The constant temperature hot wire anemometer is based on the principle of thermal equilibrium and achieves high-precision flow velocity measurement by maintaining a constant hot wire temperature. Its core principle, working mode, technical implementation, and advantages are as follows:
1、 Core principle: Thermal equilibrium and resistance temperature flow rate relationship
Fundamentals of Thermal Balance
When a metal wire (hot wire) heated by electricity is exposed to a fluid, the fluid flow will take away heat, causing a change in the temperature of the hot wire. According to the principle of thermal equilibrium, the heat dissipation of a hot wire is directly related to the fluid flow rate: the faster the flow rate, the stronger the heat dissipation, and the more significant the temperature drop. Resistance temperature correlation
The resistance value of metal wire varies with temperature (the temperature coefficient of metal resistance is positive), that is, the resistance decreases when the temperature decreases and increases when the temperature increases. By monitoring changes in resistance, temperature changes can be indirectly reflected, and flow velocity can be calculated accordingly.
Constant temperature control logic
The constant temperature mode dynamically adjusts the heating current through a feedback circuit, keeping the hot wire resistance (corresponding to temperature) constant. When the flow rate increases leading to enhanced heat dissipation, the system automatically increases the current to compensate for heat loss and maintain temperature stability. At this point, the change in current is linearly related to the flow rate, becoming the direct basis for flow rate measurement.
2、 Comparison of working modes: constant temperature vs constant current
patternConstant temperature mode (constant resistance)constant current mode
Control methodFeedback circuit adjusts current to maintain constant resistance (temperature)Maintain constant current, resistance changes with temperature
response speedMillisecond level, suitable for capturing transient changes such as turbulenceSlow, mostly used for low-speed airflow measurement
Measurement basisThe change in current is directly related to the flow rateThe change in resistance indirectly reflects the flow velocity
Application scenariosHigh speed and dynamic flow fields (such as aviation and combustion research)Low speed, steady-state flow field (such as ventilation ducts)
Advantage summary: Constant temperature mode has become the mainstream choice due to its fast response speed and high accuracy, especially suitable for complex flow field measurements that require high spatiotemporal resolution.
3、 Technical Implementation: Key Components and Signal Processing
Hotline Material and Structure
Material: Platinum, tungsten or platinum rhodium alloy, with high temperature coefficient of resistance and long-term stability.
Size: Length 0.5-2 millimeters, diameter 1-10 micrometers, extremely fine design to reduce interference with the flow field.
Probe combination: measuring unidirectional velocity component with a single wire; The "X-shaped" or three wire probe obtains three-dimensional velocity vectors through vector synthesis.
Wheatstone bridge balance control
As one arm of the bridge, the hot wire drives the feedback circuit to adjust the current by comparing the voltage difference between the hot wire resistor and the reference resistor.
Dynamic balance ensures constant resistance, and the current change is amplified and compensated to output as a flow rate signal.
Digitization and post-processing
After A/D conversion, the analog signal is input into the computer and the following functions are completed through software:
Real time calculation of instantaneous value, hourly mean, combined speed, and partial speed.
Analyze turbulence parameters such as turbulence intensity and Reynolds stress.
Frequency domain analysis (such as power spectrum) and spatial correlation research.
4、 Advantage features: high precision and multi scenario applicability
High response speed
Millisecond level response can capture turbulent fluctuations, with a frequency response range of over 400kHz, meeting the research needs of unsteady flow fields.
Wide measurement range
The speed range covers 0.02-300m/s, and can be measured from low-speed gentle winds to supersonic flows.
Low flow velocity sensitivity
It can measure flow velocities as low as 0.3m/s, which is superior to traditional equipment such as pitot tubes.
Low flow field interference
The probe has a small volume (diameter in micrometers) and extremely low turbulence in the flow field, making it suitable for precision experiments.
Multi-functional integration
Synchronized measurement of flow velocity, temperature, and density, supporting one-dimensional to three-dimensional flow analysis, suitable for various scenarios such as free field, boundary layer, shear flow, etc.
5、 Application Fields: From Laboratories to Industrial Sites
Research on Fluid Mechanics
Turbulent structure analysis, boundary layer transition, and flow stability research.
aerospace
Wind tunnel experiments, monitoring of surface airflow separation on aircraft, and measurement of internal flow in engines.
Energy and Environment
Stable combustion chamber flames, aerodynamic optimization of wind turbine units, and evaluation of indoor ventilation efficiency.
Biomedicine
Microscale flow research (such as vascular blood flow simulation), respiratory airflow analysis.
6、 Typical product case: DANTECCTA series
Technical Specifications:
Speed measurement range: 0.02-300m/s
Frequency response range: 0-450kHz
Speed accuracy: Typical value of 0.5% (depending on calibration)
Feature Highlights:
Support 11 channel synchronous sampling to achieve multi-point flow field measurement.
Provide StreamLine software package that integrates data acquisition, calibration, and statistical analysis functions.
The probe is replaceable, compatible with hot film sensors, and suitable for measuring gas and liquid flow.
7、 Summary
The constant temperature hot wire anemometer converts flow velocity measurement into high-precision detection of current changes through thermal electric conversion and precise feedback control. Its millisecond response, wide measurement range, and low flow field interference characteristics make it a core tool in fields such as fluid mechanics, aerospace, energy and environment. With the development of digitalization and multi probe technology, its application scenarios are expanding from laboratory research to industrial field monitoring, providing key data support for accurate analysis of complex flow phenomena.