ASTM D2162 Test Method for Basic Calibration of Master Viscometers and Viscosity Oil Standards
8. Calibration of Master Viscometers with Water at 20°C
8.1 Maintain the water bath at 20 +/- 0.01°C applying the necessary thermometer corrections. Two check thermometers are recommended to detect any change in calibration.
8.2 Clean a master viscometer having a calibration constant of 0.001 to 0.003 mm2/s2 (cSt/s) with chromic acid cleaning solution to remove organic deposits, rinse thoroughly with distilled water and acetone and dry with a stream of filtered air.
8.3 Clean a 50-mL Erlenmeyer flask with cleaning solution and rinse thoroughly with distilled water. Add freshly distilled primary standard water and bring to a boil to remove dissolved gases. Cover the flask to prevent entrance of dust and allow to cool. If a Cannon master viscometer is being calibrated, cool the water to 20 +/- 3°C.
8.4 Charge the Cannon master as follows:
8.4.1 Connect a rubber tube to large arm J. Invert the viscometer and dip the end of small arm A into the beaker of water. Apply suction to arm J and draw liquid through bulbs B and D to etched line E. Turn the viscometer back to its normal vertical position, wipe tube A clean, insert the viscometer into a holder and place it in the constant temperature bath.
8.4.2 Support the master viscometer firmly and align it in a vertical position with the aid of a plumb bob with a length of about 560 mm. One can be made by use of a cork to fit the large tube J, a piece of thread, and an 18-mm length of 3-mm diameter solder lead. Remove the cork (or slot it) during the test so that no back pressure is developed.
8.5 Charge the Ubbelohde master as follows:
8.5.1 Tilt the instrument about 30° from the vertical with bulb A below the capillary and then introduce enough water into large arm 1 to bring the level up to the lower filling line. The level should not be above the upper filling line when the viscometer is returned to the vertical position and the liquid has been drained from tube 1. Charge the viscometer in such a manner that the U-tube at the bottom fills completely without trapping air.
8.5.2 Place the viscometer into a holder and place it in the constant temperature bath. Align the large tube 1 in a vertical position with a plumb bob as described for the Cannon master.
8.6 Allow the charged viscometer to stand in the bath long enough for the sample to reach bath temperature. Fifteen minutes are usually sufficient.
8.7 With gentle vacuum or pressure, force the liquid about 5 mm above the upper timing mark. Avoid splashing liquid in the upper bulb or forming any bubbles in the liquid. When using a Ubbelohde viscometer, hold a finger over the upper end of tube 3 during this operation; then remove it and immediately place it over tube 2 until the liquid drops away from the lower end of the capillary.
8.8 Measure the efflux of water from upper to lower timing mark (which should be 300 s or more) to the nearest 0.1 s. Repeat this measurement two additional times and average if the lowest and highest times agree within 0.1 %. If the measurements do not agree within this tolerance, repeat the procedure paying particular attention to cleaning the viscometer, filtering the sample, avoiding contamination during filling and afterwards, checking the temperature control and the timing device.
8.9 Clean the viscometer and dry with filtered air. Reload the viscometer and measure the efflux time in triplicate. Average if the lowest and highest times agree within 0.1 %.
8.10 If the two average times fall within 0.1 %, average the two to obtain an average of the two fills.
8.11 Calculate the viscometer constant as follows:
c = 1.0034/t
where:
c = calibration constant of the viscometer with water at 20°C, mm2/s 2(cSt/s), and
t = efflux time, s.
8.12 Repeat the operations described in 8.1-8.8 with a second master viscometer having a constant not greater than 0.003 mm2/s2 (cSt/s2).
NOTE 5 - Normally master viscometers are calibrated and used in the same location. If subsequently the viscometer is used at a laboratory other than the calibrating one, the c constant should be corrected for the difference in the acceleration of gravity, g at the two locations as follows:
c2 = (g2 / g) x c1
where:
c2 and g2 = calibration constant and gravity at the new locations, and
c1 and g1 = calibration constant and gravity at the original location.
Certificates for viscometers should state the value of g at the location of the calibrating laboratory. Failure to correct a viscometer constant for change of gravity can result in errors as high as 0.2 %, which is twice the error permitted between checks in this test method.
