Preface:
Kinda long, so I made section titles
Intro:
I just want to see if anyone here has seen anything similar. A PLC5-40 series C enhanced has been chugging along for years. Now, a single output seems to be flickering a couple times a minute. The output in question is O:012/11 which drives a relay for the run contacts of a PowerFlex 40. We have not seen the anomaly on any other outputs. Bad triac or support component right? Apparently not.
System details:
On this module, O/0 is unused. O/1 through O/5 are three starters and two PF40 run relays that are always on during production. O/6 through O/12 are PF40 run relays for discharge belts of five supply hoppers that feed material. (Octal addressing is five points) Each hopper holds about 2.5 hours of material. The hoppers discharge until empty and we move to the next hopper. Ideally the hopper runs continuously until empty with speed modulation around 60-ish Hz, but a few stops here and there when a downstream surge hopper gets high is fine and normal.
O/13 through O/17 are reverse relays for the hopper drives that aren’t used for production. Overall system has 7 120Vin, 3 120Vout, 1 Ain, 3 Aout.
The problem:
Last week, a discharge started stopping and restarting suddenly. Digging into it, we found the run relay would briefly flicker off a couple times a minute. All wiring seemed fine then we scoped the output and saw truncated half waves in either direction were randomly happening which dropped out the ice cube run relay that doesn’t have enough hold to ride through. We dealt with it until down.
Attempted fixes:
During a short down window, a coworker changed the module in question. The first one tried seemingly had a backplane connection problem and the whole module flickered unless held pushed. The next module tried initially seemed fine, but after production started, it was discovered this output was stuck on. Hmmm. The module was labeled at some point output 0 bad so it was questionable. We worked around that until down again.
When down, I replaced the module again with used, working when removed. This time everything seemed fine. I ran the output a few minutes with a bit of tapping and wiggling and everything seemed fine. Again during production, it turned out to still be flickering and dropping the relay.
Next:
So, I suppose the next logical thing is replace the backplane at our next opportunity. This is just weird and perplexing and actually interesting even if it’s frustrating. So, has anyone seen anything like this, or does anyone have a suggestion other than backplane next?
Appendix:
Here’s an example of a blip and a picture of the old gal. She has about another year until retirement. With a full wave, the scope shows 118V. 108V shows on this frame with the blip.
Kinda long, so I made section titles
Intro:
I just want to see if anyone here has seen anything similar. A PLC5-40 series C enhanced has been chugging along for years. Now, a single output seems to be flickering a couple times a minute. The output in question is O:012/11 which drives a relay for the run contacts of a PowerFlex 40. We have not seen the anomaly on any other outputs. Bad triac or support component right? Apparently not.
System details:
On this module, O/0 is unused. O/1 through O/5 are three starters and two PF40 run relays that are always on during production. O/6 through O/12 are PF40 run relays for discharge belts of five supply hoppers that feed material. (Octal addressing is five points) Each hopper holds about 2.5 hours of material. The hoppers discharge until empty and we move to the next hopper. Ideally the hopper runs continuously until empty with speed modulation around 60-ish Hz, but a few stops here and there when a downstream surge hopper gets high is fine and normal.
O/13 through O/17 are reverse relays for the hopper drives that aren’t used for production. Overall system has 7 120Vin, 3 120Vout, 1 Ain, 3 Aout.
The problem:
Last week, a discharge started stopping and restarting suddenly. Digging into it, we found the run relay would briefly flicker off a couple times a minute. All wiring seemed fine then we scoped the output and saw truncated half waves in either direction were randomly happening which dropped out the ice cube run relay that doesn’t have enough hold to ride through. We dealt with it until down.
Attempted fixes:
During a short down window, a coworker changed the module in question. The first one tried seemingly had a backplane connection problem and the whole module flickered unless held pushed. The next module tried initially seemed fine, but after production started, it was discovered this output was stuck on. Hmmm. The module was labeled at some point output 0 bad so it was questionable. We worked around that until down again.
When down, I replaced the module again with used, working when removed. This time everything seemed fine. I ran the output a few minutes with a bit of tapping and wiggling and everything seemed fine. Again during production, it turned out to still be flickering and dropping the relay.
Next:
So, I suppose the next logical thing is replace the backplane at our next opportunity. This is just weird and perplexing and actually interesting even if it’s frustrating. So, has anyone seen anything like this, or does anyone have a suggestion other than backplane next?
Appendix:
Here’s an example of a blip and a picture of the old gal. She has about another year until retirement. With a full wave, the scope shows 118V. 108V shows on this frame with the blip.
