MASEngr
Member
- Join Date
- Nov 2007
- Posts
- 79
Hello forum.
I'm running into a problem with my PLC-controlled system. I'm using AD DL-06 as the main PLC with another DL-06 as the remote PLC. The remote PLC on the carriage takes input from the operator and sets the coils on the solenoids. The main PLC on the non-moving part handles a similar interface and turns on the motors.
It's transporting people and thus has to be failsafe. There's a separate set of redundant safety Grade 3 controllers that take care of collisions. The system requires power from the estop relay to function.
The communication between the two PLCs is done with RS-485. The problem is that if that wire breaks, tests show that the PLCs continue along with the last received instruction. For example, if I press "go forward" and unplug the cable, it runs along as though I was still holding the button. How can I fix this? My options are to directly wire everything, but that will be impractical at best - with the communication wire I can cut down the umbilical cord from 20+ wires down to 4, making the wiring much easier and cheaper.
I've tried resetting the coils on each pass, but they end up just staying off all the time due to the lag in reading and writing over a serial line.
A heartbeat detection system seems incorrect - the system should stop if a wire breaks, not react to the broken wire and shut something down actively.
I can't post my code; not only is there an NDA, but it's thousands of lines. What I'd like is a general solution idea or any suggestions; I should be able to work out the details.
Thank you.
I'm running into a problem with my PLC-controlled system. I'm using AD DL-06 as the main PLC with another DL-06 as the remote PLC. The remote PLC on the carriage takes input from the operator and sets the coils on the solenoids. The main PLC on the non-moving part handles a similar interface and turns on the motors.
It's transporting people and thus has to be failsafe. There's a separate set of redundant safety Grade 3 controllers that take care of collisions. The system requires power from the estop relay to function.
The communication between the two PLCs is done with RS-485. The problem is that if that wire breaks, tests show that the PLCs continue along with the last received instruction. For example, if I press "go forward" and unplug the cable, it runs along as though I was still holding the button. How can I fix this? My options are to directly wire everything, but that will be impractical at best - with the communication wire I can cut down the umbilical cord from 20+ wires down to 4, making the wiring much easier and cheaper.
I've tried resetting the coils on each pass, but they end up just staying off all the time due to the lag in reading and writing over a serial line.
A heartbeat detection system seems incorrect - the system should stop if a wire breaks, not react to the broken wire and shut something down actively.
I can't post my code; not only is there an NDA, but it's thousands of lines. What I'd like is a general solution idea or any suggestions; I should be able to work out the details.
Thank you.