HOW TO PERFORM A 2-POINT CALIBRATION VERIFICATION ON YOUR VISCOMETER/RHEOMETER

Procedure for using regular spindles LV1-LV4, RV1-RV7, HA1-HA7 and HB1-HB7; if you use any other spindles and/or accessories, or if you have a special viscometer/rheometer, please contact us.

Note: You cannot calibrate your viscometer as there is no external provision for this, e.g. you cannot adjust the span or zero; you can only verify the calibration.

What you need:

• the to-be-checked viscometer
• the viscometer's guardleg (see NOTE below)
• a constant temperature bath
• one suitable Brookfield Standard Fluid
• a 600 ml Low Form Griffin beaker (see NOTE below)

  NOTE: if the Brookfield Standard Fluid value is greater than 20,000 cps, the guardleg is not necessary for models LV and RV, and the original viscosity standard fluid container can be used.

What to do:

• pour the Brookfield Standard Fluid into the Griffin beaker (see the above NOTE) and put the beaker in the bath;
• mount the viscometer on its stand beside the bath and level it; if it is a digital, turn it on, autozero it and input the spindle code;
• attach the spindle you intend to use and, if it's the case, the guardleg;
• immerse to the appropriate depth the spindle + guardleg into the Brookfield Standard Fluid;
• re-level the viscometer;
• turn the bath on and set it up to 25 degrees Celsius then wait for at least 30 min (1 hour recommended) for the Brookfield Standard Fluid temperature to stabilize;
• before taking a reading, recheck the viscometer leveling and adjust if necessary;
• turn the viscometer on (dial) or the motor on (digital) and take a high-torque % reading after at least 4 spindle rotations; log reading details: speed, spindle, torque and viscosity;
• shift the speed down (typically half of the initial speed) and allow the spindle to rotate for a few minutes; take a lower-torque % reading and log it;
• calculate the accuracy ranges for both speeds - see below – and determine if the readings are within calculated ranges; yes means pass, no means fail.

Accuracy range calculation:

The total error is a combined error Standard Fluid - Viscometer. The accuracy for the Brookfield Standard Fluid is 1% of the actual viscosity value written on the jar . The accuracy for the Viscometer is 1% of the maximum range in use (note that is not 1% of the reading!).

During the Calibration Verification, watch for:

• air bubbles in the Brookfield Standard Fluid; they increase the reading, so wait for them to clear;
• vibrations: if the temperature bath transmits considerable vibrations to the viscometer, turn the bath off before turning the viscometer/motor on;
• an as-high-as-possible torque percentage for the first calibration point reading (corresponding to the first speed): the higher the value (75% and up) the better the accuracy.

If the instrument appears to be out of calibration:

• check if the temperature bath fluid is indeed 25 ˚C +/- 0.1 ˚C (use a certified thermometer);
• be sure you waited enough to allow the viscosity standard fluid temperature to stabilize;
• be sure you use the guardleg for LV and RV units, when fluid value isn't greater than 20,000cps: not using it can cause an up to 20% lower reading!
• be sure the viscometer is leveled properly;
• be sure the spindle and guardleg sit approximately in the middle of the beaker or the guardleg does not touch the beaker's sides or bottom;
• if using the RV spindle #1 (bell shaped) or RV #2 (disc) check if there are air bubbles trapped under the bell/disc;
• if using a dial viscometer or the old digital model DV-I be sure you use the correct spindle factor;
• if using a digital viscometer (except the old DV-I) check if you introduced the correct spindle code;
• if using a digital viscometer, be sure you did not autozero with the spindle attached or, worse, with it immersed into the Brookfield Standard Fluid;
• be sure the accuracy range calculation was done correctly.