Siemens S7-400 Installation, Introduction, Central Rack CR and Expansion Rack ER

Installing the S7-400

2.1S7-400 Installation

Introduction

An S7-400 programmable controller consists of a central rack (CR) and one or more expansion racks (ERs), as required. You can add ERs to compensate for lack of slots for your application or operate signal modules at remote locations (e.g. in the immediate vicinity of your process).

When using ERs, you need interface modules (IMs) as well as the additional racks, and additional power supply modules if necessary. When using interface modules, you must always use the appropriate partners: you insert a send IM in the CR, and the matching receive IM in each connected ER (see Reference Manual, Chapter 6).

Central Rack (CR) and Expansion Rack (ER)

The rack containing the CPU is known as the central rack (CR). The racks containing modules in the system and connected to the CR are the expansion racks (ERs).

Shown in Figure 2-1 is a rack with 18 slots configured as a CR.

PS CPU SMs

Figure 2-1 Rack Fitted with Modules in the S7-400 System

2-2	Automation System S7-400	Hardware and Installation
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