GE GFK-0787B PLC Subsystem Providing Output Data, Output Subsystem, Automatic System Test

1

PLC Subsystem: Providing Output Data

Running the same application program, each PLC (referred to here by Genius Bus Controller (GBC) serial bus addresses: 31, 30, and 29) processes the voted input data and produces appropriate outputs. Because each of the three PLCs is running the same program, they produce three copies of the same output data.

Each PLC then sends this triplicated output data on the bus.

PLC A

GBC 31

GBC 31

GBC 31

PLC B

GBC 30

GBC 30

GBC 30

PLC C

GBC 29

GBC 29

GBC 29

output

1

output

1

output

1

Output Subsystem

The basic element of an output subsystem is the output group. Each block in the group has the same reference address in the application program, so each block receives the same output data.

The output group votes on the three outputs and uses the result as the physical output.

In this example, communications are lost on bus C. Upon losing communications, the block on bus C follows its configuration instructions, which are to default its outputs to 0. However, the remaining blocks in the group continue to receive valid output data from all three PLCs over busses A and B, and the actual state of the output load is controlled properly. The loss of block or loss of bus diagnostic would be recorded, providing an aid to troubleshooting and annunciating the problem.

output 31

output 30

output 29

1

1

1

voted	C A
output
1

default output

0

A

C

B	voted
	output
	1
B
Load	voted
	output
D	1

1

1

1

1

1

1

output 31

output 30 output 29

output 31

output 30 output 29

In a 4-block output group, each field output is supported by two Genius source outputs connected in parallel on one side of the actuator and two Genius sink outputs connected in parallel on the other. Each block in the group receives outputs from each of the three separate processors.

Automatic System Test

Optional autotest routines test the complete system from input modules through to output modules, including failures in the I/O wiring. Autotesting does not affect the normal state of field devices.

GFK-0787B Chapter 1 Introduction 1-7