Siemens S7-400 Parameters, Static, Priority classes, Process Image, Programming Device PG

Glossary

Parameters, Static

In contrast to dynamic parameters, static parameters of modules cannot be changed by means of the user program, but only via STEP 7 (not in the RUN state); for example, input delay of a digital signal input module.

PG

→Programming Device

PROFIBUS DP

Digital, analog and intelligent modules, as well as a wide range of field devices to EN 50170, Part 3, such as drives or valve modules are moved to the local process by the PLC across distances of up to 23 km.

The modules and field devices are interconnected with the PLC via PROFIBUS DP field bus and are addressed in the same way as local I/O.

Priority classes

The S7 CPU operating system provides up to 26 priority classes (or “program execution levels”) which are assigned different OBs. These classes determine which OB can interrupt other OBs. Several OBs belonging to the same priority class do not interrupt each other, and are executed in sequential order.

Process Image

The process image is a component part of the system memory of the S7-400 CPU. At the beginning of the cyclic program, the signal states of the input modules are transferred to the process-image input table (PII). At the end of the cyclic program, the process-image output table (PIQ) is transferred to the output modules as the signal state.

Programming Device (PG)

A personal computer with a special compact design, suitable for industrial conditions. A Siemens programming device is completely equipped for programming the SIMATIC programmable logic controllers.

Protective Ground

Connection via protective conductor to a common ground conductor for the exposed, conductive parts of electrical apparatus which are not normally live, but at which a voltage may be present in the event of a fault, and which are jointly protected via a protective device.

Automation System S7-400 Hardware and Installation A5E00850741-01

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