Siemens Simatic S7-400 - Manual (Page 616)

Glossary
Glossary-10
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Local data
Local data are data assigned to a
³
code block that is declared in its
³ declaration section and its variable declaration. It includes (depending on the
block): formal parameters,
³
static data,
³
temporary data.
Logic block
In the context of SIMATIC S7, a logic block is a block that contains part of the
STEP 7 user program. By contrast, a data block only contains data. There are
the following logic blocks: organization blocks (OBs), function blocks (FBs),
functions (FCs), system function block (SFBs), system functions (SFCs).
M7
Owing to its standardized AT computer architecture, automation computers
M7-300 and M7-400 represent a freely programmable expansion of the SIMATIC
automation platform. The hardware configuration is similar to that of a S7-300 or
S7-400. The user programs for the SIMATIC M7 can also be programmed in a
high-level language, such as C, or graphically.
Master
When they are in possession of access rights on the
³
bus, masters can send
data to other nodes and request data from other nodes (= active node).
Measuring principle, instantaneous value encoding
A module with instantaneous value encoding is always used for very fast
measuring operations or variables that change very rapidly. In this process, the
module accesses the variable to be measured as fast as possible and delivers an
instantaneous snapshot of the signal at a particular time. Due to this measuring
procedure, the modules are more ”sensitive” than modules with an integrating
measuring procedure. Interference affecting the measured value can thus corrupt
the result. You must ensure when using these modules that the measuring signal
is clean by adhering strictly to the installation guidelines, for example.
Measuring principle, integrating
A module with an integrating measuring procedure is always used for
non-time-critical measuring operations. The integration time is inversely
proportional to the line frequency. You can set the latter in STEP 7. This then
gives you the integration time. If the line frequency is 50 Hz, the integration time
is 20 ms or an even multiple of that. Because the measured value is included up
to exactly this time period, at least one or more whole periods of the line
frequency, which may overlay the measuring signal, are also included. The
average value of the error is therefore included as zero (positive part of the first
half period = negative part of the second half period). Only the user signal is thus
recorded.