Pilz PSS SB FT, Basic license - Manual (Page 96)

6-52 Modular Block System: Burner Management
Standard Function Blocks
Timing diagrams
Valve closed without power
It is established which valve position is active on de-energising.
An inverted operating mode can be achieved by changing inputs
Dir1 and
Dir2, but the block's function mode remains unchanged.
Dir1 = 1 drives the block and the VAV output to a safe state. This safe
state can, depending on the type of the valve, be the closed or the open
valve position. It is the responsibility of the user to take the type of valve
into consideration and make changes accordingly.
To avoid any misunderstanding, the illustrations and descriptions for the
I/Os in the following function diagrams are defined as such:
• Dir1 = 1: drive command for the valve to close
• Dir2 = 1: drive command for the valve to open
• Pos1 = 1: acknowledgement feedback: valve closed
• Pos2 = 1: acknowledgement feedback: valve open
• VAV = 1: valve open
A pulse at Dir2 sets the VAV output, and the valve
opens.
A pulse at the Dir1 resets the VAV output, and the valve
closes (closed without power). The acknowledgements
from Pos1/Pos2 follow the OPEN/CLOSE commands,
but are delayed.
SB154