Siemens S7-300 - Applications 1 to 4

Digital modules
8.7 SM 326; F-DO 10 x DC 24V/2A PP (6ES7326-2BF10-0AB0)
Fail-safe signal modules
166 Installation and Operating Manual, 01/2010, A5E00085586-10
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Figure 8-56 Dark test
The typical break between two test pulses is 0.5 seconds. There can be another test pulse
① in between. The gap between the first test pulse and the additional test pulse is one
module cycle.
With redundant interconnection, both modules conduct the light and dark test in an
asynchronous manner. This can result in an overlap of the test pulses.
Avoiding dark periods when operating in safety mode
N
ote
If you are using actuators that respond too fast (i.e. < 1 ms) to "dark period" test signals, you
can nonetheless use the internal test coordination by wiring two opposite outputs (with
assigned redundancy) in parallel using a series diode. Parallel wiring suppresses the dark
periods. For more information, refer to the chapter "Application 5.1: Wiring two outputs in
parall
el for dark period suppression (Page 169)".
8.7.3 Applications 1 to 4
Applications 1 and 2 are omitted because the module supports only safety mode.
Applications 3 and 4 are omitted because the module supports SIL3/Cat.4/PLe.