## How do I correct for temperature in a refractometer?

Refractometers measure correctly at + 20 °C. Many of our refractometers have an automatic temperature correction. Since the measured temperature strongly influences the results, refractometer results which are measured at another temperature must be corrected. The appropriate corrective data can be directly read on some of our refractometers on the prism cover. Depending upon the temperature, the corrective values must be either added to or subtracted from the results. No other corrective table is needed.

When looking through the eyepiece, one can see the boundary line when water cuts the scale at -1% Brix. A correction value of +1% when the prism cover is folded up.

The corrected measurement result is therefore -1% + 1% = 0.

A rule of thumb for temperature correction of refractometers with refractive index scales: Subtract 0.0001 to 0.0004 nD per °C with a device temperature of less than 20°, if the temperature is higher, add that number. Since the effect of temperature on the refractive index is different with every kind of medium, with very precise measurements, the appropriate exact correction value must be obtained from reference books and the like. This also applies for refractometers which are only outfitted with a thermometer.

Automatic temperature-correcting refractometers automatically perform the temperature correction (primarily between +10 and +30 °C).