Hot Wire Type and Differential Pressure Type Air Flow Meter
Hot Wire Type and Differential Pressure Type Air Flow Meter
I. What is an air flow meter?
An air flow meter, also known as an air flow sensor or an air flow transmitter, is a device used to measure the air or gas flow rate in a pipe or in an open environment. Air flow meters have a wide range of applications in industries. Common applications include building management system and HVAC, air compressor systems, pneumatic systems, exhaust gas emissions monitoring, and various industrial applications.
II. What types of air flow meter are there?
There are various types of air flow meter, and hot wire type and differential pressure type air flow meter are the most common.
Hot wire type:
I. Principle
The basic principle of a hot wire e air flow meter is to place a metal wire in a fluid, heat the wire by passing a current through it, and measure the temperature change of the wire caused by the air flow and the amount of heat conducted away by the air flow. This way, the air flow can be calculated based on the wire temperature, heat conduction properties, and air properties. In addition to metal wires, other heating elements can also be used as substitutes.
II. Features
Hot wire air flow meters have high accuracy and fast response times, and can measure air flow accurately from low to high speeds. It should be noted that hot wire air flow meter is more sensitive to instantaneous changes in air temperature, and thus additional evaluation is required for applications with fast and large temperature changes. As hot wire air flow meters measure based on the principle of heat conduction, in order to ensure measurement accuracy, it is necessary to avoid impurities in the air, such as dust and pollutants, which can affect the amount of heat carried away by the air flow. Therefore, when applying meters, it is recommended to install hot wire air flow meter in a clean gas environment or after a filter. Some technologically advanced manufacturers also offer dust-resistant and corrosion-resistant hot wire air flowmeters, making them more widely applicable.
Schematic diagram of hot wire principle
Schematic diagram of hot wire principle
Differential pressure type:
I. Principle
Differential pressure air flow meters use a pitot tube to measure wind speed. The pitot tube measures the pressure difference between the total pressure and the static pressure of the fluid, and then calculates the air flow. The difference between total pressure and static pressure is called dynamic pressure, which is the pressure caused by air velocity. As dynamic pressure is proportional to the square of air velocity, air velocity can be calculated by measuring dynamic pressure.
II. Features
Differential pressure air flow meters have a simple probe structure, which have no moving or electronic parts inside the probe, making them highly stable over the long term. The measurement range of differential pressure air flow meters is suitable for most applications. As differential pressure is proportional to the square of air velocity, differential pressure air flow meters have excellent accuracy and resolution at high wind speeds, but may be limited in accuracy at low wind speeds. When measuring air flow using the differential pressure principle, a probe with an average Pitot tube structure can be used. The average Pitot tube has multiple measurement holes on both the total pressure and static pressure sides, allowing for an average of the air flow inside the tube. For example, when measuring the airflow inside a large-diameter duct, the air flow at the center and near the wall of the duct may differ significantly. Taking a measurement at only one point is not representative. The use of an average Pitot tube can average the air flow at multiple points inside the tube, resulting in more accurate measurements. In terms of air cleanliness, dust has less impact on differential pressure air flow meter. However, over time, dust may still clog the holes of the Pitot tube, so it is recommended to install it in a clean gas environment or after a filter, and to regularly clean it to minimize the impact of particles on the Pitot tube.
III. How to choose an air flow meter?
When choosing an air flow meter, it is important to consider the operating conditions, measurement range, accuracy, and other factors. eyc-tech is an expert in air flow measurement and offers a wide range of products, including hot-wire and differential pressure air flow meters. If you have any questions or need further assistance with air flow meters, please feel free to contact us. We are always ready to help. The following are product introductions:
