52 Chadwick-Helmuth Company, Inc.
Chapter 4 - Installation
4.4.2.1 Retro-Reflective Target
Keep the following important characteristics of target reflection in mind,
when using the photocell:
• Chadwick-Helmuth recommends using the retro-reflective target
supplied in the kit, with the photocell. This retro-reflective target is
unique because it reflects light back to its illuminating source. On
close examination, the target consists of thousands of small glass
beads or prisms held on an adhesive backing held in place on the
rotating component with adhesive.
• The Chadwick-Helmuth targets are only retro-reflective if the glass
beads are left exposed. Coating the glass beads with any clear sealer
destroys the retro-reflective quality of the target.
• The user can use corner-cube retro-reflective tape. The user can
identify this type of tape by a chain-link pattern on the surface, and a
glossy surface finish.
• The use of reflective tapes is not recommended. Reflective tapes have
very narrow return angles and must be mounted in such a way that
allows the background reflection to adversely affect the gain of the
photocell.
• Other retro-reflective tapes are similarly not recommended unless
they are the same material as the Chadwick-Helmuth retro-reflective
targets.
• The glass bead density (which determines the percent of retro-
reflectiveness) of garden variety retro-reflective tapes (such as that
found on highway cones or survival jackets) is less than 50 percent of
our target in most cases. In most cases these tapes are inadequate as
retro-reflective targets for the photocell.
The correct size of the retro-reflective target depends on the distance
between the photocell and the reflective target, as well as the speed of the
retro-reflective target as it passes through the photocell beam.
The orientation of the photocell can also vary, depending on the size of
the target. A single strip of the Chadwick-Helmuth retro-reflective target,
aligned so it dwells in the photocell beam for the longest period of time, is
usually adequate. For details, see the diagram on page 56.
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