K
I recently was assigned the task of maintaining several PLC-5/80s that had multiple process program files that were called by conditional JSR
instructions, depending on which process was desired. )The facility is 75 miles from my office and we try to support them via modem to save on the travel time.) Each program file used latch and unlatch coils to keep track where in the process the system was.
However, it was possible (and it often happened) where a partial sequence was executed to do clean-up activities and then the process was switched to
another program file. However, the original programmer did not reset the latch bits when the program file changed and when the first process was called again (sometimes weeks later), the system hung up. I would believe that the original programmer didn't even think that the operators would do only a partial cycle and thus blindly programmed a continuing problem that
required support.
We research this and put in the appropriate unlatch coils in the main program file #2 to prevent this in the future, but I don't even want to think about the hours of lost production and engineering troubleshooting this caused. I certainly avoid using latch coils where an alternative is available.
Russ Kinner
AVCA Corporation
Maumee, OH USA
instructions, depending on which process was desired. )The facility is 75 miles from my office and we try to support them via modem to save on the travel time.) Each program file used latch and unlatch coils to keep track where in the process the system was.
However, it was possible (and it often happened) where a partial sequence was executed to do clean-up activities and then the process was switched to
another program file. However, the original programmer did not reset the latch bits when the program file changed and when the first process was called again (sometimes weeks later), the system hung up. I would believe that the original programmer didn't even think that the operators would do only a partial cycle and thus blindly programmed a continuing problem that
required support.
We research this and put in the appropriate unlatch coils in the main program file #2 to prevent this in the future, but I don't even want to think about the hours of lost production and engineering troubleshooting this caused. I certainly avoid using latch coils where an alternative is available.
Russ Kinner
AVCA Corporation
Maumee, OH USA