Dynamic viscosity is a measurement of a fluid's resistance to flow. Water is lower in viscosity than motor oil or honey. Oil is lower in viscosity than tar or molasses. Depending on the application method, viscosity determines how well a resin fills the cavities or voids in a mold.
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Kinematic viscosity is the time required for a fixed amount of fluid or oil to flow through a capillary tube under the force of gravity. Units of kinematic viscosity are stoke, centistoke (1/100 of a stoke), and Saybolt Universal Seconds (SUS).
Saybolt Universal Seconds or Saybolt Universal Viscosity (SUV) is the time in seconds required for 60 cubic centimeters of a fluid to flow through the orifice of a standard Saybolt universal viscometer at a given temperature under specified conditions, usually per ASTM D 88. Kinematic viscosity is also described as the quotient of the absolute viscosity in centipoises divided by the specific gravity of a fluid where both are measured at the same temperature.
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Accuracy is the degree of uncertainly which the measured value agrees with the ideal value. Accuracy is measured in a percentage of the full scale range of the instrument.
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Rotational viscometry refers to the torque required to rotate a spindle at constant speed, while immersed into the sample fluid. The torque is proportional to the viscous drag on the immersed spindle, and thus to the viscosity of the fluid.
Capillary viscometers measure the flow rate of a fixed volume of fluid through a small orifice at a controlled temperature. The rate of shear can be varied from near zero to 106 s-1 by changing capillary diameter and applied pressure. A specific volume of fluid passes through the orifice and the time it takes for the volume of fluid to pass through the orifice is proportional to the fluid viscosity. However, it also depends on the density of the fluid since the denser the fluid, the faster it will flow through the orifice. The property being measured in this example is then the kinematic viscosity and not the dynamic viscosity.
In piston or falling ball viscometers, a piston or ball is moved or dropped through the test liquid, which is contained in a precise and temperature controlled tube. Under constant applied force, the time required for the piston or ball to pass a specific length of the tube is proportional to the viscosity.
In electromagnetic piston viscometers, the piston is made of a ferromagnetic material, which is driven back and forth through the liquid with constant force applied by surrounding electromagnetic coils. Circuitry in the electromagnetic piston viscometer analyzes the piston's two-way travel time to provide a measure of absolute viscosity. Electromagnetically-driven piston viscometers are well suited to in-line viscosity tracking because the piston motion also provides fresh samples and mechanically scrubs the sampling area.
In the less sophisticated falling ball or falling piston viscometers, gravity provides the constant force to move the piston or ball. Switches are used to determine the time of travel and as an indication of viscosity. Falling ball viscometers are typically laboratory bench instruments and are not suited to in-line operation.
Other gravity or positive displacement methods, needle etc.
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Newtonian means it has a shear response linear with shear force. The relationship in which viscosity is a constant regardless of shear stress or rate of shear is called Newton's Viscosity Law. Many common solvents, mineral base oils, synthetic base fluids, and fully formulated single-grade oils obey Newton's Viscosity Law and are called Newtonian fluids.
Non-Newtonian fluids are a mixture of pigments, suspenders, polymers, solvents, etc. Each of these items by itself may or may not have Newtonian characteristics, but when combined they shear in unique, non-linear ways
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Hand held and portable instruments are typically used for laboratory, pilot facilities, product plants and field applications where their portability is a useful feature.
Process or in-line viscometers enable continuous monitoring of viscosity without disturbing the flow. Process mounted viscometers also eiliminate the need to extract samples of the process media. Allows for insertion/retraction without disturbing line flow. May also include "side stream", process mounted, on-line, and in-situ types.
Device is designed for laboratory use with fluid samples.
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The device is setup or programmed through the front panel using digital keypad, menus, etc.
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Special requirements such as modem, RF transmitter, etc.
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The device is able to record and store data within its own memory, without transferring it to a separate data recorder. The instrument may also have an integral recorder.
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Video display terminals (VDT) styles include CRT, flat panel displays, etc.
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Analog current is often called a transmitter. A current is imposed on the output circuit proportional to the measurement. Feedback is used to provide the appropriate current regardless of line noise, impedance, etc. Analog current is useful when sending signals over long distances.
A change is viscosity or rheology triggers a switch or relay output. The switch or relay output is used to activate an alarm, process controller, or process equipment when the viscosity falls above or below a specified value.
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This is the full required range of ambient operating temperature.
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