The accuracy of the Brookfield CAP Viscometer is based on two independent factors. The first factor is the accuracy of the instrument and the second factor is the accuracy of the calibration solution. Total accuracy is instrument accuracy plus fluid accuracy.
Instrument accuracy is determined by referring to Table 3.1 in the CAP Viscometer Manual. The operator needs to determine whether the instrument is a high temperature or low temperature CAP, and whether it is a 1000 or 2000 model. When this information is cross-referenced using the tapered axis numbers, they will determine the numbers on the chart. This number is the percentage of full scale range that needs to be considered as instrument accuracy.
Example: CAP 1000H, tapered spindle 3 at 900 rpm.
The operator needs to first determine the full-scale range of the CAP for these conditions. Press the RPM button and the display will show 100% = X, where X is the Poise value of the full scale range. Under these conditions, the FSR is 8.333 Poise. From Table 3.1, the calculated accuracy FSR percent is 2 or 4 percent, depending on whether the calibration fluid is greater or less than 50 percent of the FSR.
If our calibration fluid is 4 poise, we calculate the accuracy as 2% of FSR, or 2% of 8.333. The instrument precision is thus .1666, which rounds to .17 Poise. Fluid accuracy is 1% of 4 poise or .04 poise. So the total accuracy is .04 + .17, or .21 Poise.
