differential stress refractometer
The LDSR Refractometer is designed
for the measurement of compression and tensional
stresses in commercial float, plate, and sheet glass. Stress measurements made with this
instrument are non-destructive and are limited to transparent flat glass.
The LDSR Refractometer consists of a total internal reflection prism, a calibrated
telescope, a light source and a mirror, all held securely in a metal housing. The prism is fabricated
from optical glass and finished to optical tolerances. It is used for measuring stress in glass
with refractive index in the range of 1.516 to 1.566. For glass out of this range of refractive
index, optional prisms covering other index ranges can be installed in the
The viewing portion of the
instrument is equipped with a reticle scale and a 10x filar micrometer eyepiece
with focusable eye lens. In use, a split image border will be observed in the
field of view. An incremental micrometer adjustment dial moves a fiducial hairline precisely one
reticle scale division for each complete turn of the drum. This gives an accurate
measurement of the split border observed in the eyepiece.
The light source is an incandescent lamp (battery included) which is controlled by a
split aperture. Light penetrates at the refracting entrance face of the prism.
Illumination is at the proper angle to insure total internal reflection in the prism.
Tables are supplied with the instrument to provide instant conversion from micrometer
eyepiece reading to stress values for plate, sheet, and float glass.
The LDSR instrument package includes: LDSR Refractometer, illuminator
carrying case, prism contact fluid, a calibration glass, and instruction manual
To measure the surface stress in
glass, light must first enter the glass, then emerge in a manner allowing measurement of
the birefringence in the glass surface. (Birefringence is the difference in refractive
index for light rays oscillating perpendicular and parallel to the plane of incidence.)
The measurement is accomplished thru the technique of total internal reflection
made possible by a prism that is placed in optical contact with the glass surface.
The magnitude of the surface
stress is directly proportional to the birefringence of the glass surface. This
relationship is expressed by the stress optic law, s = C(µ perp.- µ ||), where s is the
stress in the surface perpendicular to the plane of incidence, C is a stress-optic
coefficient, and µ perp. and µ || are the refractive indices for light vibrating
perpendicular and parallel, respectively, to the plane of incidence. C is a constant for
glass of a given composition.
differential stress refractometer
Sample Index Range:
Range, per supplied tables, for:
Glass 0-46,600 psi
Plate Glass 0-39,700 psi
Sheet Glass 0-52,200 psi
Width 57mm, Length 152 mm
volt Battery. Optional power supply with Input
110/120V, 220/240V and Output 3 to 9 volts (also available)
2 ounces provided
Index (25°C) = 1.527
This instrument is not capable of
determining whether or not glazing materials comply with a standard, nor is it capable of
accurately making measurements of the compressive stress in the surface layer of thermally
tempered glass below 10,000 PSI. Only recognized destructive testing should be used in
determining impact resistance, break characteristics, and whether or not thermally
tempered glass complies with standards such as, but not limited to, 16 CFR 1201, ANSI Z
97.1, ANSI Z 26.1, and the requirements of the Federal Railway Administration and Federal
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