Put a passworded S7-1200 in RUN mode

[grnick50]

Hello all,

I have a client who bought some machines from a vendor that passworded the PLCs. One of the S7-1200 PLCs went into stop mode. I knew that the PLC was passworded and I had no interest in recovering the code. I only wanted to switch it in RUN mode using the online access.

I think this is a huge flaw in the S7-1200 design as there is no point in that. Why not be able to set the PLC mode?
In the S7-1500 or ET200sp one can use the mode switch to put the PLC back in RUN, regardless if it is passworded or not.
Also I believe that the programmer did a poor job preventing the PLC to go in STOP mode or not warm restarting it Always in RUN mode.

 

[rQx]

Cannot help but I also wonder why "always start in RUN" after a restart isn't the standard on these PLCs.

 

[grnick50]

I tried to fool the PLC by making a test HMI (KTP700) and using the SetPLCmode events to start the PLC but unfortunately it did not work as the connection in the HMI needs the password to be set.

I agree with you. The default setting should be to restart always in RUN. Other PLCs allow you to use a DI to Start the PLC if there is no switch.

 

[grnick50]

If you think about it, restarting always in RUN could potentially be dangerous. Imagine if one would set a S7-1200 in its hardware configuration to always restart in RUN mode. Say that maintenance people Stop the PLC to do maintenance and because of bad practice they don't take other measures to prevent the machine from starting. During the maintenance the power goes out and then back on again. The PLC starts and injures or worse the maintenance guy.

The best is a switch with a key like the old S7-300 & S7-400 or AB PLCs. I think features like a RUN-STOP switch are removed to reduce the cost.

 

[Steve Bailey]

I think this is a huge flaw in the S7-1200 design

I agree, but it is a larger flaw in the vendor's design. The OEM should have provide a method to clear the fault and restart.
If I were the end user I would insist that someone from the vendor come to restart the PLC at the vendor's expense. And that each time the vendor's rep has to come restart, the warranty clock for that particular fault gets reset.

 

[grnick50]

I agree on the second part of your post regarding the liability of the vendor. However I have a feeling that in that particular case the vendor does it on purpose. In the S7 CPUs there is the STP instruction that will put the CPU in STOP mode.

I disagree with the first part of your post. I still believe it is a larger flaw on the manufacturers side because if they had done it right in the first place (allow you to start a passworded CPU without the password) then a bad vendor design or intention could not largely affect the end user because any technical expert with TIA portal could restart the PLC without looking in the top secret code.

 

[Steve Bailey]

Let's agree there is blame to go around without arguing over who has the larger share.

 

[grnick50]

Let's agree there is blame to go around without arguing over who has the larger share.

Very well said.

 

[spaderkung]

With risk of going a little OT.. A PLC that starts any (unsafe) actuators automatically after they have been stopped by em stop or fault and so on violates the European machine directive. It is required for operator to restart a motor by action to comply.

 

[mk42]

The best is a switch with a key like the old S7-300 & S7-400 or AB PLCs. I think features like a RUN-STOP switch are removed to reduce the cost.

I thought for sure the 1200 would get one of those little signal boards that had a built in Run/Stop switch, but it never materialized.

For what it's worth, the newer 1500s do have the switch, hiding behind the front display.