Strange Problems with S7-1200

Evening, 

I have some strange problems with my S7-1200 program in TIA.

I am getting quite a few unexpected things not happening as expected. I have checked memory assignments and there were quite a few overlapping, so they have been corrected.

Problem 1: I have a series of TON / TOF timers to sounds a startup sound when the machine starts, these go to Q0.0, in TIA with monitoring it shows Q0.0 as being on, but on ther PLC it isn´t.

Problem 2: An output Q1.0 starts a timer to monitor a particular function, when this is set to Positive Edge it show it as being active, but the timer after it doesn´t start. If I change it to a N/O input then it works fine.

Problem 3: there are several timers to stop the machine cycle if the timers run out, the ´stop cycle´ shows as being active in the timer Network, but in the Network where it stops the machine via a SR bit, doesn´t show as active and doesn´t stop the machine.

Is there anything simple I am missing for this to be happening?

Please bear in mind I may have missed something simple!

Thanks,

Chris

Hi,

are you sure you did not save input values to true as start values for timers (TON; TOF, TP)?

I mean taking a snapshot in the moment they are on and save it as start value.

Same thing for triggers as R_TRIG, F_TRIG.

Hi Chris12345678,

Pay attention at the jumps on your code.

I suggest you to use memory variables to save the result of timer and then use it on your code.

To answer you both, here are some screenshots of the program.

In network 4, when the HMI Start button is pressed it starts a series of timers to activate a warning sounder. The output Q0.0 doesn´t come on.

In Network 14, Q1.0 Positive Edge starts a SR which goes to a TON timer. This shows as changing from TRUE to FALSE and back, but doesn't activate the SR, despite nothing being active on the Reset. If I change it to a N/O then it works fine.

Also in this network, if the TON timer reaches the PT value then it should activate M66.6 stop cycle, it shows as being active in this network, but in the last picture where it should Reset the SR, it shows as not being active. I do not understand this.

Hello Chris.

The code segments you shared leaves me with little answers. 

1) Network 4 has several coils for the same memory bit. The next coil overrides the previous coil's result.

2) Network 14 is not clear what the issue is. I am wondering what the value is for PT in the TON. I am not liking the fact that you are using %ID2 (input double word 2) to read the elapsed time. That will cause all sorts of chaos. %ID2 overrides %I2.1. This makes me think you have other memory overlap occurrences.

3) Network ?? makes me wonder if you are using special system bits which are by default covering %M0.0 to %M1.7. But again there is an %I2.6 that has been wiped out by Network 4's usage of %ID2.

The problems are not because of issues from the software or the PLC. The problem is the buggy code.. brought on by the coding style. Analysing the full program may reveal all the problem areas.