3/17/2024 0 Comments Mass flow meter![]() While some methods are straightforward, others are complicated, time-consuming, and require the meter to be removed from the pipe. These calibration verification procedures vary from manufacturer to manufacturer. With technological advancements over the years, some mass flow meter manufacturers, including Sage Metering, have developed ways to verify that the meter remains calibrated. This recalibration can be expensive, and removing a meter from service is certainly inconvenient. Once a thermal mass flow meter has been calibrated, the question becomes, when does it need to be re-calibrated? Some manufacturers require their meters returned to the factory or an authorized NIST-traceable facility for recalibration. Annual Recalibrations are Expensive and Inconvenient When safety or hazardous conditions make it impossible to use the actual gas (or gas mixture) during calibration, use a surrogate gas with similar heat transfer characteristics combined with analytical adjustments based on the relative heat transfer properties of the actual and calibration gases.Ĥ. This process is repeated multiple times over the operating range to establish the relationship between mass flow and the signal for the gas and sensor being calibrated. ![]() A controlled amount of the specified gas flows past the meter’s sensor during calibration on a flow bench, and the signal is measured. For this reason, a thermal mass flow meter can only accurately measure the gas (or gas mixture) the meter was calibrated for. When Unable to Calibrate with the Actual Gas TypeĮvery gas has different physical properties that impact heat transfer. In these cases, vortex-shedding or differential-pressure flow measurement are options. For this reason, it is uncommon to use thermal mass flow meters in compressed gas systems with pressures greater than 150 PSI. The mass velocity measured by thermal mass flow meters increases with increasing gas density while the actual velocity at operating conditions remains the same.īecause the thermal meter loses sensitivity at higher mass velocities, there is an upper limit on velocity, and the instrument can overrange. A thermal mass flow meter calibration curve (above)Īs gas pressure increases, the gas molecules pack closer together, increasing gas density. Other flow meter types are sized based on the velocity at operating conditions. When selecting a mass flow meter for a given application, the meter is sized based on mass velocity referenced to the STP (Standard Temperature and Pressure) conditions. While thermal flow meters provide excellent sensitivity for low gas flow, there is diminished sensitivity at high rates. There is a nonlinear relationship between the mass velocity and heat transfer in thermal flow measurement. Diminished Sensitivity at Higher Velocities Angle the sensor so that if condensate develops, it flows away from the sensor.Ģ. Angling the flow sensor in the pipe is another method that can mitigate inaccuracies associated with condensed moisture.The gas flows upward and out, effectively removing moisture drops from the gas as gravity causes the moisture to fall. When gas flows into a vessel, such as a knockout drum (KO drum or knockout pot), there is a reduction in gas velocity and a change in the flow direction.Condensed moisture in the gas that contacts the heated sensor rapidly increases heat transfer, and the instrument responds with a spike, creating inaccurate flow measurement. The primary thermal mass flow measurement principle involves heat transfer caused by the gas flow. Condensed Moisture may Cause Inaccuracies Angling the flow sensor in the pipe can help combat inaccuracy associated with condensed moisture. Here are nine restraints or challenges of thermal mass flow meters and how to overcome them. However, like any technology, the flow meter’s limitations may present challenges the user should address before implementation. The meter is accurate, reliable, and cost-effective for many applications. The device is used in various industries, including oil and gas, refining, chemical, mining, and wastewater. The thermal mass flow meter is a widely accepted instrument that measures gas mass flow.
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