| Summary: | Process viscometry has many advantages in terms of saving time and gaining more immediate information about a process. However, it can also has disadvantages in terms of compromises that must be made in taking a stream of liquid and passing it through a viscosity-measuring element. The latter operation can be a strong function of flow rate through the instrument, making the measured value variable. The viscometer itself might has been chosen for simplicity of measurement, but which might actually represent a complicated flow pattern in the sense of being a mixture of shear and extensional flow, frequency and acceleration. The best practice in the area of on-line viscometry is reviewed, and the current commercial instruments are compared to this standard. It is concluded that the choice of instrument depends on the pressing need is either for quick information or for reliable information. The Nametre vibrating sphere and the Brookfield concentric-cylinder instruments are highlighted.
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