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[[File:Viscosity Process Analyzers.jpg|thumb|right|Viscosity Process Analyzers]] | |||
In the '''Viscosity Process Analyzers''' , a capillary type of viscosimeter with external pressure, the pressure drop resulting from a constant flow of a fluid through a capillary of constant dimension is measured as dynamic viscosity. The measurement is not absolute, i.e. the viscosity process analyzer has to be calibrated with two fluids of known viscosities. For a fluid of constant density the reading of the measured variable may also be interpreted as kinematic viscosity. Varying densities, however, would require measurement of the density for correction. | |||
The measuring principle is based on the Hagen-Poiseuille Equation. Continuous volume flow is forced and simultaneously measured by a pneumatically-driven metering cylinder ; piston speed is adjusted so that the differential pressure transmitter is always observed at a pre-selected point of its range . The entire analyzing procedure is microprocessor-controlled; this includes an automatic and continuous kinetic energy adjustment known as the Hagenbach Correction ; this also includes compensation for varying the piston speeds. C Temperature control of the oil filled bath is maintained within + 0,05° . Constant sample input temperature should be maintained. The inlet or outlet valves prior to the cylinder are routinely checked for tight closure . The analyzer cycle time depends on sample parameters .Repeatability and reproducibility are equal or better than the limits indicated in corresponding standards and norms. | |||