gas, Water Treatment, Food and Beverage

Suppliers 

Avnet, DigiKey Electronics, Mouser Electronics, TE Connectivity, RS

Like this article? Check out our other Meet the Connector and Connector Basics articles, our Connector & Cable Special Topics Market Page, and our 2024 and 2025 Article Archives. 

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