ASTM D3829 Predicting the Borderline Pumping Temperature of Engine Oil
9. Calibration and Standardization
9.1 Temperature Control Calibration Procedure - Calibrate the MRV temperature control by comparing the instruments displayed temperature against a thermometer in the thermowell. The thermometer used shall meet the requirements in 6.3.
9.1.1 Place 10 mL of a typical test fluid and rotor in each cell. If required, place cell caps over each cell then place cover on instrument. Cell caps shall not be used on direct refrigeration instruments (see 6.5.1).
9.1.2 Place the thermometer in the thermowell. See Note 5. This thermowell is to be used for all temperature measurements below 25 °C.
NOTE 5 - Prior to inserting the thermometer or DCT probe in the thermowell, place several drops (~3) of a heat transfer fluid such as 50/50 water/ethylene glycol mix, CCS reference oil CL100 or a dewaxed low viscosity mineral oil in the thermowell.
9.1.3 Make the temperature measurements at 80 °C then at least three measurements that are 5 °C apart from -5 °C to the lowest test temperature used including both end points to establish a calibration curve for this combination of thermometer and the instrument's temperature control. Make at least two temperature measurements at every calibration temperature with at least 10 min between observations.
NOTE 6 - All temperatures in this test method refer to the actual temperature and not necessarily the indicated temperature.
9.1.4 Follow the instrument manufacturers instructions for correcting the instrument's measured temperature. Alternatively, establish a correction equation between thermometer and instrument's measured temperature then adjust each temperature of the cooling program by the offset determined with the correction equation.
9.2 Viscometer Cell Calibration - The calibration constant of each rotor/stator combination is determined at -20 °C using a viscometric standard as a test sample.
9.2.1 The same 150 g mass is normally used for both calibration and viscosity measurements. However, different weights may be used for calibration and viscosity measurements provided they are certified to be 150 g ± 0.1 g.
9.3 Following the steps in 10.1, prepare the cells for calibration using the calibration oil as the sample.
9.4 Use the calibration temperature profile or the cooling program for -20 °C test temperature, follow the owner's manual instructions for the instrument to initiate the cooling profile program.
9.5 Place the thermometer in the thermowell at least 30 min prior to executing 9.7. See Note 5. The thermowell location is to be used for calibration and temperature monitoring during the test procedure.
9.6 At the completion of the temperature profile, check that the final test temperature is at the desired calibration temperature within ±0.1 °C. Final test temperature is to be verified independently of the instrument's temperature control with a thermometer that has been in the thermometer well for at least the time proscribed in 9.5. See Note 5.
9.7 Beginning with the cell farthest to the left facing the instrument, perform the steps in 10.6.3.
9.8 Repeat 9.7 for each of the remaining cells in numerical order.
9.9 Calculate the viscometer constant for each cell (rotor/stator combination) using Eq 8:
C = η0/t
where:
η0 = viscosity of the standard oil, mPa•s at -20 °C,
C = cell constant for an applied mass of 150 g, mPa, and
t = time in seconds for three revolutions.
9.10 If corrected values for the instrument's temperature control and thermometer deviate by more than the tolerance (±0.1 °C), use the procedure in X2.1 to assist in determining the cause and correction.
