INSTRUMENTATION • ELECTRONICS
If precise mixing is a crucial process variable, viscosity measurement may be the most accurate way to ensure optimum performance. But rotating mixers can lead to very tangled wiring. Mark Ingham looks at wireless options
M
ixing is fundamental to the manufacture of many products; in many cases this need not be a precision
operation – although over-mixing is a waste of time and energy. However, in other cases, mixing is more of an exact science; under-mixing will leave the various component materials unevenly distributed, while over-mixing may change the state of the end product. One example of this is mixing
concrete. If you are building a DIY patio, you can splash some water into a pile of ready mix and work it in with a spade, but if you are building a containment bunker for nuclear waste or the foundations of a skyscraper, quality control shifts to a different paradigm! In the latter case, the wet concrete has to be
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fluid enough to flow into every nook and cranny of the formwork and for no pockets of dry concrete that won’t cure properly.
Another example is mixing
ketchup, sauces, mayonnaise, etc. Te food industry relies on the fact that consumers can be loyal to a particular brand their whole lives, but are also so fickle that the slightest variation in texture will have them up in arms. Similarly, drugs and medicines must
have the active ingredients precision mixed with the carrier material – the consequence of poor mixing could be life threatening.
And in cosmetics and toiletries, the
users have incredibly high expectations. Even something as apparently mundane as paint requires that pigments are well
MEASURING VISCOSITY WIRELESSLY
mixed in for an even colour and that the correct consistency is attained for easy application. Tere are a number of different technologies available for measuring viscosity, but one of the most popular and widely used is the rotational viscometer, which measures viscosity by monitoring the torque required to rotate a spindle at a constant speed within the fluid. Te torque, generally measured by determining the reaction torque on the motor, is proportional to the viscous drag on the spindle, and thus to the viscosity of the fluid. Significantly, the rotational viscometer
can run throughout the mixing process, logging data constantly to provide a log of the change in viscosity over time. Tis profile can be compared with historic
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