17BTerms and abbreviations
18-4
Modbus
The Modbus protocol is a communication protocol based on
a
→
master/slave architecture and was generated by Modi-
con* in 1979 for communication with its PLCs. In industry
Modbus is the de-facto standard.
Modbus/TCP comes after
→
Ethernet-TCP/IP. Modbus/TCP
is a portion of the protocol on TCP defined for the serial inter-
face. The
→
IP address clearly defines every device in a net-
work. Therefore the slave address was used to identify sev-
eral logical units (unit IDs) in one physical device. To do so,
the extended IP addressing is used.
Example: 192.168.83.28.1 means unit ID 1 on IP address
192.168.83.28.
*) Modicon passed from AEG to the group Schneider in
1994.
OSSD OSSD
=
O
utput
S
ignal
S
witching
D
evice
= output signal of a switchgear,
here: output signal of an AS-i safety monitor
Password
In the menu "System Setup", menu item "Password" the
handling can be restricted or enabled. When delivered, the
device is in the user mode. By entering an invalid password
(e.g. 1000) all menu items that allow settings to be changed
will be blocked.
→
page 11-22, chapter 11.4 "Password protection"
PELV PELV
=
P
rotective
E
xtra
L
ow
V
oltage
Functional extra low voltage with safe separation, grounded
variant of SELV.
Extra low voltage with safe separation (grounded variant of
SELV). The specification as PELV system to IEC364-4-41
(initially DIN VDE 0100-410:1997-01) covers a measure to
protect against direct and indirect contact with dangerous
voltages by a "safe separation" between primary and secon-
dary side in the device (e.g. power supply to PELV specifica-
tion).
For this reason no separate PE conductor is required in a
PELV system. It is allowed to ground circuits and / or bodies
in a PELV system.
Pictograms
Image symbols which convey information by a simplified
graphic representation.
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