Applications 1 To 4 - Siemens S7-300 Installation And Operating Manual

Digital modules
8.7 SM 326; F-DO 10 x DC 24V/2A PP (6ES7326-2BF10-0AB0)
Figure 8-56
The typical break between two test pulses is 0.5 seconds. There can be another test pulse
①
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
Note
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
parallel 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.
166
Dark test
in between. The gap between the first test pulse and the additional test pulse is one
1
Installation and Operating Manual, 01/2010, A5E00085586-10
Fail-safe signal modules