8.5.2 Overall Response Time and Safety (Minimum) Distance
The cascaded system’s Overall Response Time (Tr) is equal to the response time of the individual sensor pair with the most
beams (the slowest individual response time), plus an adder resulting from the number of systems in the cascade. Tr can be
found by the following formula:
Tr = Tr
(max)
+ [(N-1) × 2 ms]
where:
Tr
(max)
is the response time of the slowest individual pair in the cascade (the pair with the most beams; see
on page 12).
N is the number of sensor pairs in the cascade.
Use Tr value from the formula in
Calculating the Safety Distance (Minimum Distance)
on page 19 to determine Overall
Safety Distance (Ds). This will ensure that all sensor pairs will be located at an adequate distance from the hazard, no matter
how the system is installed.
When contacts, for example, an E-stop button, are connected to a cascaded receiver, the CSSI response time is 40 ms plus
the 2 ms adder for each additional light screen, similar to the defined area Tr.
Tr
(CSSI)
= 40 ms + [(N-1) × 2 ms]
8.5.3 Cascade Configuration vs. Response Time
When light screens of different lengths or different resolutions (and therefore different response times) are used in one
circuit, their positions in the cascade may become a consideration.
For example, consider the light screen circuits shown. Each example contains three safety light screens, one 1200 mm (with
a response time of 40 ms), and two 300 mm light screens (15 ms response each). Depending on their placement in the
cascade, the individual response time for the same three light screens can vary from 40 to 44 ms.
EZ-SCREEN
®
14/30 mm Safety Light Screen
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