The mathematical relationship is based on the ASTM standard D341 and is accurate for liquid hydrocarbons and most other fluids. Temperature Compensated Viscosity (TCV) is a very accurate estimate of the viscosity of a fluid at a reference temperature that is different from the actual process temperature. What is Temperature Compensated Viscosity (TCV)? By using the ASTM temperature compensation techniques incorporated in many of our viscometers, the effects of temperature fluctuations and differences can be mitigated. In order to maintain consistency with historical data, we are sometimes asked if the in-line value could be calibrated to match the lab values adjusting for all of the process and temperature differences. Therefore the in-line instrument and the lab obtain different results because the fluid is in fact different. Any difference may cause the in-line measurement to differ from the sample taken to the lab In a flowing line it is often difficult to be sure that sample passing over the sensor is exactly the same as sample drawn from a sample port. Measurement conditions may vary from lab technician, especially with cups and capillary tubes. Measurement conditions are often consistent (experiencing the same levels of fluctuations in the process, measurement to measurement) Measurement is made at a different temperature than the process is running, and it is usually constant, ![]() Processes are frequently closed systems after the addition of the basic ingredients, water/solvents, surfactants, etc.įluid is exposed to air which changes its composition through off-gassing or other interactionsįrequently process temperatures are elevated, and often fluctuating Uncontrolled Shear from pumps and pipe bends Table: Comparison of characteristics that affect in-line and in-lab fluid measurements Characteristic Here are some of the characteristics that can affect the readings between in-lab and in-line measurements. Unfortunately, process fluids are typically not calibration fluids and are affected by the characteristics of the process itself. In such a test, both instruments should yield the same result. Specifically, by removing the process instrument from the line and testing it with calibration fluid, it can be compared to the result from a lab instrument using the same fluid. In all cases the factory calibration sheets supplied with each instrument shows the instrument maintains its specified accuracy (1% of the full scale value for the VISCOpro 2000, for instance).Ĭalibration fluids can be used to evaluate process measurements. We note the particular fluids used, their traceability and the results of the calibration. All Cambridge instruments are factory calibrated with these traceable standards, and the calibration is certified. The calibration fluids Cambridge uses have known characteristics that are documented and tied to traceable standards. ![]() This is demonstrated by using calibration fluids. What are the reasons lab measurements can differ from in-line process measurements?Ī major reason is the fluids are in fact different under different conditions. How is the viscosity of oil determined?.What is the relationship between viscosity and temperature?.Is it possible to determine gas viscosity?.What is the difference between absolute or dynamic viscosity and kinematic viscosity?.What is Temperature Compensated Viscosity (TCV)?.What are the reasons lab measurements can differ from in-line process measurements?.
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