Although the right index and left index fingers of your hands appear similar, they are actually different in their details. The variability in the sum of these heat transfer paths will be unique to the flowmeter and may differ in the same way fingerprints differ on someone’s hands. Heat transfer path variabilityĪll thermal flowmeter manufacturers need to understand not only the heat input equation and the surface area, but all the heat transfer paths. Additional variations come from the sensors themselves and how each sensor is affected across its full flow range. This is true for all thermal mass flowmeters, regardless of their measuring technique. The cooling effects are mostly a function of the properties of the gas, including its thermal conductivity, specific heat, density, and viscosity (figure 1). This temperature differential is directly proportional to the mass flow measurement.Īll thermal mass flowmeters work by measuring the cooling effect of a moving gas along a cylinder. One RTD is heated while the other provides a reference by measuring the process temperature. Thermal mass flow sensors comprise two platinum resistance temperature detectors (RTDs) that are protected within thermowells. Thermal dispersion principle of operation. Inefficient processes also frequently result in poor product quality and excessive costs, which negatively impact the bottom line and competitiveness. Poor calibration practices can result in possible safety exposures and process inefficiencies that might go undetected until the process is running and something goes wrong. This happens if the calibration is inaccurate or subject to uncertainty due to an equivalency-based calibration or simulation methods rather than an “actual” fluid calibration. Flowmeters can be built with the highest safety ratings, features, and functions and the most industrially robust sensor technology, and still deliver unsatisfactory performance. Instrument calibration should never be taken for granted, and thermal mass flowmeters are no exception. Proper calibration ensures new and old instruments deliver reliable results.
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