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PLC Automated Control Process Book

Purpose

• Most education focuses on continuous control systems.
• In practice most contemporary control systems make use of computers.
• Computer based control is inherently different than continuous systems.
• The purpose of this book is to address discrete control systems using
common control systems.
• The objective is to prepare the reader to implement a control system from
beginning to end, including planning and design of hardware and software.

S7-200 Tip : Micromaster Drives

Special Hardware Requirements:

One SIMATIC S7-200 CPU with input simulator
Micromaster-Drive and motor

Note! Starting with STEP 7-Micro/WIN Version 3.2, a USS Protocol Library (Optional Add-On Instruction Library 6ES7 830-2BC00-0YX0) was added.
As a result, the new library now provides an easier method of programming this task than is shown here.

S7-200 Tip : Wound Rotor

Special Hardware Requirements: None

This program example provides an automatic, four-resistor startup of a three-phase, wound rotor induction motor. The motor starts with full rotor resistance. After a specified time has run out, the first rotor contactor closes, removing part of the rotor resistance. As additional time intervals pass, the rest of the rotor contactors close one by one, decreasing the rotor resistance each time until the resistance is bypassed completely and the motor runs at the rated rotational speed.

S7-200 Tip : Stator-Resistance Starting

Special Hardware Requirements: None

In this example program, a squirrel-cage rotor with short-circuit soft start switching makes the automatic startup of a three-phase induction motor possible. With this short-circuit soft start, the motor starts up with a decreased rotational speed and attains the rated rotational speed only after a certain amount of time.

S7-200 Tips : Star Delta Starter 2

Special Hardware Requirements: None

This program example controls star-delta starting for a three-phase induction motor. Application Tip No. 12 is supplemented with the acknowledgement of the actual circuit states of the motor starters. If the star starter is defective, for example, the starter acknowledgement recognizes this fault. After the 5-s delay time, SIMATIC S7-200 does not switch to the delta stage and therefore avoids any possible damage.