Solutions to Sticky Problems" or by using the Auto Range button on your rheometer.
The Spindle Range Coefficient for the 21 spindle on an LV Torque instrument is 4,688.
At 6 RPM, the Full Scale Range (FSR) viscosity is 781 cP. Allow +/- 1% for the rheometer and +/- 1% for
the Small Sample Adapter. Total allowable accuracy is:
+/- 2% x 781 cP = +/- 15.6 cP
A similar calculation at 12 RPM gives FSR = 391 cP: +/- 2% x 391 cP = +/- 7.8 cP
A similar calculation at 30 RPM gives FSR = 156 cP: +/- 2% x 156 cP = +/- 3.1 cP
2) The Viscosity Standard Fluid is 101.5 cP. Its accuracy is:
+/- 1% x 101.5 cP = +/- 1.015 cP or roughly +/- 1.0 cP for further calculations.
3) Total accuracy is the sum of the values n (1) and (2):
At 6 RPM, accuracy is: 15.6 cP + 1.0 cP = +/- 16.6 cP
At 12 RPM, accuracy is: 7.8 cP + 1.0 cP = +/- 9.8 cP
At 30 RPM, accuracy is: 3.1 cP = 1.0 cP = +/- 4.1 cP
4) Therefore, at each speed, the acceptable windows within which the measured viscosity value must lie is calculated
relative to the viscosity value of the standard:
At 6 RPM: 84.9 cP to 118.1 cP
At 12 RPM: 91.7 cP to 111.3 cP
At 30 RPM: 97.4 cP to 105.6 cP
If your measured values fall outside of these windows, contact AMETEK Brookfield or your local
authorized dealer to discuss your results and determine whether your instrument is out of calibration.
M19-2101 REVISION 2.0
D V N E X T R H E O M E T E R - O P E R AT I O N A L M A N U A L
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