Handling And Role Of Initial State Relay - Mitsubishi Electric FX3G SERIES Programming Manual

Programmable controllers

Hide thumbs Also See for FX3G SERIES:

Table of Contents

Series Programmable Controllers

Programming Manual - Basic & Applied Instruction Edition

Handling and role of initial state relay

Handling of the initial state relay

• A state relay located at the head of an SFC program is the initial state relay. Only state relays S0 to S9 are

• The initial state relay is driven by way of another state relay (S24 in the example shown below). But it is necessary

to drive the initial state relay in advance by another measure at the start of operation.

• In the example shown below, the initial state relay is driven by the special auxiliary relay M8002 which turns ON and

remains ON only momentarily when the PLC mode is changed from STOP to RUN.

• General state relays other than initial state relays should be driven by another state relay. They cannot be driven

by any other device.

• The state relay which may be driven by a contact other than the STL instruction is there by defined as the initial

state relay, and should be described at the top of the flow.

Role of the initial state relay

1. Used as an identification device for inverse conversion

• In inverse conversion from an instruction list into an SFC program, it is necessary to identify the top of the flow. For

this purpose, use the initial state relay S0 to S9.

If any other state relay number is used, inverse conversion is disabled.

• Program the STL instruction for the initial state relay before the STL instructions for subsequment state relays.

Program the RET instruction at the end.

By this programming method, if there are two or more independent flows, they the separated from each other.

2. Used to prevent double start

• In the above example, even if the start button is pressed while the state relay S24 is ON, the command is invalid

(S0 does not turn ON).

As a result, double start is prevented.

Initial pulse

Ladder block

The initial state relay is

Initial state relay

35 SFC Program and Step Ladder

35.1 SFC Program

Fx3u series Fx3uc series