Process-HMI Interfacing

How do I get my HMI to display what is happening according to the inputs and outputs on my PLC/field device.

When I am working with the HMI software like the WinCC flexible. I think I connect the OP 77 to the PC, make my display the way I want. Then on the other hand, my PLC itself has a program. How do I get the HMI to display what's happening with my PLC and field devices?

I tried finding links for this, but couldn't find one that speaks clearly on the connections. I did work with the HMI programming through the software WinCC flexible, and even worked on the receipe.

But given that ultimately its my PLC (and not HMI) which has the logic of the receipe, I don't understand how programming of the HMI with a receipe makes any sense. Could anyone explain interfacing the HMI with a given industrial system/process?


Regards
Vivek.

VIVEK-V said:

......But given that ultimately its my PLC (and not HMI) which has the logic of the receipe, I don't understand how programming of the HMI with a receipe makes any sense. Could anyone explain interfacing the HMI with a given industrial system/process?.....

Click to expand...

Dear Vivek,

You are correct in your assumption that the program is IN the PLC.

One thing you must understand is FAST and SLOW.

You logic inside the PLC will detect the states of its I/Os, and it will do it FAST. It will react in accordance with whatever you have programmed it to do FAST. You even must program timers to slow it down...

BUT, in this logic you could have some Setpoints or constants used for math functions that you will need to change whenever you want to modify the way the process works.

You can have an Operator manually input some data in a touch screen or you could put all those changes reside inside a file and download it to the PLC... This would be RECIPE No.1 ... you get it?

It could even be downloaded automaticaly...

If its now or in 2 seconds... who cares... That is the SLOW part...

You want to display engeneering units after a math conversion... you could even do that in an HMI ... Slowly...

Anything that would need to be done FAST must be inside the PLC prior to the event triggering the action ... all else... HMI... PC ... whatever.

Does your HMI have the capability of monitoring the PLC ladder logic? I use Omron and this facility is built in provided you use an Omron PLC to match the HMI.

Thanks Pierre,

If I understand correctly, in actual operation, the receipe logic is contained inside the PLC CPU, right? What the HMI has is merely the program to display what is happening (like valve of ingredient 1 is open and filling the tank/bottle), right?

VIVEK-V said:

Thanks Pierre,

If I understand correctly, in actual operation, the receipe logic is contained inside the PLC CPU, right? What the HMI has is merely the program to display what is happening (like valve of ingredient 1 is open and filling the tank/bottle), right?

Click to expand...

Exactly!

The HMI will also have some place to have more than one recipe... so you could dump it in the PLC when you need it.

Like The Old Pfhaart just mentionned, there is even some HMI that do a little bit of control... Webcam, communications, MUSIC, but thats not a good idea... and not very popular.

HMI have evolve in all directions because the manufacturers are looking for more markets... but in the end what you have stated is close to be the exact usage of an HMI...

Human MAchine Interface.

Human wants to say GO to machine
Human press button on HMI
HMI send a bit to PLC
Machine Starts

By the sounds of it and what your asking, you need to associate tags to indicators on your screen within Wincc itself.

The tags allow you to specify the type of input to the screen, Like M0.0 in your plc is tagged to an indicator on your screen via a tag within Wincc labeled M0.0....

JV

Thanks guys, clarified a lot.