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It's All About Temperature Compensation
Temperature is one of the single most important factors influencing accurate refractometer readings and is one of the largest sources of error in measurement.
Refractive index is VERY dependent on temperature. It is well known that substantially all materials expand when heated (become less dense) and contract when cooled (become more dense). The speed of light in a liquid increases with temperature and the refractive index therefore decreases.
The amount of error per degree Celsius is different for every fluid and differs for different concentrations of the same fluid.
Temperature compensation relieves the user of the responsibility to measure temperature and apply a correction factor when taking readings.
Temperature Compensation Makes The Difference!
The chart above compares a temperature compensated MISCO Refractometer (red) to a non-compensated competitor (blue). It is plain to see that at 20 degrees C (68 degrees F) they are both correct, however as the temperature deviates from 20 degrees there is a marked error in the non-compensated instrument.
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