Cannon CT-500, Instruction & Operation Manual

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CANNON Instrument Company | Appendix IV - Thermometry for the CT-500 39
Appendix IV - Thermometry for the CT-500
Kinematic Viscosity and Temperature
Kinematic viscosity is an extremely temperature-sensitive measurement - a change of 1 °C can
sometimes lead to a viscosity change of 10 percent or more. Therefore, it is not surprising that
temperature measurement and control are the most common problems encountered by laboratories
performing accurate kinematic viscosity measurements.
Although capillary viscometers typically measure kinematic viscosity with a precision of several tenths of
one percent, measurements accurate to within one tenth of one percent (0.1%) are possible. To achieve
this, temperatures must be measured with an accuracy of 0.01 °C, and be maintained within a range of
± 0.01°C.
Thermometers
All measurements should be made with the viscometer properly immersed in a liquid constant
temperature bath. Ideally, a high-quality standard platinum resistance thermometer with a precision
bridge should be used to determine the temperature of the bath. Because many laboratories cannot
justify the cost of such a thermometer, Cannon Instrument Company recommends the use of a
calibrated ASTM kinematic viscosity thermometer and can provide one if requested.
ASTM Thermometers
Each ASTM kinematic viscosity thermometer measures only 3 degrees on a scale subdivided into 0.05 °C
units (equivalent thermometers are available with Fahrenheit scales). These thermometers contain an
ice-point scale which allows recalibration by determining the ice-point temperature.
Thermometer Calibration
Calibration of the thermometer is very important. Often the true temperature of a liquid differs
markedly from that shown on the thermometer scale. It is not uncommon for kinematic viscosity
thermometers to give readings varying as much as 0.1 °C from the actual temperature. The true liquid
temperature is obtained by applying the proper correction (as noted on the original calibration
certificate) to the reading showing on the thermometer scale and including any difference obtained in a
recent ice-point measurement of your thermometer.