Rotational, vibration and acoustic viscometers
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Rotational viscometers are the most widely used in process control systems (compared to other types of general industrial viscometers). Their principle of operation is based on the measurement of counteracting (rotating) moments caused by viscous friction: M =κμϖ, where k is the instrument constant (determined only experimentally); ϖ is the angular velocity of the rotating body.
Structurally, rotational viscometers differ in the shape of the rotating body and in the methods of determining the torque. Of the entire variety of rotary measuring instruments (sensing elements), three main ones can be distinguished: two coaxial cylinders; equidistant disks (plane-plane); a rotating body immersed in a liquid of unlimited volume. 
Rotational viscometers with a measuring pair of the first type: a cylinder rotating with the help of an electric motor have proven themselves quite well. A diagram of the BP-2030 type rotary transducer is shown in the figure.
The viscometer is designed to continuously convert the viscosity of a liquid into a unified pneumatic (or electrical) output signal. The principle of operation is based on the dependence of the torque of the cylinder filled with the analyzed medium on the viscosity of the latter.
The nozzle (5) is driven with a constant angular velocity of 0.15 s-1 by the motor (1) through the gearbox (2) and the coupling (3). The space between the nozzle (5) and the cylinder (4) is filled with the sample medium. As the nozzle rotates, the drag forces create a torque on the cylinder (4) that is proportional to the viscosity.
The cylinder is rigidly fixed to the end of the rod (6), which is extended from the sample chamber by an elastic membrane (8). The other end of the rod is connected to the lever of the pneumatic force transducer (7).
To stabilize the temperature of the medium, the side walls of the chamber are washed with a thermostatic fluid, which enters and leaves the chamber through flanges (9); in addition, the chamber itself and pipelines are additionally insulated.
The limit of the main permissible error is not more than ±2.5%. In connection with the improvement of the design of the primary transducers of viscometers and the use of microelectronic technology in measuring circuits, vibration and acoustic viscometers should be considered promising for use in the food industry. In addition to the above, vibration and ultrasonic viscometers are also used in the industry.
Vibration viscometers operate on the principle of measuring the frequency or amplitude of forced oscillations of a body of a certain volume and mass placed in the analyzed medium, which is a function of viscosity. Depending on the frequency of oscillations, vibration viscometers are divided into low-frequency (up to 1 kHz) and ultrasonic (from 10 to 1000 kHz).
The scope of application of vibration viscometers is limited to Newtonian liquids, the viscosity of which does not depend on the intensity of mechanical stress.
Acoustic viscometers are divided into two groups: those that use the dependence of the ultrasonic propagation speed on the viscosity of the liquid and those that use the dependence of the ultrasonic attenuation on the viscosity of the liquid. They allow measuring viscosity in a wide range with an error of ±4%. However, design, circuitry, and operational issues have hindered their use in the food industry. Well, now you can create your own blog.
