Cannon Instrument CMRV-5000 - Manual (Page 41)

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CANNON ® Mini-Rotary Viscometer CMRV-5000 Instruction & Operation Manual
Version 1.0b—August, 2011; CANNON ® Instrument Company
2139 High Tech Road • State College, PA • 16803 • USA
CHAPTER
8
CALIBRATING THE
CMRV CELLS
Initial calibration
To ensure the accuracy of sample data, the CMRV-5000 cell calibration
procedure must be completed after initial installation of the software.
First complete the temperature probe calibration (see previous chapter)
and instrument preparation (Chapter 6). Then follow the procedure in
this chapter to calibrate the CMRV cells.
Frequency After the initial calibration, CANNON ® recommends that the cells be
calibrated every 4-8 weeks at the discretion of the user. Note that some
ASTM methods may require multiple calibrations prior to sample
testing. These ASTM temperature profiles (see next chapter) will not
appear in the drop-down list of Temperature Profile software options
until all calibration(s) required by the method is/are performed.
Calibration theory
Each of the viscometric cells must be calibrated to determine the rela-
tionship between viscosity, angular velocity of the rotor, and the applied
mass. The general calibration constant is determined from the following
equation:
where C' = general calibration constant, millipascals (mPa)
r = number of full revolutions
η = known viscosity of calibration oil at the calibration
temperature in centipoise (cP)
(1 centipoise = 1 millipascal second (mPa·s (cP))
M = applied mass, grams (g)
m = mechanical friction of bearings, grams (g)
t' = time for r revolutions in seconds (s)
When this test is run according to the applicable ASTM procedures, m is
negligible relative to M, r = 3, and M = 150. Thus, for convenience, the
calibration equation can be simplified as follows:
where C = calibration constant for a specific cell for 3 revolutions
at a mass of 150 g (mPa)
η = viscosity of the calibration standard (cP)
t
3r
= time for 3 revolutions of the rotor (sec)