S7-400 414-2DP

i would like to get a comment regarding my problem of profibus network down (the led indicator for both BUSF and INTF are on on the CPU). what could possibly cause the profibus network to go down suddenly then without touching/doing anything it would come back up again?

defective profibus connectors? defective cpu? i checked the cabling and it is ok, no grounding between the red and green and the ground wire.

when i check for short between the red and green wire of the profibus network, i remove the profibus connector from the PLC, remove the green and red wires from the connectors and test for shorting from there. while all other profibus connectors are connected to their respective slave units. i just use a digital tester to check the continuity. when i put the red probe to the profibus green wire and the black probe to the profibus red wire, i get a continuity. but when i probe with red probe to profibus red wire and black probe to the profibus green wire, there is no continuity. is this a normal condition for the network wiring?

 

Hi.friend,

r u using any other drives, instrument using with profibus? If so, Check those. first try to see in diagnosis buffer in cpu module of all cpu. check terminator switches and cables are really ok. You can not find the short or bad of cable when other end is connected with bus connector. Which profibus you having problem Periparie bus or mpi? Me also having problem some time and solved...

my mail [email protected]
00965-9638100

 

Maybe you are around the limits of the Baudrate vs. length of the cable. try lower Baudrate.

 

some questions first:
baudrate
cable lenght
number of slaves
using of repeaters

 

I have experienced 100% same problem in the month of december, 2004. As your name & address is not mentioned clearly, i am unable to decide whether you are from Siemens or not...

Anyway... In my problem, we found that the problem of profibus network getting down & UP automatically after some time. This happened for about 2 weeks. After so many tests were done, we found that the problem is with the CP card which we are using. (CP:443 - 5)

The problem is sorted out by replacing the CP card with a new one.

Try replacing the CPU / look for a latest firmware for CPU. That should solve the problem.

 

The indicator BUS1F means bus failure and INTF means internal failure, it looks like one of the paticipants on the Profibus DP network as configured in the hardware configuration isn't present or has an problem. U can trace this by opening the hardware configuration online and see which participant(s) on the Profibus DP network arn't present or has/have an problem.

 

Just beware of EMC problem because its most difficult to troubleshoot for that check

1) your earth
2) difference between M and ground if isolated
3) which station is failure mostly u can chk it by seeing the digonostic buffer
4) is there any source of noise there because it really effect in case of long cable please chk if that source of noise e.g. transformer is grounded properly.

whichever fault you found please let all ppl know about it.

 

Profibus sometimes is sensitive for their end resistors, depending on the total length of the bus. For example if the length is very short you have to switch off one or even both of resistors. Also there are issued a lot of bad-made connectors. Maybe try new connectors. Another suggestion: try a lower baud rate.

 

If you need to switch off resistors, something else is wrong. Profibus is s current driven comunication and by that quite sensitive to capacity and resistance of cables (on higher speeds).

Most common problems regarding falling and coming profibus:
- End resistors not properly set, resulting in reflections.
- No supply on last station. Profibus requires an active termination. One resistor to +5V, one resistor to ground and one resistor between lines. All three resistors and the 5 V supply need to be there.
- Poor cable. Due to capacity, rise and foll time of signals ar to long.
- Short cables. Every piece of cable should be at least 1 meter. 1 short piece usually gives no problem but several mostly do.
- Length of drop cable. Above 1.5 MB no drop cables are allowed. Sometimes they work sometimes not. cutting 5 or 10 cm helps. Has to do with wavelength compared to cable length and reflections.

All those problems go away when the speed of the network is lowered.

The internal failure led most of the time is activated because one of the error OB, called by the disappearing or coming stations, is not present.

Another common problem is wrong configuration. Usually on diagnostics. The slave sends diagnostics and the Moster does not know what to do with them (no proper OB) also resulting in EXTF and INTF.

Success.

Rino Jansen (Certified Profibus engeneer)