Hot-Wire Airflow Combined with Flow Conditioning Design: Airflow Monitoring Re-evolution

In the field of air velocity and air flow monitoring, achieving stable and repeatable measurements under complex and dynamic airflow conditions has always been a technical challenge. This is especially critical in applications such as process control, cleanroom environments, and compressed air energy management, where airflow data is not just a single parameter—it serves as a fundamental input for system-wide control strategies.

Currently, two primary airflow sensing technologies are commonly used on the market: differential pressure (DP) and hot-wire (thermal) types. While DP sensors feature simple structures and offer stable measurement, they often lack sensitivity in low-velocity ranges. On the other hand, hot-wire sensors are known for their high sensitivity and fast response but can be easily affected by turbulence or installation orientation, which may lead to signal fluctuation and reduced measurement accuracy.

To address these limitations, eyc-tech has re-engineered its airflow measurement architecture with an engineering-oriented approach—integrating hot-wire sensing technology with flow conditioning structures. This solution offers improved signal stability and enhanced measurement resolution.

Air Velocity vs. Differential Pressure Relationship:

Figure 1: "Relationship Between Air Velocity and Differential Pressure"

Illustrates the classic parabolic relationship (ΔP = ½ρV², where ρ = air density):

● As air velocity increases, the resulting pressure difference grows quadratically.
● At low velocities (e.g., < 2 m/s), the pressure variation is minimal—explaining why DP sensors struggle with low-speed sensitivity.

Figure 2: "Relationship Between Differential Pressure and Air Velocity"
Depicts that velocity is proportional to the square root of pressure difference (V ∝ √ΔP):

● Velocity increases with rising pressure differential, but the rate of increase diminishes.
● In the low ΔP range, velocity changes are subtle leading to lower sensitivity.
 

Technical Advantages of Flow Conditioning

eyc-tech combines Hot-wire sensor with Venturi or Pitot-based flow conditioning. These flow conditioning structures help stabilize airflow direction and velocity distribution, leading to improved measurement accuracy and consistent sensor output. The design is implemented in two key configurations:

● FDM06-P uses a multi-point averaging Pitot tube, which samples airflow across multiple points in the duct to determine a representative average velocity.

● FDM06-I features a Venturi structure, guiding airflow through a contraction-expansion zone to ensure steady and uniform flow across the sensing element.

By integrating Venturi-based flow conditioning, thermal anemometers achieve stable, linear output with excellent responsiveness across the full velocity range.

Measurement Advantages from Technology Integration

By incorporating Pitot tube or Venturi-based flow conditioning structures, hot-wire air velocity transmitters can minimize output instability caused by flow direction variations or turbulence. Once the airflow is conditioned before reaching the sensing zone, its velocity profile and flow direction are maintained within designed tolerances, allowing the hot-wire sensing element to perform at optimal capacity. This integration brings the following advantages:

● Highly sensitive and linear output
● Maintains excellent signal resolution even at low air velocity
● Improved repeatability and long-term measurement stability

Laboratory-Grade Calibration Enhancing Application Consistency

Through real-flow calibration using wind tunnel systems, Air volume standard calibration system (Sonic Nozzle), the transmitter can reflect air flow characteristics that are closer to real-world conditions. This contributes to more stable data output in applications such as compressed air systems, gas pipelines, and controlled air velocity environments.

Key features of this calibration approach include:

● Simulation of actual duct flow conditions helps improve the transmitter’s response accuracy under field applications.
● Each transmitter undergoes multi-point velocity calibration and compensation profiling, contributing to improved accuracy and repeatability.

By combining Venturi or multi-point Pitot tube flow conditioning with laboratory-grade calibration procedures, and integrating hot-wire air velocity sensing technology, eyc-tech optimizes both measurement stability and reproducibility. This results in a reliable airflow monitoring solution that supports the high-precision and high-consistency needs of diverse industrial applications.

FDM06-P Average Flow Thermal Mass Transmitter

Sensor type : Hot-wire sensor
Turndown ratio : 100 : 1
Output : 4 ... 20 mA / 0 ... 10 V / Relay / RS-485
Accuracy : 0.5 ... 60 m/s：±(1.5% of mv + 0.8 m/s)
IP rating : IP65

FDM06-I Venturi Thermal Mass Flow Meter

Sensor type : Hot-wire sensor
Turndown ratio : 100 : 1
Measuring range : 0 ... 4000 m³/h
Output : 4 ... 20 mA / 0 ... 10 V / Relay / RS-485
Accuracy : ±1.5% F.S.
IP rating : IP65