I am running a PLC5 and FactoryTalk 8.2 to control equipment at my facility. The HMI is a legacy system upgraded a couple of times which started out as a ControlView project well before I started with the company.
We have experienced a problem a couple of times where a 'System Stop' button shuts down some of the equipment, but leaves some of it running. The button is setup to set a bit to 1 when pressed, and set the bit to 0 when released.
What I've found is that when this happens the equipment that shuts down properly is controlled by XIC instructions, and the equipment that doesn't shut down is controlled by XIO instructions. That confused me.
I added a line at the top of the affected ladder which counts up when the bit goes high, and another that counts up when the bit goes low. I added a third line at the bottom of the ladder which also counts up when the bit goes low. I verified that the all three counters were reset to 0.
I pushed the button 300 times, and I found that the two counters at the top of the ladder (one for bit high, one for bit low) are equal, but the counter at the bottom of the ladder counting low bits counted 1 fewer changes of state. I tried another 700 times and it didn't happen again.
I don't really understand how this can happen, so I'm not sure how to correct it. My plan at this point is to change the button to a momentary button, and use it to latch a new bit which controls everything and gets unlatched when all the equipment is shut down.
Anyone have any thoughts they'd be willing to share?
We have experienced a problem a couple of times where a 'System Stop' button shuts down some of the equipment, but leaves some of it running. The button is setup to set a bit to 1 when pressed, and set the bit to 0 when released.
What I've found is that when this happens the equipment that shuts down properly is controlled by XIC instructions, and the equipment that doesn't shut down is controlled by XIO instructions. That confused me.
I added a line at the top of the affected ladder which counts up when the bit goes high, and another that counts up when the bit goes low. I added a third line at the bottom of the ladder which also counts up when the bit goes low. I verified that the all three counters were reset to 0.
I pushed the button 300 times, and I found that the two counters at the top of the ladder (one for bit high, one for bit low) are equal, but the counter at the bottom of the ladder counting low bits counted 1 fewer changes of state. I tried another 700 times and it didn't happen again.
I don't really understand how this can happen, so I'm not sure how to correct it. My plan at this point is to change the button to a momentary button, and use it to latch a new bit which controls everything and gets unlatched when all the equipment is shut down.
Anyone have any thoughts they'd be willing to share?