Honeywell SYA14 Series Manual page 60

The cross monitoring of the FF-SYA static outputs does not allow to connect two receivers
in series on a single FF-SRS5939 safety control module. Indeed this will be detected by
the units as a short-circuit between the outputs. Use in this case two FF-SRS5939 as
shown below.
Figure 4-11 Connection of two safety light curtains (using two FF-SRS5939 safety
control modules)
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107031-23 EN FR26 GLO 1199 Printed in France