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ifm
System Manual
ecomat
mobile
PDM360NG (CR1080, CR1081, CR9042) Target V01
2011-07-28
Glossary of Terms
453
Process image
Process image is the status of the inputs and
outputs the PLC operates with within one
cycle.
At the beginning of the cycle the PLC
reads the conditions of all inputs into the
process image.
During the cycle the PLC cannot detect
changes to the inputs.
During the cycle the outputs are only
changed virtually (in the process image).
At the end of the cycle the PLC writes the
virtual output states to the real outputs.
Programming language, safety-
related
Only the following programming languages
shall be used for safety-related applications:
Limited variability language (LVL) that
provides the capability of combining
predefined, application-specific library
functions.
In CoDeSys these are LD (ladder diagram)
and FBD (function block diagram).
Full variability language (FVL) provides the
capability of implementing a wide variety of
functions.
These include e.g. C, C++, Assembler. In
CoDeSys it is ST (structured text).
►
Structured text is recommended
exclusively in separate, certified functions,
usually in embedded software.
►
In the "normal" application program only
LD and FBD should be used. The following
minimum requirements shall be met.
In general the following minimum requirements
are made on the safety-related application
software (SRASW):
►
Modular and clear structure of the
program. Consequence: simple testability.
►
Functions are represented in a
comprehensible manner:
- for the operator on the screen
(navigation)
- readability of a subsequent print of the
document.
►
Use symbolic variables (no IEC
addresses).
►
Use meaningful variable names and
comments.
►
Use easy functions (no indirect
addressing, no variable fields).
►
Defensive programming.
►
Easy extension or adaptation of the
program possible.
Protective measure
Measure intended to achieve risk reduction,
e.g.:
- fault-excluding design,
- safeguarding measures (guards),
- complementary protective measures (user
information),
- personal protective equipment (helmet,
protective goggles).
PWM
PWM = pulse width modulation
Via PWM a digital output (capability provided
by the device) can provide an almost analogue
voltage by means of regular fast pulses. The
PWM output signal is a pulsed signal between
GND and supply voltage.
Within a defined period (PWM frequency) the
mark-to-space ratio is varied. Depending on
the mark-to-space ratio, the connected load
determines the corresponding RMS current.
R
Ratio
Measurements can also be performed
ratiometrically. The input signal generates an
output signal which is in a defined ratio to the
input signal. This means that analogue input
signals can be evaluated without additional
reference voltage. A fluctuation of the supply
voltage has no influence on this measured
value.
RAW-CAN
RAW-CAN means the pure CAN protocol
which works without an additional
communication protocol on the CAN bus (on
ISO/OSI layer 2). The CAN protocol is
international defined according to ISO 11898-1
and garantees in ISO 16845 the
interchangeability of CAN chips in addition.