ifm
System Manual
ecomat
mobile
SmartController (CR2500) V05
Glossary of Terms
283
Demand rate rd
The demand rate r
d
is the frequency of
demands to a safety-related reaction of an
SRP/CS per time unit.
Diagnostic coverage
D
iagnostic
C
overage
Diagnostic coverage is the measure of the
effectiveness of diagnostics as the ratio
between the failure rate of detected dangerous
failures and the failure rate of total dangerous
failures:
Formula: DC = failure rate detected dangerous failures /
total dangerous failures
Designation
Range
none
DC < 60 %
low
60 % < DC < 90 %
medium
90 % < DC < 99 %
high
99 % < DC
Table: Diagnostic coverage DC
An accuracy of 5 % is assumed for the limit
values shown in the table.
Diagnostic coverage can be determined for the
whole safety-related system or for only parts of
the safety-related system.
Dither
Dither is a component of the PWM signals to
control hydraulic valves. It has shown for
electromagnetic drives of hydraulic valves that
it is much easier for controlling the valves if the
control signal (PWM pulse) is superimposed by
a certain frequency of the PWM frequency.
This dither frequency must be an integer part
of the PWM frequency.
→
chapter What is the dither? (
→
page
)
Diversity
In technology diversity is a strategy to increase
failure safety.
The systems are designed redundantly,
however different implementations are used
intentionally and not any individual systems of
the same design. It is assumed that systems of
the same performance, however of different
implementation, are sensitive or insensitive to
different interference and will therefore not fail
simultaneously.
The actual implementation may vary according
to the application and the requested safety:
•
use of components of several
manufacturers,
•
use of different protocols to control
devices,
•
use of totally different technologies, for
example an electrical and a pneumatic
controller,
•
use of different measuring methods
(current, voltage),
•
two channels with reverse value
progression:
channel A: 0...100 %
channel B: 100...0 %
E
EDS-file
EDS =
E
lectronic
D
ata
S
heet, e.g. for:
•
File for the object directory in the master
•
CANopen device descriptions
Via EDS devices and programs can exchange
their specifications and consider them in a
simplified way.
Embedded software
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.
EMCY
abbreviation for emergency
EMV
EMC =
E
lectro
M
agnetic
C
ompatibility
According to the EC directive (2004/108/EEC)
concerning electromagnetic compatibility (in
short EMC directive) requirements are made
for electrical and electronic apparatus,
equipment, systems or components to operate
satisfactorily in the existing electromagnetic
