HMI versus OIT

Hi guys just want to know the difference between HMI and OIt? Im just confused. I think OIT is also a HMI. thanks

No difference.

HMI = Human Machine Interface
OIT = Operator Interface Terminal
You may also see MMI - Man Machine Interface. Now considered politically incorrect so you don't see that as often.

All referring to an Operator Screen

Thank you..

Some projects will define OIT as the local interface for a controller. The HMI is the plant level, or SCADA interface for multiple controllers or the system as a whole.
Other projects do not specify a difference. Check the specs.

Perhaps OIT's are smarter today. Years ago, the OIT didn't have any smarts. Much like a dumb terminal. HyperTerminal, for example, except these just have 2 or 4 line LCDs.
Set up RS232, and send it text. Read key presses.
All of the processing is done inside the PLC. Send ASCII text. Read ASCII characters coming back. An absolute pain to program and test.

An HMI is a single board fanless PC. It has a built-in software, most likely running Linux.
You use a program to set up everything, and write it to the flash memory in the HMI. The PLC reads and writes registers in the background. This is all automatic, based on your address table. The only thing you need to set up is the baud rate and protocol. Modbus, for example.

Small HMI's are so cheap today, I can't justify an OIT.
For me, the difference is easy - OIT's are obsolete.

An old thread from September, 2012.

A trip down memory lane ...

I still chuckle at A-B changing they're terminology from MMI to HIM years ago. Human Interface Module on the old 1305 drives

plctech303 said:

A trip down memory lane ...

I still chuckle at A-B changing they're terminology from MMI to HIM years ago. Human Interface Module on the old 1305 drives

Click to expand...

Yea... Why not call it a KeyPad?