ifm
System Manual
ecomat
mobile
PDM360NG (CR1080, CR1081, CR9042) Target V01
2011-07-28
Glossary of Terms
447
Failure, systematic
A systematic failure is a failure related in a
deterministic way (not coincidental) to a certain
cause. The systematic failure can only be
eliminated by a modification of the design or of
the manufacturing process, operational
procedures, documentation or other relevant
factors.
Corrective maintenance without modification of
the system will usually not eliminate the failure
cause.
Fault
A fault is the state of an item characterized by
the inability to perform the requested function,
excluding the inability during preventive
maintenance or other planned actions, or due
to lack of external resources.
A fault is often the result of a failure of the item
itself, but may exist without prior failure.
In ISO 13849-1 "fault" means "random fault".
Fault tolerance time
The max. time it may take between the
occurrence of a fault and the establishment of
the safe state in the application without having
to assume a danger for people.
The max. cycle time of the application program
(in the worst case 100 ms,
Watchdog
(
→
page
)) and the possible delay and
response times due to switching elements
have to be considered.
The resulting total time must be smaller than
the fault tolerance time of the application.
FiFo
FiFo (
F
irst
I
n,
F
irst
O
ut) = operation of the
stack: the data package which was written into
a stack at first will be read at first too. For
every identifier there is such one buffer (as a
queue) available.
Firmware
System software, basic program in the device,
virtually the operating system.
The firmware establishes the connection
between the hardware of the device and the
user software. This software is provided by the
manufacturer of the controller as a part of the
system and cannot be changed by the user.
First fault occurrence time
Time until the first failure of a safety element.
The operating system verifies the controller by
means of the internal monitoring and test
routines within a period of max. 30 s.
This "test cycle time" must be smaller than the
statistical first fault occurrence time for the
application.
Flash memory
Flash ROM (or flash EPROM or flash memory)
combines the advantages of semiconductor
memory and hard disks. Just like every other
semiconductor memory the flash memory does
not require moving parts. And the data is
maintained after switch-off, similar to a hard
disk.
The flash ROM evolved from the EEPROM
(
E
lectrical
E
rasable and
P
rogrammable
R
ead-
O
nly
M
emory). The storage function of data in
the flash ROM is identical to the EEPROM.
Similar to a hard disk, the data are however
written and deleted blockwise in data blocks up
to 64, 128, 256, 1024, ... bytes at the same
time.
Advantages of flash memories
The stored data are maintained even if
there is no supply voltage.
Due to the absence of moving parts, flash
is noiseless and insensitive to shocks and
magnetic fields.
In comparison to hard disks, flash
memories have a very short access time.
Read and write speed are virtually
constant across the entire memory area.
The memory size that can be obtained has
no upper limit, due to the simple and
space-saving arrangement of the storage
cells.
