For the past 6 years I have been using Tri PLC from T100MD to FMD1616 and F1616. Recently I encountered a safety issue on output channels which should be notified via user manual and/or application notes. I'm quite disappointed, especially when I found this topic on the forum:
"Re:Output State on Power Off"
Here are some details.
PLC: FMD1616, DO#1-8 are connected to one mechanical relay and 7 SSR, which are used to control motors and high pressure valves.
Issue: at one moment, the 24V to PLC is lost, but 24V to relays and SSRs are still connected. Instantly, output #1-8 go to ON status: all the motors start running and high pressure valves start opening, which lead to an quite dangerous situation.
After some debuging, I found it is caused by the ULN2803 flyback diode. By bending Pin 10 out I solve the problem.
This can be a very serious safety issue when someone try to control a motor and high pressure gas. From this forum, I can see that Triangle knew this issue from years ago. I don't understand why this issue is not fixed, and/or at least the user should be notified to pay attention when using these channels.