DL250 CPU Fault

[watertech2]

I'm having intermittent problems w/ a CPU fault.  OEM equipment has been running fine for 1 year and is now locking up every other day, for no apparent reason.  I've tried a new base and two new CPUs.  Tech support says possible dirty power issues.  Nominal voltage looks OK, and I'm going to set up a power quality monitor today.  Old base was 12-24 vdc.  I swapped to a 240 vac base.  Would the dc base be considered somewhat filtered as it is fed from a filtered supply?  Any tips on troubleshooting and/or fixing possible incoming power supply issues would be appreciated.

[chris.zeman]

I don't know that there are really any differences between the AC and DC bases. I ordered a 120VDC base by mistake a few years ago and never bothered to return it. We had a power supply in a base go bad and didn't have any spares at the time. (Our purchasing department was taking its sweet time AS USUAL! We're finally starting to get stuff we ordered over a year ago!!!) We compared the AC base power supply to the one in the DC base and couldn't find any differences.

We connected 120VAC to the DC base and everything worked great! In fact, I think it's still in service!

Chris

[MikeS]

that sounds way strange. r u sure you don't have a 120/240VAC base that's mislabeled?

[chris.zeman]

I guess anything is possible. I'm trying to recall for sure whether there were any differences or not, but there may have been 1 additional part in one of the units. I'm just glad it worked! 

I wish I could remember where I put it into service at. I distinctly remember changing the cover on the power supply, so looking in all the cabinets wouldn't do any good.

Chris

[BobO]

Maybe not as strange as you think. Depending on the rectifier/transformer configuration, and as long as the input voltages are within similar ranges, it could work...at least to a degree. I wouldn't recommend it though...even if it seemed to be working. Ratings are based on assumptions that wouldn't be applicable. Caveat emptor.

[watertech2]

I guess that I may have led you down the wrong path.  I didn't connect the 240VAC base to the DC power supply.  I had both DC and AC power sources in the cabinet, and only had a 240VAC spare base on my service van, so that is what I reconfigured my wiring for.  The panel control circuit is the same circuit that feeds the equipment; in this case the equipment is a large DC SCR rectifier.  I was wondering if the original DC base, being that it was fed from its own DC power supply, might be less susceptible to internal equipment, or external utility caused, voltage spikes and transients.  Will a 24VDC power supply filter dirty power?  I know that a UPS system is basically an AC to DC to AC converter, and have heard that this will filter possible problems.  Has anybody else had a problem w/ a CPU fault that has eventually pointed to power issues?  If not, has anybody else had an intermittent CPU fault that turned out to be something a little more obvious?

[marksji]

I've had problems in the past with program memory getting corrupted and its always led back to a power problem of some sort.  Since that time I've switched all our equipment to 24v PLCs and put in a 60W power supply for the PLC and touch screen.  That didn't completely solve all the problems, but it did solve the majority of them.  The latest DL06 firmware also helped a LOT with our issues.

[watertech2]

Good to know that the 24VDC supply may clean up the power issues.  Maybe my original 24 VDC base was failing and I opened up a can of worms by replacing it w/ an AC base.  My program is apparently not being corrupted, as I can cycle power and the unit starts right up again- business as usual!  Then it could  be hours, days, or weeks before it fails again!  This has been a "fun one"!

[Reynaldo]

Recently (July 2007) I had similar problems with a DL-05 powered from UPS 120 VAC.  The systems was working fine 3 years but any day the CPU red led turned ON, so trying to solve the problem I downloaded the new firmware version and restarted the PLC and the systems works fine again for some days, but this problem came back some days later, so I change the power to another circuit but the problem appears again. I changed the PLC for a new DL-05 powered from 120VAC but the problem persists.  I must to say you: “The PLC always was connected to a good earth line”

At this point I knew the problem was electric noise so I decide to replace the PLC for another with connection to 24VDC power.  Since I made this change the systems is working fine again.

When you use PLC powered to 110-220VAC any electric noise must to be filtered into it but if you install a PLC powered to 12-24VDC all noise is filtered by the 24VDC external power and always you get a clean signal to power all your equipment.

[ATU]

On the note of electrical noise. Are the Comports on the CPU's optically isolated? Is the RS232 signal ground tied to the Equimpent Ground on the Power supply?

[Reynaldo]

Well Atu, the original systems was connected to a PC using RS232, this communication didn't have optical isolation, the second port was free.  The PC is used to read some memory datas but system can works without connection to the PC due to the data are saved in PLC memory until they need to be downloaded to see it in excel.

I made probes without PLC-PC connection, I unpluged communication cable from PLC, I leaved free both PLC port but the problem appeared again until I replace the original D0-05AA to a D0-05DD-D with an external 24VDC power supply.  The system don't have connected any digital I/O (his 14 digital points are free), the D0-05 PLC just read four analog input connected to a F0-04AD-1 module.

I hope this information solve your question