Siemens Simatic M7-400 Reference Manual page 623

Sequence layer
Sequence layers form the interface in M7 between the operating system of the
CPU and the user program. The order in which the blocks of the user program
are processed is defined in the sequence layers.
SFB
³ System function block
SFC
³ System function
Short-circuit
Connection with negligibly low impedance between operationally opposed live
conductors. The current is a multiple of the operating current; this can result in
thermal overloading (rated short-time current) or mechanical overloading (rated
peak withstand current) of the switchgear and system components.
Shunt resistor
Parallel or shunt resistor in electrical circuits.
Signal module
Signal modules (SM) form the interface between the process and the
programmable controller. There are input modules, output modules, input/output
modules (both digital and analog).
Slave
A slave can only exchange data with a ³ master when requested by it to do so.
Smoothing
Parameter in STEP 7 for analog input modules. The measured values are
smoothed by digital filtering. For specific modules it is possible to choose
between no, low, medium and high smoothing. The higher the smoothing, the
greater is the time constant of the digital filter.
Standard communication
Communication via standard and standardized protocols, such as PROFIBUS DP
or PROFIBUS FMS.
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Glossary
Glossary-17