Types of measurement made by current instruments

On-line viscometers use basically the same kinds of measurements made on off-line instruments, i.e.. 

Because most liquids of industrial importance are non-Newtonian, we know that the measured viscosity can vary because of the 

The result is that the one number usually produced as the output of a process viscometer, purporting to be the measured on-line viscosity, can vary enormously for a non-Newtonian liquid depending on the type of measurement. 

Also the measurement wiU be affected to some extent or other by the need to replenish continuously the fluid in the vicinity of the measuring element with fresh fluid. If this is done continually—as it is in most cases—then there is a strong possibility that the flow could affect the viscosity reading by, for instance, increasing the overall shear rate or even for vibrating 

One point that should always be home in mind is the effect of temperature on viscosity, because the temperature of the Hquid being measured on-hne is often above that used off-line. Therefore some compensation should be inserted. This is often built into the viscometer but can also be accommodated in any computerised data logging system being used, so that an equivalent standard-temperature viscosity can be displayed. For some measurements however, it might be necessary to pass the material through a heat exchanger to bring the material to the desired temperature for measurement. 

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