Thermal mass flowmeters

Whenever high turndown or low pressure losses are important in gas metering applications in any industry, thermal mass flowmeters offer a real alternative to traditional measuring techniques – whether for process control, consumption and supply monitoring, detecting leaks or monitoring distribution networks. Using insertion versions, it is also possible to measure gas flows in very large pipelines or in rectangular ducts.

The thermal measuring principle is widespread in industry and is being used successfully in many applications with gas flow, for example:

• Compressed air (consumption, distribution)
• Carbon dioxide (for beverage production and chilling)
• Argon (in steel production)
• Nitrogen and oxygen (production)
• Natural gas (for burners and boiler feed control)
• Air and biogas measurement (e.g. in wastewater plants)

Thermal flow measuring principle

This measuring principle is based on the fact that heat is drawn from a heated body when a fluid flows past.

A thermal flowmeter contains two PT100 temperature sensors for this purpose. One sensor measures the current fluid temperature as a reference. The second sensor is heated and has a constant temperature differential relative to the first sensor at “zero flow.”

As soon as the fluid begins to flow in the measuring tube, the heated temperature sensor cools off due to the fluid flowing past – the higher the flow velocity, the greater the cooling effect. The electric current required to maintain the temperature differential is thus a direct measure of mass flow.

Benefits

• Multivariable – direct measurement and display of mass flow and fluid temperature
• No pressure or temperature compensation required
• High turndown (100:1)
• Excellent low-end sensitivity
• Quick reaction to fluctuations in flow