Mantis 5000 Specifikace stáhnout pdf (Strana 8)

Sample recess

Theory assumes that the sample is placed coincident with the inside of the sphere wall,

however the sample is placed against the outside of the sphere wall. The porthole edges

have a finite thickness, and some part of the beam reflected at wide angles may be

intercepted by the sphere wall.

Figure 6: Some of the wide-angle reflection is intercepted by the sphere wall

The edges of the reflectance port are feathered to reduce this error.

Reference beam attenuation

Reference beam attenuation is most useful when the accessory or sample in the sample

beam attenuates the light beam considerably. In such situations, attenuation of the

reference beam will increase noise and considerably increase the dynamic range of the

instrument, as the detector is not then ’seeing’ two dramatically different signals. Clips are

provided at the reference beam window for this purpose. Metallic mesh screens are

recommended if reference beam attenuation is required (part number: 0110677500).

Stray light

If the irradiating beam overfills the reflectance port, a proportion of sphere wall

reflectance is mixed with that of the sample. This gives a high reading if this is not

consistent between the baseline and the sample measurement.

Gloss trap error

Gloss trap error is produced when the gloss trap is unable to completely absorb the

specular component. In the measurement of diffuse-only reflectance, a ’gloss trap’ is often

used to absorb the specular component. Gloss traps are typically glossy black pyramidal

light traps, matt black-coated cavities, or razor blade Fresnel light traps. However, the

reflectance of many samples has broadened the specular peaks which cannot be excluded

by standard sized light traps.

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Mantis 5000 Specifikace Strana 8