tia portla HMI button (basic quastion)

[gianniskops]

Hello!

I am newbee in PLC. I am facing some problems in HMI panel.
My set up is S7-1200 and a basic simatic panel.
My software is TIA PORTAL V13.
My code is a simple network in ladder with a start stop and a coil. It works fine but only when i use both NO for buttons.
start stop coil
---------| |-----------------| |-----------------( )---
|
coil |
--------| |-----


When impementing this in HMI, by seting SetBit and ResetBit. I have tried with Button Element and with pushbutton from old library. I have tried SetBit,ResetBit on Press and Release respectevely, I have tried SetBitWhileKeyPressed, i have tried both symbolic and absolute access mode, i have tried different aquitision cyclyes and even changing some of the Properties of PLC, like Cycle and monitor time..
I tried change the size of the button etc
The problem is that I have to press five times the button to activate or deactivate the pilot light. But eventually it does. That is the most confusing.

Do you have any ideas?

 

[Chris Hasler]

I like the images from Portal, makes it easy to see your problem. Your HMI is not keeping sync with the PLC. Five button presses indicates a timing issue on the HMI, where the tag is not staying set long enough to trigger the PLC logic.

I recommend having the HMI latch the commands, the PLC then deals with resetting them once the instruction is carried out.


Use symbolic access as it is much easier in TIA. For this type of tag 500ms tag refresh is fine, and the PLC cycle time does not matter if it is less than 500ms.

Switch the stop instruction to use NC as that is easier to read (i.e. why is it running with stop set on)

I would set up the start button with the following event:

On press: Setbit (START) AND Resetbit (STOP)

Then use COIL to reset the START flag in the PLC. For safety you could add a TOF instruction to reset START if it is latched on. This is so the HMI can't break and the START instruction will not get latched on for any reason.

For the stop button you can use the following:

On press: Setbit (STOP) AND Resetbit (START)

The STOP bit is reset by your start button when you want to start.

Try and work out how that is different to your current set up and you should see where it is going wrong.

 

[gianniskops]

Thank you very much for your reply!!
Could you please dicsribe to me how to switch the stop instruction to use NC in Tia portal? It would be very beneficial and I cannot figure out how to do this.

I have to fix this at first in order to follow your recommentations.

By the way, I have real start and stop buttons wiring on the same I/0. When I interact with them the HMI receive the signal accurately. Instead the opposite way is problematic. The pilot light indicator on HMI also communicates accuratelly with real time lamp.

 

[Chris Hasler]

That reply just indicated the exact problem. The HMI cannot overwrite an input. If the absolute address is in the I range, which they are, you have to map them to a M range on a slow cycle to alter them with the HMI reliably. This means that you don't update the physical inputs very often, and everything gets very unresponsive.

you would be better off adding a HMI start and stop bit as a separate start/stop command. Then your HMI does not need to overwrite the physical push buttons.


For the normally closed stuff:

On the left of your portal window is a tab called instructions, in the basic instructions section, there is a folder called "bit logic operations".

your looking for -|/|- to use a normally closed contact.

If the stop button is normally open, you can invert it by putting a normally closed contact and then a coil. Tag appropriately and your NO button can be used as a NC button.

Also put all the instructions you use frequently in the favourites section of the instructions tab. You then get these at the top of the editor, and it saves trying to work out the Portal instruction tree every time you need them.

 

[gianniskops]

Thank you once again for your kindness of explaining! Now it make sence. So i have to either control my machine from plc or from monitor. Right?

In regard to NC stop button, I know that it is stupid but when I am online pressing the momentary button the current doesn't not continue at the Stop NC contact... This is why is chose NO for STOP button in the first place.. very annoying

 

[Chris Hasler]

you would need to add another internal tag for the stop button, and invert the stop button functionality. or just use a NO contact and make sure its commented properly on the tag and the network.

If you were to use internal tags for that network, and then OR the start buttons (physical and HMI) together and OR the stop buttons together, you would be able to use two button sources.