Mantis 5000 Especificaciones descargar pdf (Pagina 38)

Alignment

Upon first time use, the sample holder should be loaded into the centre-mount port and

checked for proper angle alignment to the sample beam, the beam should strike at normal

incidence when the dial is set at 0°. If it does not, rotate the knob until the angle is normal

to the sample beam, loosen the four screws along the perimeter of the dial and rotate the

dial so it reads 0°.

The reflecting surface of the standard should be the same angle of incidence as the

intended sample. When properly aligned, the 0° dial reading on both clip style and jaw

style sample holders holds the sample for normal incidence where the reflecting surface

is perpendicular to the path of the sample beam.

Ideally, the beam geometry for a reflectance accessory should be optimized for the

application concerned. For centre-mount applications, the ideal configuration has the

sample beam focused on the front surface of the sample at the centre of the sphere. In

general, the maximum dimensions of a centre-mounted sample is proportional to the size

of the integrating sphere. It should be obvious that the smaller the sample, the more

accurate the reflectance measurements - as long as the sample beam does not overfill the

surface area of the sample. For measurements with an Edwards sphere, ASTM E 903

recommends limiting specimen size to one percent of the surface area of the sphere.

Thus, for a 150 mm diameter integrating sphere, the maximum specimen size is a total

surface area of approximately 700 mm

. Sample sizes exceeding the recommended

specimen dimensions may interfere with the radiance uniformity at the wall surface or

clip the reference beam inside the integrating sphere.

Centre-mount sample holders inflict further restrictions on reflectance samples. The DRA

accessories utilize a three position mirror to focus the sample beam at the transmission

port, sample reflectance port, or centre-mount positions, depending on the sphere

configuration. Mirror M3, however, is a concave mirror such that the spot produced by

the sample beam depends on the position of the mirror and the angle of incidence to the

sample. The spot size grows larger as the angle of incidence increases, to a point where

the spot may no longer fit on the sample surface. At near-normal angles, the specular

component of the reflected beam is rejected completely out the transmission port and is

not collected during the scan. Finally, the horizontal dimension of the sample or

reflectance standard may clip the reference beam at steep angles of incidence, thereby

placing premature limitations on reflectance measurements.

Loading a sample into the jaw style centre sample holder

Tighten the jaws using the thumbscrew. Do not overtighten the jaw mechanism as this

could damage the sample.

When loading a sample into the clip sample holder, the sample should be held perfectly

vertical by the clip with the plane of the reflecting surface along the centre of rotation of

the dial. The sample beam path will strike the sample at a point midway between the

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Mantis 5000 Especificaciones Pagina 38