Siemens S7-200 User Manual download pdf (Page 16)

Introduction

You are sure to be familiar with the stan-

dard latching function and here you will

learn how to program it.

The example:

Output Q0.30 is to be activated as soon

as S1 at input I0.0 is operated. With latch-

ing, Q0.0 is to remain active until S2 at

input I0.1 is operated and thus interrupts

the latch.

To allow the latching function to work,

the output (Q0.0 in this case), must itself

ensure, as soon as it is activated, that it

retains its "true" state and therefore

remains active.

This is achieved by switching the output

(Q0.0 in this case) as a contact in parallel

to the tripping input just in the same way

as with a conventional contactor circuit

(Q0.0 can be compared to our contactor

K1).

Latching

- Introduction

- Normally-Closed (NC) Contact

- Solution Description and Test

- A Different Take on Latching

In STEP 7-Micro/WIN open the first practice project "a:\d01.prj" from the diskette.

There are still a few elements missing in the program. Add the missing LAD elements

now as a short exercise.

1) Click on the ladder diagram field with the left mouse button and click on the STEP 7-Micro/WIN

symbol for normally-open NO contact (F4). As indicated on the symbol, you can also use function

key F4 instead of the mouse.

2) To enter the vertical line, mark the ladder diagram field of I0.0 and click on the symbol (F7).

Standard

Locking

Output Q0.0 as

an input ensures

latching

First add a contact Q0.0 at the point indicated as a parallel circuit to I0.0 (indicated by grey line)!

To enter the contact:

Latching Revision

Pulse-Oper-

ated Switch

Off-Delay

Timer

Sequencer Appendix

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 73 74

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Siemens S7-200 User Manual Page 16

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