The working principle and usage of a sugar meter
The working principle of a sugar meter
When light enters one medium from another, it undergoes refraction, and the ratio of the incident angle sine is constant, which is called the refractive index. The content of soluble solids in fruit and vegetable juices is directly proportional to the refractive index under certain conditions (at the same temperature and pressure). Therefore, measuring the refractive index of fruit and vegetable juices can determine the concentration (sugar content) of the juice. The commonly used instruments are handheld refractometers, also known as sugar mirrors or handheld sugar meters. By measuring the soluble solid content (sugar content) of fruits and vegetables, the quality of fruits and vegetables can be understood, and the maturity of fruits can be estimated approximately.
Instructions for using handheld sugar refractometer
（1） Usage
Open the cover and carefully wipe off the inspection prism with a soft cloth. Take a few drops of the solution to be tested and place it on the testing prism. Gently close the cover to avoid bubbles and spread the solution over the surface of the prism. Align the instrument's light inlet plate with the light source or bright spot, observe the field of view through the eyepiece, and rotate the eyepiece to adjust the handwheel to make the blue white boundary of the field of view clear. The scale value of the boundary is the concentration of the solution.
（2） Correction and temperature correction
The instrument needs to calibrate the zero point before measurement. Take a few drops of distilled water and place them on the detection prism. Turn the zero adjustment screw to adjust the dividing line to 0% of the scale. Then wipe off the testing prism for testing. Some models of instruments require the preparation of standard solutions to replace distilled water during calibration.
Another method is (only suitable for measuring sugar content): use a temperature correction table to add (or subtract) the temperature correction value read at ambient temperature to obtain accurate values.
（3） Precautions
The instrument is a precision optical instrument, and the following precautions should be taken during use and maintenance:
1. During use, it is necessary to be careful and follow the instructions strictly. It is not allowed to loosen the connecting parts of the instrument, drop or collide, and violent vibration is strictly prohibited.
2. After use, it is strictly prohibited to directly put it into water for cleaning. A clean and soft cloth should be used to wipe it. For optical surfaces, they should not be bumped or scratched.
3. The instrument should be stored in a dry and corrosion-free place.
4. Avoid losing spare parts.
