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Amongst various flow measurement techniques the thermal mass flow measurement based on the CTA principle is used for both gases and liquids. ‘CTA’ is the abbreviation of Constant Temperature Anemometry, which is also named ‘direct through-flow measurement’ or ‘inline measurement’. Mass flow meters based on the CTA principle cover a wide range of measurement and control applications in almost every industry sector. Examples of applications are burner control, aeration processes, gas consumption measurement, leak rate tests and environmental air sampling at atmospheric conditions. Within the Bronkhorst® portfolio, these reasonably priced flow meters enlarge the scope of mass flow measurement solutions for higher flow rates, for low pressure requirements and for conditions within an application and/or local work environment that would be unsuitable for another measurement principle such as Thermal by-pass.

Top 5 key reasons why to use flow meters and controllers based on the CTA principle:

  • It is the preferred thermal measurement solution for high flow rates of gasses, where the technical efforts of a thermal by-pass measurement with capillary sensor and laminar flow element are exceeded. The inline CTA measurement is available from a few ml/min up to hundreds of thousands of m3/h and even more.
  • Compared to traditional thermal MFMs and MFCs with by-pass, the construction of the direct measuring CTA devices is less sensitive to humidity and contamination.
  • The compact and robust instrument design provides continuous mass flow measurement with an excellent repeatability. It is extremely versatile and is used within many different industries and applications.
  • This CTA concept makes it possible to build and to calibrate an instrument with Air or Nitrogen and to then model it for almost any other gas or gas-mix.
  • The pressure loss over the instruments is almost comparable to a straight length pipe and is thus usually negligible.

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The working principle

The CTA sensor consists of two probes, the first being a heater and the second being a temperature sensor. A constant temperature difference is created between the probes. Regardless of actual flow-rate CTA is aiming to keep this delta-T or temperature difference (T) between both sensor pins at a constant level. The flow rate and the heater energy required to maintain this constant T are proportional and thus indicate the mass flow of the gas. The actual mass flow rate is calculated by measuring the variable power required to maintain this constant temperature difference as the gas flows across the sensor.

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