We are using controller AC450 in our system. On MB300 three controller have been connected. The length is around 350 meters. Two controllers (A & B) are very near to one end while the third one (C) is at the other end. The system was running very nice but for last few days the communication between PLC which is at one end with other has become very slow.

The two PLCs which are near to each other at one end are communicating very nicely, but the communication with other PLC is nearly zero.

When I connect the programmer at PLC (A) I can see PLC (B) and vice versa, but not (C).

When I connect programmer at (C), I am not able to see PLCs (A) & (B).
The end resistor at both ends are ok 50Ohms. Also at each transceiver resistance is ok. By opening end resistor at one end and checking from other is also ok, that means cable is also ok.

Any suggestion...

 

You don't say what medium you are using for communication, but you mention terminating resistors so I am going to assume that you are using co-axial ethernet of some kind.

No, your test is useful but does not absolutely guarantee that the cable is perfect.

MB300 is a synchronous bus so it should not be "slow" as such however you are probably losing messages which makes it seem slow.

First up, has anything changed in the software or hardware? Have you modified communication DataSets etc ? Installed new cables in the same duct as the MB300 etc ?

Have you checked the system message logs to see what type of errors you are getting? The logs should help you identify whether you have problems with specific datasets, a continuous problem or a random intermitant problem.

Check ALL of your communications hardware as this is the most likely source of your problem.

If you are using Thick ethernet, the installation rules are very specific and must be followed exactly. Vampire taps on the AUI's are a common source of problems.

If you are using thin ethernet then poor cable terminations and poor cable routing are common problems.

MB300 is usually quite reliable but troubleshooting problems can be difficult. Often you just need to change components 1 at a time till the problem goes away.

Good luck

www[.]lymac.co.nz

 

I agree with the previous post regarding checking the installation also check one of the terminators are earthed. Check the SQE is switched on in the transceiver.

Look at the comms card CS513 in the controller. The Run light should be lit permanently and the Tx and Rx lights should be flashing constantly. If the card is not doing this remove the comms card carrier board and re-insert it. The comms on these systems are very reliable. We have a big installed base of MP/Advant with few problems.

 

Thanks friends,

The communication card is ok. The problem is, the two PLCs nearer to each other are communicating perfectly unlike the third one which is far away from these on same bus. There is no communication with that PLC. We removed the transceiver at the third PLC and connected on HMI there, but we are not able to get signals from the other two.

 

Hello,

It sounds as if you move your HMI to location 3, then you can communicate... but now not the other two? I would look closely at the MB300 highway section between node 2 and 3. If you have access to a reflectometer, it can determine bounce backs or breaks in the line.

Also, if you are interested in upgrading your system UNIX stations to high performance machines, then I can direct you if you write me off forum at schwormr at aol. com.

Thanks.

 

Thanks friends,

Finally I found the problem in the cable and changed it partially.

 

check for dp switches in transceiver or coaxial cable from transceiver to plc. also check that the pin which pinches on cable is ok by removing transceivers top cover. sometime the pins bend.