Piston Viscometers

Piston viscometers and falling ball viscometers move or drop a piston or ball 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 electromagnetic piston viscometers analyzes the piston's two-way travel time to provide a measure of absolute viscosity. Electromagnetically-driven piston viscometers are suitable for in-line viscosity tracking because the piston motion also provides fresh samples and mechanically scrubs the sampling area..

In the less sophisticated falling ball visometers 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 an indication of viscosity. Typically, falling ball viscometers are laboratory bench instruments and are suited to in-line operation.