Direct Reading instruments only
The Direct Reading instruments have an integral L.E.D. (light emitting diode) light source for sample
illumination.
L.E.D. light source
L.E.D. arm adjustments
A dispersion drum is fitted to Direct Reading instruments to enable colours other than yellow
originating from the L.E.D (or more significantly, an alternative white light source) to be removed
from the field view. This will sharpen the borderline and allow accurate setting against the
crosswires.
High Accuracy instruments only
High Accuracy models are not fitted with an integral L.E.D. light source because a monochromatic
light source, such as a sodium lamp, is required to achieve the measurement precision.
A window and shutter are fitted in the lower prism box, which allows the instrument to be
alternatively used in reflection, rather than transmission, mode. This is useful when reading dark
samples. (See page 3-4 for more details)
Lower prism box window
Lower prism box window shutter
•
Turn the knob anticlockwise to close the shutter for transmission measurements
•
Turn the knob clockwise to open the shutter for reflection measurements
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