Flow Meters

The thermal gas mass flowmeter is designed on the basis of the thermal diffusion principle. This instrument uses the constant temperature difference method to measure gas accurately. It offers advantages such as small size, a high degree of digitalization, easy installation and accurate measurement.

II. Working principle

The sensor section consists of two reference-grade platinum resistance temperature sensors. When the instrument is working, one sensor continuously measures the medium temperature T1; the other sensor self-heats to a temperature higher than the medium temperature T2, and it is used to sense the fluid velocity, so it is called the velocity sensor. This temperature difference ΔT=T2-T1, T2>T1, when fluid flows past, gas molecules collide with the sensor and carry away the heat of T2 , causing T2  to decrease; to keep ΔT constant, the supply current to T2  must be increased. The faster the gas flows, the more heat is carried away. There is a fixed functional relationship between the gas velocity and the added heat, which is the constant temperature difference principle. 

Where — fluid specific gravity (related to density) V — flow velocity

K — balance coefficient

Q — heating quantity (related to specific heat and structure) ΔT — temperature difference

Since the sensor temperature is always automatically maintained at a constant level about 30°C above the medium (ambient) temperature,

the thermal gas flowmeter does not require temperature compensation in principle.

The applicable medium temperature range of the thermal gas mass flowmeter is-40-450°C.

The specific gravity of a fluid is related to its density   

 — medium density at operating conditions (kg/m3)

ρ — medium density under standard conditions (101.325 Kpa, 20°C) (kg/m3)

P — operating pressure (kPa)

T — operating temperature (°C)

From equations (1)(2), it can be seen that the functional relationship among flow velocity, operating pressure, gas density and operating temperature is already determined. The constant temperature difference thermal gas mass flowmeter is affected neither by temperature nor by pressure. The thermal gas mass flowmeter is a true direct mass flowmeter, so users do not need to correct for pressure and temperature.

III. Technical parameters

The thermal gas mass flowmeter has the following technical advantages:

1. A true mass flowmeter: gas flow measurement requires no temperature or pressure compensation, making measurement convenient and accurate. The gas  mass flow or

standard volumetric flow.

2. Wide turndown ratio: it can measure gases with velocities as high as 120Nm/s and as low as 0.1Nm/s , and can be used for gas leak detection.

3. Good vibration resistance and long service life. The sensor has no moving parts or pressure sensing components and is not affected by vibration in terms of measurement accuracy  .

5. Digital design. Fully digital circuit measurement provides accurate measurement and convenient maintenance.

 6. With RS-485 communication, or HART communication, plant automation and integration can be achieved. 

For more detailed information, please download the user manual