System  Concept for HIQuad X 
HI 803 211 E Rev. 1.01.00  Page 15 of 110 
3.2.1  The H51X Mono System 
Thanks to the use of safety-related modules (I/O modules, the I/O processing module and a 
processor module), the HIQuad H51X system can ensure safety-related signal processing in 
accordance with SIL 3 already when operating in a mono structure, see Figure 2. 
Figure 2:  Example of Safe H51X Mono Operation (1oo2) 
The input modules of the HIQuad H51X system safely record the values measured by sensors. 
Data is exchanged with the processor module via the I/O processing module. The measured 
values are cyclically queried by the processor module and processed by the user program. The 
user program's results are sent to the I/O processing module, which writes them to the output 
modules. The output modules thus control the field level, e.g., the actuators. 
During mono operation, the signal is forwarded by the processor module in slot 8 via system 
bus A. 
Figure 3 shows the example of an H51X mono system with system bus A. Up to 16 extension 
racks can be connected to the system bus in any UP loop, DOWN loop, or UP and DOWN loop. 
The extension racks are interconnected with system bus A via the I/O processing module, see 
the F-IOP 01 manual (HI 803 219 E). 
If the system bus connection is interrupted in a mono system, all I/O modules located after the 
interruption point are no longer available. After the interruption point, all output modules enter 
the safety-related, de-energized state. As for the input modules, the failsafe initial values are 
processed in the respective processor module.