What Is a Flow Sensor?
A flow sensor is a device that detects the instantaneous flow rate of a fluid, such as a liquid or gas.
Various measurement methods are available, including:
- The impeller method, which determines the flow rate from the number of rotations of the impeller.
- The volume/mass method, suitable for measuring viscous liquids.
- The electromagnetic method, capable of detecting even minute amounts of fluid.
The vortex flow meter has a relatively small pressure drop, making it suitable for measuring a wide range of fluids, including liquids and gases. Due to its ability to detect various fluids with high accuracy, vortex flow meters are expected to become increasingly popular.
Applications of Flow Sensors
Flow sensors find application in the manufacturing process of industrial machinery, consumer product management, and medical institutions. Flow sensors measure the instantaneous flow rate of a liquid or gas, with accuracy varying depending on the product and detection mechanism.
High-precision products, particularly, have applications in industrial machinery to monitor minute changes in fluid levels during manufacturing. Another application is the measurement of lubricating fluids like oil used in transmissions for automotive applications and fluid characteristics in vehicles, as well as the management of air conditioners in consumer products.
Principle of Flow Sensors
Flow sensors employ various detection mechanisms, with the three most common methods being thermistor, Kalman vortex, and MEMS.
1. Thermistor Flow Sensors
In thermistor flow sensors, a heated thermistor is placed in the flow path. As fluid flows through it, heat is absorbed from the thermistor. The rate of increase in resistance due to the reduction of heat in the thermistor correlates with the flow velocity, allowing for flow velocity measurement.
2. Kalman Vortex Flow Sensors
The Kalman vortex flow sensor utilizes fluid oscillation. When a rod-shaped object is placed in the flow, it acts as a vortex generator, producing alternating vortices downstream.
Under specific conditions, this vortex is highly stable, and its frequency is proportional to the flow velocity, enabling flow rate calculation based on frequency evaluation.
3. MEMS Flow Sensors
MEMS flow sensors are primarily used for gases. Since the resistance value’s dependence on flow location is proportional to the fluid’s flow velocity, they can measure flow direction and velocity by processing calculations from the MEMS’s resistance value.
Other Information on Flow Sensors
1. Flow Switches and Pumps
A flow switch, functioning similarly to a flow sensor, is a switch that operates by sensing liquid flow. When the pump runs, liquid flows, and when the pump stops, the flow ceases. Therefore, flow switches detect liquid state changes by turning flow on and off.
In most cases, systems are controlled by monitoring the liquid flow state. As a result, a pump, generating liquid flow, is used together with a flow switch to detect flow. Flow switches and pumps are designed to work as a set, ensuring effective operation.
2. Difference Between a Flow Switch and a Flow Meter
A flow switch detects liquid flow, operating either ON or OFF. In terms of voltage, they are either L (low) or H (high), in terms of microcontroller processing information, they are either 0 or 1, and in terms of display, they have only two states: operating or stopped, and are used for digital operation.
In contrast, a flow meter is an analog device measuring liquid velocity or flow rate. Displayed measurements are continuous, such as liters per minute, and shown as numerical values.
Flow switches operate via a simple detection mechanism, where a float rises with the liquid, switching off when the level reaches a threshold. In contrast, flow meters have various detection methods, including types similar to the float switch, like the differential pressure method. Choosing the most appropriate option depends on the required measurement accuracy and conditions.