Siemens SIMATIC S7 Functional Safety Manual page 203

PFD_avg
Average probability of a dangerous failure on demand (PFD_avg). An estimate of how likely
a safety function will fail to perform as expected when required to function only rarely (on
demand). PFD is typically used for safety function applications that are required to operate in
response to unusual accidental or emergency events occurring less frequently than once per
year.
PFH
Average frequency of a dangerous failure per hour (PFH). The average frequency of
dangerous failures for systems that are required more frequently than once per year to
initiate or maintain a safe state. Most safety functions associated with routine machine
operation use PFH as a defining safety metric.
PL
Performance Level (PL) : Levels "a" through "e" are defined in EN ISO 13849, with level "e"
being the high level of safety performance. A higher PL is associated with a lower probability
of dangerous failure.
PM
In the context of the F-DQ DC output module, refers to the DC output point including a switch
to P and a switch to M. The typical application is for the load to be connected between the P
and M switches, sometimes called "PM mode".
Process value bit
The data bit accessible to the user program representing the process value. If an input
channel is passivated, the process value bit is set to "0". If an output channel is passivated,
the user program can set the process value bit to "1", but this is not effective at the SM
outputs.
PROFIsafe
A communication protocol providing for secure transport of safety information, including
provisions for sequence and time monitoring of messages.
PROFIsafe address
A unique identifier for every F-IO in a network including central F-IOs. The PROFIsafe
address consists of the F-source address and the F-destination address.
S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA
Glossary
203