JRoss
Lifetime Supporting Member
Hey everybody,
I have a strange problem that had me baffled. I built a small control panel with a Mitsubishi FX5U PLC, a panel PC, a simple KB Electronics DC drive, and a Rice Lake scale indicator. The whole panel is powered off of a 30 amp 120 volt single phase circuit. It controls a crush-test fixture. The drive moves the crushing plate up and down, the scale indicator measures load and reports it to the PLC using RS232 streaming, and the PC is the operator interface and also does the data collection and report generation. The fixture is old, the panel is a replacement for the 20yo panel that came with it.
The problems began when I first powered the panel. At first I had trouble downloading to the PLC as it wouldn't go out of run mode. I had downloaded a test program before installing it. But eventually that worked and I got the drive running and the basic functionality working. Then I went to test the scale indicator.
I had bench tested the scale indicator streaming function with my laptop but hadn't tried it with the PLC. I first hooked it up to my laptop to verify comm settings, and... nothing. After time on the phone with tech support we determined the port on the indicator was dead. So I ordered a new control board.
New board came in, plugged it into the PLC, and... nothing. So I packed the indicator and both boards and sent them back to the distributor who determined both comm ports were dead, and installed and tested a third control board. At this point I also ordered another indicator of a different brand.
New control board connected to laptop... nothing. New indicator... worked! Got data into the PLC! But then I started smelling smoke and the PLC died! Lights done and went out completely. I had a second one, put it in, and the PLC serial port module was dead, as well as the comm port on the new indicator. But everything else worked fine, and I didn't the rest of the day doing development and testing on everything else.
Went home and ordered a new PLC and serial port. Ended up getting a different style because original module was backordered. Received parts and on a whim hooked up the Rice Lake indicator on the bench. Worked fine with laptop. PLC talked to laptop, but wouldn't talk to each other until I used a different serial cable. Finally success! Left it running for about 12 hours over night.
Back to panel, installed new PLC and serial module, started testing for stray voltages, bad grounds, etc. Didn't find anything. Tested indicator with laptop. Worked. Plugged indicator into PLC, RD light flashing! Started getting laptop ready to go online. Smelled smoke, and PLC had died. Just confirmed serial port died too. Though this time the indicator escaped damage.
I took apart both PLCs and the damage is at different places on the board.
So PLC works fine in panel with no serial connection. PLC works fine on bench with serial connection. But in panel with serial connection? Dead twice over. Any ideas what could be going on?
I have a strange problem that had me baffled. I built a small control panel with a Mitsubishi FX5U PLC, a panel PC, a simple KB Electronics DC drive, and a Rice Lake scale indicator. The whole panel is powered off of a 30 amp 120 volt single phase circuit. It controls a crush-test fixture. The drive moves the crushing plate up and down, the scale indicator measures load and reports it to the PLC using RS232 streaming, and the PC is the operator interface and also does the data collection and report generation. The fixture is old, the panel is a replacement for the 20yo panel that came with it.
The problems began when I first powered the panel. At first I had trouble downloading to the PLC as it wouldn't go out of run mode. I had downloaded a test program before installing it. But eventually that worked and I got the drive running and the basic functionality working. Then I went to test the scale indicator.
I had bench tested the scale indicator streaming function with my laptop but hadn't tried it with the PLC. I first hooked it up to my laptop to verify comm settings, and... nothing. After time on the phone with tech support we determined the port on the indicator was dead. So I ordered a new control board.
New board came in, plugged it into the PLC, and... nothing. So I packed the indicator and both boards and sent them back to the distributor who determined both comm ports were dead, and installed and tested a third control board. At this point I also ordered another indicator of a different brand.
New control board connected to laptop... nothing. New indicator... worked! Got data into the PLC! But then I started smelling smoke and the PLC died! Lights done and went out completely. I had a second one, put it in, and the PLC serial port module was dead, as well as the comm port on the new indicator. But everything else worked fine, and I didn't the rest of the day doing development and testing on everything else.
Went home and ordered a new PLC and serial port. Ended up getting a different style because original module was backordered. Received parts and on a whim hooked up the Rice Lake indicator on the bench. Worked fine with laptop. PLC talked to laptop, but wouldn't talk to each other until I used a different serial cable. Finally success! Left it running for about 12 hours over night.
Back to panel, installed new PLC and serial module, started testing for stray voltages, bad grounds, etc. Didn't find anything. Tested indicator with laptop. Worked. Plugged indicator into PLC, RD light flashing! Started getting laptop ready to go online. Smelled smoke, and PLC had died. Just confirmed serial port died too. Though this time the indicator escaped damage.
I took apart both PLCs and the damage is at different places on the board.
So PLC works fine in panel with no serial connection. PLC works fine on bench with serial connection. But in panel with serial connection? Dead twice over. Any ideas what could be going on?