ASTM D2162 Test Method for Basic Calibration of Master Viscometers and Viscosity Oil Standards
11. Calibration of Additional Master Viscometers and Viscosity Oil Standards at 40°C
11.1 Choose an oil with a kinematic viscosity of 6 to 10 mm2/s (cSt) at 40°C. Determine the average kinematic viscosity in the two calibrated master viscometers as directed in Sections 9 and 10.
11.2 Select a new, third master viscometer with a calibration constant in the 0.003 to 0.009-mm2/s2 (cSt/s) range. Determine its calibration constant using the 3 and 10-cSt (mm2/s2) kinematic viscosity oil standards following the procedure given in 9.1-9.6.
11.3 Calculate the calibration constant as follows:
11.3.1 For Cannon master viscometers:
C = v/[(1 + cb + cT + cs) + t]
where:
CT = calibration factor for water at 20°C, mm2/s2
v = kinematic viscosity of the oil standard mm2/s,
cb = buoyancy correction (10.1),
cT = temperature correction (10.2),
cs = surface tension correction (10.3), and
t = average efflux time, s.
11.3.2 For Ubbelohde master viscometers:
C = v/[(1 + cb) x t]
where:
C, v, cb, and t are as given in 11.3.1.
NOTE 10 - For consistency, all viscometer calibration factors are corrected back to water at 20°C. Corrections for other oils and temperatures are made from this standard condition. Calibration factors with oil at 40°C are used in routine calibration work.
11.4 Average the calibration factors found with the two oil standards if they agree within 0.1 %.
11.5 Continue to calibrate viscometers and viscosity oil standards in like manner using two or more viscosity oil standards to determine the factor of each viscometer and two viscometers to determine the kinematic viscosity of each oil standard.
11.6 Periodically clean all master viscometers with chromic acid cleaning solution to remove organic deposits.
