A magnetic flow meter measures the flow of a process material by evaluating which property of the fluid?

A magnetic flow meter operates based on the principle of electromagnetic induction, which directly measures the velocity of the conductive fluid flowing through it. The flow meter consists of an electromagnetic coil that generates a magnetic field. As the conductive liquid moves through this field, it induces a voltage proportional to the flow velocity, which is then used to calculate the flow rate.

The measurement of velocity is crucial in this context because magnetic flow meters are specifically designed for applications involving conductive liquids. The flow rate is derived from the formula that combines the cross-sectional area of the flow tube with the measured velocity. Therefore, the primary measurement property leveraged by a magnetic flow meter to assess flow is indeed the velocity of the fluid.

Other options like density, volume, and temperature do not directly pertain to the function of a magnetic flow meter. Density may be a consideration in some flow measurement techniques, but it is not a measurement directly obtained by a magnetic flow meter. Volume flow rate is a result of the velocity measurement, and temperature is important for understanding process conditions but is not utilized in the flow measurement by a magnetic method.