?:Safety when Manual-Automatic selection is from 2 locations

[nashama]

Dear All,

Consider a selector switch is located at the electrical panel and it is wired to the PLC at I0.5 (When I0.5 is low = Manual , when I0.5= high = Auto).

Also, WinCC has configured the touch panel with a button authorizing selection of Manual and Automatic.

How to make sure the safety? Just by providing interlocks in the program???

What is normally done or what is the normal practice when programming such applications?

PLease bear with such a query .... I'm still getting on with WinCC Flex (If it was only PLC involved, it could have been done with no great effort .......... but if one more device / Touch panel is authorized to make this selection, then, I'm afraid I need suggessions)

Regards

[bilbo_321]

I'll suggest you the following:
My understanding is that the hardwired signal is always at higher priority, so if manual mode is detected from selector switch at the panel, then you should prohibit selecting automatic mode from HMI (or SCADA). The idea is if somebody is working at field and has selected manual mode, you should never enable automatic mode until selector switch is back at auto mode position.
If auto mode is deselected from selector switch at the panel, then Auto or Manual mode could be selected from HMI.
Simple logic could be: if Manual mode from Panel, then reset Auto Mode bit (and eventually set Manual Mode bit). If Auto mode from Panel and Auto Mode Command from HMI, then set Auto Mode bit (and eventually reset Manual Mode bit).

That is my oppinion only.

Cheers.

[bilbo_321]

Please Ignore my previous post. I made a copy/paste mistake .

Updated answer is:

I'll suggest you the following:
My understanding is that the hardwired signal is always at higher priority, so if manual mode is detected from selector switch at the panel, then you should prohibit selecting automatic mode from HMI (or SCADA). The idea is if somebody is working at field and has selected manual mode, you should never enable automatic mode until selector switch is back at auto mode position.
If MANUAL mode is deselected (or AUTO Mode selected) from selector switch at the panel, then Auto or Manual mode could be selected from HMI.
Simple logic could be: if Manual mode from Panel, then reset Auto Mode bit (and eventually set Manual Mode bit). If Auto mode from Panel and Auto Mode Command from HMI, then set Auto Mode bit (and eventually reset Manual Mode bit).

That is my opinion only.

Cheers.

[nashama]

Dear bilbo_321,

Thanks for the reply.

When you say

" ......... if manual mode is detected from selector switch at the panel, then you should prohibit selecting automatic mode from HMI (or SCADA). The idea is if somebody is working at field and has selected manual mode, you should never enable automatic mode until selector switch is back at auto mode position."

Don't you think in this case you should not be able to select even Manual mode from HMI/SCADA for better safety? I mean what if you are in the field at the electrical cabinet with Manual mode selected and at the same time some one reaches to the HMI and accidentally makes any "Manual" movement?

Now , based on your reply , will I be correct if I say once you select "Auto" from the electrical panel, you actually consent to give control to the HMI which may , then , select either "Manual" or "Auto" movements? .....
(and will it be correct to call this type of access from 2 different places as "Local" and "Remote" controls - the former from the machine position itself or its electrical controls , the latter for a distant located control like a HMI / SCADA ?) ..........
I remember I saw this type of text - Local / Remote , on the electrical schematic in a plant some years ago. Am I reasonable?

Regards

[bilbo_321]

Hi nashama,

Don't you think in this case you should not be able to select even Manual mode from HMI/SCADA for better safety? I mean what if you are in the field at the electrical cabinet with Manual mode selected and at the same time some one reaches to the HMI and accidentally makes any "Manual" movement?

My understanding for Manual mode (selected from electrical panel, not the logical Manual mode from HMI) is that any action with the device should be done only from local panel next to device, as you have only Manual and Auto mode. It could be different if there is third mode named Local or Remote. In that case if Local mode is selected from electrical panel, then any control from HMI should be disabled.

Now , based on your reply , will I be correct if I say once you select "Auto" from the electrical panel, you actually consent to give control to the HMI which may , then , select either "Manual" or "Auto" movements? .....
(and will it be correct to call this type of access from 2 different places as "Local" and "Remote" controls - the former from the machine position itself or its electrical controls , the latter for a distant located control like a HMI / SCADA ?) ..........

Yes, that is correct.
Normally I use 3 different modes of operation - Local (or Maintenance), Manual and Auto. I put separate button or selector switch on device faceplate if there is no local selector at electrical panel, so operator should press at least 2 buttons to switch off Maintenance mode and initiate movement. Further more you can program at HMI confirmation dialog to switch off Maintenance mode.
The best way to be safe is to connect electrically local selector switch at electrical panel to cut off the control voltage from PLC output to contactor or pilot valve and use local buttons or switches at panel to operate device. That could involve modifications in electrical drawings if it is not designed properly.

Cheers.

[nashama]

Dear bilbo_321,
Thanks again for your time and attention.
I modified something in the network that selects / interlocks between the panel's Man-Auto and the TP177's Man-Auto and it is based on your 2nd post (the corrected one).
But I don't see any means to attach the screenshots here.
Regards