A refractometer is a hand-held optical instrument, which can be used to measure the mix concentration of metalworking fluids. The refractometer provides a numeric reading by measuring the refractive index of the fluid mix. This allows the operator to monitor the concentration of the metalworking fluid.
Calibration
Proper calibration of the refractometer is necessary to obtain an accurate refractive index measurement. Before calibrating the instrument, ensure that the temperatures of the refractometer, water and metalworking fluid sample are at ambient, as accurate calibration is temperature dependent. Proceed as follows:
Place a few drops of water between the plastic cover (6) and the prism (7). Hold the refractometer horizontally and point it at a light source. Look into the eyepiece (1) and adjust the scale calibrating knob (4) until the boundary line which separates the light and dark areas of the scale is aligned with the zero line on the scale. Figure 2 depicts a typical refractometer scale.