28. HMI Basics for PLC Technicians ( 28 of 35 )


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An HMI, or Human Machine Interface, is the screen that allows operators and technicians to interact with a machine or process.

A PLC controls the machine, but the HMI gives the …

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29. PLC Communication Basics: HMI, VFD, Remote I/O, and SCADA ( 29 of 35 )


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PLC Communication Basics

Modern PLC systems rarely work alone.

A PLC may communicate with:

HMI panels
VFDs
Remote I/O
Servo drives
Robots
Barcode readers
Vision systems
SCADA computers
Industrial switches
Other PLCs
Data collection systems

In older systems, many signals were hardwired point-to-point.

Example:

PLC output …

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3. HMI Communications: FactoryTalk Linx, Data Servers, and OPC


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Understanding How the HMI Talks to the PLC

In an industrial HMI system, the screen is only useful if it can communicate with the controller.

The HMI needs to read machine status …

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