Temperature Stability is Critical for ASTM D445 Kinematic Viscosity
Temperature control is the single most important parameter for obtaining accurate and precise kinematic viscosity measurements. For petroleum products even more so, as their rate of viscosity change per unit of temperature is significantly greater than other types of materials. Thus, a slight variation in temperature can have a very large effect on the viscosity of a fluid. the bath temperature for most high temperature measurements, 40 degrees C and 100 degrees C, must be controlled to within +/- 0.002 deg. C and for low temperatures, typically -20 deg. C and -40 deg. C, a stability of +/- 0.05 deg C is required. That is an extremely tight window and great care must be taken to achieve this control.
Lawler Model 86-20 High Temperature Viscosity Bath is designed with tight 0.02 degree temperature stability in mind. Instead of an open bath jar, an enclosed cabinet design is used to prevent room drafts from affecting temperature. And more importantly, a sophisticated process grade temperature controller is used with 0.01 degree resolution. It is the only one on the market used with such resolution. Other units use 0.1 degree resolution controllers which make it impossible to verify the 0.02 or even 0.05 degree stability requirement.
Lawler Model 70 Series Low Temperature Kinematic Viscosity Baths are similar and additionally are built with Lawler’s advanced refrigeration system to reach temperatures as low as -70 degrees C with +/-0.05 temperature stability or better.