Step 7 troubleshooting

Is there a way to find out where to program stops?
Lets say an operator forgets to put a part in the machine and Step 7 is looking for that input. How would someone not familiar with the process troubleshoot the problem?

Johnnie

Are you asking how to use a PC online with a PLC as a trouble shooting tool?

Or how to program 'diagnostics' to flag up a message on an HMI, to warn the operator that they need to do such and such.

Or how to find out what has made your PLC fall over?

Lets say an operator forgets to put a part in the machine and Step 7 is looking for that input. How would someone not familiar with the process troubleshoot the problem?

Click to expand...

Going by the above, the only trouble shooting to do would be to look at your inputs, an input not being made will not cause a PLC to fault. It could certainly bring the process to a halt, but the PLC will merrily keep chugging along. Now being unfamiliar with the process, could be a problem, but if you know what the end result should be, you can trace your way back to the 'missing' link, or in your example, the input not being made.

I think you need to clarify your question a bit. Then maybe we can help some more

Paul

I am wanting to use the Pc online for troubleshooting.
Can you find out where the Step 7 program has stopped? Does Step 7 have a way to do this?

Johnnie

If the PLC has 'spat it's dummy out' and fallen over, you can use the PLC > HARDWARE DIAGNOSTICS option in the dropdown menus in Simatic manager, highlight the PLC in question first. This will tell you the reason why the PLC has gone into stop mode or faulted.

Can you find out where the Step 7 program has stopped?

Click to expand...

Using your previous example regarding an input not being made, Step 7 will not tell you that an input is not made (well not directly) because that will not cause the PLC to fault. The 'conveyor belt' or whatever is relying on that input will stop, but the program within the PLC will just keep on running, it will not care that an input is not made.

In that scenario, someone (you maybe?) will have to go online and look through the code to find out what has happened to stop the conveyor running.

Paul

Hello Johnnie;
First of all you must make a distinction between the process and the controller. If your process has stopped because of a faulty input, it does not follow that the PLC will be stopped. If logic is stable, the PLC will not fault. Only a major fault will cause the PLC to stop; then you would do to diagnostics to find out what caused the fault.

Now: what you want to evaluate is the stage the process is at at any moment, following the state of various inputs. If you use an external PC with a SCADA program, say Wonderware, RSView, Citect, WinCC..., you can set up a process page where you design a flowchart, SFC-type diagram representing the successive stages your process goes through, depending on the various inputs. Then animate each stage to change color when the stage is active, and return to neutral color when the stage is inactive.
Of course you will need to program the logic in the controller to follow the sequence. Just a little more ladder, setting up flag bits to signal which process stage is active, so the animations can follow the sequence.
Or you can choose to program the process sequence directly through S7-Graph, a GRAFCET (SFC) optional module of Step7 that will control your process in state-transition format, and give you a graphical interface that follows the evolution of the process. A very neat interface package for sequential process control.
Hope this helps,
Daniel Chartier

Hi Johnnie,

A properly made program must take care of ALL the obvious stop conditions of a proces or a machine.
If an error condition as you stated occurs, then an alarm should be generated, and a well thought out operator message should be displayed on the HMI. Example: "Door opened on left side of the machine. Check door, close door, acknowledge to continue."
Additional debugging info can be provided: "Check door switch S30, Check safety relay K30, Check PLC input I3.1."
If you have to use the programming software to troubleshoot, then the PLC/HMI application isnt good enough !
You CAN use the programming software to troubleshoot. But this should only be necessary when you are still in the development phase.

The easiest way is to find the output that turns on whatever's not working. Look online with the PC with your magic Step7 glasses and see what's keeping the logic for that output from being true.
Assuming it's a photoeye for example it would be Ix.x or Ex.x depending on your language preference. Then find that input in your prints. If you see it's looking for an "End Occupied" photoeye Ix.x to start the motor, and the end IS occupied, then see if the photoeye is indeed where it's supposed to be in the process, is it wired correctly? Is it dirty? is it working? was it damaged by something. If that's what you mean,thishould get ya going in the right direction. If it's an analog signal, or some other type of interface to the plc, then things become more complicated, but if you have good prints you should be able to figure it out fairly easily.