Banner EZ-SCREEN Low-Profile Safety Light Curtain Systems - Manual (Page 62)

60
P/N 133487
Banner Engineering Corp. • Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
Overview
60
P/N 140044 rev. E
Banner Engineering Corp. • Minneapolis, U.S.A.
www.bannerengineering.com • Tel: 763.544.3164
EZ-SCREEN LP
Instruction Manual
Cascadeable EZ-SCREEN
Individual Response Time and Safety (Minimum) Distance
When calculating individual safety (minimum) distance for each
emitter/receiver pair, the pair’s position in the cascade impacts
its response time, which then impacts its safety distance (see
safety distance formulas in Section 3.1.1). The “individual”
method results in the closest possible safety distance for each
light screen in the cascade, while ensuring that each sensor pair
is located at an adequate distance from the hazard.
Response time depends on how far “downstream” the light
screen is from the machine control. Each light screen position in
the cascade, starting from the first light screen in the cascade,
increases the light screen’s response time by 2 ms.
Figure 7-5 depicts a four-pair cascade. The 25 mm resolution,
550 mm EZ-SCREEN LP emitter/receiver pairs each begin with
a response time of 11 ms. The pair in position #1 (connected
directly to the machine control), maintains its 11 ms response
time. Response time for the second pair in the cascade circuit
increases by 2 ms, to 13 ms; for the third pair by 4 ms, to 15
ms, and for the fourth pair by 6 ms, to 17 ms. To calculate
response time (Tr) for individual placement of each emitter/
receiver pair in the cascaded system use the formulas:
Position #1: Tr
(cascade1)
= Tr*
Position #2: Tr
(cascade2)
= Tr + 2 ms
Position #3: Tr
(cascade3)
= Tr + 4 ms
Position #4: Tr
(cascade4)
= Tr + 6 ms
*See Sections 7.2 and 7.3 for listed response times.
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 (i.e., 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) x 2 ms]
where:
Tr
(max)
is the response time of the slowest individual pair in the
cascade (i.e., the pair with the most beams; see Section 7.2).
N is the number of sensor pairs in the cascade.
Use this Tr value in the formula in Section 3.1.1 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 (e.g., an E-stop button) are connected to a
cascaded receiver (per Section 7.8), 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) x 2 ms]
Figure 7-5. Calculating the individual response times of four
cascaded safety light screens, each 550 mm long, with
25 mm resolution
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 depicted in
Figure 7-6. Each example contains three safety light screens,
one 1810 mm long (with a response time of 43.5 ms), and two
410 mm long (13.5 ms response each). Depending on their
placement in the cascade, the individual response time for the
same three light screens can vary.
Simplified Method for Determining Response Time
If the safety distance does not need to be optimized (at a
minimum), simply add 6 ms to the response time of the receiver
with the greatest number of beams (worst case Tr), and use that
number as the overall response time. The 6 ms adder increases
safety distance a total of 10 mm (0.4") when using 1600 mm/s for
the hand speed constant K (see Section 3.1.1).
Tr = Tr
(max)
+ 6 ms
EZ-SCREEN LP
Position #3
11 + 2 + 2 = 15
15 ms Response
Emitters Receivers
EZ-SCREEN LP
Position #4
11 + 2 + 2 + 2 = 17
17 ms Response
E-Stop (CSSI Input)
EZ-SCREEN LP
Position #2
11 + 2 = 13
13 ms Response
*Light screens of other lengths / resolutions will have different response times.
EZ-SCREEN LP
Position #1
11 ms Response
EZ-SCREEN LP Cascade Overall System Response (for system as shown)*
11 + [(4 – 1) × 2 ms]
11 + 6
17 ms response
Machine
Control
CSSI Response Time = 40 ms + [(4 – 1) × 2 ms]
= 46 ms