adccommunitymod (AutomationDirect) asked a question.
Created Date: October 13,2010
Created By: Kristjan H
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I have 10 cabinets with DL06, DL205 (260 CPU) and DL405 (450 CPU). Each of the cabinets has a 6 " C-More Micro mounted in the door. On three cabinets, the CMM is causing a lot of noise on RTD modules. Two cabinets with DL405 and one with DL205. On the other seven cabinets the CMM doesn't seem to affect the RTDs at all. All CMM panels are well grounded. How do I know it is the CMM that is causing the noise? With the CMM connected the signals jump randomly 2°C. After disconnecting the CMM the signals quiet down. Is this a known problem? What is the cause? What is the solution? Would an RS232 opto-isolator between CMM and PLC solve the problem?
Created Date: October 14,2010
Created by: billf_Clark_Pulley
Is your 24VDC (-) also connected to ground and if more then on dc power source tie all commons together and tie to ground. Had that problem on a 15 " C-more using a rtd card with a dl-260. Hope it helps
Created Date: October 18,2010
Created by: Kristjan H
Bill, thank you for your tip. I connected -24vdc to ground and it didn't improve the noise. So I tried several other things:
1)I disconnected the 24vdc power supply to the panel and the noise disappeared. The panel keeps running in low-power mode (DV-1000CBL cable supplies 5vdc).
2)I tried running the panel with 24vdc power supply and EA2-CBL cable on COM2 and the noise came back.
3)I tried putting in a different panel and the noise is still there.
This was experimenting with the DL205, the DL405 didn't seem to respond as clearly.
I would still like to run the panel with 24vdc for better visibility. I might end up with trying a ferrite core or an opto isolator on the comm cable.
Created Date: October 19,2010
Created by: Do-more PE
I have never seen this before. I would tend to say that either it is a EMF problem or a ground loop of some kind. It is possible that the noise is originating from some other source and the Cmore Micro is causing it to become more apparent.
Is the Cmore Micro grounded? If not then do so. If it is, you might want to check out your grounds to see if there is something feeding back on one of them.
If checking the grounding fails, I would try ferrite cores on both the com cable as well as the incoming power to the Cmore Micro.
If that doesn't work, then I might go to a comm isolator.
Created Date: October 19,2010
Created by: a agnone
I had to use a separate 24v power supply for the display, in one case and it worked. Another time I used a linear power supply and that cleared up the noise. Just depends.
Created Date: October 13,2010
Created by: Kristjan H
I have 10 cabinets with DL06, DL205 (260 CPU) and DL405 (450 CPU). Each of the cabinets has a 6 " C-More Micro mounted in the door. On three cabinets, the CMM is causing a lot of noise on RTD modules. Two cabinets with DL405 and one with DL205. On the other seven cabinets the CMM doesn't seem to affect the RTDs at all. All CMM panels are well grounded.
How do I know it is the CMM that is causing the noise? With the CMM connected the signals jump randomly 2°C. After disconnecting the CMM the signals quiet down.
Is this a known problem? What is the cause? What is the solution? Would an RS232 opto-isolator between CMM and PLC solve the problem?